View Full Version : Steering and relative angles

24-05-2010, 07:19 PM
OK, this post is pretty much up Lauren's knowledge base, but all input is welcomed. For those who have been following, ya'll know that at least my car is running and driving... sort of. I was able to drive it on and off the trailer at the kit show this weekend, but found a fatal flaw: I have no turning capability at all. At first I put it off to replacing the rack with a power unit, but now I'm not so sure. See the following photos.

This photo is as the car sat in the warehouse before it was sold. Notice the angle (or lack thereof) of the tie-rods and the A-arms. Pretty parallel to the ground, as it appears:

Now here's a photo of the car sans body. Notice the angles now:

My driveway does have a crown, but not that bad. I put it off as the weight of the body pressing down on the front suspension and old components that "leveled" out the tie-rods. With the body off, the pressure was off and the suspension rebounded, right? OK... fast forward to replacing the components, which included tie-rod ends, ball joints and the steering rack. With the body off, the new rack has approximately the same "droop" - looked good when I put it on. Place the body and....still the same "droop", which might explain why I had no turning radius so to speak. I figured the angle of the droop directly corresponded to the turning radius, and if the tie-rods were parallel to the ground, my wheels would correspondingly turn further outboard/inboard. I have yet to test that theory, but were coming on a long weekend, so I might have a chance. But I digress. To correct the droop with all the components in place would require me to place the tie-rod to the top of the spindle mount and maybe slightly above it, maybe an inch or so. Trouble is, the ball joint is at the bottom. I have started research on Heim joints for this application but Im not convinced that Heims are legal for road use here in the States. All the websites state that, though Im sure they are covering their butts.

But now Im thinking that particular train of thought may be misleading I can accomplish the same thing with all the parts in the stock position by a shorter spring. But cutting the spring (again these were stockers that had been modified to fit) will increase the spring rate which may or may not be too bad. Or I might even be able to remove them totally and rely just on shocks. The nose weight now really isnt much, maybe 20% of the total car weight, if that. I can stand on the cross beam of the front suspension and not deflect it more than a couple inches (at 215 lbs), so Im thinking much has to do with the current springs.
Ive been reading as many articles as possible having to do with Ackerman angles, toe and all the related angles and my eyes start glazing over. I flunked geometry in school, so Im totally useless in this situation.
Anyone for suggestions to try before I start resorting to tearing apart the suspension once again?

24-05-2010, 08:10 PM
The inner front portion of the front wheelwells (under headlight area) had to be modified on mine. I fgure that you would have thesame issue since both ofour front ends are basically identical. This seriously limited my turning radius.


24-05-2010, 08:50 PM
Uh, yeah, but that's not it, Rob. There is a geometry issue here that I'm not entirely familiar with. The car has significant modifications to the bodywork that tire scrub shouldn't be an issue.

24-05-2010, 09:29 PM
Hmm, interesting. Your geometry looks pretty good from what I can see - the rack height is approximately on the same level as the lower radius arm pivots, which is a good way to zero the bump-steer. This means that whatever the angle of droop, the amount of steering lock you have should not change by much. So I am wondering about the rack itself, and the steering knuckles - are the latter longer than stock, for example, which would slow the ratio down and limit the lock? Or have lock-stops been cunningly fitted inside the bellows (like I have on the Green Machine) to limit tyre/body contact?

Do you know what the standard spring rates are Rick? From your description, 2" static deflection with 215 lb means 107.5 lb per wheel, or ~54 lb/in. That seems a bit soft to me, even accounting for the leverage ratio, which you should ideally measure.

Unfortunately, as I demonstrated over the Winter, spring removal is the only way to work this issue through, but check the steering knuckle lengths to see if there is a shorter arm you can use to change the ratio. How many turns lock-to-lock?


24-05-2010, 11:11 PM
If this was how it was built and was run on the road, did it previously have any issues. If it was ok before when on the road then why is it not right now, get some real weight on it to equal the body weight to see if it drops to the correct level.
If you set it up without the weight of the body when you drop it on, you may have gone too far the other way.

24-05-2010, 11:28 PM
The rack shown in the photo is not the rack that's currently on there. The current rack is power, and therefore a little longer in the body. I had to cut off about 3" from the tie rod ends just to come close to the old rack. The tie rod ends - the knuckles - are almost identical in length to the OE setup. There are no shorter rod ends, but there are longer. I'm starting to wonder about the rack, too. It has approximately 3.5 turns lock to lock, and it doesn't seem to be binding anywhere (except through the steering column multi-joint... that may never be a good angle!). Never thought about internal stops... I'll have to peel the boots and check that out.
I have no clue what the spring rates are, Lauren. Being '68 Mustang with cut springs, I don't know how much had been cut out initially to make the fit. How would I even figure leverage ratio?
Jim, the previous owner won't talk to me, so I can't even guess how it was initially. Reports were that is was rarely driven, so he may have had issues from the get-go. Who knows? But even with the body on, I've changed the weight distribution by ridding the front end of the gas tank and adding a radiator. I was replacing piece for piece as best I could and to my knowledge didn't change any dimensions or mounting points. All that were changed were ball joints and shocks!

25-05-2010, 11:46 AM
Thanks for clarifying Rick - I think its the rack travel that is the problem, although the length of the rack is clearly an issue too. By cutting down the track rods you have compensated for a rack that is longer than the original, so the inner balljoints will no longer be in the same place as the lower radius arm pivots (length of radius arm = length of track rod with steering centred = no bump steer). The additional length of the rack body is limiting the total movement of the rack from one lock to the other. 3.5 turns lock-to-lock is surprisingly high-geared for a power rack - I was expecting maybe 2.5 turns.

If the steering arms on the uprights (knuckles) are unchanged from the stock Mustang II units (and the original rack was a Mustang II unit) then there is no problem there. I think you can see where this is going... have you still got the original non-power rack? With trackrods...?

The problem you have, as I see it, is that there are not enough machined teeth in the rack bar to provide the amount on movement you need to turn the wheels. If you can shorten the steering knuckles that would increase the wheel angle on turns, but unless the distance between the rack inner balljoints replicates the distance between the radius arm pivots you will have bump-steer, which you probably didn't start with :(

I think the best approach to take with the front springs is to remove them altogether and replace with coil-over shock units. That way you can fine-tune the spring rates by specifying the poundage, length etc., that you need. I have a spreadsheet to calculate optimum spring rates which I have used on both Green Machine and Nova Nigel's car, with good results (even though in NN's case we had to estimate the vehicle mass and weight distribution). The leverage ratio is difference between the spring acting directly on the radius arm outer balljoint (physically impossible) and the point on the radius arm where it does act. Because this increases the lever arm ratio, the effective spring rate (the wheel rate) will be less than the rating of the spring itself. Its a long story, but if you have an idea of the all-up vehicle mass (single occupant, reserve fuel), the estimated front/rear distribution (45/55 perhaps?) and the length of your lower radius arm and the distance from the centre of the spring plate to the inner pivot I can start plugging some numbers in...

The good news is, I'm sure I've seen Mustang II front beams used on pro-street cars with re-rated coil-overs, so the necessary parts are available. Also good is the fact that you can do something about this, and the steering rack, without taking the whole car to pieces again (like wot I had to do)!


25-05-2010, 12:49 PM
Good deduction, Lauren. I hadn't considered the rack itself to have a limited number of teeth for the internal travel. I had assumed, incorrectly of course, that the tooth count might be the same as the non-powered rack. And yes, I do still have the original rack that was in there, but not the mounts as they were scrapped. Easy enough to re-fabricate though. And damn... that power steering pump was expensive!

As for the spring rates... I could always get some cheap floor scales and put 'em under each wheel. Problem at the moment is that I have no fuel tank fitted - and I have no idea where I can put one! I have an obvious choice which places a tank right above the transaxle between the mufflers, but it gets hot there.... very hot. Unless I can figure a heat shield of some sort, I'm stuck looking for other locations. Once I get that figured out I'll certainly pick your graph for the spring rates!

25-05-2010, 08:07 PM
To replicate a fuel tank use 5 gallon water containers and put them where your tank would be to give you some idea of weight.

25-05-2010, 09:07 PM
Hmm. No room in between the front bulkhead and the front suspension? Sidemount fuel cells are rather frowned upon these days, although the GT40 would be a clear inspiration here, particularly as there is more body width in your car than a standard Sterling.

Alternatively, both the Lamborghini Countach and Lancia Stratos used twin fuel cells either side of the engine behind the rear bulkhead. The latter having a transverse V6, the cells were tall and narrow inverted cones. With adequate heat shielding/firewall to separate them from the engine compartment, I think this would be the optimum location - all of the fuel mass will be concentrated within the wheelbase, so no danger of a shift in CoG as the fuel level drops (my CoG shifts rearwards by a couple of percent from full to empty, like the original Miura).

Clearly the tanks would have to be custom fabricated to fit the available space, but should otherwise be relatively straightforward...

Take the springs off, support the chassis at the ride height and measure the unsprung weight of the wheel/tyre/upright/brake assembly on some scales. I forgot to mention that. Corner weight measurements are really not much use until later in the assembly process.


25-05-2010, 11:06 PM
Ok.... a little experimenting after work today. Dug out the old rack and pinion and did a distance measurement - full turn to full turn. At the rod end, it was approximately 5.5". Took the driver's side wheel off the car and did the same with the new rack and.... 5.5" lock to lock. Even the new Flaming River racks don't go over 6" in full travel, so I started experimenting. I popped the tie rod loose and saw the wheel through it's full range. At full left turn it hits part of the suspension, at full right, the brakes hit the spring. So... I placed the tierod end loosely upside down on the steering arm and put the car back on the ground and gave it a couple bounces to settle the springs. Next, I centered the wheels (as best as I could) and placed a board flat against the wheel, making sure it was in contact in at least three places - tire centers and the bottom of the tire. I marked the floor with chalk along the bottom of the board. Did that to both wheels. Turned the wheels full lock right and marked the pavement, and same thing full lock left.
Now remember, nothing is tightened down on the driver's side, nor is the spring set the same as it was on the passenger (it may be slightly "lighter" as I moved where the bottom coil sat). I measured a distance out from the place where the two full lock turns met, about 10" and drew a perpendicular line to the "centered" line as a reference. Then I measured the distance between where that line met across both full lock lines. The passenger side measured about 8.5", the drivers... about 9". The difference seemed to be that the tie-rod end was basically horizontal, rather than at the angle it had been. True, I can't mount it that way, but I'm going to start researching alternatives (like Heims) to mount instead. It will certainly be cheaper than a new rack with only a 1/2" more play (but I'm checking into that, too, just in case!).
If I can cobble up at least a testing rig for not too much money I think it will reveal a lot. I'm already suspecting that even with the OE manual rack, this thing must have been a pig to drive, since the tires don't have the rotational swing I thought they might (interference with the suspension pieces). We'll see... stay tuned!

Oh, and Lauren nope, no room in the front. The open area behind the rad has the water pump, the suspension fills the rest. There are open spaces between the body shells and a couple small areas behind the engine.

26-05-2010, 11:34 AM
So the suspension is limiting lock in one direction and spring contact in the other? OK, that's a good start - going to coil-overs with either 2.25" or 2.5" ID coils will give you more clearance around the brakes. What about the suspension contact? Is it designed to limit lock (like a lock-stop), or does it appear to be unintentional contact?

Foreshortening of the trackrod could cause a change in steering angle if your bump-steer geometry is poor. The way to counter this is to provision for vertical adjustment of the rack height. Keeping the trackrods parallel to the ground at normal ride height is one way of minimising tracking changes if the geometry is poor. With optimised (zero bump-steer) geometry it wouldn't matter what angles your trackrods were at, the tracking would still be correct. Of course that assumes you have sufficient range of travel to cater for all suspension angles :D

It seems like there is some development work needed to get all the bits to play nicely, but my initial concern regarding the rack length and travel would appear to be negated. So the power rack stays (whoo-hoo :clapping:)

Where was the fuel tank in the cars original incarnation? I suppose with the radiator in the back, the fuel tank could have gone ahead of the front axle?


26-05-2010, 12:24 PM
The suspension/steering arm isn't designed to limit the lock. On full left lock, the tire itself contacts a torsion arm, on full right, there is a portion of the brake caliper assmbly that contacts the suspension spring. I could, in theory, move the rack downwards to keep the trackrods parallel to the ground, but that would force me to go to a 'front-steer' rack with the pinion on top of the rack. Which may not be a bad thing, as the Mustang II racks are rear-steer, and the pinion angle is piss-poor and the housing is actually resting on the frame.
I think the first thing is to find out why the car isn't settling on the springs to where the lower A-arm isn't parallel to the ground. I've been trying to follow a link I found on Heidts website (http://www.heidts.com/support_suspension_101.html) for basic set-up:

http://i16.photobucket.com/albums/b31/letterman7/SNR%20build/IFS.jpgBut all that doesn't explain why the car won't settle! I'll have to pull the springs, put the shocks back in and see where it sits. The fuel tank was originally in the boot under the bonnet (and definately was larger than 10 gallons), with the radiator in the back. Since that has been removed and a lightweight radiator up front, I'm sure that has a huge impact on weight distribution. Onwards...!

26-05-2010, 05:48 PM
Hi Rick - your diagram shows the suspension arm angles I would expect to see. If your angles were as they are now, on the road, your front roll centre would be miles off the ground!

I think you have stock Mustang spring rates, and shortening them only increases the effective spring rate. Imagine what those springs were intended to support - an iron-block V6 and radiator, plus an all-steel bodyshell. And crash bumpers!

The torsion bar is the front anti-roll bar (sway bar). It is a custom fabrication (not OEM), because it is adjustable. There are three positions for the drop links which allow the effective roll stiffness to be increased. Its on its softest setting at the moment, which is hardly surprising considering how much understeer you could dial in by stiffening the front. Can the transverse bar length be shortened? I assume that is what is hitting the tyre/wheel on full lock. TBH I would remove the front anti-sway bar altogether until you have everything else sorted - the lower radius rod fixing also has two holes, and again it is on the softest setting, so this bar is as decoupled as you can get - suggesting that even less roll stiffness is required at the front...

As I mentioned above, the OEM springs have a large diameter, which a coil-over shock unit would not have. Remove the sway bar and replace the OEM springs with coil-overs and you should get your steering lock back. You know it makes sense :D

Race car shops remove the springs and use turnbuckle adjusters in place of the shock absorber to set the optimum ride height - you might want to fabricate something similar to determine the ground clearance, suspension angles etc., before specifying the shock body length and stroke.

As your steering rack is in front of the axle line it is front steer - I take it the rear steer rack you are referring to would be mounted upside down, but still in front of the axle? Or would you put the rack behind the axle for true rear-steer?

(the latter would help your Ackermann geometry, although this is only a second-order effect - Green Machine has quite a lot of Ackermann, all front steer suspensions do, but it doesn't affect the steering as much as you might think, and in fact can be used to advantage as it promotes high speed stability...)

Ahhh, there's nothing like a good geometry problem for... sending people to sleep :yawn:


26-05-2010, 09:20 PM
See... that's why I enjoy talking (well, writing) with people that know what the hell they're talking about :cheers: . First things: the roll bar/sway bar. I thought that this might actually be OEM to early Mustang, as all the replacement components are readily available. If I were to remove the sway bar, I'd have to grind the mounts off. Can't really shorten it, either, as the ends are grooved to accept the drop link arms. But yes, that is the portion that's hitting the tire at full lock. If the car will turn adequately with that still in place, all's good. If not, I'll have to grab the grinder!
As for the coil-overs... the more I think about it the more it makes sense. I'll pull the coils, button everything back up and roll it around the yard and drive (lots of little bumps and dips) to settle the suspension, then see where it sits. I think the coil-overs available for this year suspension only comes in one size, but it's adjustable for ride height.
Front steer vs rear steer: Ok... I admit, I'm still a little lost with the exact definition. I thought that it meant the center of the rack (or tie rod) was either behind or in front of the mounting hole for the steering arm on the spindle. If you look back at the photos, the original rack - early manual Mustang/Pinto has the pinion part of the steering shaft on top of the rack. The Mustang II replacement rack I purchased has the pinion on the bottom, which makes for a lousy steering wheel angle. I hadn't given any thought to the front/rear steer thing until I read about it - and really gave the replacement rack not a second thought on why the pinion was mounted on the bottom! I may just call a supplier to see if there is such an animal as a MII style mount with the pinion on top. It would solve a bunch of issues with the steering wheel shaft. Oh, back to front/rear. After reading what I thought was the correct definition, I took it that the OE Pinto rack was front steer since it had the pinion on the top, and the MII rack was rear steer with it's bottom mounted pinion. Both are basically in-line with the eye on the steering arm, which is leading in front of the suspension. So... what I really need is a front steer rack, anyway, right?

27-05-2010, 12:10 PM
Hi Rick - I enjoy these discussions too!

The thing that's bothering me about that sway bar is the fact that (a) the torsion bar is very long, which is why it is contacting the tyre on full lock (i.e. its as soft as possible), (b) the reaction arms attached to the splined ends are also relatively long (making the bar softer still), and (c) all of the adjustment available (two holes in the lower track control arm and three in the reaction arm) are set to the softest setting possible. This would suggest that the sway bar is waaaaay too stiff for this application, and even if it is just acceptable, the indications are that any further adjustment would be to make the bar softer still - either by increasing the length of the torsion bar (tyre contact) or the length of the reaction arm, which doesn't look practical.

Over a certain spring poundage chassis roll stiffness is controlled by the suspension springs - and yours are currently rock 'ard, so I would be very surprised if the sway bar does anything at all, except add weight, although it could come into its own with correctly rated springs. But I think you will need a softer sway bar for that.

Softer means either longer (no good), or narrower, which would necessitate starting again. If you choose the latter path, how about using some old VW front torsion bars? I was wondering if you could fabricate or salvage clamps that would keep the stack together, feed them through bearings on the chassis and fabricate reaction arms that clamp the ends of the stack. If you design it right you can affect adjustment by either adding or removing leaves, or moving the position of the reaction arm along the bar. There are various formulas you can use to work out the optimum sway bar diameter and length, but with so many other variables undefined at the moment, this might be the best way forward.

My personal recommendation would be to remove the sway bar altogether - on the grounds that the CoG is very low, the roll centre axis is also low (or will be, once you get the ride height sorted!), so weight transfer in cornering will be minimal. Increasing front roll stiffness is only necessary if you want more understeer, which is undesireable for fast road use - and you can counter oversteer tendancies by reducing roll stiffness at the rear, which is easy - soft(ish) springs and no sway bar - or even adjusting tyre pressures and using wider tyres at the rear, like the good old days...

I'm glad you are coming round to the idea of coil-overs. As long as the spring is removable, and a range of spring rates are available, you should be fine. I've been through 3 iterations of spring length/rate to get to my optimum (although the first two attempts were blind guesswork), and Nigel had to change his front spring rates once before finding the best solution - in his case my analysis concluded 110 lb/in was optimal, but only 100 lb/in and 120 lb/in were available in the correct size - Nigel intially opted for the stiffer spring which was too much.

Most coil-over shock units have adjustable spring plates which allow fine tuning of the ride height over 2, 4, sometimes 6 or 8 inches. However, the free length of the spring will still need to be specified, and that will be based on the axle weight of the vehicle...

A front steer rack is where the entire steering rack operates steering arms (knuckles) that face forwards, usually with the rack in front of the axle line. Rear steer is where the knuckles point backwards, and the rack is usually behind the axle line. Your set-up is front steer, but you can appreciate that if you put a front steer rack on a rear steer knuckle you would reverse the steering direction (steer left and the car goes right, and vice versa). But if you turn the rack upside down (and use a RHD rack instead of a LHD rack) you can restore the steering direction. As you correctly point out, this would put the pinion either above or below the rack, depending on the specific design. My Cortina rack, for instance, is front steer, with the pinion above the rack. Sounds like the Pinto rack is front steer, but with the pinion below - not so nice for steering column angles...


27-05-2010, 05:20 PM
As Arty Johnson used to say in the old 'Laugh-In' series... "Vetttyy Innnteresting"! I just took a quick peek at the setup again, and there are a couple of grub screws that seem to be holding the torsion bar to the mounts on the chassis. So, with some penetrating oil, I may be able to tap that through and out... maybe! But what does the lower track control arm do? It's suspended into the chassis via a couple of rubber snubbers on either side of the chassis (and we're talking large snubbers here). With the torsion arm free, I can easily move the lower control arm up and down (sans coil spring, of course). If I kept it, that would keep me from sealing up large holes in the chassis...and maybe a future mounting point for another roll bar setup if needed.

As for the steering... yeah... I think another front steer rack is for order, if nothing else than to restore some of the column angle. The double jointed steering joint is still hanging just a little, and I'd like to get it much smoother than it is now, of course. Oddly, both the Pinto (front steer, pinion over) and MII (rear steer, pinion under) racks both turn the same way!

Lauren... remind me to send you something for Christmas!

27-05-2010, 06:23 PM
Aww, shucks :blushing: I enjoy this sort of conversation, life would be boring if I had to do rocket science all day...

Did I not see a circlip holding the reaction control arm onto the end of the sway bar? If you removed that, could you not pull the bar through the chassis mounts from the other side?

The lower track control arm is there to control the braking loads from the radius arm (which carries the spring pan and lower balljoint). Essentially the radius arm and the TCA form a long base wishbone. It does need to be there. The Cortina suspension is identical - actually even GM cars from the period used the same arrangement - Chevy Chevette etc. The big rubber bushes sound like they are shot and need replacing - they are stepped in section so they locate in the large hole in the chassis. There should be a nut and large washer on the back which needs to be torqued up. The rubber allows the TCA to move up and down with suspension travel. You can get urethane replacements that help to locate the suspension better, and for race applications the rubber bush is replaced with a heim joint.

Big Orange (my 1972 Vauxhall Firenza) had machined Nylatron bushes, which certainly improved the steering response, but the TCA bolts needed re-tightening every week!

Actually, looking at my pictures of the Pinto rack, its not at all clear whether the pinion is above or below. Logic dictates that for a front steer rack, clockwise movement of the pinion should move the rack bar to the right, which could only happen if the pinion was below the rack. I suppose the pinion diameter is actually quite small, and when meshed with the rack bar is so close to looking like it runs through the middle its difficult to tell!

Anyway, fit the rack that goes in the right direction for you. Check the length of the rack between the inner trackrod balljoints - if the distance is more than the distance between the suspension radius arm pivots, the rack will have to be raised up a bit anyway - maybe then the steering column UJ's will stop binding?

I need to draw something to illustrate the point, I'll pop back later...


27-05-2010, 09:13 PM
OK, that makes sense. This is my first real foray into this type of suspension... I'm used to Beetles! I'll order new bushes for the TCA arms next week when I get a moment to track some down. That might be another reason why the suspension is acting funky - the spring itself is forcing everything apart. As for the torsion arm... why yes, there are circlips on the ends!
http://i16.photobucket.com/albums/b31/letterman7/SNR%20build/th_NRSsus3.jpg (http://s16.photobucket.com/albums/b31/letterman7/SNR%20build/?action=view&current=NRSsus3.jpg)
So I should be able to take those clips off and wrestle the reaction control arm off. The assembly is a bit corroded, so some persuasion may be in order!

The steering rack... tight quarters, for sure:
http://i16.photobucket.com/albums/b31/letterman7/SNR%20build/th_NRSrack.jpg (http://s16.photobucket.com/albums/b31/letterman7/SNR%20build/?action=view&current=NRSrack.jpg)
I've got about a 1/2" between the outer fluid transfer tubes and the back of the tub. I'll make something work with a different rack... Flaming River, though expensive, has generic racks that have 6" of travel. And another company sells adapters to bolt onto a MII mounting pattern to hold Pinto (clamp) style racks. Could get interesting!

Lauren, as always, I'm grateful for the knowledge you've accumulated! Thanks - I can't say that enough :group:

28-05-2010, 06:29 PM
Seriously Rick, its no trouble - happy to be able to contribute to this exciting build!

So you are not going to keep the power rack then? And that's because of the binding UJ's? Or do you think there is still not enough travel to give you the steering lock that you need? Could you not get a more favourable angle by tilting the top part of the column down a bit at the front, and maybe shortening one of the shafts? Or is there just no way to get it through?

Space is limited around the rack, its true, but no worse than the clearance on the Green Machine - but other than adjusting the track rod ends, you shouldn't need regular access to this area...

Check the TCA nut is tight before condemning the bushes - they may just have been left loose by the previous owner (it happens :D). Replacing them with new rubber, or urethane, will sharpen the steering response.

When I first put wheels on the Green Machine, I thought the steering lock was brilliant - then I realised that the tyres were rubbing against the chassis members - and that was with the temporary 13" Escort wheels. With the 7 x 15" wheels the situation got worse. However, this last rebuild I centred the rack properly, reset the lock stops so that tyre contact was eliminated and I have about 35 of wheel angle. With this angle I can negotiate all but the slowest, tightest hairpins - T-junctions and the like are no problem, and in the last 5 years of driving I have never "run out of road" due to limited steering lock. I crudely calculated my turning circle based on the wheel angle, but of course the Ackermann geometry will affect the result, so it isn't by any means accurate, but I get a turning circle of about 44 feet. Bear in mind many modern FWD cars have ridiculaously poor steering lock, due to the popularity of 16/17/19" wheels, wide tyres and a transversely mounted engine!

The more I look at your pictures, the more I am convinced that CCC designed a zero bump-steer geometry based on keeping the steering rack level with the lower radius arm pivots. It would be good to see what the bump-steer looks like with suspension travel, which you can do once you've taken the springs off (see Green Machine Inactivity thread for details).


28-05-2010, 06:50 PM
Actually, the MII rack that's there now is placed due to it's construction and actually sits slightly lower than the original Pinto rack. But yes, I probably will change it out for a 'pinion-over' like the Pinto. They are available as a power unit and I can specify to some degree how long the tie rods need to be along with the overall throw. I'd keep the MII, but I hadn't considered the angle off 90 degree that the pinion shaft actually sits - it's more like 35 degree from perpendicular to the rack, and that's what's really screwing up the steering shaft geometry. True, nothing is really bolted tight save for the shaft, but an aftermarket replacement will have a 90 degree pinion... and that would solve lots of issues. I can't tilt the column itself up (and therefore the pinion end down) any more than it is already and the MII rack won't pivot around it's axis due to the mounting bolts. No matter, I'll feel better knowing that the "correct" rack is in place and besides... it's chrome and will look cool.. :rofl:

I'll check the TCA nuts this weekend as it's a holiday weekend here. I suspect they are tight. If the bushes are anything like the motor mounts (I could almost swing the motor 90 degrees off axis) it's time to replace those, too!

One question, though. Most of the coil over kits available have, of course, different rate springs. The lightest weight spring is 375 pounds according to this chart:

Adjustable Mounting Bracket Included No
Adjustable Valving Yes
Bushing Color Black
Bushing Material Rubber
Coil-Over Kit Position Front
Coil-Over Springs Included Yes
Crossmember Included No
Gas Charged No
Hardware Included Yes
Lower Mount Bar pin
Notes For front end weights of 1150-1350 lbs.
Number of Valving Selections 12
Quantity Sold as a kit.
Shock Body Finish Clear anodized
Shock Body Material Aluminum
Shocks Included Yes
Spring Finish Silver powdercoated
Spring Rate (lbs/in) 375 lbs./in.
Suspension Height Adjustment 0.0-3.0 in. lowered
Upper Mount Stud
Welding Required No

Taken from an eBay auction for a QA1 system. Now I doubt seriously that even when everything is in the car, me, whatever gasoline tank I put in, and all the accessories that the front end on this thing weighs more than 400 pounds. I will definitely have to get four cheap scales to check, but even if its twice that, wont even the lightest weight springs be too much?

28-05-2010, 09:52 PM
Hi Rick - you need to get aftermarket coil-over shocks. If the units you describe have standard coil springs with an internal diameter of 2.25" or 2.5" then you can get lots of different spring rates to suit any application you like. The spring rates described here are front springs for a front engined V8, which could be too stiff. Trouble is, until we crunch some numbers I can't be certain what you need - but lets take an educated guess...

Green Machine is mid-engined, with an all-up mass of 831 kg split 46:54 front/rear. My optimum spring rates are 225 lb/in front and 325 lb/in rear. With your extra bodywork, iron block and heads and "robust" Ford/GM based suspension, how much heavier would your car be? 100 - 150 kg perhaps? So that's 931 - 981 kg, with approximately the same mass distribution (my 831 kg is with reserve fuel, so the weight of the front fuel tank doesn't make much difference).

So if we increase the spring rates proportionately, to a first approximation you would need... 252 lb/in on the front, and 364 lb/in on the back, or nearest equivalent (usually in 25 or 50 lb increments).

So 375 lb/in would be OK on the back, but not the front. The above rationale makes loads of assumptions regarding unsprung weight, suspension lever arm ratios, suspension natural frequency etc., but at least gives you a starting point. We can refine the model when you measure up the suspension arms.


These are the type of shocks you need - standard spring (not tapered), for 2.5" coil springs. Spring rates are here...


10" free length length have the best selection of rates (from this supplier, there are others), and seem about right lengthwise, although this will depend on the damper dimensions you choose.

Most of the custom MII conversions seem to use the tapered springs which dont put the full suspension loads through the top shock mount - but in your case you can, as the front of your car is several hundred pounds lighter than a ton of V8!

Suspension tuning 'Stateside seems to differ from the UK and Europe, where standalone coil-over shock units are the norm. Sorry for my ignorance!


28-05-2010, 10:57 PM
No, no ignorance at all. I admit I haven't researched coil overs, just as a generic "Mustang II coilover" web search, but the QA1 site keeps popping as the first, and most of the big suppliers here carry them as direct replacements due to the coil pocket on the top A-arm : http://qa1.thomasnet.com/keyword/motors ... stang%20II (http://qa1.thomasnet.com/keyword/motorsports-street-rods-shock-absorbers?&plpver=1001&key=all&keycateg=1030&keyprod=&SchType=2&keyword=Mustang%20II)

But now seeing the Proshock setup where the spring is "internal" to the shock body and not relying on the suspension members makes a huge difference... and even with the coils they are still cheaper than the QA1 units! So basically, where I should start is A) tighten or replace the TCA mounts and fasten to the lower A-arm. B) remove factory spring C) remove (or for the moment unhook) the torsion bar D) keep current shock absorber for the moment. Then, put everything else back together and move the car as much as possible through it's range of motion down the drive or wherever to set the front suspension height. Then, measure the distance between the interior surfaces of the A-arms to determine how long a spring (assuming the suspension settled to where it should be or close to), then "best guess" on the spring rate. Since the ProShock site already has MII style shocks available, I shouldn't have to worry about their total travel length.

Sound about right? :wink:

29-05-2010, 02:39 PM
I think that's a good plan, but when you remove the factory springs there will be nothing supporting the front of the car, so it will drop onto the fully compressed dampers. If you remove the damper as well, and replace it with a turnbuckle, you can play with the ride height until its just right, then work out what the range of suspension travel is (full bump to full droop) and specify the replacement shock unit accordingly. Once you know how compressed the shock has to be to get to your ideal ride height (determined with the turnbuckles) you can specify the free length of the coil. The coil rate will be determined analytically based on measured or estimated vehicle weights, mass distribution, lever arm ratios and selected natural resonant frequency (boulevard ride, slightly sporty, fast road or full race). The compressed coil length to give the proper ride height will be based on exponential interpolation from the free length, if that makes any sense - what I mean is that for a free length of 10" and a rate of 100 lb/in, compressing by 1" increases the rate by 100 lb, so the next 1" requires 200 lb, not 100 lb... and so on. Initially I made the mistake of assuming a linear rate of increase when I specified my springs and was surprised to find that I needed all of the adjustment available on the spring plates!

I'm hoping that the car has been designed to sit "just right", with the lower radius arms/steering trackrods horizontal, and the corresponding upper wishbone angle slightly "dihedral" if you'll pardon the aviation term. With the top wishbones in anhedral, like your unloaded chassis pictures above, the roll centres are way too high. I think the car will sit "just so" because the original barn-find pictures seem to confirm this.


31-05-2010, 09:36 PM
Oooh..kay.... took the springs out and the torsion bar off today in our nice little 95 degree sweatfest of a weekend. Bolted everything back up and let the front end drop... to the ground, as expected. Good thing I still had the trolley jack under the chassis! I jacked the car back up to what I thought was a decent ride height; the lower A-arm is sort of, not quite, parallel to the ground (angled ever so slightly downwards). The upper arm is basically parallel to the lower arm, also slightly angled downwards. It appears the only way to change their relationship and relative angles to one another is to install a different spindle with wider b/j mounts, if that makes sense.
I've looked through the ProShocks site and at some of their calculators for spring weights, heights and so on, and they have a calculator for determining approximate spring rates. The term "ball joint rate" keeps popping into the equation, but I have no idea what that means? My best educated guess for a proper spring rate for this car is about 225 pounds, simply based on the overall vehicle weight distribution. If the coil-overs are adjustable and can change the rate of the spring, I'm guessing that this might be a good starting point, if not a little 'soft'. I still have to measure for the free height...I think the 10" will work, as the overall height of the stock shock (at ride height) is about that. Oh.. and with the lower arm parallel and the tie-rod parallel, the overall throw of the rack changed only a little - not enough to make a huge difference in the turning radius. So, no matter what, I'm stuck with changing the rack. So... things are going to stall for a while as the funds just aren't there for a rack and the coil-overs!

01-06-2010, 11:50 AM
Hi Rick - good work. I'm surprised the upper and lower arms are near parallel, but that's OK from a geometry perspective, although drawing out the effective swing-arm length has its difficulties as the two meet at infinity! If you can get the top wishbone outer end higher than the inner end at an acceptable ground clearance that would be optimum.

I have not come across the "ball joint rate" before, but I assume it is analogous to the "wheel rate", i.e. the effective spring rate at the ball joint/spindle position. If ball joint rates are marginally lower than the spring rate associated with it, then that would be a fair assumption.

225 lb/in is clearly not a million miles from my crude assumption above. This is the spring rate I am using on the Green Machine, so I assume that your centre of mass will be/is further towards the rear of your car. One very important point though - you can adjust the vehicle height using the adjustable spring plates, but this does not increase the spring rate. A 225 lb/in spring will still be a 225 lb spring. However, depending on how compressed the spring is, it will be exerting more force on the suspension, and will be able to support greater loads at that ride height. But the rate will not have changed.

This is why I have been through 3 sets of coil springs - 250 lb, 8" long (too short, just about correct poundage), 300 lb, 9" long (waaaaaaay too stiff) and now 225 lb, 9" long (Goldilocks zone).

I don't know how complex these on-line calculators are, but if they are going to be remotely accurate there is a long list of variables to fill in. My recent swap to alloy front hubs, by decreasing the unsprung weight by 4 lb per side means that my 225 lb springs are now a bit too stiff. I haven't run the numbers to see what they ought to be now, mainly because I know I won't be able to get a 1.9" ID spring that is any closer to the optimum rate.

Sounds like you have close to zero bump-steer geometry, which is good. If you can keep the scrub radius to a minimum (but still fill the wheelarches) then you should have minimal kick-back through the steering.


01-06-2010, 01:16 PM
:wink: One finds all kinds of weirdness with previously owned cars. I think the A-arms are about as far "spread" as I can get them with the current spindle. Methinks that the original spindle may have been Pinto rather than Mustang, and may have had a different height. The Mustang spindle was no doubt used to lower the front end a little and to gain the larger brake surface. The other thing I found just be looking at replacement pieces is that the OE Mustang had a forward facing anti-sway bar, one each side, that attached to the chassis ahead of the engine. The torsion rod that I removed has unknown origins...and the tabs that are welded to the rearward facing TCA arms are just that - welded tabs. OE TCA's don't have those. So... I can see why CCC built that system, but geez... you'd think that they would have thought the weight differential through a little more. The guy that supposedly built this chassis was a respected chassis builder for the hot-rod community.
I knew in the back of my mind that the spring rates wouldn't change if the height adjustment on the shock changed, but for some reason I thought it would "stiffen" the spring more. Good point to remember... and it will help if I need to fine tune the ride height. The wheel and tire combo I have on there now (215/60R15) look good and seem to have adequate clearance, so I probably won't change those (well.. new tires anyway :D ).

I think your assumptions on the weight distribution are right on the money, Lauren. The motor is not too far behind the centerline of the car; it weighs some 375 pounds. The bare chassis with suspension... maybe 400 pounds (I was able to just lift one side on one end to move it while the motor was out... not recommended with a bad back...). The transaxle... about 100 pounds. All the bodywork - heavy mods - are done from the front of the canopy aft. I'm guessing the body weighs somewhere around 300 pounds without glass. So... weight distribution...somewhere in the 35/65 front/rear axle is my guess. With my fat ass in the seat, it'll be closer to 40/60 :laugh: .

As always :notworthy: to you!

01-06-2010, 09:24 PM
Now stop that! If it wasn't fun, I wouldn't do it... but thanks anyway, its nice to be able to help.

If you put an 11" spring on a shock with a maximum 10" open dimension, the spring will be preloaded before any of the cars weight is applied - so if it had a spring rate of 200 lb/in it would already have 200 lb preload on it. So when you put the weight of the car on the spring, it will compress less than the same spring that wasn't preloaded. So you can effect a change in ride height by this means alone, even though the spring rates remain the same throughout.

I looked at the Wilwood MII uprights, which are forged steel as opposed to the wimpy machined alloy uprights we get here (for 7evens), but the dimension between the top and bottom balljoints was too large compared to my existing Cortina/Taunus/Pinto set-up, so I went for the repair option instead. As for the chassis design - well, with the average hot rod chassis being a ladder frame with a transverse leaf sprung front beam axle and quarter elliptics on the back... nuff said. The main thing is your Sterling chassis is built stout, the front and rear geometry is good, steering is nearly bang-on... you're most of the way there. The front sway bar would have been perfectly suited to a front engine; and that's what most custom car builders know. Unless your car rolls like a cork in a storm (highly unlikely) you shouldn't need one at all. And if you do need a sway bar, it will have to be a lot lighter than the current one - probably not much stiffer than a Beetle sway bar, only better located.