Phill's Nova Project finally begins

[islandman]

They're fine Alistair - and I did wonder myself about adding some weight to the front. Nova Cars back in the 80's used to recommend carrying a spare wheel in the front compartment to help the weight distribution. Or maybe I should add a front spoiler to create downforce on the front of the car?

Having said that - under normal (sensible) driving it's really not a problem.

Mine benefits from the added weight upfront of Pop-Up Lights (they are actually quite heavy), Radiator and pipework and heavy Duty Battery

[NovaF4]

I'd like to reinforce David's comment about brake bias.

From experience driving my nova a heck of a lot for about 8 years, a brake bias is essential. My nova also used to lock up it's front wheels under heavy braking. The weight of the engine in the rear thows its weight forwards when braking, therefore a brake bias helps to overcome this issue provided it is set up for more bias toward the rear brakes.

The Citroen brakes should be an excellent upgrade as they are good quality items - lighter calipers and and larger pads, although it may be difficult nowadays to get spares (?).

Also with a brake bias installed I don't think it's necessary to carry a spare wheel in the front compartment.

[Phill]

There is but, you do need to add a brake bias adjuster valve to the circuit to shift some braking force to the rear

Thanks for the advice NovaF4. How do I increase the bias to the rear on a standard VW dual circuit master cylinder?

There are seperate feed pipes to each of the front brakes from one circuit - and a single feed to the rear drums from the other circuit - where would I place the bias valve? Or would I need two (to decrease the pressure to each of the front discs) or do I need a different master cylinder altogether?

[BlueNova]

Thanks for the advice NovaF4. How do I increase the bias to the rear on a standard VW dual circuit master cylinder?

There are seperate feed pipes to each of the front brakes from one circuit - and a single feed to the rear drums from the other circuit - where would I place the bias valve? Or would I need two (to decrease the pressure to each of the front discs) or do I need a different master cylinder altogether?

I'll be doing the hydraulics on my brakes soon and would really appreciate some help on this issue too.

In principle a brake bias valve sounds sensible, but does it operate by simply restricting the flow to the front brakes, (and hence reducing the total braking pressure available to the 4 wheels) or does it actually reduce the flow to the fronts and increase that to the rears?

Apologies for my inexperience in hydraulics .... I've mostly left that department to the local garage in the past! It's just that when I last drove my Nova (in 1991) I recall having to apply a fair bit of pressure to the brake pedal in light of the lack of servo assistance and the thought of reducing the overall braking pressure sounds counter intuitive, even although I understand the desire to stop the fronts locking up.

Alistair

[NovaF4]

As far as I know (please anyone correct me if I'm wrong)...

A proportioning valve is used to reduce brake line pressure to the line it is fitted to, not to increase it. You need to locate it onto the front caliper feed to reduce the pressure of the front calipers. Having said that I'm not certain if this does in fact increase the pressure onto the rear brakes. For example, if it starts off as 50/50 pressure front and back, with the valve you can make it 30/70, or 40/60 (front/back) etc.

My 'screw type' brake proportioning valve is located just behind the front bulkhead (the rear wall of the bonnet space) slghtly off centre toward the drivers side. It is attached to my RED9 front axle support frame. The bulkhead has a hole cut in it for accessing the valve to adjust it. With the wheel off it can be accessed through the wheel arch as well.

You must connect the outlet of the dual master cylinder to the inlet of the proportioning valve. The outlet of the proportioning valve is connected to a 'T' splitter which has two lines, leading to front calipers. You may need to change the configuration of your front brake lines for this to work (I can't be sure from your description).

Rotating the adjustment knob in a counter-clockwise direction will reduce the pressure to the front brakes.

I had a VW expert mechanic fit it as part of a large IRS suspension modification job many moons ago.

Can someone check this over and make sure I've got this the right way round! I probably haven't explained this very well. David! Lauren!

[Phill]

I probably haven't explained this very well

Yes your explanation makes perfect sense and is pretty much how I thought it should work. My concern had been that there are two outlets ports on the master cylinder for the front brakes (on for each side) but I'm guessing only one should be used (the other blanked off) and the "T" piece after the bias valve is used to feed each side? I recall my old mini (circa 1967) had a non adjustable brake bias valve fitted (I think these were standard on all minis) but this was to limit pressure to the rear brakes and so providing more braking at the front (as the car had drums all round).

[Spacenut]

Hi Phill - yes, that should work OK. From what I can see of the VW master cylinder design, the two separate front brake ports share the same piston, with the rear port supplying the rear brakes. So blanking off one of the ports will not affect the brake bias in any way. Put the proportioning valve in the single front port and then split the feed.

If you apply a specific pressure to the brake pedal, the force applied to the master cylinder will be shared between the front and rear circuits. With a proportioning valve in place, the force that is lost from the front circuit will be apportioned to the back instead, so no braking effort is lost. Hopefully the result is a front axle less likely to lock up early and therefore more stopping power overall - with a well-balanced braking system you will be able to apply more pedal pressure before any of the wheels lock.

The goal is to ensure that the front wheels lock ever so slightly before the back wheels, typically in dry conditions as this will be when the car is used most. Brake bias is a compromise, it can never be right for all conditions, which is why race cars have the ability to adjust the bias while on the move.

Lauren

[Spacenut]

There are other ways of changing the brake bias. In no particular order,

(i) 20lb of lead in the front bumper (early Porsche 911), in fact anything that changes the front/rear weight bias
(ii) Mini proportioning valve in the front brake circuit
(iii) Reducing the width of brake shoes (not really an option if the bias is to the front, unless you can fit smaller disc pads)
(iv) adjusting tyre pressure
(v) adjusting damper settings (if adjustable)

Best by far to go with an adjustable proportioning valve or a brake balance bar and twin master cylinders. Anything else is just a dreadful compromise

[BlueNova]

Hi Phill - yes, ......

If you apply a specific pressure to the brake pedal, the force applied to the master cylinder will be shared between the front and rear circuits. With a proportioning valve in place, the force that is lost from the front circuit will be apportioned to the back instead, so no braking effort is lost. Hopefully the result is a front axle less likely to lock up early and therefore more stopping power overall - with a well-balanced braking system you will be able to apply more pedal pressure before any of the wheels lock.

The goal is to ensure that the front wheels lock ever so slightly before the back wheels, typically in dry conditions as this will be when the car is used most. Brake bias is a compromise, it can never be right for all conditions, which is why race cars have the ability to adjust the bias while on the move.

Lauren

Thanks for this Lauren, you've put my mind at rest (see my earlier post above) .... I'm going to set up my brakes with a proportioning valve too!

Alistair

[NovaF4]

hope this helps...

IMG_0872.jpg

IMG_0482.jpg

184.jpg

not sure why one has uploaded sideways. You'll have to tilt your head.