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Thread: Front Disc Dust Splash guard bolts

  1. #1
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    Front Disc Dust Splash guard bolts

    I'm just replacing front disc calipers, master cylinder, and the dust guards.

    Having now painted the dust guards and tried to fit them using the original M7x12 and 2 M7x20 bolts each side, I have managed to strip one bolt and strip the thread in the steering knuckle on the other side while trying to torque to 36lb ft. as per the Haynes and Autodata books.

    When I removed the guards again, they are really 'squashed' the metal around the mounting holes...

    I have since found reference to two (or three!) tightening torques for bolts in various places on the net;-

    Front Wheel Brakes

    Backing plate to steering knuckle bolt (36)
    Splash shield to steering knuckle bolt (7)
    Caliper housing screw (14 - 18 )
    Cylinder to backing plate bolt (18 )
    Caliper to steering knuckle bolt (29)
    Bleeder Valve in cylinder/ caliper (3.5 Max)
    Hose to cylinder/ caliper (11 - 14)
    Screw for clamp nut (7 - 9 Max)


    Now not being a genius, but I'm sure there is only one plate that is bolted to the steering knuckle... so my question is what is the correct torque?

    There is mention above of a 'backing plate' at 36lb ft, as well as a 'dust shield' at a much lower 7lb ft. (I have also seen this quoted as 14lb ft?)

    What is the difference between a backing plate and a dust shield - there can only be one fitted?!? (unless I'm missing something `¬)

    I did wonder if there is confusion between a 'backing plate' used with front drums and a 'dust shield' used with front discs.

    Any info would be good, as I do not want to strip any more threads, but need to ensure I've got it right!

    P.S. is the two pin brake light switch on the m/c supposed to be normally closed or normally open - mine is normally closed and am assuming it needs replacing... unfortunately I have already removed the master cylinder, so cannot test it (I should have done that first I know...)

    P.P.S the caliper mounting bolts are only 29lb ft in comparison!
    Last edited by MartinB; 18-10-2017 at 04:31 PM.

  2. #2
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    Although I have been advised by a well know VW parts supplier that the correct torque for the M7 bolts for the dust/splash shield is 36 ft lb, I am going to ignore them as I believe they are confused with the front DRUM backing plate bolts (which I think are M10).

    The drum backing plate supports all the brake shoes etc and uses the larger M10 bolts.

    The disc dust/splash plate is secured with the M7 bolts and has no other parts attached to it.

    This seems to be common sense, and is pretty close to the torques specified for the metric torque chart for hex head cap screws here https://www.imperialsupplies.com/pdf...rqueCharts.pdf

    Its no wonder the M7 bolt stripped... just need to get some helicoils now.

    Also got a new 2-pin brake light switch, so also now know that my original is faulty.

  3. #3
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    Stripping threads on something like a steering knuckle is a nightmare.
    I couldn't help on your original post but it looks like you
    have done your research and got a way forward on this.
    Good that you posted back, you may save someone else from the same issue.

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    Thanks Steve `¬)
    I have also wondered that I could probably use a nut on the back of a longer bolt as its only securing the plate. I have got some M7x40 bolts that would need to be cut to length, (the sheered one has an M7x20 normally) but looking at the back of the knuckle there seems to be room to extend to say 25mm without fouling anything. Not very pretty, but a helicoil kit to do the repair is only marginally cheaper than a new stub axle it seems! (although a lot more work to replace it...)
    I expect I'll use the helicoil though, as it feels the better job than a nut!
    `¬)

  5. #5
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    Quote Originally Posted by MartinB View Post
    Thanks Steve `¬)
    I have also wondered that I could probably use a nut on the back of a longer bolt as its only securing the plate. I have got some M7x40 bolts that would need to be cut to length, (the sheered one has an M7x20 normally) but looking at the back of the knuckle there seems to be room to extend to say 25mm without fouling anything. Not very pretty, but a helicoil kit to do the repair is only marginally cheaper than a new stub axle it seems! (although a lot more work to replace it...)
    I expect I'll use the helicoil though, as it feels the better job than a nut!
    `¬)
    This is one I can comment on since I've had similar dealings with stripped threads and I had to resort to the following because of where it was:

    Firstly, I drilled out the old sheered bolt, and tapped a thread for a larger bolt, in my example, it was an m12 thread. (I used what I had).

    Since I had some m12 threaded rod, I drove that into my newly threaded hole and locked it home permanently, by drilling a small hole through where the threads meshed and drove a locking pin into the hole to make sure it couldn't turn, and ground both the front and back of the rod down to be flush with the metal plate, I then drilled and tapped an m7 hole through the center of the rod...

    Hey, it mightn't be what others would do, but it worked for me and I've had to do similar to an engine, where part of the injector array stripped its threads.
    Both worked for the life of the respective vehicle without any detrimental effect

  6. #6
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    That's an interesting solution! I'm not sure I need to go to that extreme in this case, but very clever in the execution! I will have to remember that if I have similar issues else where `¬)
    I had considered drilling and tapping to a larger size, but in this case it is just securing the splash guard.

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    Quote Originally Posted by MartinB View Post
    That's an interesting solution! I'm not sure I need to go to that extreme in this case, but very clever in the execution! I will have to remember that if I have similar issues else where `¬)
    I had considered drilling and tapping to a larger size, but in this case it is just securing the splash guard.
    Hey, it worked; I was working on a budget and had to literally use what I had on hand in a place where using a larger bolt wasn't viable .
    I already owned the necessary materials to do the repairs and for me, it was an easy and VERY cheap solution.
    Especially with the injector array, I needed to use my van that same day and it was a desperate attempt to get it back on the road, since the alternative was removing the head and sending it off to be repaired... not a viable option at the time...
    Last edited by Gaisa; 30-10-2017 at 06:06 PM.

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    I agree with you! `¬)
    If it works and you have the bits, then it makes total sense.
    I actually think its a very clever solution!
    I tend to overthink everything and not get anywhere...

  9. #9
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    thank you

    Believe me, you aren't the only one to overthink things, I still do it regardless of my being an avid fan of K.I.S.S (Keep It Simple Stupid) and I spent quite a bit of time on both occasions running in mental circles before literally slapping my forehead and pretty much impersonating Homer Simpson's "Doh!" moment when I worked it out.
    Last edited by Gaisa; 30-10-2017 at 07:51 PM.

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