504 front bumper problem
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  1. #1
    Fellow Frogger!
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    Default 504 front bumper problem

    The chrome front bumper on my 74 504GL is held on by 4 bolts, one at each corner and 2 others that each go through 10 cm by 10 cm sheet metal plates in the body and then through v-shaped bumper mounts that then attach to the bumper itself. The bolt that goes through the passenger side bumper mount is broken, no problem except that the head end of this broken bolt resides at the bottom of the engine compartment and within what looks to be a sealed structural component/rail of the car. Have no idea how to replace this bolt if the head end is essentially sealed in the bottom rail of the car. Haynes manual and shop manual are no help at all, am I missing something?

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  2. #2
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by rpieper View Post
    The chrome front bumper on my 74 504GL is held on by 4 bolts, one at each corner and 2 others that each go through 10 cm by 10 cm sheet metal plates in the body and then through v-shaped bumper mounts that then attach to the bumper itself. The bolt that goes through the passenger side bumper mount is broken, no problem except that the head end of this broken bolt resides at the bottom of the engine compartment and within what looks to be a sealed structural component/rail of the car. Have no idea how to replace this bolt if the head end is essentially sealed in the bottom rail of the car. Haynes manual and shop manual are no help at all, am I missing something?
    Unless you remove the end off the subframe assembly you can't replace the bolt. Even if remove the bracket by breaking the spot welds you would have to grind the old bolt out. Unless you have welding gear I wouldn't approach the job that way.

    I would grind the old bolt flush with the bracket. Then mark the centre with a centre punch and drill a 5 mm pilot hole through the middle of the old bolt.

    After that drill and tap to M10 /1.5 (I belive that is size -17mm nut size). You can then use a bolt to fit the bracket. If it a bit wonky, you could use a stud with a couple of tack welds to stabilise it.

    Either way it promises to be fiddly thing to repair neatly and retain originality.

  3. #3
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    Default 504 bumper

    I agree this is going to be tough repair, I just can't believe the bumper is held on in this manner, why?

  4. #4
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by rpieper View Post
    I agree this is going to be tough repair, I just can't believe the bumper is held on in this manner, why?
    Not really too hard compared to rust repair in these cars. All you need a m10/1.5 taper tap and a 8.5mm drill, plus the pilot drill.

    The RWD Pugs from 403 on used a similar system so it's been proven by the test of time. The nut probably rusted on to the stud and sheared off because too much force was applied.

    I've used stainless steel nuts on my 404 which uses a similar system.

  5. #5
    Fellow Frogger! Doush_504's Avatar
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    Robmac, so changing to stainless steel prevents this ?
    Chadi

    1982 504 SR white manual sedan with A/C (257 000 Km)
    2012 308 1.6 VTi Vapor Grey manual H/B (35000 Km)
    1994 405 1.6 white manual sedan (208 000 Km)
    1992 605 SV24 (91 000 Km)
    2005 406 2.0L automatic (Replaced with a 2013 C5)
    1983 505 GR white manual sedan with A/C (170000 Km)

    All since new


  6. #6
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by Doush_504 View Post
    Robmac, so changing to stainless steel prevents this ?
    At least one of the thread surfaces is inert and won't rust.

    It just gotta be better than two ferric materials rusting together.

    In another 40 years I'll tell you if it's successful.

    But based on the results of using stainless nuts on the exhaust manifold it should be.

  7. #7
    Fellow Frogger! Doush_504's Avatar
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    Quote Originally Posted by robmac View Post
    At least one of the thread surfaces is inert and won't rust.

    It just gotta be better than two ferric materials rusting together.

    In another 40 years I'll tell you if it's successful.

    But based on the results of using stainless nuts on the exhaust manifold it should be.
    Fairly logic
    Thanks
    Chadi

    1982 504 SR white manual sedan with A/C (257 000 Km)
    2012 308 1.6 VTi Vapor Grey manual H/B (35000 Km)
    1994 405 1.6 white manual sedan (208 000 Km)
    1992 605 SV24 (91 000 Km)
    2005 406 2.0L automatic (Replaced with a 2013 C5)
    1983 505 GR white manual sedan with A/C (170000 Km)

    All since new


  8. #8
    1000+ Posts Peter Chisholm's Avatar
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    Quote Originally Posted by rpieper View Post
    I agree this is going to be tough repair, I just can't believe the bumper is held on in this manner, why?
    May seem to be a poor way to attach a bumper but, except in your case, it seems to work well. I've owned quite a few 504s over the years and have never had this problem. What I have experienced is the stud being bent a bit due to a previous accident. Unfortunately, you may just be unlucky.

  9. #9
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    Default 504 bumper

    Thanks all for the advice. I took another look at the bolt/stud that protrudes out from the body and its definitely broken, about 3 cm left of it with the nut on it outside of the car. I'm not sure however if the bolt is broken in its middle or just broken off from where it was attached to the frame as i dont see any remaining bolt attached to the frame. Is the bumper mounting bolt/stud welded to the frame and then allowed to stick through the square sheet metal plate? If so am wondering how to get that stud reattached to the frame. Car is getting resprayed sooner or later and the bumper isnt going to fall off in the mean time but I am curious as to how this mounting system works. Bt the way, the bolt/stud does not look rusty but the 10 x 10 plate is rusty around the hole in the middle through which the bolt passes.

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