Heartbreak-broken rear shock mount

Stevehose

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This might be overkill? I'd rather weld a plate than drill holes in the floor. The original tower top shock mount area has a few crappy spot welds holding it on and is thin, I think the new steel plate will be more than adequate moving forward. Just wish I hadn't waited till now.


I may not have this in time but I'm working with my neighbors who build custom instrumentation for oil pipelines and they have a pretty extensive machine shop across the parking lot from us here at work. I want to develop a brace that solves this problem without any welding, however will require 2 holes to be drilled in the trunk floor at the base of the shock tower and be tightened around the smaller cone that the rear shock attaches to. It will also include a ring around the top where Steve's tore. This will transfer the stress to the floor, which can be braced from below. I will check on the progress later today after a meeting I have. I started working on this when I noticed that the Polaris coupe had no additional welding on top and I think the Bilstein shocks do cause additional stress there because they are harder to compress and the springs take less of the burden.
 

Nicad

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Sorry to hear that Steve. You'd think BMW would eventually get this right as the E36 and E46 were plagued with shock mounts ripping through just like yours. My E46 is also known for the subframe ripping away from the floor. I bet the newest stuff is even worse!!

Looking forward to seeing what reinforcements happen to get your Coupe back on the road.
 

tmason

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Sorry to see this Steve.Your car is so nice I would of never thought this could happen like that? If my skin was mint I would offer to you because your car is that nice + you are even nicer! I'm going to check my out with I put the used Bilsteins I just purchased.
 

CSteve

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Steve, I know it's small consolation but you can take some in knowing you have saved many, all if they are smart, from your fate. As soon as the snow is gone and the roads are washed clean of salt I am on my way to my mechanic/welder. Post haste!
Steve
 

rsporsche

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i think its also a Karmann issue. a friend of mine had a similar issue with pushing a shock thru an early 911
 

Luis A.

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I feel partly responsible for the mishap as I was riding on the side that suffered to pop-out... Sorry Steve. It was a very strange noise, not metallic in any way and trying to remain blindly optimistic, I thought it was the rear deck speaker that had partially come off and was 'hinging' down on the strut top

I have not once thought about inspecting mine but I will now and effect a prophylactic repair over the winter months.

For Sven or others who have done this, how do you assure that the scrap piece that gets tack welded temporarily, with the guiding pilot hole for the saw, is placed exactly centered on the tower top or existing hole?

And for the large 'washer' that gets welded in from below (Sven's technique), you probably have to cut and shape its circumference by means other than the same hole saw otherwise the washer would be too small, correct?
 

Ohmess

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Hi Peter -- I might be interested in acquiring one of these if your friend makes more than one.

Two thoughts: In the 72 restomod clubracer thread, the rear brace was tied to the dif mount under the floor; this seems like a good idea. I wouldn't go with a 2" pipe bolted directly to the dif, but perhaps a floor plate inside the trunk with spacer tubes underneath for the four bolts that the dif mount bolts into. Again, maybe cutting holes in the trunk isn't worth it here.

Second thought would be to incorporate a plate for moving the battery into the trunk into your brace.


I may not have this in time but I'm working with my neighbors who build custom instrumentation for oil pipelines and they have a pretty extensive machine shop across the parking lot from us here at work. I want to develop a brace that solves this problem without any welding, however will require 2 holes to be drilled in the trunk floor at the base of the shock tower and be tightened around the smaller cone that the rear shock attaches to. It will also include a ring around the top where Steve's tore. This will transfer the stress to the floor, which can be braced from below. I will check on the progress later today after a meeting I have. I started working on this when I noticed that the Polaris coupe had no additional welding on top and I think the Bilstein shocks do cause additional stress there because they are harder to compress and the springs take less of the burden.
 

Stevehose

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Nah I have people riding shotgun all the time, and was glad to have you there for moral support! It did derail the coupes & c0cktails event for the night but I made up for it after I dropped you off.

I just returned from the bodyshop and it will be going in the week after next. He's working on a coupe now and I suggested he contact the owner to do the repair while there and after seeing the fugly pic of mine he readilly agreed. In the meantime I will prep the trunk for the repair and ensuing mess and do my other maintenance I had planned (steering linkages, driveshaft bearing/guibo etc. Hopefully back on the road by the end of the month.


I feel partly responsible for the mishap as I was riding on the side that suffered to pop-out... Sorry Steve. It was a very strange noise, not metallic in any way and trying to remain blindly optimistic, I thought it was the rear deck speaker that had partially come off and was 'hinging' down on the strut top

I have not once thought about inspecting mine but I will now and effect a prophylactic repair over the winter months.

For Sven or others who have done this, how do you assure that the scrap piece that gets tack welded temporarily, with the guiding pilot hole for the saw, is placed exactly centered on the tower top or existing hole?

And for the large 'washer' that gets welded in from below (Sven's technique), you probably have to cut and shape its circumference by means other than the same hole saw otherwise the washer would be too small, correct?
 

decoupe

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Me too.

And for the large 'washer' that gets welded in from below (Sven's technique), you probably have to cut and shape its circumference by means other than the same hole saw otherwise the washer would be too small, correct?

Pretty sure that the washer is actually welded in from above as seen in the last picture and by the text accompanying it. I don't think it would be physically possible to weld it from below (let alone the clean and prep required) given the confines of the tower. Doing the welding from above is going to be hard enough though in my case, a 6" rear speaker hole is centered on the shock mount so that will help.

Remember to do a thorough rust prevent treatment of the weld area from below as any protection that was there will be compromised by the welding. Cleaning and a good blast of POR 15 or similar as a minimum.
 

Ohmess

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Steve - are you going to have anything else done simultaneously, or just the shock tower tops?
 

Peter Coomaraswamy

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Chris, et al- I plan on incorporating the battery tray as well, I have wanted to do this for a while and wish I had earlier. Not sure what type of steel we will use but I did a little picture if anyone has some suggestions. I would like to make the battery tray optional so the only additional weight above doing it as 1 piece will be a few bits of hardware. This is what we came up with as a strengthening for the shock towers vs. a rear "stiffening" brace.
 

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Sven

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For Sven or others who have done this, how do you assure that the scrap piece that gets tack welded temporarily, with the guiding pilot hole for the saw, is placed exactly centered on the tower top or existing hole?

Carefully. In my case the tops were still in place (not busted through), so I just tacked a piece with the correct size pilot hole centered on the big hole. I suspect if you are off a bit it probably won't matter that much since it is just a shock and shouldn't affect the wheel alignment.

The big "washer" is inserted from below and jammed in place with a long stick. The lip on the washer fits under the tower sheet metal edge. Welding is from the top. I wanted the washer to be wide enough so the edges would be closer to the curved part of the tower top (stronger than the flat flexible middle section). Of course rust proofing underneath and top afterwards goes without saying.

Good luck everybody. I expect a report from at least a dozen coupe owners who will be proactively fixing their mounts this winter ;-)
 

adawil2002

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Steve that really sucks, the picture of the broken tower are heart wrenching and could happen to many of us running Bilsteins. Metal fatigue is a scary.

Just read this entire thread. The same thing happened to Doug Dolan's car, his is pristine too and highly modified. He was talking about it last year at The Vintage in W-S.

I am taking these cases as fair warning and will ask VSR to reinforced Athena's while she's there.
 
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Ohmess

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I'm no engineer, but it looks like your idea is to distribute the forces around the wheel well.

The battery mounts appear to rely on a curved brace secured to the shock tower by screws. Perhaps the rounded piece that surrounds the tower on your design could be fashioned to accommodate the brace from an existing battery mount, alleviating holes in the shock tower?

Chris, et al- I plan on incorporating the battery tray as well, I have wanted to do this for a while and wish I had earlier. Not sure what type of steel we will use but I did a little picture if anyone has some suggestions. I would like to make the battery tray optional so the only additional weight above doing it as 1 piece will be a few bits of hardware. This is what we came up with as a strengthening for the shock towers vs. a rear "stiffening" brace.
 

Luis A.

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Thanks Sven, that makes sense.

Since mine have not yet busted through, would simply welding a disc above the tower work? Or does the top need to be cut out as you did and then a new disc welded in. It looks like Bert's repair is just a disc welded on the top, is that correct?

It would be so painful to pre-emptively fix this and then have them bust through anyway...

Carefully. In my case the tops were still in place (not busted through), so I just tacked a piece with the correct size pilot hole centered on the big hole. I suspect if you are off a bit it probably won't matter that much since it is just a shock and shouldn't affect the wheel alignment.

The big "washer" is inserted from below and jammed in place with a long stick. The lip on the washer fits under the tower sheet metal edge. Welding is from the top. I wanted the washer to be wide enough so the edges would be closer to the curved part of the tower top (stronger than the flat flexible middle section). Of course rust proofing underneath and top afterwards goes without saying.

Good luck everybody. I expect a report from at least a dozen coupe owners who will be proactively fixing their mounts this winter ;-)
 

Sven

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Luis - I would not recommend it. You would have two layers of metal. On the good tower this would increase the overall thickness of the hole and may make it difficult to fit the rubber grommet (not sure of the tolerances). It would also be tricky to rust proof the area between the top of the tower and the underside of the new washer. Imagine trying to do that from below. my $0.02,
 

decoupe

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Sven,

Having already done this before, is there anything you would do differently to make it easier or "better"?

I thought bevelling the edge of the "washer" would be easier than cutting in a lip and accomplish the same thing - providing a good welding contact joint and positioning the washer in the hole. ==/ \== the bevel would determine how high in the hole the washer would project above the tower.

Doug
 

Sven

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No, no change.

The bevel would probably work fine as well.
 
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