Heartbreak-broken rear shock mount

[halboyles]

I have been collaborating with @Stevehose to create a 3D model that can be used to CNC the shock tower reinforcement cap. I've had the model created and added a 15mm lip around the top to make it easier to fit and weld. I've done some research into having them made out of mild steel rod and it cost about $50 each plus shipping. That price is for 26 pieces or enough for 13 vehicles. So the total would probably be around $125 for a set shipped.
If anyone knows a machinist that can do this for less and is stateside, that would be much better as far as quality control and shipping goes.
Here are some pics of the reinforcement cap.

 

[m5bb]

FYI- I had this repair done of the left rear (driver) when I was on a trip and it broke through.
Tank was not removed.
As long as there is no open vapors in the area it should be safe. Electric welding may be safer than gas.
The shop just made a new top out of metal and welded it on.
Many of the tops just separate at welds and can just be rewelded with a better job of welding than original.
Gary

 

[teahead]

I'll definitely be up for a pair.

 

[Bmachine]

I have been collaborating with @Stevehose to create a 3D model that can be used to CNC the shock tower reinforcement cap. I've had the model created and added a 15mm lip around the top to make it easier to fit and weld. I've done some research into having them made out of mild steel rod and it cost about $50 each plus shipping. That price is for 26 pieces or enough for 13 vehicles. So the total would probably be around $125 for a set shipped.
If anyone knows a machinist that can do this for less and is stateside, that would be much better as far as quality control and shipping goes.
Here are some pics of the reinforcement cap.

That could be interesting. Considering the benefits, $125 seems like a fair price.

 

[autokunst]

I have been collaborating with @Stevehose to create a 3D model that can be used to CNC the shock tower reinforcement cap. I've had the model created and added a 15mm lip around the top to make it easier to fit and weld. I've done some research into having them made out of mild steel rod and it cost about $50 each plus shipping. That price is for 26 pieces or enough for 13 vehicles. So the total would probably be around $125 for a set shipped.
If anyone knows a machinist that can do this for less and is stateside, that would be much better as far as quality control and shipping goes.
Here are some pics of the reinforcement cap.

I'm not entirely sure I can visualize how these fit/interact with the existing metal, but I think the price sounds reasonable and I'd be in for a pair, too.

 

[Stevehose]

I'm not entirely sure I can visualize how these fit/interact with the existing metal, but I think the price sounds reasonable and I'd be in for a pair, too.

Hal @halboyles, correct me if I'm wrong but you'd cut the curved top of the tower off and slip these inside down to the lip then weld.

 

[halboyles]

you'd cut the curved top of the tower off and slip these inside down to the lip then weld.

Yes, exactly. I put the lip on there to provide a depth measurement for cutting and to make it easier to weld. So, the curved top of the strut tower would be cut 15mm from the top of the existing hole. Here is my adjusted model with the lip based on your hand-drawn model.

 

[Gazz]

The thing to remember is that it's the vapor that's going to burn quickly, and it prefers a Stoichiometric ratio. A full tank is less dangerous than a partially empty one. No air to burn means you can't get an explosion. Fire maybe, if your tank or lines are leaking, but an extinguisher should be at hand anyway.

In my youth I deliberately lit a rag at the open mouth of a VW gas tank that just had gas vapors in it. I was watching from behind solid protection and it took a while to ignite, which resulted in a whoosh and a slight bulging of the tank, but nothing really dramatic. Not enough fuel for any real destruction. I've read some statements that a tank full of gas has the power of several sticks of dynamite. Sure, when properly mixed with oxygen and ignited you'll get that much power from it, but in its liquid state, it's simply not going to ignite all at once. It's not an explosive after all. A fan to disperse any vapors in the vicinity of the trunk would be prudent.

It's not hard to pull the tank and that gives you a bit more room in the trunk, so I'll likely pull mine when I get to that repair.

That's not what happens in movies. Sorry but I've seen too many exploding cars from gunshots and flicked cigarettes to trust your advice. Just a bulgy tank? Hrmph! Which, by the way, is the sound of an exploding gas tank.

Apparently some scientists experimented with flicking lit cigarettes into gasoline vapours. They tried it 4500 times and not once did it ignite. Unfortunately they all now have emphysema and lung cancer.

 

[Bmachine]

I'm not entirely sure I can visualize how these fit/interact with the existing metal, but I think the price sounds reasonable and I'd be in for a pair, too.

I think @Stevehose 's pics in posts 103 and 112 illustrate the principle. The main difference is that @halboyles design adds a 15mm tall outer ring so you can simply slide the whole unit down into the tower which was cut off 15mm from its top. The outer ring keeps the unit from falling inside the tower and makes it easy to preserve the proper height.

 

[Arde]

How about getting BMW to issue a recall and have the dealers fix this problem for free?

 

[Bmachine]

Yes, exactly. I put the lip on there to provide a depth measurement for cutting and to make it easier to weld. So, the curved top of the strut tower would be cut 15mm from the top of the existing hole. Here is my adjusted model with the lip based on your hand-drawn model.

I sent this to a machinist friend of mine who may be able to make them. He pointed out that the CAD drawing as well as the hand drawn sketch indicate a very thick 10mm wall. In post 112, @Stevehose mentioned that his machinist suggested bringing that down to 5mm instead which seems more than enough.

 

[Bmachine]

So the profile would be something like this:

 

[halboyles]

He pointed out that the CAD drawing as well as the hand drawn sketch indicate a very thick 10mm wall. In post 112, @Stevehose mentioned that his machinist suggested bringing that down to 5mm instead which seems more than enough.

If that is the consensus, I can have the model modified and provide the .step file for CNC.

 

[rsporsche]

Hal, i have a question and maybe a suggestion. question first - can you install @daddywad 's rear strut brace over the new piece? if not, does it make sense to make the new cap to allow the brace to be attached

follow up to Bo's drawing ... wouldn't this raise the back of the car as it would remove the curve and lower the mounting point? seems to me that the height of the existing top of the cap should match the height of the new top.

 

[paul]

I used a standard mild steel schedule 40 pipe end cap. 115mm od x 33 mm high. (any petrochem guy will know what I am talking about) from memory it fitted over the top of shock tower and had about 1.5 mm clearance all around. (which is ideal for welding) I had the end bored out to just outside the 3 holes on top of tower. I did minimal amount of welding on top as this is the weak spot on these towers....and as you can see full penetration welds on the side where it is stronger. So far I have not had issues and I am running 10" wide rear wheels on the car. This is all buy over the counter stuff except the boring out. I think I posted this up before when someone asked about them in a trunk shot of my car. That's my 2 bob's worth....happy new year.

 

[daddywad]

Hi all, going on the photos showing the end cap, my braces would not likely fit under the cap around the existing tower. the brace ring width is 40mm

 

[tferrer]

So far I have not had issues and I am running 10" wide rear wheels on the car.

More importantly, how did you get 10" wheels under your coupe? ! Any pictures?

 

[halboyles]

i have a question and maybe a suggestion. question first - can you install @daddywad 's rear strut brace over the new piece? if not, does it make sense to make the new cap to allow the brace to be attached

follow up to Bo's drawing ... wouldn't this raise the back of the car as it would remove the curve and lower the mounting point? seems to me that the height of the existing top of the cap should match the height of the new top.

I'm not sure about the fitment of the brace with the new cap. Maybe someone else can chime in.
The original geometry would have to be honored whichever reinforcement option is used. That requires careful measurement of the position of the top of the mount before cutting and during welding.

 

[daddywad]

the brace is adjustable width ways as shown

 

[Bmachine]

In my view, the way I envisioned it in the drawing above, the outer shape of the shock tower should be very similar to the original shape. Therefore that strut brace should fit just fine. For that, the outer ring that @halboyles added to @Stevehose’s design should be the same thickness as the shock tower wall.

@rsporsche The overall height of the shock mounting point should also be exactly the same as it was in the original tower. We first cut 15mm from the top and then we add a cap which protrudes 15mm above that cut. So, there should be no change in ride height or geometry