Heartbreak-broken rear shock mount

[Stevehose]

Yes, I haven't measured yet but the thickness could very well end up that much.

I don't know anything about welding so if it is better to weld the disk inside the tower instead of on top like a cap for strength then so be it. It would make the disk all the much thicker but the dish out/bevel would just have to be deeper to offset it.

So it's a cap on top vs fitting it inside? Again, cap would be easier given the possible variances involved in fitting it snuggly inside the tower. And the bottom tower welds are butt welds yes?

Steve, that looks good. I know you didn't draw it to scale but my guess is that the disc will be pretty thick, maybe 1/2 to 3/4" thick. Not sure if that impacts anything. I always envisioned the disk as fitting inside the diameter of the tower. The resulting overlap weld would be easier (stronger?) than a butt weld to the edge of the cut tower and prevent the possibility of damaging/burning out the relatively (to the disk) thin edge of the tower. Thoughts?

 

[Ulrich 3.0 CSA]

Hello all,

a friend of mine has this as a solution if the tower cracks:

Ulrich

 

[Stevehose]

Can you give more details, how it is made, installs, etc? Thanks.

Hello all,

a friend of mine has this as a solution if the tower cracks:

Ulrich

 

[Stevehose]

Dimensions

Approx dimensions are:

104mm tower diameter
2.5mm metal thickness (seems very thin!-what is standard coupe sheet metal thickness?)
15mm curved top section

So in order to insert the disk into the tower it would have to be 15mm + desired amount in the tower - say a 1" disk allowing 10mm inside then dished approx 21mm or so leaving the top thickness for the shock at 4mm (vs 2.5mm original) which is about 3/6" assuming the rubber bushing would mount on the added thickness. I'd go as thick as the bushing would allow (customizing it to accept more metal if possible) and dish out less.

Would it be advisable to not only weld the top section where the top of the tower and the side of the disk insert meet but also spot weld the sides for added up and down strength?

My knowledge of welding ends with pronouncing the word. I am going to a CNC place tomorrow for an initial conversation on making this so any further input is appreciated.

 

[Luis A.]

Steve, I think all of that sounds good. The best way to get the exact dimensions of the ID of the tower would be to measure it off the sawed off section; easier than measuring inside the trunk. However you need to ensure that the tower doesn't taper in or out and the measured ID at the cut line carries through the next 8-10 mm. Drilling 3 or four holes around the tower to also weld the disk on its side would be simple but it is my feeling the circumferential weld will be very strong for the loads seen at that site.

 

[Stevehose]

Agreed. I will have the tops cut and measured before giving final specs to CNC shop. The tower does not appear to taper.

The best way to get the exact dimensions of the ID of the tower would be to measure it off the sawed off section; easier than measuring inside the trunk. However you need to ensure that the tower doesn't taper in or out and the measured ID at the cut line carries through the next 8-10 mm.

 

[dang]

I think it would need to be welded in though as the shock puts stress on the metal both going up and down.

Automotive epoxy bonded to a large surface area like that would probably hold as good or better than a weld, without adding the rust prone areas that welds do. In addition, the "sleeve" would be added to the existing shock can from underneath so the original material would still be there and help hold it in place.

It would probably work just to bond a large washer on the underside of the top surface. That would probably transfer enough of the load to the outer edge and reduce the flexing.

 

[Peter Coomaraswamy]

I am afraid to re-assemble the trunk until I do some kind of reinforcement to the rear shock mounts. The top of the mount definitely has a lot of stress on it with the Bilsteins and I wonder how much those yellow shocks contribute to the condition Steve and others have had. Maybe people who have had this problem can chime in on that. It seems that with a softer shock more stress can be transferred to the spring perch, and so the question continues, do the lowering springs contribute as well? Look and ride may be an improvement but I feel there may be an additional price to pay-

 

[Stevehose]

Update

I went to a machine shop today and showed them my problem and proposed fix. No problem on making the piece. Instead of dishing out the underside it will likely be more squared off but no big deal.

About $100 for both give or take a few $$.

So I plan to cut the towers at the start of the curved section on top, come up with a final dimensions, and have them made. I will probably bring them the cut tower for preliminary sizing.

Then back to the shop for insertion and welding.

The machinest said the top weld with the piece slipped inside the tower should be more than adequate.

Then I will rust proof accordingly and hopefully this will last the life of the car.

More to follow.

 

[Luis A.]

There's a factor we have not discussed as a possible cause/accelerator for this failure. Sven brought this up. Are the non-factory shocks we are all using now, when fully collapsed, even a small amount longer than the distance allowed with the spring fully compressed and against its bump stop? This would put a tremendous amount of stress on the tower top and bear the full brunt of the car's weight at that moment.

 

[Stan]

14" x 16" Wheels

I am very curious to learn the wheel size on the cars that experienced shock tower failure. Dies this happen more often in cars with Bilstein shocks and 16" wheels than with OEM shocks and 14" wheels?:?:

 

[Stevehose]

The articles in the old CS Registry in the 80's and early 90's fingered the blame mostly but not entirely on the stiffer Bilsteins. Empirical, nothing scientific.

Now 30 years later I can't imagine any car that is driven wouldn't be susceptible to the metal fatigue no matter what shock is back there but that's just my guess. It's a design flaw possibly accelerated by stiffer schocks. That top curved metal area is very thin and brittle. Mine had no rust up there.

The roads in New Orelans are very bad and the frequency of my driving most certainly accelerated my problem.

I am very curious to learn the wheel size on the cars that experienced shock tower failure. Dies this happen more often in cars with Bilstein shocks and 16" wheels than with OEM shocks and 14" wheels?:?:

 

[Lotuss7]

There's a factor we have not discussed as a possible cause/accelerator for this failure. Sven brought this up. Are the non-factory shocks we are all using now, when fully collapsed, even a small amount longer than the distance allowed with the spring fully compressed and against its bump stop? This would put a tremendous amount of stress on the tower top and bear the full brunt of the car's weight at that moment.

Very interesting thought.

When I replaced the stock setup with lowering springs I also used specially set up Bilsteins (valving / stroke) designed for use with the springs by Hardy and Beck.

With a shorter stroke I had really thought of them as more effectively keeping the spring in place when fully extended such as when the wheel is off the ground. If the shock is not shorter I suppose there is the potential for it to bottom out and exert force on the perch beyond the bump stop limitation.

Ouch.

 

[Stevehose]

I have never bottomed out that I can recall.

 

[Bwana]

I am very curious to learn the wheel size on the cars that experienced shock tower failure. Dies this happen more often in cars with Bilstein shocks and 16" wheels than with OEM shocks and 14" wheels?:?:

Mine failed but from what I could tell it always had the OEM wheels and shocks installed

 

[Ohmess]

Steve - So, is the solution a top mounted piece, replacing not only the flat portion of the mount but the curved shoulder too, along with a sleeve on the inside?

 

[Stevehose]

That is what I am doing, yes. I am cutting off the tops right where they start to curve and fitting in the machined top and welding at the seam.

Steve - So, is the solution a top mounted piece, replacing not only the flat portion of the mount but the curved shoulder too, along with a sleeve on the inside?

 

[rsporsche]

here's a pic from CsI's garage

 

[jefftepper]

In the Vintage Mustang universe, (of which I have been immersed for the past 15 years), the rear upper shock mounts are standard unreinforced sheet metal. Back in the day, one school of thought was to jack up the rear with air shocks thereby transferring the weight from the rear leaf springs to the sheet metal. Needless to say there are a number of examples of torn upper mounts when the sheet metal fatigues from the added weight. Not sure if the modern gas pressurized shocks on E9's extract the same toll over time. Reinforcement of the sheet metal seems like the obvious fix.

 

[twistinglane]

One failed on my car-entirely stock- which po blamed on a pothole. Seemed adequately fixed with some metal welded on.