Front spring top caps broken

[Ride_on]

Just overhauling front struts now and unexpectedly saw a resurfacing of an old problem. These struts had new parts when the car (GLT saloon) was driven and not many miles were done. Eventually the car was scrapped and struts kept. These was little rust on the spring cap but the RHS has snapped out 3 of the spot welds, the remainder could be broken off with a bit of wobbling with hand only.

Many years ago the 360 GLE had the same problem, but had radial cracks in the same area.

I'm having difficulty understanding the cause, if a design weakness, poorly designed aftermarket parts or bad assembly. Doesn't make much sense as the top layer is not bent much, but maybe I just pulled it apart during disassembly pulling at the bellows.

Top spring cap

Top spring cap

Possible causes;
Design weakness - the metal is too thin, or not enough spot weld.

Aftermarket parts - The shock doesn't really interface with the spring cap atall, it sits in the bearing

Bad assembly - Could putting in the bearing upside down cause it? Both bearing seemed to be in the same way from the marks on them. Bearing Cup side down for the shock absorber shoulder to sit in? What if the shock rod retaining nut was not sufficiently tight?

[classicswede]

I think the problem is with the welding. The older version do not suffer as badly but can still crack.

I always seam weld them up and have not had any problems with them once welded.

[Ride_on]

Ah goodstuff, I was thinking some seam welding might be the answer. I was wondering how to keep the bearing surface flat, and did you just weld the inner edge?

[Chris_C]

I think the problem is with the welding.

Normally, I'd agree with you bud, but I think Ride_on is on to something here. I'd been assuming that the upwards pressure of the spring on the cup and downwards pressure of the bearing on the seat caused the spot welds to fail as a side effect of causing the cracking we see.

With no cracking, it's as though the bump stop cup has been pulled downwards, not the seat pushed downwards. I can't get my head round it at the moment.

Ride_on, I think you've seen these, but might help
viewtopic.php?f=52&t=5953&p=149329#p149329

To keep the bearing seat flat, I put the pieces in a couple of clamps and watched what happened to the seat as it was pushed together. At a certain point, it closed up the cracks and the seat went flat, so that is how I clamped them during the weld and it held when removed.

[mac]

Obvious reasons for the bearing support plate cracking - but at first glance there seems to be no force acting on the bump stop/bellows support cup.
The cup spot welds seem to have failed with a downwards movement of the cup - a force that can only appear to come from the rubber bellows!
Even under full compression the bump stop is acting along the axis of the damper rod and giving no tendency to load the cup welds.

Three thoughts -

1. Under full compression the bump stop enters the cup and distorts (spreads) loading the sides of the cup which would give a levering force about the cup upper edge and loading the spot welds.
2. Under steering forces a cyclic "ripple" distortion is generated within the spring cup assembly which loads the spot weld causing eventual fatigue failure.
3. Under suspension movement the spring cup assembly is "belling" upwards caused by spring pressure acting on the periphery allowing a levering action on the spot welds.


Durrr - my brain hurts - Mac.

[Ride_on]

Interesting replies.

The bearing seat seems to be sightly off flat, as there is a little wobble when refitting the bellows cup, so I think it has distorted slightly and the general flexing has weakened the metal around the spot welds, which has fractured on a high impact. The bellows cup adds strength and is maybe stronger than the top part.

I'm thinking the following mods;

easy:
1. weld the top reinforcement at the outer edge to reduce the spring force leverage at the inner
2. Fillet Weld the bellows cup outside curve to the spring plate

More difficult;
3. Cut a step (increase the hole size) at the inner edge of the bellows cup and weld to the spring plate. Grind the inner edge round with a stone or spiraband.

The failed unit above will require some top welding

[macplaxton]

I think it's probably a good thing that they flex and break their welds. It's probably a bad idea if they were granite-solid and passed the buck to the next poor, weak-spot in the chain.

[classicswede]

The key to the problem is you have three thin plates of steel that are only bonded to each other by 4 projection welds each.

As o the real cause of what causes them to fail there was a clue in my previous comment about the early ones not suffering as badly. The only difference is in them is the holder for the rubber is shorter and has a sort of barbed section to hold the bellows on. The difference in the cup is most likely misleading to what the problem really is. So what else is different about the early cars compared to the later ones. The early strut top mounting is a stronger design and are much rarer to fail than the later ones. I think the big part of the problem is where the rubber top mount fails and rather than the loading being on the bearing the top cup is taking the forces. This will include back and forth turning forces and we know if you flex a piece of metal back and forth it will eventually crack.

Even so if I am right in what I am thinking its still worth welding them up stronger especially if they are to be used with stronger spring rates than original.

[Ride_on]

I am feeling that the welds are the problem, probably too few, and/or too narrow.
Notice this after blasting. A ring crack has appeared that is between (not touching) the top reinforcing plate weld and the rubber cup weld, don't understand the mechanism for that. There is also a radial crack from one weld to the other, the welds are in-line radially.

I thought I had an older type lying around but can't find it. The difference might be interesting.

[Ride_on]

Final version of mods (on undamaged sample);

Seam Weld outside circumference of top reinforcer
Seam Weld outside circumference of cup to main plate
Drill out welds for cup from underneath, add 4 more holes (6mm) and plug weld.

No disturbing or grinding of the bearing seat. Although still leaves the top reinforcer hanging out there., maybe 8 plug welds from above or have I done enough?

[classicswede]

That should cover it

[LadbrokeOB]

Sorry to bump and hijack the thread but I went e to change my springs over today and noticed the exact same thing on my '88 340.

I was looking for a possible way to fix them like above, but I fear they are too far gone!
opinions?




Does anyone know of an aftermarket supply of the top spring cups or even know of anyone who has a decent set lying about?

Would be really grateful for a quick reply as i'm off the road until I can find some!

[classicswede]

They could be repaired up if you still have all of the peices

[LadbrokeOB]

I do still have all the pieces, but i'm no welder!

I guess like above... the easiest repair would be just to clamp it into shape and have someone weld up the fractures once they have gone back to the original shape? Then id imagine i should move on to seam welding the re-enforcing plate on the rear and same again for the bump stop cup on the other side?

With the re-enforcing plate, the cut out in the disc... does this have any particular purpose or can I just weld it in any old position?

[Ride_on]

Just checking another unit that is not damaged, but was surfaced rusted. No cracks and the top and bottom spot welds are not aligned, not 45deg out but maybe 20deg. Possibly too much stress betwen the spots when they are aligned? Just seen the pick above, would seem to disprove that theory, must have gotten a good hammering.

I have that 1 spare at the moment, and maybe 2 more in comming weeks. Its been acid dipped and has no cracks as above, the top reinforcer was a little warped from the seam rust expansion. You can have one on an owed favour (I have many needs ) and send me the bad one(s). I can repair/uprate and spray if you are prepared to pay for the effort (the one I have or the broken ones).