BMW E36 M3 - Rear Shock Mounts

Last Wednesday evening, I noticed a rattling sound in the boot on the left hand side which I recognised straight away from pre-purchase web research as a failing shock mount on a rear damper. I limped home (all of a mile or so) and parked up the car.



I went and bought two ^^ new ^^ shock ^^ mounts for the back of the car on Thursday and was delighted that I would be back on the road by the weekend. I never even pulled back the carpet before I got the mounts (hey, they have a reputation for going so I just assumed...). Not having all my tools at home, I had a peep under the carpet on Friday first thing to see if I had all I needed here at home for the repair...Oh Fcuk is all I can say

This is what I found !!!!!!!!!!



Yes, it is an other soft spot on the E36's especially cars that have to pound around Irish roads with dodgy left hand margins - FCUK and FCUK Again!

It is not rot, it is just fatigue in the area of the nuts holding the mount to the bodywork. From a pure design standpoint, it is flawed in my opinion. The mount is bolted up against the bodywork and is quite stout. This means that in a bump situation, the load is distributed widely through the footprint of the mount. On rebound however (something that we have far too much of in Ireland thanks to our really really sheite roads) the entire spring load resisted by the damper is placed on the spot facings of two M8 nuts. It means that there is a highly stressed area around each nut and it is the transition between here and the surrounding area that fatigues. You can see that the high stress areas gave way and were doing so for a little while with the rust visible.

There is (thankfully) a "Proper and Permanent" way to repair this and it is what I have started already. I have bought two shock towers from Frank Keane BMW. These are steel pressings that are welded into the wheel "cans" and are of stouter material than the surrounding bodywork. If you look closely at the pic of the failed area in my car, you will see a sort of ridge through the seam sealer. This is where the shock tower is fitted into and spot welded up inside the wheel arch from the underside. These replacement sections will be in stock next week so I have a bit of time to cut out the old damaged mounts. I bought a couple of "Z3 reinforcing plates" from eBay this morning. Worth fitting whether your shock mount towers are failing or not, thy spread the rebound strain a bit wider than the metal just under the nuts.

Here are some pics (borrowed from the web) of the new part and the old one when you drill out the spot welds...


And the Z3 reinforcing plates I bought


You might understand that I am pretty p!ssed off with the whole problem but on the same breath, I am somewhat relieved that it has happened. I am comfortable for the single reason that it is a very straight forward repair, all be it quite serious and one that needs cutting and re-welding. It is a job I am capable of doing myself and if done correctly will be in theory stronger than the factory job (larger welds with a better weld process). I will rest easy safe in the knowledge that there is fresh steel in there, reinforced with the Z3 plates and properly sealed, a job crossed off...

H

The Repair Process - Taking things apart

Today I started the repair, taking out the old shock mount turret as the replacement should be in tomorrow. I started this process by taking the seam sealer off the inside of the weld area. This stuff is like slightly elastic primer so it does scrape quite easily. I then used a bit of 80grit oxide paper to take the towers to bare metal around the welds. This highlighted where each of the spot welds is. The objective will be to drill sucessivley larger holes right through the centre of each weld such that eventually expanding beyond the weld area and hence releasing the sheets of steel from each other.

Here I have removed the paint and sealer to expose the spot welds


The next part of the process is to take away some of the underseal in the area of this shock tower in the wheel-arch. A word of warning to anybody taking on this task. Regensburg underseal will stop a large caliber bullet at short range, possibly even point blank! This part of the job caused me to perspire profusely while I the whole time dislodging tons of crud from the wheel-arch. Looking somewhat like a miner coming back to the surface, I took this photo of the underside...

Here I have started to remove the underseal that the tower is buried in


After some coffee and coughing up of dust, the next thing to do is to centre punch and pilot drill a hole through each weld. This is simple and fast if you remember to use a drill of 4mm diameter or less, and to keep your cutting speed low. All of these holes took a total of about five minutes to pilot. Have a look at the picture below.

Here I have pilot drilled each weld to a diameter of 4mm


If you are well practiced at drilling by hand, you can steer the drill as it cuts. I had a close look at each of the pilot holes to see, after the fact, how close to the centre of each weld I had piloted. I then stepped up in 2 mm increments, steering the drill as I went to separate the sheets. Some tapping with a light hammer will help you to see if the sheets are separating. Patience required! Drilling up to a diameter of about 10mm is OK in my experience, but around 8 or 9mm is my preferred size. The specific reason is that welding in the new part involves welding around the inside of each of these holes. The objective will be to trace a circle with the MIG torch such that when you finish your circle, you have a very shallow dome with the tiniest little "donut" dimple in the middle. In fact, when you get the hole the right size, the welding current and wire feed just right, these welds are superbly strong with good penetration into both sheets and almost flush on the surface.

Here I have opened each hole up to 8 or 9mm (one to 10mm) to release the welds


It will be apparent after some tapping with your hammer that the sheets have in fact released. I was starting to think that I had missed a couple of welds at this point but it was the super bullet proof Regensburg underseal holding it all together. I progressively got more forceful with my koshing tools and away she went. I took a couple of pics of both the wheel "can" with one gaping hole and loads of little pretenders and a pic of the failed part of the tower.

Here are the parts separated - The chassis


And the failed shock mount tower


This is as far as I have gone today besides some cleaning up and making sure that there is no paint in the way. MIG welders don't like paint or contamination and the welds suffer a bit. For nice clean and easy welds, clean metal is the way to go.

I will update this thread once I collect the parts and start my next job...


Huggie

The Repair Process - Sticking things back together

Right then, time to see if welding is something one can forget how to do. I suspect yes

The quality of the new shock tower that I got from BMW appeared to be spot on. Even offering it up to the wheel can it seemed to fit like a hand in a glove. I had to make some very small adjustments to both the new part and to the very light metal of the wheel can but the parts mated together very well. The scene was slightly "agricultural" for want of a better word. The car was on a stand but because the rear suspension was intact bar the damper, it was not possible to push the shock tower up with a jack like I had hoped. It meant that I had to use about a metre of 2" x 1" timber to wedge the part in tightly.

Now amateurish as it must have looked, it is pertty vital that the two steel skins are very snug fitting. This is to allow the suspension loads to be evenly distributed across the footprint of the shock tower. If a space was left between the skins, then the suspension loads would be transferred from one skin, through the weld to the other skin. The area immediately surrounding each weld would then strain and would in pretty short time, fail like the original part did. I was pretty careful right through the welding to check that all was fitting snugly.

Here you can see the replacement part trial fitted in place while adjustments were made


Once happy with the fit, it was all about cleaning. I made sure that there was no traces of paint on the new part anywhere I expected to weld and also cleaned any paint and sealer that might have found its way into the welds from behind. I have to say that I did struggle to get nice neat welds and was in a state of mild depression for a day after doing the repair as I know I have done fantastic looking plug welds in the past but just didn't seem to be getting the result I wanted here
The way these are done is to strike the ark on the back piece of metal and sort of half fill the middle of the hole with a nice fluid weld, then move the ark out from the centre to start penetrating into the top skin, nice and steadily tracing around the hole to join the weld in the centre to the skin. A combination of being very difficult to fit my head with a welding helmet on and two hands into the space around the wheel can made it very difficult to do. I did feel like I had done a couple of days of non-stop yoga after I untangled my other limbs and spilled out of the boot aperture like some blob of alien goo. The resulting welds are perfectly OK as welds but wouldn't be photo material for a welding text book. I took a few pictures of this stage but must have been shaking as a result of my exertions as they were mostly a bit blurred. Anyway, see the pic below for some idea of how I got on...

Here I have started to plug weld the parts together using a MIG welder


At this stage, I scrutinised the back of the repair carefully to ensure that each of the welds had in fact penetrated nicely into the repair section and that there were no gaps between the skins. I was happy enough that the repair was sound and perfectly OK from a structural point of view, but as I said above, I thought I could do a neater job. Some seam sealer was on the cards to protect the area around the repair. The stuff I got was as high quality as I could find and made by 3M. Brush on, with good elasticity and supposedly easy finishing. I put this stuff on both sides of the repair particularly working it in around the edges. It is not the easiest stuff to use neatly being a bit too thick to brush out neatly but a bit too thin to put on a heavy coat (as the brush just dragged it around everywhere!). Anyway, I forgot to take a picture with just seam sealer over the welds and joins, but did think to go and get the camera while the primer was drying.

Here I have just put on a second coat of primer over the seam sealer and bare metal


That was about all I could do on Wednesday (day 2) so I went off to get an aerosol of Daytona Violet paint made up in Vinny Byrnes. It is a handy service as it means that non fussy repairs can be done with a reasonable degree of color match. I have to say, I put a little of the made up paint directly over some factory paint in the spare wheel well to see what the match is like and I can not find it now bar the fogged edge! Impressive match . That evening, I sort of dusted / spattered some body colour paint over the repair to see if I could replicate the sort of oversparay finish from the factory. As you might imagine, the new paint has a sort of treacle shiny finish compared to the 14 year old factory paint that has lived under sound proofing and carpet all its life. Maybe in time it will calm down a bit!

Here is the finished repair with bodycolour paint


Here is a before & after image. Both shots taken with my phone camera for comparison


Well there you have it, all done and dusted, a real DIY repair.

H

HOoly Fookballs Batman!!!

That looks soo nasty, but sounds like you've got the fix sorted - how much for the welding job? Needs to be pretty precise I imagine.....

ouch! but by no means not repairable..

One thing you may want to consider is taking the bolts out of the bmw top mount ( these push out dead easy or a light tap with a hammer ) and tack welding them to the re-enforcing plate so the bolts face downwards, this way they nuts are accesable from underneath the car so you don't need to climb around in the boot to take the shocks out.

Makes the job about 50% quicker for the future.

Originally Posted by UCJ

ouch! but by no means not repairable..

One thing you may want to consider is taking the bolts out of the bmw top mount ( these push out dead easy or a light tap with a hammer ) and tack welding them to the re-enforcing plate so the bolts face downwards, this way they nuts are accesable from underneath the car so you don't need to climb around in the boot to take the shocks out.

Makes the job about 50% quicker for the future.

@UCJ: I considered doing this but on consideration, I will probably cut a "flap" in the carpet over the shock to allow access to the shock in case I end up with top adjustables. I will do a tidy job with some Velcro to hold down the access.

H

Originally Posted by Kingers

HOoly Fookballs Batman!!!

That looks soo nasty, but sounds like you've got the fix sorted - how much for the welding job? Needs to be pretty precise I imagine.....

Well you see Kingers, when I am not doing my regular stunt cock duties in the Porno industry, I have spent the last twenty years restoring old cars and building competition cars in my spare time. I studied mechanical engineering and ran manufacturing business's for a few years so this stuff is easy peasy. I just never hoped this sort of thing would be on the agenda in the first months of ownership, but it will be a DIY repair.

In fact, I will be editing the top of this thread so a re-read may be more informative in time.

H

Not a nice thing to happen but looks like it'll be better than new when your finished.

I'd love to have the skills 'n tools to fix something like that.

this happened to my e36, just grind out the old top hat and weld in the new one, jobs oxo!!

god i love seeing pics and good descriptions - when i can't do half it myself it makes for really interesting reading - pretty damn cool

huggie's got skills