Diff mount repair tomfoolery?

[TiminMb]

Before I purchased my Z3M, I took it to a local import specialist for a pre purchase inspection. I specifically asked them to look at the Differential mount to look for signs of failure. They told me everything was fine.

Fast forward a year and half. I notice sometimes a kind of bottoming out feeling, not a clunk, when I hit the gas near full throttle in first or second. Maybe its got to do with the rear diff, or maybe its just the rear end squatting and bottoming out?

So, I decide to put the car up on ramps and look at the rear differential myself. First, I note that the subframe bushings are green urethane. That looks good. The differential bushing is rubber. Not sure what kind of condition it is in, but from what I can see, it looks fine. It does look awefully close to the left muffler's mounting flange. Only about 1/8" gap.

Then I look at the differential mount. Its been welded. And rather roughly at that.

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Then I look at the reinforcement along the front edge. It has threads and nuts sticking through.

IMG_0959.JPG

So, I'm confused. This is clearly not factory. Where are the telltale bolt heads in the trunk? I remember inspecting the trunk area before I bought the car. Then I see this:



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It would appear someone added this 1" square cross tube, and cleverly disguised it.

There are no signs of the cross member having been separated from the trunk floor, from underneath. The weld on the diff mount looks dodgey, but isn't cracked.
What do you think?

[BimmerBreaker]

Thats some straight up hood shit man...

[Mr Bingley]

?!?

[TiminMb]

Is there any way to purchase just the diff mount bracket and replace it? Everything else looks solid. There are no signs of pulling of the spot welds in the next row.

Edit: I see the bracket is available as part number 41118398664 for cheap. Luckily, still available.

[ProductUser]

This kind of addition raises more questions than answers. Why was this done? Prevention? Existing problem? It may be time to pull back the sealant and perform a more in-depth inspection.

[TiminMb]

I'm thinking I'll drive the car for the summer, it has seen at least 3 years on it since these crappy repairs and mods were done. Then, in the fall, I'll do the job properly. New brackets, doubled up, and internally reinforce the cross member like Randy Forbes does. I enjoy welding and metal fabrication, just wasn't happy to see this shitty repair done on my car, and most of all, I am really disappointed in my pre-purchase inspection, because I specifically asked that they look at the differential mount, knowing it was an area of weakness. Had I know it has this half assed welding done to the bracket (not enough weld, craters, irregular profile, etc.), and it really looks like some kid that works at a muffler shop did the work, I would not have paid what I did for the car.

I might just re-do the weld right away, so it doesn't haunt me all summer.

[TiminMb]

There is no welding of the crossmember to the trunk area, nor are there reinforced ends on the cross bar, linking it to the sides of the trunk area. It is simply a bar laid across the flat of the trunk.

The work illustrated in the photos is highly questionable, as is the comment above.

To the original poster (AKA OP), I suggest removing the trunk trim and posting photos of the modifications.
You should probably start a conversation with Randy Forbes.

[Randy Forbes]

I don't begrudge the individual that wants to repair his/her own car, even when blatantly copying what I created, but there have been multiple instances where said individuals have posted on this forum that they would've saved time, aggravation AND MONEY if they had just bought my reinforcement/mount kit.

Just sayin'

[/high-pressure sales pitch]

[328 Power 04]

Heheh, things are slow at the Z3 ranch?

[MRFAST]

I don't begrudge the individual that wants to repair his/her own car, even when blatantly copying what I created, but there have been multiple instances where said individuals have posted on this forum that they would've saved time, aggravation AND MONEY if they had just bought my reinforcement/mount kit.

Just sayin'

[/high-pressure sales pitch]

Hear me now, believe me later

[Randy Forbes]

Heheh, things are slow at the Z3 ranch?

Hardly, five (5) cars in queue on the premises, and another six (6) on the waiting list.

Hear me now, believe me later

Indeed, but it's all good

[doclip]

Hardly, five (5) cars in queue on the premises, and another six (6) on the waiting list.

I would like to get on the waiting list as well please

[Mr Bingley]

That is unfortunate. I'd like to see more pics of the trunk floor and the odd reinforcement to see how much damage was done --if you're lucky, Randy's kit can be installed without more serious rebuilding. Don't compound the problem with another home built job instead of a Forbes kit, that would be foolish indeed--you can see where that got the last guy. Instead, use this as an opportunity to get it back on track and make it worth what you paid. Why not post the name of the shop that performed the PPI, sounds like that would only be fair under the circumstances.

[TiminMb]

Fr*** Motors in Winnipeg did the pre purchase inspection. And I specifically asked them to look at the differential mount because I had read it was prone to failure. I am very disappointed in them. I relied on their experience in making the purchase decision. My level of trust was such that I hadn't even given it a thought until I put the back end up on ramps recently and saw that horror show.

- - - Updated - - -

That is unfortunate. I'd like to see more pics of the trunk floor and the odd reinforcement to see how much damage was done --if you're lucky, Randy's kit can be installed without more serious rebuilding. Don't compound the problem with another home built job instead of a Forbes kit, that would be foolish indeed--you can see where that got the last guy. Instead, use this as an opportunity to get it back on track and make it worth what you paid. Why not post the name of the shop that performed the PPI, sounds like that would only be fair under the circumstances.

What is exposed in the trunk shows no signs of failure or deformation. What's underneath the 1" square bar, I would have to remove it to find out. I'll scrape away the sealant on the bottom side to see if there are exposed pulled welds, cracks, etc.

I will not do a half assed repair job. None of what he has done is going to remain in place in the long term. I might re-weld the over the existing crappy weld just to get me through this summer. I can easily plate over it as well.

[TiminMb]

Randy Forbes kit looks well designed for a conversion to a dual ear differential cover. Having it's vertical deflection stiffness design as an H beam, it is well thought out for the centrally located hangers for the dual ear diff cover, as they attach directly to the centrally located vertical member. I don't want to spend the money on a dual diff cover, speed sensor, nor do I potentially want to interfere with the existing dual exhaust system. I prefer to stay with the original factory design of the single ear diff cover and its two hangers that are located at the outer edges of the cross member. For that purpose, I don't see the H beam design of Randy's kit being optimal, it having no substantial support at the outer edges of the box, aside from the steel lying flat in the horizontal plane. I see it as a compromise for that application. I would prefer to go with a box design so that the vertical stiffness is at the outer edges where it connects to the factory style mount, not the center.

[Randy Forbes]

My '99 M Rdstr was done by the local BMW dealership in 2004, using my I-beam and doubling up the single differential cover mount. That car has been on & off supercharged in the ensuing years, nearly doubling its horsepower. With the sole exception of them not doing the paintwork on the underside as well as I do, it is every bit as strong and secure as it was over twelve (>12) years ago; you're welcome to come inspect it for yourself.

Sure, maybe it is a compromise, as you say, but it sure as hell stood the test of time, and the over zealous applications of my right foot!

Possibly 15-20% of the hundred (100) cars I've personally repaired/reinforced have opted for the single ear approach for differing reasons; some to save money and others just to maintain a completely original appearance, all coupled with the peace of mind I deliver.

You can theorize all you want about the design, meanwhile, I and perhaps another thousand people all over the planet__on six (6) of seven (7) continents__have been implementing it for over a dozen (>12) years.

I'll give you this: if you want to rag on a design, ask yourself what people are thinking when they drill holes for bolts in a component that is already too weak to begin with? I've got some really pretty pictures of the aftermath. Or when they think simply rewelding the fractured spotwelds will suffice?

An M Rdstr arrived here last week that someone else rewelded the xmbr to the floor, and as it sits now, there's nearly a two inch (<2") GAP where the floor used to sit alongside the LH longitudinal rail. The collateral damage from a failed repair can exceed the the cost of repairing it right the first time, and I take no joy in relating that information to an unsuspecting owner.

[TiminMb]

It's the best kit out there Randy, no doubt. Provides a great starting point for professionals to do the repairs. And heads above simply trying to patch up the inadequate factory design with more welds. Or worse, as in the previous owner of my car, with bolts.

Me personally, a guy that takes pleasure in metal fabrication, and see it as a pastime, I would prefer to make my own full width box design and weld the doubled up factory mount directly to it. That just means my current project, a Miller inspired cyclecart, gets done a little later.

[Randy Forbes]

I hear you, I'm just standing my ground (it's a Florida thing, perhaps...)

If you or someone else already made the kit available and I was faced with the dilemna, I'd probably still do my own repair too; because we can!

[TiminMb]

Just to not leave any stone unturned, I have called the shop that did the pre-purchase inspection in December 2015, spoke to the manager, told him my story, and he has promised to get back to me. I'd be happy for them to look at it and see how obvious it is that it isn't a recent repair, and that they should have caught it. There's no way I would have paid what I did for the car if I had known about that problem. I doubt the lady I bought the car from knew either. I give her the benefit of the doubt. Probably the guy she bought it from. As she only owned it for a year, told me she took it to BMW for service, and there is no way they did that shoddy work. That welding, it makes my eyes bleed.

[TiminMb]

Got a call back from the shop owner today. He says he reviewed the technician's notes and says there is no mention of problems with the differential support. He says they are quite familiar with the issue, and that if the technician had any concerns with a poorly done repair, he would have noted it. I told him the welding looked like crap and was completely inadequate. No offer to look at it. I then told him that I have put only 900 miles on the car since buying it, and that he is free to look at it and give his opinion on whether this repair would have been worthy of note in a pre-purchase inspection report. He said they are busy for the next couple of weeks, but that he would talk to the shop foreman about doing that. I will probably just end up wasting my time with this, as it seems unlikely they will take any responsibility for an inspection they did a year and a half ago. My fault for not double checking their work at my earliest opportunity.

[Mr Bingley]

Yeah, they're not taking any responsibility if by that you mean paying money out or fixing it for free. A PPI is like a home inspection--liability is limited to a refund of the price of the inspection. You might get them to refund that if they actually look at it, maybe, probably not though. Sometimes it's possible to forget that we're all descended from monkeys, only to be rudely reminded of the sad truth by a random flinging of poo.

[e31gixxxer]

Got a call back from the shop owner today. He says he reviewed the technician's notes and says there is no mention of problems with the differential support. He says they are quite familiar with the issue, and that if the technician had any concerns with a poorly done repair, he would have noted it. I told him the welding looked like crap and was completely inadequate. No offer to look at it. I then told him that I have put only 900 miles on the car since buying it, and that he is free to look at it and give his opinion on whether this repair would have been worthy of note in a pre-purchase inspection report. He said they are busy for the next couple of weeks, but that he would talk to the shop foreman about doing that. I will probably just end up wasting my time with this, as it seems unlikely they will take any responsibility for an inspection they did a year and a half ago. My fault for not double checking their work at my earliest opportunity.

Name and shame at every opportunity. Plenty of bad press,it will make you feel better.

[MrBlonde]

I don't begrudge the individual that wants to repair his/her own car, even when blatantly copying what I created

Yeah you the man Randy!

[BimmerBreaker]

it seems unlikely they will take any responsibility for an inspection they did a year and a half ago

Yes it does indeed seem very unlikely.