Rear Subframe Question

[BD40]

After reading everyone's posts about the notorious subframe/diff hanger issue, we thoroughly checked out my wife's 2000 Z3 before handing over money to the seller. Although all the spot welds on the subframe of her car look fine from both top and bottom, has anyone tried reinforcing this joint and the trunk floor to try to prevent a failure? For example, has anyone tried welding or bolting a large plate inside the trunk over the spot welds and then bolting the subframe to the plate?

[Donlundm3]

I have installed Randy Forbes reinforcement kits in both my M Roadster and M Coupe as preventive maintenance. They were both in good shape when this was done, making it much easier to do than if there was lots of damage. There are other, less well thought through solutions, but if you want to do it right, his kit is the best.

[saneesh8]

I have the same car (2000 Z3 2.3 auto) with 119K on it. No reinforcement and it looks fine. No issues there. may be it will create problems only for those with high torque coming to the differential like M or stick shift.

[JustinHalverson]

I thought of reinforcing with plate(s) and bolts, then I realize that the bolt holes would most certainly be a spot that would rust and allow road dirt and grime int the trunk.

[BD40]

I thought of reinforcing with plate(s) and bolts, then I realize that the bolt holes would most certainly be a spot that would rust and allow road dirt and grime int the trunk.

Yeah, I had the same concerns about punching extra holes in the trunk floor.

[Mr Bingley]

People has taken a host of different preventative measures, but the most effective appears to be poly subframe bushings. If you're going to do something structural, install the RF kit.

[stanley]

This is what I did, all painted now, these go out to the frame. And can be removed if needed. this is on a 375 HP m Coupe with 3.73s gears. no problem.

[beautyspotlover]

That is pretty slick, I like that!

[JustinHalverson]

This is what I did, all painted now, these go out to the frame. And can be removed if needed. this is on a 375 HP m Coupe with 3.73s gears. no problem.

So, is that metal cross member welded to the frame? I'm installing the IE poly subframe bushings as I write this. I might have to mimic your idea. Adding a little extra reinforcement would have to help prolong the life of the subframe mounting points and trunk.

[Randy Forbes]

After reading everyone's posts about the notorious subframe/diff hanger issue, we thoroughly checked out my wife's 2000 Z3 before handing over money to the seller. Although all the spot welds on the subframe of her car look fine from both top and bottom, has anyone tried reinforcing this joint and the trunk floor to try to prevent a failure? For example, has anyone tried welding or bolting a large plate inside the trunk over the spot welds and then bolting the subframe to the plate?

I guess you didn't see any of the posts I've made on the subject in the last ten (10) years...?

My advise is, was and always has been: You know where to look, you know what to look for, so periodically check the area for signs of the spotwelds fracturing. There is never a catastrophic failure, always a gradual degradation, allowing the remedy to be administered somewhere between the first spotweld going and the differential dragging on the ground.

Since you just got the car, take a look inside the trunk once a month__lifting up the false floor__and thereafter maybe a couple times a year. Unless you live where there are severe potholes, treacherous railroad crossings or your wife having a lead foot, your car will probably never have problems. If it ever does, there's a remedy.

If you want to see what I've been doing for nearly a decade (10th anniversary is actually right now, for my '99) then take a look at the pictures in my gallery: www.spcarsplus.com/gallery3

Here's a few of the most recent cars I've done:





Both examples shown above have the same trunkfloor reinforcement; a fabricated I-beam concealed inside the XMBR

[dcrothers]

My dual ear is being done by Tony at TC Design Fab in San Jose next week....Very stoked to finally do this..

[kornfeld]

Bump. I'm talking with Performance Technic about having the rear subframe on my car done as a bit of preventative maintenance. While I understand that they have installed a ton of the Randy Forbes kits and do great work, they also have a pretty steep hourly rate. So I'm doing some comparison shopping to see if I can get this taken care of at a high level of quality and a reasonable price.

After searching around, I see that TC Design Fab and Edge Motorworks are possibly other options around the bay area...does anyone know of any other options that I should check out? I would be willing to drive as far away as the distance to LA, as I think I could save a very healthy chunk of money by going elsewhere...but I still want to work with a reputable shop. Thanks in advance.

[BimmerBreaker]

Please post up what you find kornfield. I'd like to find a shop to do it for a decent rate and don't mind going anywhere from LA to SF to make it happen. Have a few in my area I'm shopping but would rather find one with previous experience having done the RF kits.

[dcrothers]

TCDesign did a great job for a reasonable price.... I did all the prep work. They finished with primer, ready for me to paint....

[kornfeld]

Excellent. I'm going to be reaching out to them tomorrow.

[BimmerBreaker]

How much is a reasonable price?