Question for Randy Forbes...

[tracecom]

or anyone else who knows.

I have read a lot of what's been posted about the subframe issue and have looked under the center mat in the trunk. The spot welds are seemingly perfect - no sign of even hairline paint cracks. I have not removed the carpeted panels on the sides of the trunk because (1) I don't quite know how and (2) it seems that the problem always shows up first at those spot welds at the top center section of the trunk. What should I do next in terms of an inspection? Of course I want to believe that I don't have any problems but would rather know than just hope for the best.

Thanks.

BTW, the car is a 2000 2.5L roadster with 37k miles. I want to post pictures, but can't yet.

[wheelieh]

or anyone else who knows.

I have read a lot of what's been posted about the subframe issue and have looked under the center mat in the trunk. The spot welds are seemingly perfect - no sign of even hairline paint cracks. I have not removed the carpeted panels on the sides of the trunk because (1) I don't quite know how and (2) it seems that the problem always shows up first at those spot welds at the top center section of the trunk. What should I do next in terms of an inspection? Of course I want to believe that I don't have any problems but would rather know than just hope for the best.

Thanks.

BTW, the car is a 2000 2.5L roadster with 37k miles. I want to post pictures, but can't yet.

You can get a great look underneath the car.

I inspect and detail the underside of my car once a month, I have ramps that make it very very easy to drive up & take a look from under.

I have seen others with damage, you can spot problems from underneath also.


Heath

[Randy Forbes]

Here's a look at a 2.3...

[tracecom]

You can get a great look underneath the car.

I inspect and detail the underside of my car once a month, I have ramps that make it very very easy to drive up & take a look from under.

I have seen others with damage, you can spot problems from underneath also.


Heath

I can get my car onto a lift, but I don't really know where to look. I have seen some of the pictures, but haven't been able to relate those to what's underneath the car. I have only had the car on a lift once. I looked it over and didn't seen any problems, but there again, I didn't know exactly what to look for and where to look.

What would be nice would be a wide angle picture of the underneath of the car with an arrow (or arrows) pointing the areas to be inspected and then closeups of each of those areas with details of what to look for.

It's obvious what a noob I am.

ETA: Randy Forbes posted pics while I was writing this post. I had previously seen them, but can't relate to where to look under the car. Maybe if I print them out and take them with me to put the car on the lift.

[JoshS]

From underneath, you are looking for the transverse (left-to-right) rail from switch the diff is hanging. Look at the bracket between that rail and the diff, and then look at where that rail connects to the rest of the trunk floorpan, especially towards the left side.

[yamag7d8]

i hear most of these things happening to the 6cyl... is that true randy?

[SunzOut]

The under car pics thar Randy posted are of the bracket that holds the differential.

The differential is directly between the rear wheels.

The green bar in one is the sway bar (not normally green - that look aftermarket).

The last picture is the underside of the the trunk floor, after the suspension and other parts are removed - so don't expect to see that much with everything in the way.

[tmaher]

to self: wonder how badly over-inflated tires for better MPG and non-OEM bushing and sport suspension have to do with this problem.. Or, at the least, cause for expediting the problem..

Sucks to see

[GBimmer]

to self: wonder how badly over-inflated tires for better MPG and non-OEM bushing and sport suspension have to do with this problem.. Or, at the least, cause for expediting the problem..

Sucks to see

actually stiffer bushings might help keep you problem free. The diff moving and tugging on the subframe is the cause of the cracks. By putting in stiff bushings, you limit that movement and brace the diff on the sides as well as the hanger.

[tmaher]

But all the photos I've seen look like stress cracks.. Softer bushings would absorb more of the stress instead of transferring it to the sub-frame. No?

I ask because I used to deal with body stress, i.e; eliminating cracked windshields and mis-aligned doors by using front/rear sub-frame connectors in my Fords..

EDIT: Isn't the differential on a pivot? Free from the sub-frame? It would seem to me that if stiffer suspension and more vibration were to make it into the sub-frame via the harder bushings and stiffer springs, etc, the more likely the failure because the components weren't absorbing that energy?. Just asking. Need to learn...

[Randy Forbes]

Well, of all the cars I've repaired, only three (3) had urethane suspension carrier bushings upon arrival; two (2) cars with green ones, and one (1) with purple.

Come to think of it, they had minimal damage too, but nothing scientific to back that up, could've just been timing on the part of getting the work done.

ALL the others have been fitted with Ireland bushes before leaving.

[tracecom]

I can't get under the car until tomorrow, but if I knew how to remove the carpeted piece on the driver's side of the trunk, I could at least inspect that section of the trunk from the inside. How is that piece held in?

[SunzOut]

But all the photos I've seen look like stress cracks.. Softer bushings would absorb more of the stress instead of transferring it to the sub-frame. No?

I ask because I used to deal with body stress, i.e; eliminating cracked windshields and mis-aligned doors by using front/rear sub-frame connectors in my Fords..

EDIT: Isn't the differential on a pivot? Free from the sub-frame? It would seem to me that if stiffer suspension and more vibration were to make it into the sub-frame via the harder bushings and stiffer springs, etc, the more likely the failure because the components weren't absorbing that energy?. Just asking. Need to learn...

The problem is mis-named...it really has nothing to do with the subframe.

The failure is related to the trunk floor, the cross beam that forms a support for the floor and that the diff hangs from and lastly the metal bracket that is used to connect the diff to the cross beam.

Two specific failures occur - normally at the same time but may be separate.

Failure 1 - Shown in the first of Randy's pictures is the cross beam separating from the trunk floor. In the worst case the box section that forms the cross beam can crack as well as separating from the floor.

Failure 2 _ Shown in the 3rd Picture. The diff bracket fails. Cracks form in the bracket along the horizontal fold or in other parts of the bracket.

[tmaher]

I see.. So the 'sub-frame to body' connection is the failure. I did notice how it was spot welded. I wonder, would simply adding more spot welds help keep it together before it failed? If so, that's a damn simple fix (sort of) but very economical at least.. Still sucks no matter how you look at it.The worst I ever encountered were torn frame ends separating from the uni-body. Drill, re-weld, use front to rear sub-frame connectors and it was a done deal.. If you did that, you could put 800 HP to the Ford 9" and be safe.. I'm learning...

[dozerslobber]

Just curious, does the diff bracket failure come first or does the trunk floor separation come first.... generally?

[tmaher]

Now that I understand the problem better, I would expect (speculation here) that the dif ear is welded sufficiently enough to the brace that it's able to exert enough force on the support brace and causes the brace to separate from the floor. Though, it would seem to me that if enough torque was applied, the ear would fail first. Awaiting the expert opinion...

[z3mshootbrake]

Randy, I sent you an e-mail last week trying to get some prices. The e-mail is adragich@gmail.com. Could you try and get back to me?

Thanks.

TOny

[JoshS]

I see.. So the 'sub-frame to body' connection is the failure.

Not really. The subframe consists of the suspension carrier and the diff as a unit. The diff is a "stressed member" of the subframe. This subframe assembly mounts to the chassis at three points: 2 at either end of the carrier and one at the diff.

The failure occurs, as noted, at two places: the diff bracket (which is in fact arguably a "subframe-to-body" location, plus is also transferred to the trunk floor itself: the transverse trunk floor brace separates from the floor itself.

Note that the E36/E46 chassis also has "subframe mount" issues, but they are truly at the subframe-to-body location. It's different.

FWIW, on my race car, I did add a few extra spot welds and have yet to have any failures. I have very stiff subframe bushings. But I would not consider the success of one car (so far) to be indicative of a success. These failures, curiously, do not seem to correlate to how the cars are driven.

[SunzOut]

I see.. So the 'sub-frame to body' connection is the failure. I did notice how it was spot welded. I wonder, would simply adding more spot welds help keep it together before it failed? If so, that's a damn simple fix (sort of) but very economical at least.. Still sucks no matter how you look at it.The worst I ever encountered were torn frame ends separating from the uni-body. Drill, re-weld, use front to rear sub-frame connectors and it was a done deal.. If you did that, you could put 800 HP to the Ford 9" and be safe.. I'm learning...

Some Z's (and it does not look to be year specific) have additional tack welds along the same area that the spot welds are.

So BMW knew something was up but why not all cars after specific date we don't know.

If you catch it early, you can re-weld (or as you suggested even weld before it fails).

I spotted 3 welds srarting to go and re-welded them, fingers crossed..so far so good

[Randy Forbes]

Randy, I sent you an e-mail last week trying to get some prices. The e-mail is adragich@gmail.com. Could you try and get back to me?

Thanks.

TOny

It was two (2) days ago. Answered.

I see.. So the 'sub-frame to body' connection is the failure. I did notice how it was spot welded. I wonder, would simply adding more spot welds help keep it together before it failed? If so, that's a damn simple fix (sort of) but very economical at least.. Still sucks no matter how you look at it.The worst I ever encountered were torn frame ends separating from the uni-body. Drill, re-weld, use front to rear sub-frame connectors and it was a done deal.. If you did that, you could put 800 HP to the Ford 9" and be safe.. I'm learning...

Sometime during model year 2000 (which began as early as 4/99) additional stitchwelds were added between the spotwelds. It might help, but it wasn't a cure.

In Spartanburg's defense, it was probably all that they could do, without changing the chassis dynamic, and requiring the chassis to be re-crash tested. Pure speculation on my part.

[tracecom]

Some Z's (and it does not look to be year specific) have additional tack welds along the same area that the spot welds are.

So BMW knew something was up but why not all cars after specific date we don't know.

If you catch it early, you can re-weld (or as you suggested even weld before it fails).

I spotted 3 welds srarting to go and re-welded them, fingers crossed..so far so good

So, is that the first sign - the spot welds sinking?

And how do I get that driver's side piece of carpet out of the trunk so I can look at that left seam?

Thanks.

[SunzOut]

Yes, That's the start of the spot welds pulling a part.


There are a couple of clips at the top of the panel.

One is just a simple twist, the other needs to be pulled out - a forked trim puller works best.

[z3mshootbrake]

[QUOTE=Randy Forbes;16860333]It was two (2) days ago. Answered.

Oops, I stand corrected. Thanks for the reply.

[adonnan]

It's annoying that i can't check the spot welds to that floor unless I rip up the sound deadening tar. We're going to look underneath the coupe this weekend for signs of failure.

[khammack]

I can't get under the car until tomorrow, but if I knew how to remove the carpeted piece on the driver's side of the trunk, I could at least inspect that section of the trunk from the inside. How is that piece held in?

The "carpet" covering the trunk floor is held down by Velcro at the far side of the "carpet". Just pull up. The side "carpet" is held in by the buttons around the top edge of the trunk. They can be pulled out using a small pry bar. You should be able to reuse them. There is one twist hold down on the driver's side behind the tail light. You may need a light to see it. Once they are out the side "carpet" can be pulled out. The tail lights may be a bit in the way, but you should be able to work it out. Everything is easy to put back, just note what overlaps what as you take everything out.