318ti Randy Forbes Reinforcement

[sooky123]

After being requested some info on the kit, I figured I'd make a thread for anyone else interested on the kit.

The journey begins at our local Autox, While my car was being tech inspected I noticed in the trunk that I was seeing light through the floor. Immediately thought to myself "Well that's not good," after they were done with the inspection I went back to park and started looking at it a little more closer. What I found ruined my day, I found that I blew out a few spot welds and the floorpan was cracked at the seams and sagging.









Jacked the car up to check out the underbody and found this...











I knew about this problem with Z3's. Especially M roadsters and M coupes, with the power many of them have popped a few spot welds or even broken diff mounts. BMW has a fix, Dinan has a fix but after hours of research the best was from Randy Forbes. There are cars with globs of power that have yet to destroy Randy's kit. Even BlueBimma with his 357ti hasn't destroyed his as yet. Hopefully he'll share a few words on the topic.

So after months of the car just sitting, I finally took the car to a Local Indy BMW shop to get the job done. They have done the repair on a Z3 Mcoupe so they were quite familiar with the kit.

Randy sent us the template from Tony's (BlueBimma) car which, correct me if I'm wrong, is a 1996.


http://s251.photobucket.com/albums/g...psb656001c.jpg

[sooky123]

I'm not too certain, but it seems as though at least with the later model cars BMW might have changed the design to the rear crossbeam. Buddy of mine has a ti with a M52 with a AA blower that pushes just about 400hp or so. His car has the rear clip of a 1995. Comparing the two, you can tell that the 95 had a slightly beefier crossbeam compared to mine which is a 1998. I haven't seen too many other ti's to be able to confirm that a change has been made so I might be wrong.

Anyway, because the template was different from mine (larger plate for the crossbeam) it needed to be altered to fit. One of the top plates that the kit came with was also smaller than the area it was supposed to cover. Therefore, a new one had to be made to fit there.






Time to repair the cracks and floor pan...










And finally all done...










If you guys have any thoughts or concerns I'll be happy to answer.

Thanks fellas!

[BlackBMWs]

Thanks for posting this, interesting read. What engine/drivetrain do you have in your ti?

Is increased power the main cause or is it also the type of driving you do?

How long did this repair take?

Regards...

[chrisbec]

Nice, that looks like a lot of work!

Did you have to "alter" your crossbeam to get the differential to fit (assuming you were running a medium case differential)?

[1996 328ti]

Yes, thanks for sharing.
I'll need to take a closer look at my car this weekend.

[studio2]

This is extremely helpful as I know my mount is going to be toast after a few autocrosses with my new blower and Hoosier A6's
Great documentation & detail.....
Thanks again for posting!

[BimmerBum]

I saw this car for sale on CL... looks like a nice clean car.

The differential stays the same you just need the cover from a standard E36.

I think they produced some of the ti's in SC (I could be wrong on that). If they did it would be interesting to find out if this car was produced in SC. This is not a real common issue with the ti but it is a very common issue with the Z3... all the Z3's.

Off to examine the floors of my ti's.

[chrisbec]

For the Z3 this was/is a regular issue but pretty uncommon to hear about it for a TI or even a e30 for that matter (they all use the same T/A rear axle with a single ear diff mounting). Although it does happen to all of them to some degree or another it is hard know if it will happen to your car.

Some people have an interference problem when switching to a medium case differential and one of the fixes it the 'beat-to-fit' technique to get the medium case diff to fit. The edge of the beam that gets in the way is crushed in to get rid of the interference. I stands to reason that that this technique could potentially cause 2 problems. First, hammering on the beam stresses the beam and all of the welds in the trunk floor that hold in place. Also, caving in that cross beam will weaken it (make it less stiff) because it has a smaller cross-sectional area and the steel has been yielded (or bent). Sheet metal parts get their strength from the materials they are made from and their shape. The way I see it using the beat-to-fit solution would only contribute to a problem like this.

Having said all of that I know a lot of people have used the beat-to-fit technique when installing their medium case diff. Knowing how many people that have done this it still doesn't really seem to be that much of an issue for the TI.

[sooky123]

The car has a M52, ZF trans and 3.73 rear end. Lots of other little things but that's the main stuff.

It previously had an S52 in it as well and the PO blew up the diff. He was running the stock small case. During the install we found that the crossbeam was tweaked a bit so the diff might have put a lot of pressure on it when it blew up which may have caused it to blow out the welds and cracked in those spots. Again, we're not sure that's what happened but putting 2 an 2 together that's what we think.

As chrisbec said, some people have to beat the crossbeam so that they can fit the medium case but, because of the crossbeam change I didn't have to. The diff fits perfectly in with no hammering. On my friends car he had to hammer out his which is a 95 but his has the larger crossbeam.