Subframe opting out of the torque

[OldRanger]

I have a 2002 M3 that has about 320 hp at the wheels and a 4.10 differential. When I did the Vince bar, I installed Bimmerworld solid subframe bushings. I used a light coat of grease to aid the bushing install.

I have learned that hard acceleration (track conditions) can Actually force the subframe away from the body on the rear mounting points with enough leverage that the subframe slide slides out of place (vertically) on the rear bushings. The OEM washer retains it, preventing a catastrophic situation.

Is this a ‘me problem’?

I’m trying to determine if I can solve for this (a second time) by having some sort of spacer machined or printed to hold

[Slideways]

Custom Racetech in Germany uses grub screws to secure solid subframe bushings. Not a bad idea if you don't mind drilling and tapping the subframe.

Skip to 2:10

[bigjae46]

I imagine it could be an issue with poly bushings since they are squishy. I'm pretty sure most people choose poly because its easier to install.

I can't imagine OE rubber or solid allowing the subframe to slide off. It is a such a MF'er to press them in.

[OldRanger]

It is a such a MF'er to press them in.

Right!?
(I did use a light coat of grease)

The grab screws idea Slideways shared is interesting. I’m looking for a solution that doesn’t require removing the subframe.

Background:
The first time it happened when I put the hammer down to spin the tires and remove some of the scrubbed rubber that accumulates on track.

Options:
I snugged it back up to the top of the bushing/flange (while the subframe was installed) using the hardware and Vince Bar installation as an anchor. That was handy.

I think this is a sign I need a 3D printer.

[OldRanger]

By the looks of this…I’m guessing I installed them upside down. 🤦🏼♂️.

Edit: (Here is a screenshot from that video Slideways posted above). Also, I checked our other car and I confirmed my mistake

[oceansize]

By the looks of this…I’m guessing I installed them upside down. 🤦🏼♂️

Yep, lol.

[OldRanger]

Well…I’m batting .500 on this job. Did it properly the first time on the 2005. Geesh.

I guess I get to do another subframe job.

Maybe this is affirmation I really didn’t want the 4.10s on the 2002…and this is the sign I should switch those out in the process

[Obioban]

Removing 4.10s is always an upgrade

[OldRanger]

Removing 4.10s is always an upgrade

+1. For sure on the street.

But that 3rd gear pull…is a riot.

And I think it might actually be equally capable as the 3.62 on the tracks I drive. Especially Summit Point Main, which is a favorite. It’s an experiment. 🤷♂️

[Obioban]

+1. For sure on the street.

But that 3rd gear pull…is a riot.

And I think it might actually be equally capable as the 3.62 on the tracks I drive. Especially Summit Point Main, which is a favorite. It’s an experiment. 🤷♂️

A lot of the tracks I drive I'm regularly RIGHT at the top of 4th, but never have to go to 5th-- excellent for not money shifting. It's shocking how of the stock gearing feels perfect for track use.

[Cubieman]

Maybe the design is completely different, but the CMPs with a similar shape seem to go the opposite way of the photo you posted.

Was the photo you posted how you installed them or how they should be installed?

[OldRanger]

This is the proper orientation. This subframe stays put.

these are the Bimmerworld product

[oceansize]

This is the proper orientation. This subframe stays put.

these are the Bimmerworld product

I have never seen a set of subframe bushings which correct geometry that didn't have the flat end against the RACP. I cannot believe that is correct. Why would they not want the most surface area resting against the RACP? Seems highly unlikely.

[OldRanger]

Good question. I’m not sure.

Here’s how I chose to install the same BW bushings on the 2002. I’m not sure what my rationale was, but I was probably rushing, or frustrated I was working on an E46 subframe, or tired at the time. Notice the gap between the subframe and the bushing flange in the images. I presume this is the wrong orientation. The subframe twists downward off the rear in response to engine torque.

Also, for anyone looking at this picture, I have intentionally installed the OEM ‘washers’ upside down to minimize the extent that the subframe could slip/move on the bushing. (These probably aren’t even required with solid bushings.) I did this after I used installation tools to snug it back up during my pre-track inspection)

What you’re seeing here: this was an expedient, temporary solution to enable a track session.

It slipped about 5mm even taking it ‘easy’ on track out.