Subframe can shift upward w/ solid aluminum subframe bushings??

[IamFODI]

Mentioned this in another thread but felt it deserved its own.

Most solid aluminum subframe bushings are 1-piece cylinders with flanges on one end but not the other. Pretty sure the flanges end up on the bottom in most cases. I've heard it said that these designs can allow the subframe to shift vertically. Has anyone experienced this, or even heard of it?

[Gossypiboma]

Never heard of this and don't see how that would even be possible.

[Thumbie]

Don't the rubber ones have a flange on just one side also?

[IamFODI]

Originally Posted by Thumbie

Don't the rubber ones have a flange on just one side also?

Yes. But the flanges are on top for the front ones and on the bottom for the rears. For the 1-piece solid aluminum mounts, all 4 flanges are on the bottom.

[pbonsalb]

Is that what the installation instructions say or is that just the way some people install them? I installed 75D poly, but kept the flange orientation as stock since I did not change my subframe design. My F90 M5 had the flanges on top in the front and on the bottom in the rear as well. I don’t know why BMW does it that way. Sure makes installation a pain. E36 and E46 can tear the front subframe mounting points. I cannot recall whether flanges are in top in the front or not on those cars, but if not, maybe a change was made because flanges on top helps support the load. Just a guess. How are the flanges oriented in non-M models?

[IamFODI]

Originally Posted by pbonsalb

Is that what the installation instructions say or is that just the way some people install them?

Installation instructions. Both TMS and Bimmerworld.

Originally Posted by pbonsalb

How are the flanges oriented in non-M models?

All on the bottom.

[pbonsalb]

Instructions can be wrong. TMS is just an online presence for ECS now. Bimmerworld actually races cars do so I would trust them more. But they could be wrong also. Or the could have decided it does not matter. I would want to know why BMW puts the flanges on top for the M cars — it is probably not to just make on car removal harder. Anyone know?

[IamFODI]

Originally Posted by pbonsalb

Instructions can be wrong. TMS is just an online presence for ECS now. Bimmerworld actually races cars do so I would trust them more. But they could be wrong also.

All of them, in the same way?

These guys seem to agree – though I guess they could be just copying BW/TMS: https://shop.redline360.com/products...08-13-aluminum

Agree Bimmerworld seems far more trustworthy because they race these cars. That's what clinched my decision to go with their product in this case.

Originally Posted by pbonsalb

Or the could have decided it does not matter.

This is my favorite hypothesis RN.

But...

Originally Posted by pbonsalb

I would want to know why BMW puts the flanges on top for the M cars — it is probably not to just make on car removal harder. Anyone know?

Agreed. Super curious about this.

[pbonsalb]

Is the front of the subframe moving upwards since the instructions say to put the flange in the bottom instead of the top? This would slightly change the pinion angle of the driveshaft and the suspension. Or is that not actually happening due to the design of the bushing?

It has been years since I did this job so I can’t remember much in the way of details other than that BMW put the front flanges on top so I put the flange on top. I found this comment from another DIYer in an old thread.

“The front, rear subframe bushings have a hole that goes straight through them like any other bushing. However, the opening of the hole differs in width from top to bottom. One opening is wider than the other. Keeping that in mind, the orientation of the M3 front, rear subframe bushing is opposite in terms of up and down vs the OEM bushings, when condsidering the location of the flange. To explain further, the flange on the OEM bushings are on the bottom, and the bottom has the smaller hole. The flange on the M3 subframe bushings is on the same side of the extra wide hole, which must go on top. The side that has the extra wide hole must go on top because it slides onto the notch located on the body. The notch on the body must slide into the wider hole of the rear, front subframe bushing, in order for the subframe to be flush to the body when it is secured to the car. Therefore, be careful not to make the mistake of putting the M3 bushings with the flange down just because the flange on the OEM bushings was on the bottom. “

[IamFODI]

Originally Posted by pbonsalb

Is the front of the subframe moving upwards since the instructions say to put the flange in the bottom instead of the top? This would slightly change the pinion angle of the driveshaft and the suspension. Or is that not actually happening due to the design of the bushing?

So the vertically-shifting-subframe allegation came from RevShift. And yes, they told me not having a flange on both sides could allow the subframe to shift. They said it could be "about an inch" of movement.

RevShift's solid aluminum subframe bushings are 2-piece, with flanges on each side, no flange cutouts, and 6 flats in the barrels to permit an easier fit. They brag that their design "sandwiches" the subframe to prevent that vertical movement.

They never told me they've actually seen it happen, and AFAICT they've never said that publicly either. It's just an allegation about what "could" happen.

Seems implausible that they know something Bimmerworld doesn't. To me it's easier to believe that this vertical movement idea is just a way to sell their design. Maybe they need flanges on both sides because their design fits more loosely (they say all you need for the install is a rubber mallet – no press required). But, IDK.

[amg6975]

Originally Posted by IamFODI

So the vertically-shifting-subframe allegation came from RevShift. And yes, they told me not having a flange on both sides could allow the subframe to shift. They said it could be "about an inch" of movement.

RevShift's solid aluminum subframe bushings are 2-piece, with flanges on each side, no flange cutouts, and 6 flats in the barrels to permit an easier fit. They brag that their design "sandwiches" the subframe to prevent that vertical movement.

They never told me they've actually seen it happen, and AFAICT they've never said that publicly either. It's just an allegation about what "could" happen.

Seems implausible that they know something Bimmerworld doesn't. To me it's easier to believe that this vertical movement idea is just a way to sell their design. Maybe they need flanges on both sides because their design fits more loosely (they say all you need for the install is a rubber mallet – no press required). But, IDK.

Yeah sounds like the classic "vendor that sells product says competitor's product could have issue xyz."

Anyone who's pressed in solid subframe mounts will tell you, there's no way in hell they're moving.

[pbonsalb]

The issue is not the aftermarket subframe bushings moving within the subframe. The issue is whether the location of flanges on top versus bottom serves and purpose and whether the aftermarket bushings with no flanges on top have the recess for the locating stubs that are on the car body.

If the location of the flanges serves no purpose, why does BMW put them on top in the front for M cars instead of on the bottom as with non-M cars? A flange can spread the load. Years ago, BMW M cars sometimes tire the front subframe mounts out of the car body.

Regardless of the flange, my belief is that if the bushing has a recess where it meets the stub on the car body, the subframe won’t move.

If the flange was 1/4” thick on top for front factory bushings and that spaced the subframe down, but aftermarket bushings are flush, the geometry has changed for the driveshaft pinion angle and the rear suspension. Probably not enough to matter, but I don’t know that for sure.

[amg6975]

Originally Posted by pbonsalb

The issue is not the aftermarket subframe bushings moving within the subframe. The issue is whether the location of flanges on top versus bottom serves and purpose and whether the aftermarket bushings with no flanges on top have the recess for the locating stubs that are on the car body.

If the location of the flanges serves no purpose, why does BMW put them on top in the front for M cars instead of on the bottom as with non-M cars? A flange can spread the load. Years ago, BMW M cars sometimes tire the front subframe mounts out of the car body.

Regardless of the flange, my belief is that if the bushing has a recess where it meets the stub on the car body, the subframe won’t move.

If the flange was 1/4” thick on top for front factory bushings and that spaced the subframe down, but aftermarket bushings are flush, the geometry has changed for the driveshaft pinion angle and the rear suspension. Probably not enough to matter, but I don’t know that for sure.

I've used Turner and Bimmerworld solid bushings and they both have the locating recesses for the front two positions and the "bottom" flange is a positive stop to where you push the bushing into. You could not put a flat bushing in, as there are locating pins in the front where the bolts go in.

They do not change the location or geometry of the subframe at all. They will not move, the subframe will not slide on them. This is a complete non problem.

[Fisssh]

Sounds like a bunch of marketing BS to me.