BMW differential bushing fitting

[dva99999]

In trying to fit the BMW diff bush using various methods I couldn’t see how it could possibly fit. Whether it was my eyesight but the BMW supplied differential bush didn’t seem perfectly circular.

when I measured the outside diameter against the powerflex bush they were different.

The powerflex bush measured 84mm all round whereas the BMW bush was 85mm horizontally and 83mm vertically.

Is that how the BMW is supposed to be?

I’ve looked online everywhere but cannot find an answer which leads me to believe that either
A. The problem doesn’t exist anywhere so I’ve received a duff diff (?) or
B. This is how the BMW bush is supposed to be and only a machine press can get them in (in the absence of online methods.

Does anyone know the answer to this?

Thanks

 

[andyglym]

I believed one of the reasons people fit a polly diff bush is because it just slots in where as the OEM one requires further stripping down to fit. @Lee will have the answer.

 

[Lee]

Yeah I just stick it in a vice. Takes little effort to fit the OEM bush.

Edit: to answer your question they will be different in size because the oem bush is interference fit aka needs pressing in.

 

[dva99999]

Yeah I just stick it in a vice. Takes little effort to fit the OEM bush.

Edit: to answer your question they will be different in size because the oem bush is interference fit aka needs pressing in.

I’ll keep at it then. I do have a vice but I knackered up the first bush using it.

 

[t-tony]

When fitting a steel shelled bush such as that you can make it easier buy grinding/filing a slight taper around one end of the steel shell and press that end in first. Also lubricate the shell and the aperture , don't try to press it in dry. The slight taper will have no effect on the bush at all.

Tony.

 

[dva99999]

When fitting a steel shelled bush such as that you can make it easier buy grinding/filing a slight taper around one end of the steel shell and press that end in first. Also lubricate the shell and the aperture , don't try to press it in dry. The slight taper will have no effect on the bush at all.

Tony.

Nice one, I’ll give that a go,

 

[Lee]

When fitting a steel shelled bush such as that you can make it easier buy grinding/filing a slight taper around one end of the steel shell and press that end in first. Also lubricate the shell and the aperture , don't try to press it in dry. The slight taper will have no effect on the bush at all.

Tony.

The bush does have a tapered edge on one side for this reason. I also gently give the ally edge on the casing a taper.

 

[dva99999]

You know when you just want it to all go away

 

[Lee]

You know when you just want it to all go away View attachment 170887

That made me chuckle. I’ve done that once lucky had a large socket to push it back out.

 

[dva99999]

That made me chuckle. I’ve done that once lucky had a large socket to push it back out.

I can get it back out again but have to wait until my tennis elbow subsides caused by hammering the thing in.
What’s the danger in leaving it as it is, bearing in mind the boot floor and diff bracket have been reinforced. It’s making me wonder if I should refit the powerflex one that caused the problem in the first place, seeing his that reinforcements have been done and the subframe bushings are also polybush.

 

[Lee]

You could leave it as is if you like. Personally I would be having an OCD melt down knowing it’s not straight. The bush won’t be fully effective absorbing the movement I guess.

 

[t-tony]

I don't think its far enough out of line to really affect its operation. Plus when its mounted you can't see it.

Tony.

 

[Dino D]

I can get it back out again but have to wait until my tennis elbow subsides caused by hammering the thing in.
What’s the danger in leaving it as it is, bearing in mind the boot floor and diff bracket have been reinforced. It’s making me wonder if I should refit the powerflex one that caused the problem in the first place, seeing his that reinforcements have been done and the subframe bushings are also polybush.

don’t know why the power flex Bush gets the blame for the weak welds popping. Mine has had the powerflex one in for 6yrs and around 15-20k miles of hard use. Car is on 137k now.
@Lee has it all apart now and no damage.

I spoke to a place that so played diffs for rally cars. He said they have plenty of cars competing still just on single mounts with no issue, he said if it wasn’t broken by now it’s not worth spending money on double ears etc - his opinion was that is was something wrong in how it was built rather than the cars use.

my case seems to back that up - it’s pretty crusty, been worked hard and not broken yet but you see other low mileage pampered cars with this issue.

The power flex does transmit a bit of diff noise (whine) so if you don’t like that that stick with OEM.

 

[t-tony]

I think you’re spot on Dino, the problem was inbuilt when the cars were made, but I do think if a car has a weak floor the stiffer bushes don’t help.

Tony.

 

[Nodzed]

I have often wondered if the floor issue is also related to the beam bushes, the diff is mounted to the beam so if the beam bushes and the diff bush are worn surely the movement at the diff bush/hanger would be exaggerated? @Lee? Maybe worn bushes at the rear in general and a heavy right foot results in helping failure. If this is the case maybe PF beam bushes are the way forward as they flex less than new OEM?

 

[Lee]

I have often wondered if the floor issue is also related to the beam bushes, the diff is mounted to the beam so if the beam bushes and the diff bush are worn surely the movement at the diff bush/hanger would be exaggerated? @Lee? Maybe worn bushes at the rear in general and a heavy right foot results in helping failure. If this is the case maybe PF beam bushes are the way forward as they flex less than new OEM?

Defiantly agree with all the extra movement at the rear resulting in extra diff hanger movement. I think we’ll be forever theorising the exact cause without doing a FEA/CFD study (The forces where etc) something i was looking into before going Zedshed full time.

My personal opinion is the driver. Some people don’t drive very mechanically sympathetically and dump the clutch etc without loading the drivetrain up first. Then you have other situation where corrosion has set into the hanger causing premature failure. Hurts my head thinking about it all

 

[dva99999]

It’s possible when I bought the car over 5 years ago that the floor was already weakened. Adding a stiffer bush to it just exacerbated the problem because there was definitely cracks either side of the diff mount and on the diff mount as well. Powerflex beam bushes have also been added. The rear anti roll bar was done around the same time as the diff. I’m going to chance it and leave the diff bush as is. The ear has had a new one welded over it and the floor has been strengthened using a combination of a Randy Forbes inspired method and Airbus sealant.
Hopefully that boot floor will stay on the car.

Now I want to weld something else