Urgent help please, Z4 E85 3.0si diff replacement/options.

C

Commando_Rob

Member
 London
Afternoon all,

So after buying Wilksd Z4 3.0si I’m looking at my options for repairing/changing the noisey rear diff.

My thoughts,
1 replace like for like with same E85 3.0si manual 3.23 ratio diff, quite a few on eBay so most sensible option.
2 change for a E86 3.0si manual rear diff to improve acceleration as believe this is a 3.46.
3 fit LSD assume will ideally need a working diff before doing this? Have contacted Birds and they want 2.5K for Quaife! Don’t want to spend this much.

Any help advice really appreciated.
 
Straight swap. I should clarify the 3.73 must be from a roadster auto, coupes with auto came with a 3.64 iirc.
 
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You could look at the Blackline which is half the price of a Quaiffe. I just fitted one to my 130i. It transforms the power out of corners, tracking you around them and firing you out. Get a good local diff rebuilder to do the swap and it should be around £700 on top of the LSD purchase with new bearings plus about £100 to swap the diff in and out. Worth a look. They have got very good reviews on the Baby BMW forum. You can get 5% off a first order.
 
Hi all just to update on this I’ve got abit of a situation that could really really do with some help please, so I’ve purchased a diff, from fellow z4 enthusiast 2004 e85 z4 manual 2.5 m54 3.23 diff PN 7514149 that from research should be compatible with my 2006 manual 3.0si, who also said he would fit for a reasonable fee, so long drive to his location, old diff out and we’ve got the new diff in but there is a 7mm shortfall from prop shaft to diff! Any ideas or help
and advice really appreciated as car is on axle stands on side of a road.
 
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Swap the input flange from the old diff to new? Obviously measure first, in case they are the same
 
Guide to swapping the flange here

J

Thread 'Greasing Differential Input Flange - Fix for Clanking Differential - E85'

The Problem

My 2004 BMW Z4 E85's differential clunks on acceleration, specifically in 1st 2nd, and 3rd gear, at low speeds. The clunk only happens when engaging or disengaging the accelerator. I lift my foot off the petal and *clunk* it disengages, and I put my foot back on *clunk* it engages.

The sound seems to come from the back of the car and is really starting to annoy me because it is audible from outside the car, and can be felt on the inside.

For more information on how this repair was researched & which options were considered please view this thread...
  • Like

They might be the same, but... Worth checking
 
TriggerFish said:
Swap the input flange from the old diff to new? Obviously measure first, in case they are the same
Click to expand...
Thanks for the reply 🙏🏼
Yes will get my mechanic friend that’s doing the work to re measure the two different flanges incase that’s where the 7mm difference is, I’ve contacted a number of breakers Quarry motors, Bavarian BMW Parts & EP who are also selling the same diff as a direct bolt on replacement for the 3.0si and all seem to think the diff should fit!
 
Good shout! There is indeed, and it has an accordion type cover over it. It can be very stiff to move (I had to hammer mine apart to change the center bearing). Maybe that compressed up removing the old diff, and is being really stiff to mate up to the new diff?

I coated mine in grease when refitting it, and it made it a lot easier

Screenshot_20260727-151810.png

This is where the rubber boot should be (mine fell apart, I was waiting for a replacement when I took this photo)

Screenshot_20260727-151900.png
 
Also - Mark the two halves in case it comes apart if you try and move it. I believe it is balanced in the factory and it needs to go back together the same way.
 
Thanks for replies all this is helpful will relay back to my mechanic, at the moment he is saying the 7mm gap is due to the M54 cars (M54B30 and M54B25) came with a prop that was 7mm longer (1230mm) The N52 cars came with a 1223mm prop shaft so that’s the issue! Would changing the flange from my N52 diff that’s knackered to the donor diff M54 2.5i diff we’re trying to fit make any difference? Or does he just need to pull on the prop more, or maybe both?
 
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So just to update all on this diff situation and may help others in future. My mechanic friend has measured the input flanges from my old noisey N52 3.0si diff, and from the replacement m54 2.5i diff and they are the same length, so no point swapping over, the issue is the distance from the diff case and shorter propshaft of the N52 3.0si, he has pulled the propshaft more as was stiff and it has released enough to close the 7mm gap, hopefully this will work and the shorter prop and less splines engagement won’t be an issue. Some pics from my mechanic as we all love a pic!
 

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