E85 E86 Z4M Diff Rebuilds
Do you have a clunk, knock, bang, or just general loose/play feel within your drivetrain?
Well, you may have the infamous 'M-clunk'.
CHECK OUT OUR 'M-CLUNK' PAGE HERE FIRST
Introduction:
Over time the Z4M Differentials have worn (as all mechanical components do), and some have developed the infamous 'M Clunk'.
This 'wear' in the Differential comes from a mixture of some or all of these problems:
1. Poor maintenance (lack of oil change).
2. Excessive back-lash (usually introduced during the Pinion Input Oil Seal change).
4. GKN 2nd generation LSD Cluster Play (seen at the left hand side Output Flange).
5. Friction material worn away from Clutch Plates.
BMW say these Diff's are 'sealed for life' and they offer no spare parts for the internals.
Rebuild standards:
These Diff's are perfectly rebuildable and we carry out the following items on every build.
All E8x Z4M Diff Rebuilds come with the following:
- Strip down and chemical clean of components.
- Corrosion removal & treatment of Iron Diff Casing.
- Painting (Black) of Diff Casing and associated external parts.
- Supply & installation of all New Bearings for Input & Outputs.
- Supply & installation of New Crush Sleeve.
- Professional assembly of entire unit especially pinion & carrier preloads
- Professional setup of backlash & gear mesh pattern for throttle & coast.
- Supply & installation of New Oil Seals for Input & Outputs.
- Supply & installation of New Diff Rear Aluminium Cover.
- Supply & installation of New Diff Oil.
Option 1:
(No longer available).
OEM Rebuild as per list above
PLUS New Quaife Limited Slip Diff (the best way to eradicate the 'M-clunk')
Ratio change:
The Z4M left the factory with a 3.62 Final Drive Gear Set inside the Differential.
Being the flagship Z4 model and aiming itself firmly towards the performance orientated owner, some felt it should have come with a shorter ratio final drive.
However, all Z4M's have the standard 3.62 ratio.
Luckily, BMW Motorsport came up with a different final drive gear sets for their racing program which happen to fit inside the Z4M's 'Large Case 210 Diff'.
Amazingly, still in 2025, BMW Motorsport are selling these Motorsport Gear Sets - but we don't know how long for. It might be just selling off old stock - who knows?
One favoured ratio (3.91) has already been discontinued and is NLA (no longer available).
These are the Gear Sets which BMW Motorsport produced.
Some are currently still available - but that could change at any time:
- 3.91 - No Longer Available.
- 4.10 - Limited Availability - sporadic availability due to BMW supply issues.
- 4.44 - No Longer Available.
- 3.62 (OEM) Fitted as standard to all Z4M's
- 3.91 (BMW Motorsport) Improved acceleration. Aimed at Fast Road Drivers.
- 4.10 (Motorsport) Further improved acceleration. Aimed at Fast Road / Track Drivers.
- 4.44 (Motorsport) Heightens acceleration experience. Aimed at Short Track / Rally.
(No longer available).
OEM Rebuild as per list above
PLUS New Quaife Limited Slip Diff (the best way to eradicate the 'M-clunk')
But including using a BMW Motorsport 4.10 Gear Set.
This is an exchange program where we specially build you a Diff to whichever spec you choose, before your vehicle arrives with us.
We then keep your current Diff which goes back into our exchange program.
Alternatively, you're welcome to pay a £750 surcharge to have your old Diff returned to you.
If you would like to discuss Diff Rebuild options, or make a booking for this service, please Contact us and speak with General Manager Simon Edwards who will be more than happy to help you.
To make a booking for a differential rebuild we require a £1000 deposit.