Does a z4 m 2007 have a limited slip differential?
- Thread starter Ricard
- Start date
:driving: 
No its not electronic mechanical.
Afaik it is a gerotor or shear pump actuated clutch pack, so different in workings than a standard clutch pack LSD (the progressive clutch pack, the most commonly used type nowadays, there are also clutch type lsd's with a fixed spring tension and fixed lockup).
A standard clutch pack diff engages by the drive force put on the diff (the planet gear axes are pushed against ramps that press on clutches), and the gerotor/shear pump actuated diffs engage by speed difference between both wheels. The gerotors /shear pump is an oil pump that is driven by the speed difference on both wheels, and that pump actuates the clutches. I don't know if it uses a separate oil reservoir in a blatter or the oil in the diff for the actuation mechanism.
The difference between the two is that the first locks up as soon as power is applied, and the second locks up as soon as one wheel starts to spin.
So there are 3 'types' of passive clutch actuated lsd's:
Fixed ratio (fixed tension spring presses on clutch, the friction force between the 2 wheels is always the same)
power actuated ratio (clutch pressure/lockup increases as throttle/power is applied more&more)
Speed actuated ratio (clutch pressure increases as turning speed difference between wheels (=loss of traction) increases)
But it's certainly not a controlled electronic-mechanical diff. There are not control wires going to the diff. I think that was first applied in the F10 M5 and the later F80 m3/m4
Afaik it is a gerotor or shear pump actuated clutch pack, so different in workings than a standard clutch pack LSD (the progressive clutch pack, the most commonly used type nowadays, there are also clutch type lsd's with a fixed spring tension and fixed lockup).
A standard clutch pack diff engages by the drive force put on the diff (the planet gear axes are pushed against ramps that press on clutches), and the gerotor/shear pump actuated diffs engage by speed difference between both wheels. The gerotors /shear pump is an oil pump that is driven by the speed difference on both wheels, and that pump actuates the clutches. I don't know if it uses a separate oil reservoir in a blatter or the oil in the diff for the actuation mechanism.
The difference between the two is that the first locks up as soon as power is applied, and the second locks up as soon as one wheel starts to spin.
So there are 3 'types' of passive clutch actuated lsd's:
Fixed ratio (fixed tension spring presses on clutch, the friction force between the 2 wheels is always the same)
power actuated ratio (clutch pressure/lockup increases as throttle/power is applied more&more)
Speed actuated ratio (clutch pressure increases as turning speed difference between wheels (=loss of traction) increases)
But it's certainly not a controlled electronic-mechanical diff. There are not control wires going to the diff. I think that was first applied in the F10 M5 and the later F80 m3/m4
Argenta said:Its not mechanical.
Its electronic-mechanical and locks 0-100% depending on various conditions.
Sometimes called M-diff and is also on M3 E46.
There ya go.
As guido says, it's definitely not electronically controlled and will not lock to 100% (in practice) it's limited to 0-25%. It also does not work like a traditional clutch pack diff.
The difference between the M Variable Diff and a traditional LSD is how it achieves that lockup. The M Variable Diff uses a shear pump driven by the wheels. When there is a difference in wheel speed, that pump creates pressure and loads the differential accordingly. When there is no difference there is no preload on the diff. A traditional LSD always has its clutch packs preloaded which can be undesirable.
M Variable
To accomplish this, BMW is using a sheer pump located inside the differential. One drive wheel is connected to one part of the pump and the other wheel is connected to the other part. As wheel speeds differ, the pump provides a variable pressure that applies multi-disc clutches preventing the spinning wheel from turning faster than the other wheel.
Traditional LSD
Conventional limited slip differentials use a little constant pressure on their clutches to preload the differential. This works fine for performance applications but it is undesirable on ice. When two wheels are "locked" constantly together even with limited force, they tend to fight each other when the vehicle turns corners and the wheels have to travel different distances. On slippery, icy road surfaces, the action tends to cause both drive wheels to loose traction. This can have a dramatic effect on lateral stability.
Guido and Tom are correct, I had the variable disk in my hands today. It's more like a swash plate. No ramps, no electric pumps.. just a variable pump disk. It's a complete self contained unit. (The guys at Gear Masters are great)
Oh.. good luck with opening the lsd to get a look at that puppy.. it took us a 4 meter extension bar hooked into a press to open the top. This is not for the faint of heart. (And that's after drilling out the locking ball bearing)
So the variable swash plate acts like the ramp, so how do you define lock then? Well there are 17 clutches in the pack and you can active all of them or only some witch will give you lock up to 100 %.
17 maximal number of active clutches as default setup and that is - clutch - disc - clutch - disc ...etc.
If you change clutch order to - clutch - clutch - disc - disc ...etc. you will decrease number of Active clutches by 50% and lock percentage as well.
So 8x clutch/friction disc
9x steel plates.
I also noted that after installment of the 4.1 gears, that I couldent get the preload into spec, so I'll need to get a shim kit...
Might be easier just to buy a racing LSD..lol.
Oh.. good luck with opening the lsd to get a look at that puppy.. it took us a 4 meter extension bar hooked into a press to open the top. This is not for the faint of heart. (And that's after drilling out the locking ball bearing)
So the variable swash plate acts like the ramp, so how do you define lock then? Well there are 17 clutches in the pack and you can active all of them or only some witch will give you lock up to 100 %.
17 maximal number of active clutches as default setup and that is - clutch - disc - clutch - disc ...etc.
If you change clutch order to - clutch - clutch - disc - disc ...etc. you will decrease number of Active clutches by 50% and lock percentage as well.
So 8x clutch/friction disc
9x steel plates.
I also noted that after installment of the 4.1 gears, that I couldent get the preload into spec, so I'll need to get a shim kit...
Might be easier just to buy a racing LSD..lol.
That’s not 100% correct.Argenta said:Its not mechanical.
Its electronic-mechanical and locks 0-100% depending on various conditions.
Sometimes called M-diff and is also on M3 E46.
There ya go
The diff in the Z4M is not the same as the E46 M3 despite both sharing the name of ‘M-Diff’.
