Can new diff oil change locking effect of diff?

beanie

beanie

Active member
 Bournemouth/Turin
Bit of a strange one this so wondering if anyone has experienced the same thing.

I recently had my diff oil changed as part of an inspection 2 and have noticed that since this it has been more willing to slide around. Before it had mega traction all through the corner but now I seem to have more options at all points but ultimately a little less traction on the way out.

I can't see bushes having magically worn out at the same time the work was done so the only logical reason is the new oil has altered the way the diff is working. I've heard that the friction modified oil can reduce the locking effect and I believe that is what was in the diff when I bought the car (as recommended, I asked for it to be put in again, however what actually went in I don't know for certain.) so it stands to reason the oil could effect things in this way but I hadn't heard of it in all my hours trawling the forums.

Whatever the case, I actually prefer it like this as I can have fun at lower speeds as the limits are lower and it seems more progressive :D there are no untoward noises either and all tyres have good tread on them all the way across.
 
the only way i could see a diff being LESS effective is if too much friction modifer was used.... in its very essence it actually hinders the diff performance in a bid to quieten down the normal noise a diff makes....
 
I'm not sure what oil was used and I guess, more to the point, I'm just not sure if this is a symptom of being more or less effective (locking up sooner or later) -I've convinced myself there good logic for both trains of thought :?

It's not like it's become wayward and tbh the difference is slight in terms of traction, but where before it would need to be provoked quite deliberately and would be quite snappy, it now responds in a much smoother fashion and transitions in to small slides more fluidly.

I've had a quick poke around underneath and can't see anything untoward or obviously worn as I keep wondering if it's a sign of failing RTABs but frankly, if this is the result, I'm loathed to change them! I guess a geo check wouldn't hurt either as its been a while and the roads out here are pretty shitty at times but if both of those things check out then I'm at a loss.
 
Does anyone know. What type LSD BMW fitted in the Z4M? Torsen? Viscous coupling? Is it purely mechanical or is there any electronic control wizardry??
 
Spaniarduk said:
Does anyone know. What type LSD BMW fitted in the Z4M?
Click to expand...
Its a gerotor type LSD. (although technically it doesnt have a gerotor I think...)
 
https://en.wikipedia.org/wiki/Limited-slip_differential#Gerotor_pump

A gerotor type lsd has a clutch pack that is actuated by a piston.
The 'gerotor' is the oil pump that actuates the piston. However I think technically there isnt a gerotor pump inside but a shearpump. That also fits the size of the diff more. The pump has to be in the shape of a large ring (going around one of the drive axles)
The pump pumps because of the speed difference between the left and right wheel (so one wheel is connected to the pump housing and the other one to whatever impellor it has).
I think it has its own oil supply (because the diff oil is flung around the housing which would give lots of air into the piston).
And the piston will be a large plate (about as large as the clutch plates) that comes out of one of the diff halves (only for 1 or 2mm), pressing on the clutches, locking the diff.

So the gerotor style LSD gets lock after there is wheel slippeage (speed sensitive type), in contrast to for example a salisbury type lsd which gets lock as soon as the engine gives torque.
 
It's definitely a gerotor type, I remember talking to JC Racing about my old M3. It's not as aggressive as a clutch type or as reliable as a Torsen but for the DSC system it's the only suitable type.
 
Torsen works excellent with DSC&ASC. A torsen isnt aggressive at all.

BTW here you can see the diff half with the piston inside:

dxy835.jpg


The flat area where you see that little hole in is the complete piston.
You can also see on the inside where the driveshaft splines grab the splines of the pump.
The thing on top is a seperate part (which also gabs the splines of the pump) and grabs 1 side of the clutches.

The little hole in the piston with ball inside is I think a little check valve to fill the piston with oil and bleed the air out.
 
buzyg said:
MACK said:
Good this just be less grip from the tyres as its been a bit colder recently?
Click to expand...

That was my first thought too.
Click to expand...

It's an old thread and from when the weather wasn't cold :)

I remember noticing it at the time and it coincided perfectly with the diff oil change hence my thoughts. I can't say I'm particularly convinced either way but it's not been an issue nor got any worse so who knows?!
 
beanie said:
buzyg said:
MACK said:
Good this just be less grip from the tyres as its been a bit colder recently?
Click to expand...

That was my first thought too.
Click to expand...

It's an old thread and from when the weather wasn't cold :)

I remember noticing it at the time and it coincided perfectly with the diff oil change hence my thoughts. I can't say I'm particularly convinced either way but it's not been an issue nor got any worse so who knows?!
Click to expand...

I should have gone to specsavers. :wink:
 
You must log in or register to reply here.
Back
Top Bottom