Observation & possible solution (LSD)

[SQ13]

I always thought diff fluid change was based on age (like two years). Whoops. I’ve only driven the silver car 29k miles in the eight years I’ve owned it, and I could’ve been changing the fluid less often lol.

[lemoose]

How much does it cost to get a new diff or just to rebuild it?

I think youre looking at 3k at least for that. From what i can gather, though, as long as you can hear/feel your diff binding when taking tight turns (think multilevel parking garage) i wouldnt worry about it.

[Obioban]

Every winter I do the same test— put one tire on ice, one on pavement, see if I can go. It has never failed— including the 200,000+ unit in my wagon.

That said, my coupe now has a wavetrac, that supposedly never wears out (no clutches).

[Mattn1192]

Every winter I do the same test— put one tire on ice, one on pavement, see if I can go. It has never failed— including the 200,000+ unit in my wagon.

That said, my coupe now has a wavetrac, that supposedly never wears out (no clutches).

It doesn’t spin no matter how hard you try to spin the wheel that is in the air?

[loudspeaker69]

Every winter I do the same test— put one tire on ice, one on pavement, see if I can go. It has never failed— including the 200,000+ unit in my wagon.

That said, my coupe now has a wavetrac, that supposedly never wears out (no clutches).

When you do this test, what is the result you are looking for to know the diff is working properly?

I presume the opposite result proves the differential is malfunctioning / needs replacement.

[heinzboehmer]

When you do this test, what is the result you are looking for to know the diff is working properly?

I presume the opposite result proves the differential is malfunctioning / needs replacement.

If you move forward, LSD is locking. If you don't, LSD is dead, essentially acting like an open diff and sending all the power to the wheel with the least traction. There's obviously also varying levels of "go" in between, depending on the health of your diff.

Used to do this all the time as well when I lived in a place with snow. Diff always locked up immediately. Tiny bit of spin, then it felt as if it wasn't on ice at all (cause the diff locked up and tire that wasn't on ice got power sent to it).

[loudspeaker69]

If you move forward, LSD is locking. If you don't, LSD is dead, essentially acting like an open diff and sending all the power to the wheel with the least traction. There's obviously also varying levels of "go" in between, depending on the health of your diff.

Used to do this all the time as well when I lived in a place with snow. Diff always locked up immediately. Tiny bit of spin, then it felt as if it wasn't on ice at all (cause the diff locked up and tire that wasn't on ice got power sent to it).

DSC on or off when performing this test?

I presume off?

[jet_dogg]

DSC always off at all times

[heinzboehmer]

I presume off?

Yes

[sapote]

When I got the RACP reinforced I also took the time to service the diff. It had the usual play and I went for this https://racingdiffs.com/products/bmw...d-clutch-plate, the shim did somewhat cure the free play issue but not 100%. But what we saw is that the clutches were in relatively good shape (car has probably over 300k km or 200k miles), so I'm not sure what wears quickly.

The diff made noise at low speeds on tight corners, like parking garages, and it still does with the new clutches. I'm using Liqui Moly 75w140 LSD fluid at the moment, unsure what the car had in it before the "rebuild".

Attached pictures of the old clutches.

The concave shim? How much backlash it has on the right side output flange? The left side has none?

Did you measure the total stack height of old and new clutch stacks? This will tell how much wear on the old one. But the new one is not OEM so it's apple to orange.

when turning the clutch stack will slip and make some noise, but should not chattering noise.

[sapote]

I’m assuming mine failed test? I jacked up my RR tire & it would clunk when I would move it left to right. But it doesn’t free spin. I’d have to apply a bit of power to turn the wheel completely.

engine running in first gear? Sure this would spin the jacked up wheel. The front wheels were chocked?
Initially the airing wheel spins , then the diff pump running and locking up the clutches tighter, then the car tried to move forward. Don't force the wheel to spin too long as this will wear the clutches. If you can feel the car tries to lurch forward with airing wheel, then clutches are still good.

[Mattn1192]

engine running in first gear? Sure this would spin the jacked up wheel. The front wheels were chocked?
Initially the airing wheel spins , then the diff pump running and locking up the clutches tighter, then the car tried to move forward. Don't force the wheel to spin too long as this will wear the clutches. If you can feel the car tries to lurch forward with airing wheel, then clutches are still good.

Car in neutral

[sapote]

Apply power? Hand power?

[Mattn1192]

Apply power? Hand power?

Yes, hand power (I should have been more specific)

[sapote]

Yes, hand power (I should have been more specific)

I believe the side-gear and spider is 1:1 ratio, and spider to the LSD housing diameter is about 1: 2, and so it only takes about 2x of your arms torque to cause the clutches to slip, then I would say no good. But remember that as the wheel spins faster, the LSD pump will kicks in and lock the clutches more.