Look inside of a diff that had the M Clunk

[sapote]

I thought M-Clunk was present from day one with these cars and not something that developed. Weren't people discussing this way way back in the day or am I wrong? Or perhaps we just notice more because it gets worse with mileage?

I never had the chance driving a new car so don't know about how loud the M clunk characteristic. But the old worn clutch pack caused the clutch to be jerky instead of smooth slip, and this made the loud clunk when the side gears hit the spider gears.

[sapote]

Likely what's going on with mine, I have the diff. out and the passenger side OPF not only has what I feel is too much (I know there should be some) rotational play but also some up/down play.

Where do you source the spider gears once worn down? I would love to take this opportunity to rebuild the diff. but unsure of my ability to put it together correctly.
.

The 4 spiders (small ones) and the 2 side gears (large ones) don't rotate on a straight road, so they are harmless. They rotate only during a turn. I wouldn't replace these gears for no reason.

Just shim up the side gears for less plays between side gears and spiders.

[bigjae46]

The dont sell it separately any more as i wanted to buy it and they said i would have to buy it in a package with other parts.

There’s really no reason to just put the shim in. You have to take the LSD carrier apart to get the large spider gear out to install the shim. You’d at least want to replace the clutches and steel plates.


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[0-60motorsports]

There’s really no reason to just put the shim in. You have to take the LSD carrier apart to get the large spider gear out to install the shim. You’d at least want to replace the clutches and steel plates.


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Yeah I got it but also labor is cheaper here so I wouldn’t want to do the new clutches and steel plates on my low mileage diff that only has some play but not much and just install the shim.

I guess I’ll just wait and do a full rebuild in a year or so.

[mrgizmo04]

Here is by far the simplest/best explanation of how a diff works: https://youtu.be/yYAw79386WI

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[mrgizmo04]

Does anybody know the part # axle cap bolts? I don't know that I should re-use these..

I think what you want is these, but honestly, folks reuse them. These bolts go through the cap and the case, and main thing for these is to use a thread sealer so that diff fluid doesnt leak out.

https://diffsonline.com/cap-bolt-for-carrier-in-210mm-differentials.html#.Yh-_HLeIadM

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[mrgizmo04]

Yeah I got it but also labor is cheaper here so I wouldn’t want to do the new clutches and steel plates on my low mileage diff that only has some play but not much and just install the shim.

I guess I’ll just wait and do a full rebuild in a year or so.

To get the spider gear shim in, you have to take out the clutch pack anyway. Clutches don't last more than about 25k miles until they develop play, so even "low mileage" could benefit from it. Work wise, to get the clutch pack back in, you might as well use a new set...

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[maupineda]

I dont like the idea of racing diff clutches lasting much less. OE one last for sure way more than that. That is why I wont rebuild my low miles diff. It locks fine and the clunk is not bad enough to make me want to mess with it

[0-60motorsports]

To get the spider gear shim in, you have to take out the clutch pack anyway. Clutches don't last more than about 25k miles until they develop play, so even "low mileage" could benefit from it. Work wise, to get the clutch pack back in, you might as well use a new set...

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I understand your logic, and that is why i will wait for a sale on the parts, buy them and keep them on stand by for summer or after and do the job then

[bmwfnatic]

Does anybody know the part # axle cap bolts? I don't know that I should re-use these..

Mind you that all this information regarding the diff in the torque spec PDF is pretty much wrong.

The specs quoted here make very little sense, but I believe they are based on the specs for a K type differential (K stands for german Kurz, which means short, which refers to the output flange style).

Those specs are 10 Nm + 40deg.

However, our M3's don't have a K type differential, but rather the old style output flange. Which should just be torqued to 22 Nm!

Furthermore the PDF calls for Loctite 242/243 which are medium strength threadlockers, while TIS calls for Loctite 270 which is a high strength threadlocker.

Since these bolts should just be torqued to 22 Nm, they are not torque to yield and don't need to be replaced.

Hope this helps.

[Cubieman]

Mind you that all this information regarding the diff in the torque spec PDF is pretty much wrong.

The specs quoted here make very little sense, but I believe they are based on the specs for a K type differential (K stands for german Kurz, which means short, which refers to the output flange style).

Those specs are 10 Nm + 40deg.

However, our M3's don't have a K type differential, but rather the old style output flange. Which should just be torqued to 22 Nm!

Furthermore the PDF calls for Loctite 242/243 which are medium strength threadlockers, while TIS calls for Loctite 270 which is a high strength threadlocker.

Since these bolts should just be torqued to 22 Nm, they are not torque to yield and don't need to be replaced.

Hope this helps.

This does help, thank you.

I do want to apply some RTV to the bolt threads as well as threadlocker but not sure if that would work with both compounds on the same bolt.

I would think one could put the threadlocker down at the end (tip) of the bolt threads and then the RTV sealant above it as to hopefully not let the RTV cover over the threadlocker as the bolt is installed.

Any thoughts?

[bigjae46]

Holes don’t go through the case so RTV would serve no purpose. You should blow out the holes to make sure there is nothing in there.


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[bmwfnatic]

This does help, thank you.

I do want to apply some RTV to the bolt threads as well as threadlocker but not sure if that would work with both compounds on the same bolt.

I would think one could put the threadlocker down at the end (tip) of the bolt threads and then the RTV sealant above it as to hopefully not let the RTV cover over the threadlocker as the bolt is installed.

Any thoughts?

If you would want to apply both, then yes your way of doing it makes the most sense versus doing it vice versa.

However keep in mind that RTV isn't the same as thread sealant, and they serve different purposes.

When I rebuilt my diff I used Permatex High Temp Thread Sealant https://www.amazon.com/dp/B000AAJTYS

On the data sheet it states that it resists vibration loosening and works up to 400F, so it seemed ideal for this application, and eliminated the need to use an additional threadlocker for me, my bolts have not come undone and aren't leaking either 😁

[bmwfnatic]

Holes don’t go through the case so RTV would serve no purpose. You should blow out the holes to make sure there is nothing in there.


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They do, they go all the way trough.

[bigjae46]

They do, they go all the way trough.

https://youtube.com/shorts/JF3N1MsaB_8?feature=share

Do not. There is a bump on the backside. It’s a blind hole.


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