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      08-12-2013, 03:09 PM   #1
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FM booster for DCT cars with differential noise

I've been noticing a grinding noise while right turning at low speeds. I did some research and found out the "SAF XJ +FM booster" is the solution for this.

But one question, how can the differential fluid be different in a exact same model car with different transmissions? The reason why I'm asking this is because I noticed some posts mentioning the FM booster formula is not to be used in a DCT car.

First, is this true? Second, if so then what's my option?

Thanks in advance
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      08-12-2013, 07:18 PM   #2
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I don't know if the diff fluid is different but the dealer tech probably failed to add the friction modifier when the diff fluid was changed at the 1200 service. I'd take it back to the dealer who performed the 1200 service. When you don't have the FM, the little clutch plates in the diff slip which accounts for the squeaking or grinding noise.
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      08-12-2013, 07:24 PM   #3
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My car is a mid 08 model and according to the service records, the previous owner had this same issue at around 20,000 miles under the warranty and the car is now at 53,000 miles. I don't mind getting differential fluid changed, I just want to be sure that they put the right stuff in.
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      08-12-2013, 07:29 PM   #4
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Quote:
Originally Posted by m6pwr View Post
I don't know if the diff fluid is different but the dealer tech probably failed to add the friction modifier when the diff fluid was changed at the 1200 service. I'd take it back to the dealer who performed the 1200 service. When you don't have the FM, the little clutch plates in the diff slip which accounts for the squeaking or grinding noise.
FM booster actually accounts for more slip
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      08-12-2013, 08:02 PM   #5
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Well I'm relying on my experience with a non-BMW that had the diff fluid changed and it required a FM, but that was left out by the dealer. The FM was added separately in a little botltle The diff squeeked and grinded like crazy whenever making turns. The dealer said oops and added the FM and that solved the problem. It could be that the FM is not in there to make it more slippery. Maybe the opposite. I have to admit I know next to nothing about diff lubes in general or diff lubes in particular in BMWs. I remember that some of the early BMW manual trannys couldn't tolerate tranny fluid that was too slippery - -the syncros couldn't gain traction. Or something like that. It's all lost in the mists of time for me.
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Last edited by m6pwr; 08-12-2013 at 08:11 PM.
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      08-12-2013, 08:13 PM   #6
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I used the non fm for about 500 miles in my dct and it started grinding pretty bad when turning right. I sucked it up and bought 3 bottles of the diff fluid with fm booster already in it. Within 50 miles the noise went away.
The fm booster makes it more slippery so when it breaks loose it will continue to slide and not break.grab.break.grab
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      08-12-2013, 09:23 PM   #7
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Quote:
Originally Posted by kawasaki00 View Post
I used the non fm for about 500 miles in my dct and it started grinding pretty bad when turning right. I sucked it up and bought 3 bottles of the diff fluid with fm booster already in it. Within 50 miles the noise went away.
The fm booster makes it more slippery so when it breaks loose it will continue to slide and not break.grab.break.grab
Yes, I think you are right (and I was mistaken).
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      09-17-2013, 12:03 PM   #8
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Had the same issue, took it into the dealer, FM booster was the solution
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