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Discussion Starter #1
Alright everyone ive been here before with this problem and got solutions which were tried but no luck. Before i start all these things were recently done.
- Diff fluid change(most likely not with FM)
-New Rtabs
-New differential bushings
-New subframe bushings
-full subframe reinforcement
Side note (guibo is good)


So for a while now when driving the car the differential whines and groans and makes a rubbing sound when making tight turns. If the car isnt fully warmed up it will make awful noise when going around a turn in road. But when warmed up the sound isnt so bad at all. But when it is fully warmed up i cant even describe the sound/physical hesitation of the diff. It is unbelievably loud. So this leads me to believe that its a fluid thing. So my first plan of action is to buy a FM and add it into existing fluid since its new. My question with this is what FM ? And how much fluid should i take out of diff then replace with this? Any tips about this?

2nd problem. Theres still a thud/ clunk coming from rear end(i assume differential area) when shifting/pressing accelerator. Some notes about this:

-The thud gets worse when shifting at higher rpms.
-releasing pedal also helps with thud.
-SMG transmission
- the faster the shifts are set to the worse.

Does anyone have any idea about what is causing this despite all the new parts? It is obnoxious. Im stumped. Are these problems both from same thing or different? Is the differential bad? Even though the car drives fine besides this. Side note( slight whine when releasing pedal and coasting above 40mph) not sure from where but it doesn't seem like diff. Could this be a tranny problem! Driveshaft? I need advice please.
 

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Just some suggestions here based on my personal experience: I use and most of the forum guys use Liquimoly 75-140. it has the FM built in. You may want to use that. Pretty inexpensive.
Clunks: did u tighten everything ? The lower front bushing bolt is to be torqued to 120 ft/lbs. I had stripped mine hence not properly torqued. It banged ungodly bad/ even shifting in reverse to 1st etc.
Did u change out bushing to polyurethane or still oem? Since I've switched to AKG red bushings I've noticed its a bit noisy during shifts.
Good luck. I probably didn't answer everything but it's all solvable !
Mine is 03 m3 SMG.
 

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Discussion Starter #4
Just some suggestions here based on my personal experience: I use and most of the forum guys use Liquimoly 75-140. it has the FM built in. You may want to use that. Pretty inexpensive.
Clunks: did u tighten everything ? The lower front bushing bolt is to be torqued to 120 ft/lbs. I had stripped mine hence not properly torqued. It banged ungodly bad/ even shifting in reverse to 1st etc.
Did u change out bushing to polyurethane or still oem? Since I've switched to AKG red bushings I've noticed its a bit noisy during shifts.
Good luck. I probably didn't answer everything but it's all solvable !
Mine is 03 m3 SMG.

Same here o3 m3 smg. But it clunked before new bushings and after so it is unlikely both times they are loose. And since i was getting subframe welded a very reputable shop did the bushings so i have doubt anything is not tightened properly. And i also have polyurethane bushings but oem+ feel and im aware there will be some noise but no way would it be as awful as mine. But thanks for suggestions! Ill look into fluid.
 

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Re: the diff:

Add BG brand friction modifier. Go out in a parking lot and do a dozen tight, slow turns in both directions.
 

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Discussion Starter #7
Re: the diff:

Add BG brand friction modifier. Go out in a parking lot and do a dozen tight, slow turns in both directions.
So this is the BG LsII limited slip axle additive concentrate? And how much should i add into existing diff fluid?
 

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Discussion Starter #8
A side note/update. When making tight turns in both directions after car is at operating temperature there is no chatter at all really. It's very silent. But before fully warmed up the sound is miserable. So a friction modifier would help with this?
 

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I am having the same issue. I have read somewhere on bimmerforums that bmw upgraded from a previous fluid to something new that will cure that friction noise issue.
 

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Discussion Starter #10
I am having the same issue. I have read somewhere on bimmerforums that bmw upgraded from a previous fluid to something new that will cure that friction noise issue.

Im aware, but as i just changed fluid im choosing to add a FM instead. Does your sound improve when car is warmed up?
 

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been testing the car out more since the weather is warmer recently and noticed that when turning, if i step on it, no noise... but when i let the car roll as it turns, it will grind when (only when cold)....
 

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^ I have the same thing

I've just filled with Castrol 75w140 with FM fluid (4%) and waiting to see it recover. On the third sharp turn the diff began to whine less like if it was hesitating ! Impressive ! Mine was filled with wrong fluid in factory.
 

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Discussion Starter #14
^ I have the same thing

I've just filled with Castrol 75w140 with FM fluid (4%) and waiting to see it recover. On the third sharp turn the diff began to whine less like if it was hesitating ! Impressive ! Mine was filled with wrong fluid in factory.

Ive been bust with a coilover install and haven't gotten to buying a modifier lol. I hope yours helps. But as of 4% is that the recommendation for FM to fluid?
 

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I've been using the Redline Friction modifier. They say 8% for break-in and 4% normally. Sorry I am away from the car for a while so I cannot tell you if 4% did make the whine totally disappear.

Some products already inlude friction modifier, like Redline 75W90NS and 75W140NS and you can add some FM if it's still too noisy. But I've also read that you shouldn't add too much or the locking function could get too slippery. Only add a little amount to reduce the whine.
 

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Discussion Starter #16
I've been using the Redline Friction modifier. They say 8% for break-in and 4% normally. Sorry I am away from the car for a while so I cannot tell you if 4% did make the whine totally disappear.

Some products already inlude friction modifier, like Redline 75W90NS and 75W140NS and you can add some FM if it's still too noisy. But I've also read that you shouldn't add too much or the locking function could get too slippery. Only add a little amount to reduce the whine.

Well a shop changed my fluid with oem/ and i take it that it definitely wasnt the updated one with FM. My diff is super noisy when not warmed up. So ill probably go straight to 8% a fellow guy in here recommended BG brand FM which im about to order. But percents dont mean much to me what would 8% be in relation to quarts? How much should i take out of existing fluid?
 

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Well it's about 1.3 Liters/Quarts. Just measure drained oil volume and add 4% before refill. Since my FM bottle is 250 ml, I used only 125 ml with 1.3L Castrol 75W140 and reserve the next 125 ml for enhanced noise reduction or future flushes.

What fluid did your shop put in ? Was it the expensive BMW's "SAD-JX + FM" ?
My BMW mechanic who wanted to put the BMW fluid said that it took about 1000 miles for the noise to reduce (in his clients cars), then he put new BMW fluid back in again and the noise was gone.

I like OEM route... but 400$ when the BMW fluid is essentially Castrol... just too much !
 

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Discussion Starter #18
Well it's about 1.3 Liters/Quarts. Just measure drained oil volume and add 4% before refill. Since my FM bottle is 250 ml, I used only 125 ml with 1.3L Castrol 75W140 and reserve the next 125 ml for enhanced noise reduction or future flushes.

What fluid did your shop put in ? Was it the expensive BMW's "SAD-JX + FM" ?
My BMW mechanic who wanted to put the BMW fluid said that it took about 1000 miles for the noise to reduce (in his clients cars), then he put new BMW fluid back in again and the noise was gone.

I like OEM route... but 400$ when the BMW fluid is essentially Castrol... just too much !

Honestly i can't remember off the top of my head, but if you say its 400$ then they for sure didn't use that. And id say its been around 1000 miles for sure. Either way thanks!
 

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Having similar problem with my 02 330 ci with about 180k on the clock. Just changed out rear diff fluid and put in Royal Purple with FM. It sounds better (less noise) after I drive it for about a half hour at highway speed. Still sounds like a meat grinder at startup. Hoping it will bet better after some more miles. Any info on why it takes so much time/miles for the lubrication to improve?
 

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Any info on why it takes so much time/miles for the lubrication to improve?
Good question. Maybe the small clutch disks inside needs to be "impregnated" by new fluid, and since it is not a break-in they are less permeable. I've seen a guide on a diff overhaul, they let the new clutch disks in oil a while before reassembling the diff.

I just hope that it's not that our diffs have internal wear and this noise comes from too much internal gear backlash...
 
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