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Discussion Starter #1 (Edited)
Hello.

Over the winter I replaced some worn out and leaking parts, namely guibo, csb, and differential pinion seal. Used LM 75w-140 diff oil from FCP.

It sat for a bit after the repairs. Took it for a spin and there was whining/moaning sound from the diff when in gear and not accelerating. Put about 20 miles on it and parked it. Thought changing over to the genuine BMW diff oil would perhaps solve (fingers crossed) the noise. Guess what, no luck. Sound still there and unchanged. I will note the LM oil I drained out was dirtier than it should have been for only 20 miles use).

Read up on the possible causes of the whine and was led to believe there is a high probability the input flange was not installed correctly by me. I followed the Bentley and other advice here for the install. Match-marked the pinion and nut. Counted the turns during removal and reinstalled the same amount of turns while matching the marks.

So today I tore back into the rear (I despise rework). Once the driveshaft was moved out of the way I found, in my opinion, too much slop in the input flange/pinion. I'd say 2mm either way radially, slightly less axially.

This seems like too much play and possibly the cause of the noise. Please yield a second opinion and recommendations for actions going forward. If it is the bearing, is a rebuilt diff the answer or can just the bearing be replaced? If a rebuilt diff is required, what business is recommended? So far I have found Turner units from ECS and Diffsonline. They appear to be the same money, approx. $1400.

I looked into rebuild kits and DIY, but I am willing to admit when something is beyond my capabilities. It is not worth trying to save $800 by doing it myself when there is decent probability I will end up where I started.

Thanks in advance fellas!

PS - history of the diff. Car currently has 168k miles. The original diff was replaced by the last/original owner. Leafed through the service records and found diff is only 40k miles/6yrs old.
 

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All you can really do is tighten it up some more. I've never found the mark and reinstall method to be reliable.

Rebuilding the diff isn't that hard. Fresh bearings only should not require the use of alternate shims to set the gear lash. All you have to do is get a new pinion crush sleeve and set the nut torque to the desired drag specified by most diff rebuilds.
 

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Discussion Starter #3
All you can really do is tighten it up some more. I've never found the mark and reinstall method to be reliable.

Rebuilding the diff isn't that hard. Fresh bearings only should not require the use of alternate shims to set the gear lash. All you have to do is get a new pinion crush sleeve and set the nut torque to the desired drag specified by most diff rebuilds.
You're suggesting tightening up the pinion nut more?

One other detail - car has been driven approx 150 miles since the work was completed.

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All you can really do is tighten it up some more. I've never found the mark and reinstall method to be reliable.

Rebuilding the diff isn't that hard. Fresh bearings only should not require the use of alternate shims to set the gear lash. All you have to do is get a new pinion crush sleeve and set the nut torque to the desired drag specified by most diff rebuilds.
Agreed - You should always add about 1/8 turn on the pinion nut since the crush leave is already compressed. We've done dozens while I had my shop and this seems to work best. Probably why it whines at neutral throttle, accel loads the gears since they are helical cut.
 

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Discussion Starter #5
Agreed - You should always add about 1/8 turn on the pinion nut since the crush leave is already compressed. We've done dozens while I had my shop and this seems to work best. Probably why it whines at neutral throttle, accel loads the gears since they are helical cut.
Thanks for the reply. I like the sound of this much better than the alternatives.

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Thanks for the reply. I like the sound of this much better than the alternatives.

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How can it hurt at this point :)

Unless you've driven ALOT of miles in this condition, the ring and pinion will not have suffered any damage. Long term it knife edges the gears...
 

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Discussion Starter #7 (Edited)
150 miles max since the initial repair. I dont consider that alot. What say you?

Also, I read somewhere in a post that approximately 300-400 #lbs is required to tighten the pinion nut. Is that accurate? Is so, I dont recall expending that much torque during the repair.
 

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Discussion Starter #8
I am claiming a small victory. Put everything back together last night after work. I reinstalled the input flange to exact point it was upon disassembly and it was very loose, the way I left it last time. I began tightening it further with a 1/2" ratchet and counter-holding the flange. As I tightened the nut the slop began to go away. I checked the running torque frequently. It was hanging at 10 inlbs for most of the process. For the last bit of tightening I used a 3/8" breaker bar for max torque.

I ended up turning the pinion nut an extra 1/2 turn past where I started. This left me with 15 inlbs of running torque. Perhaps I could have torqued slightly more, but I was afraid of going to far and ruining the crush sleeve.

Took it for quick spin and the differential was completely silent! The machine sounded like it did last fall when I put it away for the winter.

I plan on changing the oil once more - reason being I suspect there is some metal and other undesirables in the oil caused by 100 or so miles driven with the pinion not torqued properly thus changing how it meshed with the ring gear. If nothing else, it is a cheap insurance policy to prolong the life of the differential. $100 worth of oil vs $1400 for rebuilt unit.

Let this be a lesson that the Bentley manual is not always accurate.

I know a 1/2 turn is a fair amount more than an 1/8, but that seemed to be where the flange needed to be seated. Time will tell if the fix is permanent. Thank you gentlemen for the recommendations. Your input was key to the resolution.
 

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I am claiming a small victory. Put everything back together last night after work. I reinstalled the input flange to exact point it was upon disassembly and it was very loose, the way I left it last time. I began tightening it further with a 1/2" ratchet and counter-holding the flange. As I tightened the nut the slop began to go away. I checked the running torque frequently. It was hanging at 10 inlbs for most of the process. For the last bit of tightening I used a 3/8" breaker bar for max torque.

I ended up turning the pinion nut an extra 1/2 turn past where I started. This left me with 15 inlbs of running torque. Perhaps I could have torqued slightly more, but I was afraid of going to far and ruining the crush sleeve.

Took it for quick spin and the differential was completely silent! The machine sounded like it did last fall when I put it away for the winter.

I plan on changing the oil once more - reason being I suspect there is some metal and other undesirables in the oil caused by 100 or so miles driven with the pinion not torqued properly thus changing how it meshed with the ring gear. If nothing else, it is a cheap insurance policy to prolong the life of the differential. $100 worth of oil vs $1400 for rebuilt unit.

Let this be a lesson that the Bentley manual is not always accurate.

I know a 1/2 turn is a fair amount more than an 1/8, but that seemed to be where the flange needed to be seated. Time will tell if the fix is permanent. Thank you gentlemen for the recommendations. Your input was key to the resolution.
That’s great news and you were more careful than we were :) we cinch past the mark we made when we disassembled and called it a day ;)
 

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Replaced my front diff bushing several weeks ago and all seals (input & output). Same thing happened, whine at coast not during acceleration.

Must not have precisely lined up the nut based on my markings or need to go a little tighter. Either way I'll be digging back into this soon. Fingers crossed I have the same positive outcome.

This time will also replace (press out/in) the diff cover bushings with e36 m3 bushings. I dont believe I need to drop the diff again, and think I can just remove back cover (2 rear bolts, several cover bolts).

Anyone have experience just dropping the rear cover?

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Hardest part with dropping just the cover is using the 11mm open end to get the 2 rear bolts out. I've swapped diff covers with diffs on the cars, not too bad.

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Discussion Starter #12
Replaced my front diff bushing several weeks ago and all seals (input & output). Same thing happened, whine at coast not during acceleration.

Must not have precisely lined up the nut based on my markings or need to go a little tighter. Either way I'll be digging back into this soon. Fingers crossed I have the same positive outcome.

This time will also replace (press out/in) the diff cover bushings with e36 m3 bushings. I dont believe I need to drop the diff again, and think I can just remove back cover (2 rear bolts, several cover bolts).

Anyone have experience just dropping the rear cover?

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I can report the differential remains quiet after about 1k miles. It is an extra vehicle so it doesn't see a lot of action, maybe 2k miles/year.

When you disconnect the driveshaft check how much play you have with the input flange.

Good luck!
 

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Not that I agree with overtightening the input but, as one does so it's not the crush collar you need to worry about. It just sets the depth and holds it, an one time adjustable spacer in the collapsible direction only if you will...

The real issue is that when you make the nut tighter, you draw the pinion shaft and gear further forward and create a different mesh pattern between the ring gear and the pinion gear. Sometimes over tightening too much can create too much driveline lash when on/off the throttle. Can also cause pinion gear whine.

If one must....... I'd say limit it to 1/8th of a turn. Marking perfectly before removal is paramount. I use a pin punch and take my time. When I'm done, the two dots line up. Paint or crayon can be wiped off unintentionally.
 

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[

The real issue is that when you make the nut tighter, you draw the pinion shaft and gear further forward and create a different mesh pattern between the ring gear and the pinion gear. Sometimes over tightening too much can create too much driveline lash when on/off the throttle. Can also cause pinion gear whine.

If one must....... I'd say limit it to 1/8th of a turn. Marking perfectly before removal is paramount. I use a pin punch and take my time. When I'm done, the two dots line up. Paint or crayon can be wiped off unintentionally.
[/QUOTE]
The real issue is that when you make the nut tighter, you draw the pinion shaft and gear further forward and create a different mesh pattern between the ring gear and the pinion gear.

Sometimes over tightening too much can create too much driveline lash when on/off the throttle. Can also cause pinion gear whine.
Not true. The pinion depth is fixed by the inner bearing and shims, so the pinion cannot be drawn forward further. If the nut was over tighten then the bearings drag torque would be very high because the pinion moved a few micrometers forward to change the gear mesh pattern.
 

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I ended up turning the pinion nut an extra 1/2 turn past where I started. This left me with 15 inlbs of running torque. Perhaps I could have torqued slightly more,...I know a 1/2 turn is a fair amount more than an 1/8, but that seemed to be where the flange needed to be seated. Time will tell
Op, you only changed the oil seal and keep everything original; this means no dimensional change to any metal parts, and so if the nut was tighten to the same old place then the pinion bearings should be loaded exactly as before. But now you had to add 1/2 turns more to get the gear mesh quiet. 1/2 turn is a lot and so I believe you missed count the number of turns of the nut by 1 turn less. Which means you’re still short of another half turns to get to the original bearing load point.
 

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I've only worked on GM diffs, no BMWs. But in general I've found that replacing the crush sleeve and tightening the pinion nut to the proper running torque whether 15"# or whatever is the way to go. If you're really anal you can use a blue dye or marking grease to check the gear teeth pattern on the pinion and ring gears, but normally that's not required.
 

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Discussion Starter #17
Sapote, thanks for the insight. Are you suggesting I take action, ie tightening the nut another 1/2 turn? Or is this just an observation? Like SloopJohn said, during the last tightening of the nut I got to the approximate 15# running torque and left it go with the idea of less is better and can always tighten it more. Conversely, too much torque is worse than not enough.
 

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Unless you disagree with my analysis on the turns miscounting, I would slowly tighten the nut and watching the drag torque, until met the mark or drag torque increased too much.

if left it 1/2 turns less than spec the mesh pattern changed and could lead to noisy in future.
 

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Discussion Starter #19
Unless you disagree with my analysis on the turns miscounting, I would slowly tighten the nut and watching the drag torque, until met the mark or drag torque increased too much.

if left it 1/2 turns less than spec the mesh pattern changed and could lead to noisy in future.
No sir, don't disagree at all. I'm always open to suggestions and advice. Ill weigh my options. Thanks for the info!
 
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