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Discussion Starter #1
Good morning,

'02LT with 73K miles. No gear oil leaking from the rear drive. Did a routine check for rear drive play by grasping the tire at 12 and 6 o'clock positions and detected a small amount of wiggle. I don't have a dial indicator, so I don't know the exact amount of play. Is ANY play at all acceptable, or is it time to get the crown wheel bearing replaced?

Thanks,
Ken
 

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Good morning,

'02LT with 73K miles. No gear oil leaking from the rear drive. Did a routine check for rear drive play by grasping the tire at 12 and 6 o'clock positions and detected a small amount of wiggle. I don't have a dial indicator, so I don't know the exact amount of play. Is ANY play at all acceptable, or is it time to get the crown wheel bearing replaced?

Thanks,
Ken
Hey Ken, if there is play, there is no preload on the internal taper bearing.


The assembly of the FD requires shims to be installed to apply a preload on the taper bearing inside the FD. This takes up all the play in the FD. If you are detecting play then it should be looked at. Detecting play at 73K, I would expect to replace the crown bearing and check/replace with the proper thickness shims to reapply the proper preload as long as there are no other issues like creeping pinion race, spun taper seat, leaking pinion seal or excessive wear/chipping of the crown and pinion gears.
 

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Just a thought,...The pins the final drive attaches to the swing arm with ,may be a little sloppy...Or not...:wave
 

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Just a thought,...The pins the final drive attaches to the swing arm with ,may be a little sloppy...Or not...:wave
Good point, I just read that same thing on a different forum. A good idea to check the pivot bearings before tearing the FD apart. Make sure they are properly adjusted and not worn.
 

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Had it happen on my first LT, by coincidence an '02.
Just did my 01 FD with 56K, pivot bearings are like new. No history if they were ever swapped out though. Play is now gone after the proper shims were put in on the new bearing.
 

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Is there play when you move the wheel side to side e.g.. 9 o'clock and 3 o'clock. When I had play with my R850R, 12-6 o'clock had play but 9-3 didn't. Turned out to be the joint between the final drive and the swing arm... just a thought.
 

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Discussion Starter #8
Just a thought,...The pins the final drive attaches to the swing arm with ,may be a little sloppy...Or not...:wave
Good points all who replied. I'll check the pivot bearings tomorrow.

Thanks,
Ken
 

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Easy check is to watch the brake rotor relative to the caliper - if no movement there it IS the pivot pins. If it is the bearing you will see relative movement at the caliper.
 

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Discussion Starter #10
Is there play when you move the wheel side to side e.g.. 9 o'clock and 3 o'clock. When I had play with my R850R, 12-6 o'clock had play but 9-3 didn't. Turned out to be the joint between the final drive and the swing arm... just a thought.
Took a few days with work commitments and other "stuff" but finally checked to see if grasping the wheel at 9 and 3 o'clock and rocking it back and forth had play. It did, so I removed the rear drive and set it up to test the play with a dial indicator. Took several measurements with all of them being right at .003 inch. The tapered roller bearing and race appear to be on good shape, though.

I suppose the .003 inch free play indicates a new crown wheel bearing, oil seal and shimming. Any other option make sense (like reshimming only)?

Thanks,
Ken
 

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Took a few days with work commitments and other "stuff" but finally checked to see if grasping the wheel at 9 and 3 o'clock and rocking it back and forth had play. It did, so I removed the rear drive and set it up to test the play with a dial indicator. Took several measurements with all of them being right at .003 inch. The tapered roller bearing and race appear to be on good shape, though.

I suppose the .003 inch free play indicates a new crown wheel bearing, oil seal and shimming. Any other option make sense (like reshimming only)?

Thanks,
Ken
I would say that is the right option. Do you have something accurate enough to measure the shims you took out? I just bought a flebay FD and am going to rework it as a spare. I took it apart and it looks OK, a 99 with 40K on it. Going to measure before I pull the old bearing to see how well shimmed it was. It had a .6 and a .15 shim for .75 total. My FD on the bike had .7 in it and was over shimmed. Just curious what yours comes in at assuming it has not been done before.
 

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Discussion Starter #12
I would say that is the right option. Do you have something accurate enough to measure the shims you took out? I just bought a flebay FD and am going to rework it as a spare. I took it apart and it looks OK, a 99 with 40K on it. Going to measure before I pull the old bearing to see how well shimmed it was. It had a .6 and a .15 shim for .75 total. My FD on the bike had .7 in it and was over shimmed. Just curious what yours comes in at assuming it has not been done before.
I should have been clearer in how I measured the free play. I did not open up the rear drive at all. I measured the free play using the DMAN method, but without opening up the drive. I'm the third owner of the bike. I understand from the PO that the rear drive I took off the bike and measured was a used, but rebuilt, unit. He had the original rear drive, too, and threw that in the sale.

A question I have is whether the .003 inch free play is enough to damage the crown wheel bearing, assuming it had that free play for 50K miles.

I do have calipers accurate to .001 inch that I will use to measure the shims when I open up the drive.

Thanks,
Ken
 

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I should have been clearer in how I measured the free play. I did not open up the rear drive at all. I measured the free play using the DMAN method, but without opening up the drive. I'm the third owner of the bike. I understand from the PO that the rear drive I took off the bike and measured was a used, but rebuilt, unit. He had the original rear drive, too, and threw that in the sale.

A question I have is whether the .003 inch free play is enough to damage the crown wheel bearing, assuming it had that free play for 50K miles.

I do have calipers accurate to .001 inch that I will use to measure the shims when I open up the drive.

Thanks,
Ken
Ken, that .003 of play at the crown wheel will allow the tapered bearing to slap back and forth against the bearing seat as the weight transfers from side to side and the thrust angle changes. If left alone, it will eventually damage the seat and rollers and the bearing and race will need to be replaced. Got some pics from Dave ( saddleman) on one of his posts to show what can happen when there is no preload from under shimming.

The DMAN method is good as long as you make sure the crown wheel is fully seated back down on the taper bearing for a zero. Tapping is usually in order on the down swing and a reset of the zero reference especially if you still have the seal in place and have not heated the casing to allow the bearing to move more freely up and down. Is .003 enough to cause damage? I have not seen data on that in any post i have read but it won't get any better. If you can feel the play at the wheel, imagine what that taper bearing is doing inside that race over every bump. It is not transferring the load evenly to the race if it is not in contact with it 360 degrees around.
 

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...I did not open up the rear drive at all. I measured the free play using the DMAN method, but without opening up the drive...
There should be no axial movement of the crowngear assembly in a properly assembled final drive. That you were able to detect measurable movement is a clear indication that something isn't right inside that drive.
With proper preload on the crowngear assembly as established by the crownwheel bearing shim, there should be absolutely no detectable axial movement.

If I follow your description above, this final drive was rebuilt during the prior ownership.
I helped to pioneer some of the DIY rebuild methods, but eventually started recommending against DIY rebuilds. There is a learning curve to doing these and many confounding variables come into play. This wouldn't be the first case of undershimming that resulted from a DIY rebuild (if that is what the problem is).

I don't follow these threads as closely as I used to, so I may have missed something. But if you find dark color lube you could have a spinning tapered roller bearing or a spinning crowngear assembly trunnion; either of those could have caused wear leading to axial play. However, on a previously rebuild drive, my first suspicion is under shimming due to measurement errors during that rebuild.

In any case, the drive needs open and inspection for the usual suspects: i.e. creeping input pinion bearing race, spinning tapered roller bearing, spinning trunnion, and rebuild with a new crownwheel bearing at a minimum. With detectable wobble, the tapered roller bearing would be very suspect for microspalling and should be replaced too...
 

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...The DMAN method is good as long as you make sure the crown wheel is fully seated back down on the taper bearing for a zero. Tapping is usually in order on the down swing and a reset of the zero reference especially if you still have the seal in place and have not heated the casing to allow the bearing to move more freely up and down...
You are touching on an important variable regarding the DMAN final drive rebuild method.
During my years of inquiry into these final drives, I compared the outcomes of the DMAN method to the BMW Service Manual method. Both methods are capable of giving the same results, but both methods are fraught with their own set of confounding variables.

In the DMAN method, final drive cover temperature is an important factor in consistent results. The crown gear assembly can resist movement down resulting in the tapered roller bearing failing to fully seat in its race. Or, the crown gear assembly can resist movement up so that the crown gear bearing fails to seat fully in the cover. AND it can do this in a way that makes you think you are getting repeatable results! The consequence of this is under shimming (which I have seen and read reports of; and it sounds like the issue in the subject drive in this thread).
 

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Discussion Starter #16
I finally had a free weekend day to take the rear drive apart. Found the taper roller bearing to slip off the end of the trunnion. I measured the trunnion end diameter and got 24.97 mm. The bearing has an inside diameter of 25 mm. So, a pretty small gap. I need to use one of the Loctite products to fill the gap and secure the bearing on the trunnion. I was thinking about using Loctite 640. The specs on it seem to fit what I need. Thought I would ask the LT group for comment on my choice. Also, will acetone work to clean the trunnion and bearing, or do I need the Loctite primer?

Thanks,
Ken
 

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I finally had a free weekend day to take the rear drive apart. Found the taper roller bearing to slip off the end of the trunnion. I measured the trunnion end diameter and got 24.97 mm. The bearing has an inside diameter of 25 mm. So, a pretty small gap. I need to use one of the Loctite products to fill the gap and secure the bearing on the trunnion. I was thinking about using Loctite 640. The specs on it seem to fit what I need. Thought I would ask the LT group for comment on my choice. Also, will acetone work to clean the trunnion and bearing, or do I need the Loctite primer?

Thanks,
Ken
Saddleman is the current authority on the FD rebuilds. I know he uses something and leaves it in a press overnight for the taper bearing.
 

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I finally had a free weekend day to take the rear drive apart. Found the taper roller bearing to slip off the end of the trunnion. I measured the trunnion end diameter and got 24.97 mm. The bearing has an inside diameter of 25 mm. So, a pretty small gap. I need to use one of the Loctite products to fill the gap and secure the bearing on the trunnion. I was thinking about using Loctite 640. The specs on it seem to fit what I need. Thought I would ask the LT group for comment on my choice. Also, will acetone work to clean the trunnion and bearing, or do I need the Loctite primer?

Thanks,
Ken
Ken

Go look at this thread . It shows how I fixed my rear drive with the same failure.
 

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Ken

Go look at this thread . It shows how I fixed my rear drive with the same failure.
John, that was an excellent thread. I have my spare apart and am going through it now. No lose taper bearing and no sign of needle bearing creep. So far, I am happy with my Ebay purchase. New pinion seal and the pinion seems much tighter than before. Shims are the same, bearings are the same as I saw no pitting or wear on them. It does take more force to turn the pinion without the crown installed than I remember. Is that the new seal causing that? I would expect it to be similar to when I first disassembled it. It is a double lip seal and not the BMW supplied one. No sign of interference with the pinon nut and the seal.
 

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An alternative to the wonderful sleeve made for me is to have the mandrel knurled at a machine shop to increase the diameter. Then use sleeve retainer loctite on the bearing.

I did the sleeve because I had one and it was so thin I may have been better off with a knurl job.
 
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