Any Ideas?

[pablo666]

Dear collective wisdom. I have searched here and looked at all the posts on FD failures, but this is personal!

I replaced the crown wheel bearing and seal 7500 miles ago. I used the methods described here and am certain it was seated properly and all was fine.

Today I did a service and found churned up metal flakes in the FD oil. I'm guessing that the bearing cage is disintegrating again, but only after 7.5K miles is a tad disappointing.

Now the question for all you spanner monkeys is: should I have measured and put in new shims etc? The wisdom before was that the factory set shims should be ok for the new bearing. Have you found this to be the case?

St. Eptoe in particular, you must have done a fair number of these? What's your thoughts on re-shimming? Should I just bite the bullet and expect to replace this bearing every year as a service part?

Yours Humbly
Pablo

 

[Timolgra]

I've never re shimmed when changing the bearings and have had no problems at all.
The way I see it from an engineers perspective is the bearings 'should' always be the same size.

Before finally tightening the cover I turn the bevel gear several times, some suggest heating the cover to allow it to slip more easily over the newly fitted bearing both with the idea of centralising the bearing, then fitting the seal. It's hard to say whether either of the above makes any difference.

It may be worth you removing either just the seal or the cover to inspect at least one side of the bearing cage

 

[Pekkavee]

Me neither
Reshimming is not needed, I think.
The bearings are good in tolerances.

What has caused this.
I can not imagine.

Pekka

 

[Canuck]

My thought is that if one is having repeated FD bearing failures... and everything else back there is good (other bearings) then why assume that the shimming was spot on from the start. It doesn't take very long to check the shims so why skip that step.

 

[uncle dick]

I'm not sure if it applies to this but on some bearings you can get a standard or a 'close tolerance' variant. Worth asking if you're using aftermarket suppliers.

 

[pablo666]

My thought is that if one is having repeated FD bearing failures... and everything else back there is good (other bearings) then why assume that the shimming was spot on from the start. It doesn't take very long to check the shims so why skip that step.

I hear you, but it's not repeated failure, the first lasted 50K, the replacement only 7.5K. Also I don't have a micrometer or dial gauge, would have to relearn how to use them and need to get the bike fighting fit for the 17th May and have no days off work between now and then! If I had the time I would, and if this goes again, I will invest in said equipment next year or change the bike

For the first suggestion of a possible cause. Any others out there?

 

[pablo666]

Well I've just pulled the bearing. The cage is intact and no wear on anything BUT the ball bearings are breaking down in the cage! You can see chunks chipped off the balls. I would say this was a faulty part. The only other thought is that I missed a peice of swarf when I cleaned it all up last time. (I don't know how as I'm pretty scrupulous). Would a stray peice from a previous breakdown, cause the balls in the race to chip off substantially? I think the effect is stress chips of the balls rather than wear.
Any ideas from the collective?

 

[pablo666]

Ok two points, young teen looking guy at BMW counter says replacement at 7.5 K is not unusual!

Retired engineer of serious machinery (JCB and up size) says these bearings should last 50-100K. He had a look and says the most likely reason for the failure is contamination. He is going to check the shimming/pre-load for me.

Many thanks to all.

 

[Canuck]

Good luck with the fix. I'd say 7.5 is too short for my understanding of bearings... but I only service my own bikes... well... and a few mates but that just seems too short but I don't see the quantity of bikes that proper mechanics see so maybe that's acceptable.

 

[warmshed]

Where did you source the bearings? Were they a known make? lots of Chinese or Indian bearings about, cheaper but...

 

[MattW]

Where did you source the bearings? Were they a known make? lots of Chinese or Indian bearings about, cheaper but...

+1
For the sake of a few quid I'd always use OEM (or at least a good European brand like SKF etc).

 

[Pekkavee]

+1
For the sake of a few quid I'd always use OEM (or at least a good European brand like SKF etc).

And you can get the big bearing cheaper in a BMW store than a special bearing store.

Pekka

 

[pablo666]

Where did you source the bearings? Were they a known make? lots of Chinese or Indian bearings about, cheaper but...

I bought the failed bearing from 'Motorworks' it has no manufactuers mark or number on it. I've ordered a new one from BMW price about the same.

 

[Timolgra]

My thought is that if one is having repeated FD bearing failures... and everything else back there is good (other bearings) then why assume that the shimming was spot on from the start. It doesn't take very long to check the shims so why skip that step.

....

 

[nigel tailyour]

Final Drive bearing replacement and measure the shims

I found this great but amateurish video about shims, bearings and seals on the BMW final drive. It shows how to measure the free play, how to calculate the correct shims and how to fit them.
Ignore the horse at the beginning and other "faults" - It is not your computer at fault.
http://www.bmwlt.com/uploads/lt_final_drive_rebuild.wmv

 

[magicstu]

I hear you, but it's not repeated failure, the first lasted 50K, the replacement only 7.5K. Also I don't have a micrometer or dial gauge, would have to relearn how to use them and need to get the bike fighting fit for the 17th May and have no days off work between now and then! If I had the time I would, and if this goes again, I will invest in said equipment next year or change the bike

For the first suggestion of a possible cause. Any others out there?

Im only down the roads. If you want to borrow a digital vernier and a micrometer. Yo are more than welcome to.

 

[magicstu]

just noticed the dates!!!