BMW Luxury Touring Community banner
1 - 3 of 3 Posts

·
Registered
Joined
·
4,404 Posts
Discussion Starter · #1 · (Edited)
I have been asked many times by folks what to do with their FD that is working fine. Many people buy a K1200LT, read about final drive problems, and then wonder what to do.

Here's a summary of my current thoughts on the subject:

The "plume" of crownwheel bearing failures seems to have occurred in the 1999-2005 model years. This failure I have come to call the "classic" crownwheel bearing failure to distinguish it from other types of failures; the classic crownwheel bearing failure is the most common cause of final drive problems.

The evidence is pretty good that excess preload shim thickness is the cause of the classic crownwheel bearing failure. The majority of final drives assembled during this period are probably just fine, but it is impossible to know if a drive is properly set up without rebuilding it. (This problem has affected BMW RTs and GSs equipped with similar final drives).

If you have a bike from these years, should you do a preemptive rebuild?

My answer to this question is based on looking at the cost of a preemptive rebuild as buying road insurance. What risk are you willing to accept regarding a breakdown that might take a few days to get fixed, and what are you willing to pay to reduce that risk? The cost of a preemptive rebuild by someone like Saddleman who is a highly qualified professional mechanic and knows what he is doing with respect to final drives would be a lot less than a stay in a motel, trailering the bike to a dealer, and the dealership repair costs. For the long distance rider with 30K+ miles on their bike, a preemptive rebuild, done by a reliable mechanic, makes sense to me. But that's just me, your risk analysis might be different. Would a breakdown ruin a vacation or make you miss work? That can be costly. For the low mileage rider who never ventures far from home, the cost of a preemptive rebuild makes less sense.

I have a different sense of concern for 2005 models where the "spun tapered roller bearing" failure occurs. This failure will cause the lube to turn dark as very fine aluminum particles become suspended in the lube. If left to progress, this failure will destroy the crowngear assembly making repair of the FD not cost effective. Caught early, this failure can be repaired.

Another failure that also generates aluminum is the "creeping" pinion needle bearing race. This problem can also lead to an non-repairable final drive. This failure, like the spun tapered roller bearing failure is a slowly progressing one, and increasingly dark lube due to aluminum suspension is the best indicator of a problem.

The low tech way to watch for this problem is to always use the same kind of gear lube and change the lube at consistent intervals so that color changes over time can be noted. (It doesn't matter what kind of lube you use as long as it meets the BMW specs in the owner's manual). Saving a small quantity of lube in a little glass jar from each lube change will allow objective comparison from one lube change to another. Considering that lube changes only need to be done every 12K miles this isn't that onerous a task.

After 2005 the number of FD failures seems to have dropped off significantly. I suspect that by that time, BMW had brought some quality assurance efforts to the final drive assembly line and things got "cleaned" up a bit. I don't ever suggest a preemptive rebuild for a post 2005 FD unless the lube is becoming increasing dark over successive lube changes.

If shiney metal flakes are found on the drain plug magnet something is already failing. The final drive needs to be repaired. Increasing amounts of grey fuzz on the drain magnet can also be an indication of ongoing failure and the drive should be rebuilt. In these cases I no longer consider these "preemptive" rebuilds; these would be "repairs". For more on signs of impending failure read here: http://www.bmwlt.com/forums/showthread.php?t=63109

In summary:

Other than paying attention to the color of the lube and quantity of grey fuzz and/or shiny metal flakes on the drain plug magnet during routine lube changes, I don't suggest anything preemptive for a post 2005 FD.

The decision to do a preemptive rebuild on earlier bikes depends on your personal risk avoidance mindset.

I hope this post helps folks decide to do "preventive maintenance" on their final drive or to "just ride it".
 

·
Registered
Joined
·
185 Posts
Thank you for your article.

When you do preemptive rebuilds do you measure the pre-load of bearings and other critical parts?

Like many owners I have an '05 with 70K miles and a perfectly performing FD. (At least until I wrote this!)

When you tear down an operable FD do you compare clearances of good ones to bad ones?

Your FD posts are very informative.

Thank you.
 

·
Registered
Joined
·
4,404 Posts
Discussion Starter · #3 · (Edited)
ridinredfox said:
.....
When you do preemptive rebuilds do you measure the pre-load of bearings and other critical parts? ....
When you tear down an operable FD do you compare clearances of good ones to bad ones?....
Yes, and yes.

The whole purpose of a preemptive rebuild in the effort to prevent the classic crownwheel bearing failure is to properly set the preload of the crownwheel assembly.

It is impossible to check the clearance of a failed bearing. However, since bearing dimensions are highly controlled by bearing manufacturers, a good indication of how a final drive was originally set up can be established by measuring the preload shims that were originally in there. All of my data regarding crownwheel bearing shims is based on a comparison of the original shim thickness with the shim thickness called for by measuring the new, replacement bearing. The methods and limitations of this analysis have been discussed in previous posts.

When a final drive is open, other things to look for are the spun tapered roller bearing race and the creeping pinion needle bearing race. Absent any of these additional findings, nothing else needs to be done during a preemptive rebuild as other components of the final drive do not have a significant history of problems. In my experience, with the exception of occasional lube leaks at the input pinion seal and locking ring, and the creeping needle bearing race, the input pinion assembly rarely needs to be disassembled.

(Note: I am not currently accepting final drives for rebuild or repair. I recommend anyone seeking help with a final drive contact Dave Selvig, aka Saddleman on this site.)
 
1 - 3 of 3 Posts
Top