'96 R1100RT Final Drive Failure

At 54K on the odo, I'm seeing the tell-tale signs of final drive failure, i.e., rear wheel side-to-side motion, metal in final drive oil and leaking seal, all pointing to the crown bearing wearing out. I realize 1996 was the first year of the R1100RT but obviously interchangeable parts (such as crown bearing, final drive unit, etc) were used on prior models. Thus, my question is what is typical mileage that the final drive fails and other than changing oil, what can be done to prolong the life of same?

I'll be having my unit rebuilt in the next couple weeks. I'm in so deep on maintenance cost now, I might as well spend more to have a dependable ride.

Your questions have been asked before many times on this and other forums, and since a lot of folks here don't have oilhead RTs anymore, and some never did, you might get more thorough answers by searching for older threads - either using the search function here, or just using google and with "site:bmwsporttouring.com" as part of your query.

I don't think I ever saw a "typical" mileage for your final drive - some bikes eat them regularly and some make 100,000 miles or more on the original. I'd say it's not unexpected though between 50k and 100k miles.

Proper preload setup when installing/shimming the internal bearings, proper set up of the pivot bearings, and regular changes with the proper fluid are probably the best way to get the longest life out of a final drive.

At 54K on the odo, I'm seeing the tell-tale signs of final drive failure, i.e., rear wheel side-to-side motion, metal in final drive oil and leaking seal, all pointing to the crown bearing wearing out. I realize 1996 was the first year of the R1100RT but obviously interchangeable parts (such as crown bearing, final drive unit, etc) were used on prior models. Thus, my question is what is typical mileage that the final drive fails and other than changing oil, what can be done to prolong the life of same?

 

I'll be having my unit rebuilt in the next couple weeks. I'm in so deep on maintenance cost now, I might as well spend more to have a dependable ride.

Morning Roger

As posted above no real good way to predict final drive crown bearing life. Some lasted 20,000 miles & some went the life of the bike.

Initial set-up is a big factor but if yours went 54K then initial set-up is probably pretty good.

Usual failure mode is the crown bearing ball separator breaking/splitting then allowing the balls to all go to one side of the bearing. The actual cause of that has never been proven to me. (dirt in the final drive is one theory, obviously initial set up is another, & even tire induced static electricity pitting the balls & outer race is not out of the question).

Bottom line is: they DO fail.

BMW monkeyed with the crown bearing over the years with a 17 ball try then a 19 ball try (some riders claim one lasts longer then the other).

One thing I can say is that I have found a trail or dirt/sand on the internal porch in the final drive vent area on some failed final drives. There is no doubt in my mind that s-o-m-e final drive crown bearing failures are/were caused by road water/dirt entering through the vent. On my personal 1100/1150 bikes I would remote vent the final drive to high under the seat or into the air box (I ride all weather & dirt roads are fun to me not something to avoid)

If you are having someone else rebuild your final drive then question the heck out of them on HOW they set up the bearing preload. Some shops just toss in a new bearing, charge a lot of money, then send you down the road. They know darn well that no matter the poor set up it will at least get you through their warranty period & hopefully a long way from their shop when it re-fails.

Good info, dirtrider. I believe the tech who will probably do the crown bearing replacement is aware of the different thicknesses of the shims and I feel confident he will do the job right.

Your questions have been asked before many times on this and other forums, and since a lot of folks here don't have oilhead RTs anymore, and some never did, you might get more thorough answers by searching for older threads - either using the search function here, or just using google and with "site:bmwsporttouring.com" as part of your query.

 

I don't think I ever saw a "typical" mileage for your final drive - some bikes eat them regularly and some make 100,000 miles or more on the original. I'd say it's not unexpected though between 50k and 100k miles.

 

Proper preload setup when installing/shimming the internal bearings, proper set up of the pivot bearings, and regular changes with the proper fluid are probably the best way to get the longest life out of a final drive.

Every time I do a search on this forum, I get 60 pages of posts--not necessarily related to my search question.

Yes - I do understand that the search function here is not the easiest to get good results - that's why I suggested using google, like this:

"site:bmwsporttouring.com final drive rebuild"

If you plug that into your google you will get a good list of threads here with loads of info.

Roger, I don't know how firmly committed you are to your contracted workshop for the FD rebuild, but if you lay out a few snoojits on a couple of bearing pullers, you CAN do this job yourself, provided you are a reasonably competent and undaunted wrencher.

Here's my shortened version of James's long ruminative how-to video, filmed at his London UK workshop called superbikesurgery.

It's a "private" video, so you need the password - watchthis

vimeo.com/216576324

Even if you're not willing to tackle that job yourself, at least you'll see from watching the video, exactly what's involved. Most people agree that if you have the FD in bits anyway, you might as well go the whole hog and replace everything - not just the big bearing; seals, taper bearing, etc.

Best o' luck !

AL in s.e. Spain

That video seems to provide a good overview, but I wonder about a couple of things. Primarily, it assumes that the preload provided by the large shims is correct - and since the OP made it 54k it probably was - but also that it will continue to be correct with the new bearing.

Maybe there is not enough potential variance in bearing thickness to warrant rechecking preload, but I thought best practice was to do so. Or perhaps that bit of the video was edited out?

That video seems to provide a good overview, but I wonder about a couple of things. Primarily, it assumes that the preload provided by the large shims is correct - and since the OP made it 54k it probably was - but also that it will continue to be correct with the new bearing.

 

Maybe there is not enough potential variance in bearing thickness to warrant rechecking preload, but I thought best practice was to do so. Or perhaps that bit of the video was edited out?

 

 

Morning szurszewski

No way to know UNTIL it is properly checked. I check them ALL when installing a new crown bearing & some are OK & some are way out of spec.

The ones that don't get checked & set properly are the ones that tend to fail early (usually far from home).

In terms of replacing the crown bearing myself, even after seeing excellent videos, I will let an experienced BMW master mechanic do the work. I am so sick of working on this bike but rolling it in the river would pollute the water with the FD leaking like a faucet.

Yes - I do understand that the search function here is not the easiest to get good results - that's why I suggested using google, like this:

 

"site:bmwsporttouring.com final drive rebuild"

 

If you plug that into your google you will get a good list of threads here with loads of info.

szurszewski, thanks for the tip on searching for specific topics. I substituted "front brake switch" for "final drive rebuild" and got 3 posts which answered my question (which I didn't have to ask in a new post).

Yes - I do understand that the search function here is not the easiest to get good results - that's why I suggested using google, like this:

 

"site:bmwsporttouring.com final drive rebuild"

 

If you plug that into your google you will get a good list of threads here with loads of info.

 

szurszewski, thanks for the tip on searching for specific topics. I substituted "front brake switch" for "final drive rebuild" and got 3 posts which answered my question (which I didn't have to ask in a new post).

Excellent!

mine failed at 90,000. i had it rebuilt and it didn't last more than 2000 miles. bought a used one with around 20,000 on it . bike now has 200,000 miles so far so good so thats around 130,000 miles on this one

Steveg—

Only 2K on a rebuild? That's not much, is it. Who did that rebuild for you?

A small shop in southern ct. Not a dealer, it wasn't a total rebuild just reshimmed the bearing, not sure if he shimmed it too tight or if it was already too far gone those are tricky to work on, the tolerances are very tight

I looked in my Chilton shop manual: precious little info on rear drive repair. Questions:

So what do the shims alter? Gear lash ? Can you adjust the gear mesh pattern as well?

I assume it's a put it together, measure, take it apart to change the shim process?

Thanks!

Afternoon Dave

Questions:

So what do the shims alter? Gear lash ?-- Yes, shims are used to alter gear lash, gear tooth contact, & bearing preload. When ONLY the crown bearing is replaced then usually only the crown bearing preload is set. (it's kind of complex to re-shim especially if ring gear position is impacted.

Can you adjust the gear mesh pattern as well?-- Yes, that can be adjusted but that setting is mostly pinion position related.

I assume it's a put it together, measure, take it apart to change the shim process?--This depends on how it is done. Most of the internal shim settings are done with special BMW setting fixtures before assembly. (there are some home brewed workarounds & those usually require assembly, measurement, shim selection, then reassembly) with some Kentucky windage thrown in.