Rear Bearing Failure

[James_H]

I just had what I think is a rear bearing failure in my 2000 R1100 RT. I stopped at a rest area, the bike was making a strumming sound, rythmatic, seemed to batch wheel rotation by not same freqency. When I did, I noticed oil driping from the final drive area onto the rear wheel. Since there was no oil on the wheel unless I stopped, it seemed, I headed down the road to get to a more convient place to call for a tow. Got it towed home.

 

Can somone point me to a thread on the disassembly of the rear drive. I have done a search and it seems that the best course of action is to remove the rear drive and let BMW repair it. I have read that they replace rather then repair.

 

Any comments or alternatives welcomed.

 

Thanks.

 

Jim

[RFW]

Can somone point me to a thread on the disassembly of the rear drive. I have done a search and it seems that the best course of action is to remove the rear drive and let BMW repair it. I have read that they replace rather then repair.

If it is only the oil seal, then the procedure to replace it is fairly straightforward. But the problem you describe sounds like the seal was damaged as a result of bearing damage.

 

Likely as not, the taper roller inside is OK, but the big ball bearing is shot. Replacing either of the bearings requires checking the preload shims and replacing them with the required thickness needed for the new bearing. This is manditory! Tolerances on bearing side clearances are relatively big, and the only way to guarantee correct preload is to check and replace shims when the bearing is replaced. Using the old shims will virtually guarantee the wrong preload, and possibly early bearing failure (again).

 

In any event BE SURE your new bearing is the 17-ball version , and NOT the 19 ball version! Almost all of the problems with early bearing failure over the last 10 years, was the result of the use of a FAG bearing with 19 balls. The ball retainer in the bearing was not robust enough and tended to disintegrate, destroying the bearing in the process (even though there was little actual wear in the balls and races).

 

If you want to go ahead and do it yourself, PM me and I can send a couple pages from the manual for the K1200RS. Not the same bike as yours, but this procedure is the same for all BMWs, so this directly applies to your bike.

[flat_twin]

Hi James, Sounds like the big bearing is toast. Mine failed much like yours. Rhythmic growl then the seal starts leaking. I had mine repaired at the dealer for $274.

My RT had 50k at the time of the failure. It has 62k on it now and is doing fine. I now change the rear drive lube with each oil change just to keep an eye on it.

[James_H]

Hi James, Sounds like the big bearing is toast. Mine failed much like yours. Rhythmic growl then the seal starts leaking. I had mine repaired at the dealer for $274.

My RT had 50k at the time of the failure. It has 62k on it now and is doing fine. I now change the rear drive lube with each oil change just to keep an eye on it.

 

Mark,

 

That sounds like it. Hope that is all that is wrong. My bike has about 48,000 on it so the timing is right.

[BUSTED]

I had my rear diff rebuilt by www.brunos.us, no problems since.

[OoPEZoO]

Welcome to the club, mine went out on my '00 R1100RT in August at 71k miles. I replaced both of the bearings in the rear myself. If you don't have access to the proper equipment, then I would suggest doing what you said and removing the entire rear assy and taking it to the dealership. Thats what I will do if mine fails again. I saved a good bit of money doing it myself, but it was a royal PITA

[James_H]

Welcome to the club, mine went out on my '00 R1100RT in August at 71k miles. I replaced both of the bearings in the rear myself. If you don't have access to the proper equipment, then I would suggest doing what you said and removing the entire rear assy and taking it to the dealership. Thats what I will do if mine fails again. I saved a good bit of money doing it myself, but it was a royal PITA

 

Thanks for the information. I guess I feel strongly both ways. I'd like to do it myself. I don't need the bike at this moment, I have another ride. I guess I'll take it out and have a look and see. Make the decision then.

 

I do like hands on. I know what how it was done and don't have to worry about someone taking a short cut. Of course I could do a poor job also.

 

Thanks.

 

Jim

[cgdR]

Jim, if you are not replacing the tapered bearing, you can re-use the original shims (Bob has the right to think otherwise, but that's what you dealer will do). The hard part is to remove the old bearing because there is not enough room between the bearing and the bevel gear for a gear puller. You will have to use some chisels and a big hammer. The re-assembly is easier because you pre-heat the bearing and chill the bevel gear. Don't hesitate while you shove the bearing in. The etched label normally faces outward. Shouldn't take you more than 3 hours.

[RFW]

Jim, if you are not replacing the tapered bearing, you can re-use the original shims (Bob has the right to think otherwise, but that's what you dealer will do).

It is not what I think that matters. If you read and actually understood the published data from the manufacturer of the bearing, you would come to the same conclusion. Put simply, the axial tolerance from one bearing to the next, is MUCH larger than the preload tolerance BMW requires.

 

In real numbers, the axial tolerance on this bearing is greater than 0.2mm yet BMW requires a preload of 0.05mm ~ 0.10 mm. That is, the tolerance on the preload shim is only 0.05 mm. Exactly how can you possibly stay within this tolerance, when the axial tolerance from one bearing to another can be greater than 0.2mm???? The answer is you must do as BMW states in its repair manual, check the preload and replace the shim if necessary with the correct thichness needed for the new bearing.

 

Any dealer who reuses the same shims without bothering to check preload, is violating BMW's published repair instructions (check for youself!), and should have his dealership yanked!

[ShovelStrokeEd]

Of course, you could always buy a micrometer and learn how to use it and then go to the bearing supply house and buy a bearing with the same dimension. So long as the bearing is the same size, you could, assuming the original spec was met, reuse the same shim pack.

 

Might have to do some convincing at the bearing house though. They don't really like to unwrap bearings and let folks handle them.

[bmwmick]

WOW,

I guess the dealer should be thrown in jail if they sell you a new 19-Ball carrier bearing following your logic.

Our local dealer had been receiving 17-Ball final drive bearings for several months but now they seem to be receiving 19-Ball bearings again. The ball count has no bearing (pun not intended) on our final drive problem.

 

Mick

Tucson

[RFW]

WOW,

I guess the dealer should be thrown in jail if they sell you a new 19-Ball carrier bearing following your logic.

Our local dealer had been receiving 17-Ball final drive bearings for several months but now they seem to be receiving 19-Ball bearings again. The ball count has no bearing (pun not intended) on our final drive problem.

 

Actually, it does ...indirectly.

 

The failure of these bearings is NOT caused by wearing out. The balls and races appear still in good shape. The problem is that the 19-ball bearing has less space for the ball retainer, than the 17-ball bearing. The weaker retainer tends to disintegrate. I have seen several photos put on various sites of disassembled rear ends, and they all showed a bunch of twisted shrapnel that was once a bearing retainer. This is emphatically NOT normal.

 

Worn out bearings will still have an intact retainer, even though the balls and races may show wear. The process of wearing out causes no stress on the retainer. There is no rocket science to wheel bearing design. BMW has used a type of bearing well suited for the job. The problem here of very early failure appears simply that Fischer ("FAG") has tried to cram more balls in there, and in the process this has weakened the retainer. Circumstantial proof of longevity is that my old K100RT has the original 17-ball bearing and it works fine after almost 200,000km.

 

As for the dealer still selling 19-ball types, why buy bearings from the dealer, anyway? This bearing is an industry-standard type 6917 deep groove ball bearing. Buy an SKF one from a bearing supply place; it will be less than half of BMW's price, and it will be the identical part once supplied to BMW.

[bmwmick]

Actually,

The bearing is a 61917/C3 (the C3 s the lateral clearance spec).

 

Over on the LT board, several of the failed bearings were analyzed (with microscopes and stuff ) by a bearing engineer from SKF. In all cases, the failures were attributed to spalling which was caused by brinneling either during installation or during shipment of the bearing. The destruction of the retainer was only a result of the spalling, not the cause. Once the balls begin to 'skid' rather than 'roll', the balls begin to exert force on the retainer (separator) and it eventually fails because it was not designed to 'push' the balls around the race, only separate them.

 

You can choose to believe whatever you like.

 

Mick

Tucson

[Stan Walker]

So long as the bearing is the same size, you could, assuming the original spec was met, reuse the same shim pack.

 

You do make an assumption that it was properly shimmed at the factory......

In fact, one theory of the higher failure rate for certain years of RT's is that the factory got sloppy!

 

Stan

[cgdR]

one theory of the higher failure rate for certain years of RT's is that the factory got sloppy!

The theory would make sense for bearings that fail by fatigue, but isn't it unlikely that an improper preload would cause the cages to fail?

[RFW]

Actually,

The bearing is a 61917/C3 (the C3 s the lateral clearance spec).

Yes, I know. I dropped the "1" as a typo (sorry about that!). I also left off the "C3" because I was just trying to illustrate the point that this was a generic bearing available off the shelf.

 

You can choose to believe whatever you like.

Well, I choose to "believe" that when BMW states you MUST reevaluate the shim thickness, and when the axial tolerance on the bearing is as sloppy as it is, then replacing the bearing without reevaluating the shim thickness is risky. I will continue to "believe" that until someone shows me the numbers that prove this is unnecessary. So far, a tolerance analysis shows that checking the preload (and reshimming if needed) is indeed a requirement, just as BMW states it is.

[bmwmick]

You can choose to believe whatever you like.

Well, I choose to "believe" that when BMW states you MUST reevaluate the shim thickness, and when the axial tolerance on the bearing is as sloppy as it is, then replacing the bearing without reevaluating the shim thickness is risky. I will continue to "believe" that until someone shows me the numbers that prove this is unnecessary. So far, a tolerance analysis shows that checking the preload (and reshimming if needed) is indeed a requirement, just as BMW states it is.

 

I agree that the side loading MUST be checked when the bearing is replaced.

 

I do NOT agree that the number of balls and the retainer style has much to do with the longevity of this bearing in OUR applications. That is what I commented on, not the clearance check.

 

Mick

Tucson

[RFW]

Actually,

The bearing is a 61917/C3 (the C3 s the lateral clearance spec).

Actually, this is not correct. Looking at thr SKF site, they clearly state the "/C3" designation refers to the radial (NOT AXIAL) clearance between the balls and the race.

 

The "normal" 61917 bearing has a min/max radial clearance of between 12 and 36 microns. The "C3" version has a "sloppier" clearance of between 30 and 58 microns.

 

There are two things to note here. First, the increased ball clearance improves the side loading capability of the bearing, because side thrust will cause the balls to move more toward the side of the race where the bearing is more capapble of tolerating side loading. If there were ZERO clearance, a side load would theoretically result in infinitely high forces on the balls and races, because the angle of contact between the balls and races would be zero.

 

So in recognizing that significant side loading could occur, BMW has chosen a bearing option with increased clearance that can thus tolerate the side load.

 

The second thing is that the radial tolerance difference within the "C3" option (that is, the bearing can have a radial clearance anywhere between 30 and 58 microns) AUTOMATICALLY results in increased axial tolerance. A bearing with a radial clearance of only 30u will deflect axially much less than one with a 58u radial clearance. Because the angle of contact is very shallow, the 28u difference between minimum and maximum radial clearance will result in a MUCH larger axial bearing tolerance.

 

It is THIS very tolerance that is wht BMW REQUIRES checking the preload (and possibly reshimming) each time the bearing is replaced.

[cgdR]

Bob,

Have you actually done a bearing replacement? It sounds like you are taking a theoretical point of view, including the assumption that you can buy one at a bearing supplier at half the price. If this is true, please give some details. Also, notice that the bearing is installed in an interference fit over the bevel gear. Before installation, the bearing has a significant amount of axial free play. Once it is in place, however, there is none. That does not mean that the forces are infinite? No, the steel deforms elastically and the loads are spread over a non-zero area. As it deforms, there is an axial displacement that is dependent on preload. Even a relatively small preload will give a measurable axial displacement.

In summary, it is theoretically better to measure the clearance according to the specified procedure. In practice, an inaccurate measurement will make things worse than resusing the old shims. Finally, most people are incapable of doing the measurement correctly so they would be forced to have it done at the dealer. Some people have a good dealership, others do not. The choice is yours. I chose to do it myself at a cost of $110 and 3 hours of work. I have put 10,000 miles on the new bearing so far and it is still looking good.

[Stan Walker]

In practice, an inaccurate measurement will make things worse than resusing the old shims.

 

Again, the assumption that the factory measurement was correct!!! If so, why the early failures? Many final drives see well over 100,000 miles without any bearing failures.

 

Also I would like to point out that we are in most cases changing the brand and number of balls. Perhaps even other specs like clearances?

 

It would seem like the prudent thing to do is check the preload.

 

most people are incapable of doing the measurement correctly so they would be forced to have it done at the dealer. Some people have a good dealership, others do not.

 

Having attempted to do this measurement (and failed), I have to agree that it is unlikely that the typical shade tree mechanic will have the required measuring tools on hand and not everyone will have the skill to use them. In my case I have since gone out and purchased a depth micrometer accurate to 0.001" to use the next time I work on a final drive. I haven't put it to the test yet.....

 

In an earlier post this year I discussed a possible alternate means of making this measurement. Totally untested by me, but I think it might work.

 

Stan

[RFW]

Have you actually done a bearing replacement? It sounds like you are taking a theoretical point of view, including the assumption that you can buy one at a bearing supplier at half the price. If this is true, please give some details.

I have done many bearing replacements over the years. Wheel bearings, transmission bearings, complete differential rebuilds etc. I have not (thankfully) had to replace the rear wheel bearing in my bike (yet!).

 

For all the bearings I have ever replaced, I always bought them at a bearing supplier, never from the dealer. An example that comes to mind some years ago is when I replaced the front wheel bearings as well as the right rear wheel bearings on my '82 BMW 320i in the late '90s. All of them were bought at BC Bearing Supply here in Vancouver. The front wheel bearings cost about $30 for each side (2 tapered roller bearings on each side). BMW wanted well over double that price.

 

The rear wheel bearings were replaced in my back yard in a snow storm (!!!). Lots of fun! All these bearings are interferance fits. That is normal.

 

Also, notice that the bearing is installed in an interference fit over the bevel gear. Before installation, the bearing has a significant amount of axial free play. Once it is in place, however, there is none. That does not mean that the forces are infinite? No, the steel deforms elastically and the loads are spread over a non-zero area.

As a mechnical engineer, this is not exactly news to me. My point about theoretically infinite loading, was that if the balls fit perfectly in the races, with no play whatsoever, the near-zero contact angle of the balls with the races when side thrust is applied, would result in a massive "wedging" effect and huge compressive stress on the balls and races. This is why there is an intentional gap. When greater side loading is required, one chooses a "C3" or even "C4" or greater bearing option. The higher the "C" number, the greater the radial gap, and the more the balls tend to contact the grooves on the sides rather than nearly at the bottom of the groove when axial thrust is applied.

 

In summary, it is theoretically better to measure the clearance according to the specified procedure. In practice, an inaccurate measurement will make things worse than resusing the old shims. Finally, most people are incapable of doing the measurement correctly so they would be forced to have it done at the dealer. Some people have a good dealership, others do not. The choice is yours. I chose to do it myself at a cost of $110 and 3 hours of work. I have put 10,000 miles on the new bearing so far and it is still looking good.

 

It is not just theoretically better to do the job right. It is better in practice too. Remember that bearing tolerances follow a normal distribution curve. Luck is on your side that things will work out even if you do not change shims, because most bearings will have tolerances somewhat close to the mean. But this is no guarantee. It is less likely, but still easily possible that you can end up with a bearing clos to the tolerance limit, and if this happened, you will end up with either excessive preload, or actual play in the wheel. Basically, you are just playing the odds.

 

As an exercise, I am thinking I should work out the difference in axial location of the inner race, as the radial tolerance reaches the lower and upper limits. Might be interesting.

[RFW]

One thing that I should have mentioned previously, applies to those rear wheel bearings that "wore out" (that is, that did not suffer from disintegration of the bearing cage or separator, but suffered from brinelling to the balls and races).

 

A major cause of this type of failure of a preloaded bearing is excessive preload. In the case of the BMW rear drive wheel bearing, the situation exists where heat from the brake disk is transferred directly to the hub and the inner race of the bearing, while the outer race (mounted in the relatively cool housing) remains cooler. This will cause the inner race to expand, reducing the radial ball clearance, and indirectly increasing the preload.

 

BMW recommends a preload of 0.05mm to 0.10mm. Considering the above possibility of inner race heating and thereby causing preload to unavoidably increase, I suspect it is a good idea when replacing the bearing, to reshim and target the preload to the lower limit of 0.05mm. Even a mere 0.05mm difference in preload will make an enormous difference in axial preload force. Reducing the preload to the minimum recommended value will probably ad thousands of kilometers to the bearing life .... that is, providing the ball cage does not disintegrate first as it seems to have a habit to do!