Clean vs Standard Bearings in Tranny

[Ozonkiller]

My '96 RS just rolled over 100K miles, so I finally broke it down for a new clutch, spline lube and such. All of the suspension bearings and the input splines were still wet with grease. Apparently the "grease guy" was on the job that day at the factory :clap

I popped open the tranny to inspect it as I had traces of "stuff" on the drain plug and the gold colored tranny oil indicating worn shift forks. Sure enough the 1st and 2nd gear fork had some wear. All of the gear teeth and shift dogs are perfect as are the bearings, which brings up my question.

Should I upgrade to the clean bearings? and if so why. I'm not sure that I see the advantage of a bearing that is bathed in fresh oil vs. a bearing that is sealed and thus has to rely on the small contained amount of lubricant in that bearing.

I do understand that if there are issues somewhere else in the transmission that generates debris then the clean bearings remain clean.

Do any of you guys have any experience showing that once a transmission is converted to the clean bearing design it is even more reliable than before.

I guess I'm asking cause I'm hard pressed to believe that the old bearing design is lousy after 100 thousand miles, 70K in the last 4 years.

Thanks for your input :beer

Tom

[GlobalRider]

Should I upgrade to the clean bearings? and if so why. I'm not sure that I see the advantage of a bearing that is bathed in fresh oil vs. a bearing that is sealed and thus has to rely on the small contained amount of lubricant in that bearing.

I do understand that if there are issues somewhere else in the transmission that generates debris then the clean bearings remain clean.

Tom

After all these years, you learn something new.

I've never seen a sealed bearing in a transmission, but then, I haven't had that many transmissions apart.

When I first read "sealed" on another thread some weeks ago, I thought "packed with grease" because that is what I understand a "sealed bearing" to be. I thought, that doesn't make any sense!

So do these bearings have seals (similar to dust seals) on them that retain fluid within the bearing, or do they have seals with small pin holes to enable tranny oil to enter and exit the bearing? Which brings me to another question. How do they come from the manufacturer...pre-filled with SAE 90? Somehow I doubt that.

I can see a sealed bearing keeping slivers of metal out of the bearing.

[CTHalk]

If it ain't broke, don't fix it. How many 250,000 mile trannies are out there? If the oil is kept clean and at level, the bearings may well keep going. but, you are in there...... Tough call!

[MCMXCIVRS]

From my own experience, I'd say if you have it apart now and have the time, replace the bearings. I had no where near the good fortune you have had with your transmission. I had three sets of bearings fail in my gearbox in under 40,000 Kms before I replaced it with a complete updated rebuilt transmission from BMW. The rebuilt transmission has all of the updated components and is equal to a M97 (post 1997) transmission. The new clean bearings are a sealed, lubed for life bearing.

BMWs position on the bearing failures with the old style open bearings is that it is due to debris in the oil damaging the bearings. I personally feel that the problem is due to poor design which causes the bearings to recieve inefficient lubrication (but of course if they admitted that, they'd have to accept resposibility for the repairs). I had hundreds of transmissions apart in my career in automotive mechanics, and never saw any that had bearings fail due to debris in the oil. In fact, I have never ever seen any other gearbox in any application that required a sealed and prelubricated bearing.

I performed annual oil changes on my original transmission and never noticed any excessive amounts of metalic debris. I always used the reccomended grade of lubricant. When I swapped the gearbox (my own expense and labour), I switched to Redline Shockproof synthetic lube, and continued the annual changes. The "new" unit has lasted for over 75,0000 Kms with no further bearing failures or trouble of any sort.

There is a kit to replace the old style bearings with the new ones, leaving the rest of the internals original, or you can do all of the upgrades as you see fit. There are some special tools required to accurately shim the bearings on the shafts, so you may wish to have a shop do at least that part of the job.