Originally Posted by kdog
No, have you? All I've seen is the single quote, repeated in many places. What does the article say? Got link?
Slow down there, fella. Transmissions have both gears and ball bearings, just like final drives. The final drive crown bearing just happens to be a big bearing. Now why that particular bearing can't handle a multi-grade synthetic oil would be beyond me. But again, I didn't read the article. So please enlighten us.
My point was that BMW makes no distinction in the oil they recommend between the final drive and the transmission. There's some conjecture that the reason that BMW doesn't mention anything about synth in the LT's manuals is because those manual sections were written before synth was available -- probably for some older bike models and copied and recopied. Hilton mentions that the newer manuals do mention synth. So there you go.
The only thing I feel strongly about is some out-of-context hearsay that's flying around the internet and has everybody in a panic. I merely mentioned my mileage to illustrate that running synth in your final drive is decidedly NOT going to kill it. If there's actual FACT why we should switch to 90W single weight oil besides "something I read on the internet", let's hear it.
Remember, don't shoot the messenger. I'm just relaying what Paul Glaves said. (And yes, I have read his article that started this mess. He's very consistent in what he writes and says.)
The difference between the oil requirements of the FD and Transmission is the abuse the FD takes from the pounding from the road. Every bump you feel from the road (potholes, expansion joints, speed bumps, rumble strips) in your butt has been muted from the spring/shock, frame, and seat. The FD has nothing to mute the shocks. The tranny has the spring/shock and drive train to mute the shocks to it. That is why the heavier lube is spec'd in the FD. Also, BMW has written that the syn is an acceptable replacement in the tranny but not the FD.
In the new ('05 and later I believe) LTs BMW has specified syn in the FD. But the bearings are different. But that's the only LTs that are approved to run syn in the FD. (Also, as an aside- BMW introduced the 75w140 syn gear lube in 96 or 97 or earlier if I recollect right)
The actual FACT that 80/90/80W90 gear lube should be used is that those grades are the ONLY ones mentioned in the operators manuals, service manuals, and service bulletins published by BMW. Glaves has found NO mention from BMW authorizing the use of syn in the FD of LTs prior to 2005.
He sort of finished the discussion by saying that if you have syn in your final drive you should get it out right away. But, if you're convinced that syn is the way to go- fine. Just don't piss and moan (my paraphrase) too much when you FD goes south.
RE: shimming the FD. The question was asked- The FD in this guys RT failed. His dealership replaced the ball bearing and used the same shims. Should he be concerned?
Glaves said that if the 17/19 ball bearing was the ONLY bearing replaced AND the shims showed no damage or wear then it should be OK. The shims he was talking about have no bearing on the mesh of the pinion and crown gear, just the mating of the case halves. He said the tolerances of the bearing dimensions (specifically the width, are so tight and well controlled (?) my paraphrase) that if the bearing is properly seated all should be well.
Oh, and KDOG, I'm not picking on you, but your post contains the gist of most of the other posts/replies.
HTH. If my memory's jogged any further or if I can clarify something better I'll post again, but this is it for now.