Final Drive Oil ?

[ebincia]

Recently, I’ve read much-heated debate regarding the correct final drive lube. My question: Is BMWs Super Synthetic SAE 75W140 Gear Oil acceptable for the final drive. I’ve been using this product in both the final drive and transmission for several years without any problems. Your thoughts and insights please.

Ebincia

[boxermania]

Yes, the product is satisfactory for both applications, albeit the 75W90 is acceptable as well for the FD.

[marine dad]

from advrider...
"the 75W90 will lubricate better with less fluid drag, the slightly lighter fluid is better for the bearings... Heavier fluids with higher temp. ratings (140) work well for extreme temperature's (hotter than your final drive gets) and higher shock loads, otherwise the lighter fluid is a better lubricant overall"
mike

[wncbmw]

I proclaim no great knowledge but the mechanic columnist for the BMWMOA magazine has a theory that the 75/140 oil may contribute to the rash of FD failures. I used the 75/140 in both tranny and FD but after a final drive failure, have switched back to the 75/90 for the FD. Just in case!

[ProductUser]

It kind of depends where you live. I ride in a lot of hot temps, so I've been using 75-140 for 67k miles on the advice of my BMW mechanic. People that say that using 75-140 trashed their drive is a claim based on speculation.

PU

[Buckster]

I agree...my mechanic said the same.

[boxermania]

Multi grade oils are blended to operate within a defined temperature range, when cold they are less viscous and as the temperature increases viscosity increases.

The 75W90 and the 75W140 are both close to the 75 viscosity at the same temperature and the viscosity will increase as the temperature increases, the difference between the two is that the 140 has a higher operational temperature than the 90. It is also well known in the oil business that the majority of wear between rotating parts occurs during initial (cold) start-up.

That being said the above pretty much invalidates the BMWMOA columnist theory. No, it is not my intent to match wits with the columnist, but oils are one of the things that I know a little bit about.

As a matter of fact I will also contibute a theory on FD failures, the early ones were due to improper bearings for the application, the later ones due to installation/fitment issues and all sourced at the factory. My theory is based on what I have seen and experienced personally and through the various forums.

In closing, we live in different locations and ride differently and what works for one might not work for the other and that my friends is the beauty of experimentation.

[towerworker]

Been running Lucas 80/90 with no problems in 42K on an 03 and currently 30K on an 04. Change every 12K.

[kantuckid]

As referred to above: In the BMWMOA ON magazine article by Paul Glaves, a professional wrench and excellent writer he states in an article on the FD's that the syn lubes contribute to FD leaking and should be avoided for that reason-said to be OK for the tranny.There is an bunch of great info(RE: bearings used , repair procedures,lubes,etc) on the FD & @ the club website too. Also a "list of failures" thread that grows...

[ebincia]

Thanks all. I am now more educated to make a decision on the issue.

[challey]

Not to add more fuel to this fire, but at a seminar at the Intl Rally in VT 2 years ago, Paul Glaves recommended 2 things to help detect and prevent premature FD failure:
1) changing the FD fluid each time the crankcase oil was changed and;
2) using conventional, not synthetic, 75W90 gear lube.

With respect to changing the FD fluid when the engine oil was changed, his point was that a close inspection of the FD oil every 6,000 miles would provide a warning of impending failure (abnormal sheen to the oil or visible metal flake or chips). If the drive was going to fail, changing the oil wouldn't help but you'd at least have some advance notice. His recommendation to use conventional oil was based on his feeling that conventional, because it is less slipperry, was retained better on the bearings and provided an important lubricating film when starting from cold. He also said that he felt synthetic was uneccessary in the FD since, unlike the transmission, it's normal operating temperature was relatively cool and the fluid was not under a lot of stress.

I'm not necessarily advocating for his position just passing his remarks along. For the record, I've been changing my FD fluid in sync with engine oil changes but I've been using Red Line 75W90 synth since I invested in a couple of quarts. When it runs out, I'll think about using conventional gear lube.

Charlie