Boxerworks.com

Anybody using synthetic in their gear box and rear end. I haven't tried it because someone, A LONG TIME AGO, told be its not designed for these old bikes. Is this a wives tale? If it is a wives tale I would like to try some. Is 75/90 ok to use?

Thanks
Regards
Kelly

I've had synthetic 75W90 in all 3 parts of the transmission for several years. No problems in terms of leaks and the oil is much thinner when cold which reduces drag. With the bike on the stand and cold oil try spinning the rear wheel by hand in neutral. You will feel substantial oil drag. Do the same when the oil is hot and the difference is incredible. 75W90 reduces much of that cold oil drag.

Look at the difference in cold viscosity between two different mineral 80W90's and a typical synthetic 75W90. The way I look at it we lose a lot of power between the flywheel and the rear wheel and if I can get a few percent of that back for negligible cost it's worth while. I do daily short commutes where the oil never really gets hot so I probably benefit more than most.

Inserting graph. probably going to use it next change. Is the same true for engine oil? I've never tried synthetic in the motor either.

Thanks
Kelly

KellyVB 75R90S wrote: ↑Sun Nov 04, 2018 9:43 am Is the same true for engine oil? I've never tried synthetic in the motor either.

I currently use a 5W40 synthetic for engine oil for much the same reasons as my oil hardly ever gets up to temperature. Many people think that a 5W40 is vastly thinner than 20W50 but it isn't except when it's cold. BMW's oil grade tables permit the use of a 5W40 in my climate so I have no hesitation in using it.

The manual for the R90S called for 20w50 engine oil...probably the best oil which is best of both worlds (dino vs synthetic along with ZDDP) is the Golden Spectro product. Another quality product (dino oil) is Valvoline VR1 racing oil. The knock early on for synthetic was that it tended to leak, but it wasn't long before synthetic oils began to include seal swellers which takes care of the early issue. As for gear oil, the manual calls for a quality GL5 80w90. Last time I looked, just about all of the gear oils were synthetic.

Kurt in S.A.

You can't go wrong in using the oils specified in the bikes manual.

However the manuals supplied with our bikes over 40 years ago are not BMW's last word on oil recommendations. Updates were issued on several occasions in the form of service bulletins and as late as Dec 1995 they were still updating oil guidance for models as far back as \5. This guidance gradually accepted the use of thinner synthetic oils and gave owners a wider choice. The only stipulation about using synthetic even in a \5 was not to do so until the engine had run 6000 miles. The oil chart that I use which permits the use of synthetic 5W40 is this one.

The only downside to the use of synthetics in older machines I've found (apart from the cost of course) is that old oil seals are more prone to leak. Don't know why but I have experienced it in the transmission of my R100RS. Filled with Synth... leaked like a seive. refilled with mineral... dry as a bone.

Rob

I remember reading Duane Asherman's comment that synthetic gear oil greatly extended gearbox life. I've used it in R60/2, R90, R100, without a problem. IMO it's worth the small investment for the small quantity required. I use a major brand.

I've used synthetic everywhere for years. But after the last change the engine has started to weep while parked. Suspect the oilpreassure-switch or thereabout. Don't know if it's the oils fault though

I use only synthetic oil everywhere in both of my BMWs. (94' R100R and K75) I haven't had any problems. Use Mobil products. I was glad that I had synth in my engine coming back from VA as we were stuck in slow traffic for an hour with no good place to pull over. I think synth oils are better with high temps in air cooled engine as well as better gear protection.