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I have been trying to find the recommended fork oils listed in the Haynes manual locally. None of my local shops have any of them. Is there a Motul substitute that works well?

I'm a heavy guy, should I look for a thinner of thicker oil?

opinions?

Any good brand I think, 7.5 wt. for average joe.

Try a google - there is a good article out there on current suspension fluids

Maxima and Bel Ray HVI Synthetic fluids both come out well, and 7.5 Bel Ray works for me.

It reduces stiction so improves fork action, it is naturally multi grade so damping doesn't fade, and it stays in grade much longer too so it is well worth the extra.

Motul is great oil and they list both a 10w and a 5w semi-synthetic oil for forks. I run all mine on their 5w with no problems, but you could mix their 10w and 5w 50/50 to get a 7.5w oil if you wanted something a bit heavier.

ME 109 wrote:Any good brand I think, 7.5 wt. for average joe.

+1 on the 7.5 weight, although my Monolever has better different forks.

My "guess" is that mixing different weights of fluid, even from the same manufacturer, won't get you the linear combination of the two. Just as with regular oils, significant engineering goes into designing a given weight of fork oil to include viscosity modifiers such that combining two weights will greatly change the modifiers and how they act. Mixing oils from two different manufacturers would have unknown effects as the viscosity ratings is not nearly as consistent across the board, not to mention the use of different modifiers.

Kurt in S.A.

7.5w. Should be good, maybe10w to reflect the weight. Your bike as a 78 should have the fork damping upgrade that BMW fitted in late 75. Charles

Kurt in S.A. wrote:My "guess" is that mixing different weights of fluid, even from the same manufacturer, won't get you the linear combination of the two. Just as with regular oils, significant engineering goes into designing a given weight of fork oil to include viscosity modifiers such that combining two weights will greatly change the modifiers and how they act. Mixing oils from two different manufacturers would have unknown effects as the viscosity ratings is not nearly as consistent across the board, not to mention the use of different modifiers.

Kurt in S.A.

Kurt is right on this one. I know nothing about oil, but was lucky enough to have an oil formulation engineer out to my shop. He basically said the same thing. That was 100 years ago and things may be different today, but I suspect that it is even more true.

10 + 5 ≠ 7.5 ... It just don't work that way !

I've always been suspicious of mixing 2 viscosity's.

I just go to the BMW dealer and buy a bottle of 7.5.