Here, read what Redline says about MT-90 and synchros, gears and coefficient
of friction, etc. http://www.redlineoil.com/product.aspx?pid=46&pcid=7
Mike MacLean
On Tue, Mar 23, 2010 at 8:52 PM, David Riker <davriker@nwi.net> wrote:
> Dean,
> Bearings like lubrication, syncros do not. The syncronizer teeth have to
> bite into the opposing cone in a balancing act that eventually wears the
> syncronizer out. As the syncro bites at the cone, the cone spins up to
> match the speed of the syncronizer, and then the gear change is possible.
> If the lubricant is too thick, the film prevents the teeth from biting into
> the cone. If the lubricant is too slippery, the teeth can't bite into the
> cone. So you need a lube that is strong enough to protect the gears and
> bearings, but not so slippery or thick as to prevent the syncros from
> performing their function. Too thin of a lubricant, and you will get
> premature wear of the gears and bearings. Thicker lubricants acts as a
> cushion between the gears, quieting noisy gears. Then again, without the
> heat produced by combustion, there is far less heat generated in the
> transmission than in the engine, so a muli-viscosity engine oil may never
> behave like the higher number would suggest.
>
> Here is a link to a viscosity chart:
> http://www.bobistheoilguy.com/visc.html
>
> As you can see, 85W gear oil is the same viscosity as 30W engine oil.
> Thus,
> the recomendation for a 75W-90 seems to make sense, however the use of
> synthetic may be counter productive as it could be too slippery for the
> syncros to function correctly.
>
> Dave R.
>
> ----- Original Message -----
> From: "Dean Hedin" <dlh2001@comcast.net>
> To: "David Riker" <davriker@nwi.net>
> Cc: <spridgets@autox.team.net>
> Sent: Tuesday, March 23, 2010 5:31 PM
> Subject: Re: [Spridgets] Motor Oil in the Gear Box
>
>
> > It's a little perplexing...
> >
> > On one hand the original Datsum manual specifies 80W-90 or even the
> > heavier
> > 140wt for higher temperatures as Mike indicated
> >
> > But we observe that the notchy shift goes away as the tranny wams up.
> > This seems to imply that a overall thinner gear oil would be prefered,
> > such as the multi-weight 75w90 that is suggested by Rivergate and others.
> >
> > It's contradictory, I mean that I would have thought that a thicker gear
> > oil would
> > help the action of the sychros, but that appears not to be the case.
> >
> > I'd like to believe that I could put in a API-GL4 lube and my notchy
> shift
> > would
> > magically disappear, but somehow I don't think that will happen.
> >
> > Unless of course, someone else out there had a notchy shift and it went
> > away when they
> > swaped in Redline MT-90 or something similiar.
> >
> >
>
>
>
>
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