[Spridgets] Motor Oil in the Gear Box

[David Riker]

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 at comcast.net>
To: "David Riker" <davriker at nwi.net>
Cc: <spridgets at 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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