The Stovebolt Site Forums The Shop Area Driveline Synthetic oil in 3 speed man

Ok so will synthetic oil eat my tranny gears? I cannot find a positive yes or no in the forums. I read somewhere g5 eats ferrous ( brass ) metals.
Now,I almost took out a crown gear in a snow blower auger box with
synthetic g5 once. It was a nasty mess.

So some guys here run synthetic I take it??

This is from the Novak transmission folks.

When filling your transmission with gear oil, we recommend that you select a conventional mineral oil or a para-synthetic in lieu of a full synthetic oil. Properly assembled manual gearboxes do not have the thermal strains seen by combustion engines or hypoid gears. Synthetic fluid in these gearboxes, while not harmful, is probably an economic waste.

Hypoid gear oil is sulphurized higher than transmission oil and can be mildly corrosive to the non-ferrous alloys used for synchros, bushings and thrust washers in these transmissions.

An 80W-90, API-GL5 or MT-1 rated fluid is very good. Some claim faster shifts from using a 50W engine oil in their transmission and we do not consider this to be contradicted unless you operate your vehicle in a very warm environment.

We don't know what kind of or what year truck/car you're asking
about but I don't believe the synthetic oil is going to hurt
anything internal. I assume what you've read about is the
damage to the "brass" in a manual transmission. Those concerns
are with the high sulfer content of some Hypoid greases.

The one problem you may run into unless the trans is designed to
use synthetics is with the syncros. The syncro rings may not
grab as good with the synthetic, which can result in clashing
of the gears. This is especially bad whith the SM420. I suspect
it's because its gears have more mass than a 3 speed or the late
model 4 and 5 speed transmissions.
Give it a try, if it causes a problem shifting, drain it out and
refill, all you've lost is the cost of the synthetic.
Denny G

Oops, looks like Brad was up early also, ya out fumbled me
again buddy while I was correcting my spelling.

DG

...craigK, by the way, welcome to the Stovebolt Page. There are several, no many, Canadians here and maybe some close by.

Brass is not ferrous.

I just drained and filled my transmission and everything I read recommended non-synthetic oil and recommended GL-4, so that's what I used.

Everything I read said 80w-90 gear lube. AutoZone sold me 80w-90 multi-purpose GL-5, so that's what I used.

Why was I told to use ATF in my T5?

maybe it's a 'world class' version, see here, seems like ATF is what GM says

Bill

I can only wish for something called "world class" Guess I will change today. Thanks all.

T5 uses Dexron III (non synthetic)
Synthetic & semi synthetic fluids can degrade may older gasket materals and some RTV sealants (as used on the T5) causing them to leak.
NV4500 uses synthetic gear lube ONLY, has syncro rings with fiber surface, will eat them up if mineral oil is used.
I ran a M20 (brass rings)for sevral years w/ that syn gear lube, shifted better, brass syncro seemed to grip just fine.

I settled for a hydrolic / transmission cross. It is meant for tractors that run the same hydrolic as tranny fluid in a common oil pan. It will not eat brass. Then I had to fix a lot of leaks. Nothing new there. With no oil in the old one there was nothing to leak. 3 speed manual, 53 gmc.

Synthetic GL-4 will work just fine.

I've had synthetic gear oil in my 1952 3 speed for several years and have changed it a couple times mostly just to inspect it and learned I went there unnecessarily. Never had any gear clashing issues and double clutching at speed into low to navigate rush hour works extremely well in my case.

In a prior vehicle (48 Dodge) I tried full synthetic 85wt in the tranny. Only negative I noticed was I had to wait to downshift to first (non syncro). Prior to the synthetic, I could stop at a light and downshift from 2nd to 1st right away. With the synthetic, when first stopped, if I downshifted immediately the gears would clash - found I had to wait for several seconds to go into first. I assumed the synthetic worked so well there was still gears spinning in the gearbox.