75w-90 synth oil

[Kelly]

can someone tell me why u cant use full synthetic gear oil in a t-5??

[BP Convt]

I believe the reason is primarily that transmission fluid will get into some of the places in a t-5 better than what a thicker gear lube can. Example: older transmissions didn't have needle bearings supporting the gears. I'm not sure if gear lube creates a compatibility problem with the blocker ring material. Shifting is easier when transmission fluid is cold. Shifting gears with cold gear lube is harder.

Best reason in my mind is that a lower viscosity oil creates less friction. Less friction means more horsepower.

[dave bandt]

Depending on the blend, some oil compounds attack brass alloys. That would be the only reason that I can think of that would prohibit running any type of oil in a gear box. It also have to have an EP additive designed for gearboxes too, though.

[portponies]

The T5 needs thinner oil due to the close tolererances of the needle bearings under the gears.

I have had a few T5's come thru here that were run with gear lube, and the bearings were pretty toasted.

Tremec recommends using Dexron III, Synchromesh, or a synthetic equivelant to those two.

[BBATCO1]

You can even crack the case with gearlube beacuse of those close tollerences....

[dave bandt]

Tremec recommends using Dexron III, Synchromesh, or a synthetic equivelant to those two.

Out of curiosity.....what's the synthetic gear lube equivalent to that light of an oil? I'm thinking it would almost be like a hydraulic oil......i.e. 10 - 20 weight.

I do know that we ran an oil in a gear box up in MN that had an additive package that disolved the bushings. Luckily our oil analysis program caught it. Viscosity issues aside.....that is something that a lot of people aren't aware of.....myself included until i saw it happen.