Which oil to use in gear box and rear diff?

[allessence]

Hi, I know it's a 75W-90 synthetic. My question really is what to use that has good shift qualities but offers little more protection to gears/syncro's.

Is the factory stuff good.

Redline MTL, RP maxgear 75W-90.


Who's running what and with what kinds of driving?

Thanks Jennifer

[Seerlah]

I use Amsoil GL4 75w80 manual transmission fluid mixed with Red Line Shock Proof in my transmission (manual). And I use Amsoil GL5 75w90 gear oil in my rear differential. Overall, I like it. It offers smoother shifts. And no more cold start synchro grinds, unless I shift at maybe anything above 3.2k RPM before the tranny oil warms up a bit. But compared to how it was with the OEM tranny fluid before I switched to Amsoil, it made an incredible difference.

Choice is really up to you on which one you would preferr. It's all about perferance. I am an Amsoil guy, so that is what I use (including motor oil). Others preferr Mobil 1, Royal Purple, Lubro-Moly, Red Line, Motul, etc. I drive rather agressively, but like to drive subtely at times.

[allessence]

Hi, Thanks,

Yeah, I know it's mainly personal preference. I rebuild transmissions and fab headers and intakes, but most of the draggers, heavy footers and such are on here and can give better insight than me buying 5 Gallons of each to try.

Thanks again. Please keep it coming.

[Seerlah]

It is really all the same, as long as you go full synthetic. The Shock Proof is really for those whom like to do hard launches. That is why some like to mix it into their tranny fluid of choice, like me. You can place up to 1/4 of the amount of tranny fluid is necessary (we take roughly 3l of tranny fluid, so roughly 3/4 L should be the limit). I have maybe 10-15% Red Line Sock Proof and the rest is Amsoil manual tranny fluid.

[allessence]

I have 4 gallons for the heavy weight shockproof on the shelf. Does anybody run this stuff straight?

I also have RP maxgear 75W-90. Trans or Rear diff?

[MOtown A4]

has anyone seen that lucas oil gear oil additive? i forget what it's called, but they have the little displays at murray's/o'riellys, autozone, etc. i always wondered if it would enhance or inhibit anything.

[mrbacardi35]

MT90 w/ heavy shockproof on the tranny and redline 75W90 for the rear.

[dangerous_dave]

For a street driven car there is no difference. Any full synthetic 75-90 gear oil will do. Just get whatever brand your local parts store sells.

[twinpop171]

Watch what you buy. Make sure that it is GL-4 compliant for your synchros pleasure. I just changed my trans and diff oil and almost used Mobil 1 in the tranny which is not GL-4 compliant from the research I did. Maybe someone else can chime in about Mobil 1 but I didn't want to take a chance on killing my synchros.


I used the Royal Purple Max Gear 75w90 in both. I've only had it in for about 2k but have no complaints. As Seerlah stated too, my oil needs to warm up a bit for smoother shifts as well. My Avant has 121k right now BTW.

[baudi21]

MT90 w/ heavy shockproof on the tranny and redline 75W90 for the rear.

a lot of subies you this combo with great results. i know i did.

[allessence]

Okay, I'm far from a light foot. have all ready ported the exhaust manifold and have a KO4 in. Planning of fabbing up some more go fast parts all ready have the jig made up for a tube type exhaust manifold.

210K on the car. So really a mixture of Redline in trans and then 75W-90 rear.


Anybody else?