90W question
 

So i have been thinking about changing my 90w in my tranny and rear end. Wondering what brand has people used and would recommend. I thought about royal purple but the price is pretty stiff..

Thanks for any input.

I use RedLine MT-90 (75w-90) in my Mazda6. I was thinkin of changing my 85' Rx to it.

I always used 50/50 mix of lucas gear oil and atf. Now, I run super tech gear oil from walmart. It might not be the best, but its next to nothing and oil has to meet standards to go on the shelf so i'll use it...

in the trans i like a 50/50 mix of atf and 75/90. i've tried all the synthetics, the 50/50 mix shifts just as well, if not better.

in the rear i like redline 75-90, shockproof if the car see's the track.

I used motomaster synthetic... Canadian Tire special. Plus a little lucas gear oil mixed in.

I use Redline MT-90 in the Transmission and Redline 75W140 gear oil in the differential.

Extremely smooth shifting after a couple minutes of warm up. However, my transmission and differential have both been rebuilt in the previous 3k miles so everything inside is pretty new and your mileage may vary.

I use the Royal Purple 90w in the tranny and rear end. Easy to get and it works fine.

Castrol. In later years, with a squirt or two Lucas mixed in.

Currently running Redline D6 ATF in the trans by itself. And heavyweight shockproof in the rear end.

For the trans be sure to buy something that is brass / yellow metal compliant. As the synchros are made of brass and the newer high sulfur gear oils will corrode the brass. It needs to be GL-4 spec. Almost everything you'll find at the local auto parts store is wrong. Including the Royal Purples; there are tales of Rx-8 owners switching to Royal Purple trans gear oil then it shifts notchy. If it's MT-1 spec don't buy it. API Category MT-1 designates lubricants intended for non-synchronized manual transmissions used in buses and heavy-duty trucks.

MT-90 if you have $ or Sta-Lube 85w90 from Napa Auto Parts. The Sta-Lube can also be used in the diff and is $34/gallon, enough to do both the trans and diff. It's thick and quieter than the cheapo stuff, and shifts wonderfully once warmed up.