I have a 2004 Rx8 manual transmission with about 80,000 miles and I am wanting to change out the transmission and differential oil. I have heard so much talk about what kind to use and I was going to go with the Royal Purple Max Gear 75w90 gear oil in the transmission and differential. I would appreciate any input on this.

 

The Royal Purple hasn't been the best choice for our transmissions..it tends to cause syncro grinding in some cars

There are other choices out there that have yielded better results....

Redline is what I have been sing in my car and have had good results

 

would you recommend from redline the MT-90 in the transmission and the 75w90 regular gear oil in the differential then?

 

From what I have read on this site, that would be very close, if not the most used combonation with the best results.

 

Using MT-90 in my transmission as well with no ill effects

 

MT-90 is 75w90 GL4
the diff probably needs a GL5 and different weight

 

I did redline for both, MT90 in the trans and whatever was recommended in the dif. Made a great deal of difference in the trans shifting almost immediately and the oil in there was only a year old.

 

As far as the differential goes, instead of doing a drain and fill take it apart and clean it. Its really not all that hard. You will need a new gasket and it will take longer, but you can do a really really good cleaning job that way. Redline will actually make a recommendation for you on these but I use Heavy Shockproof Gear Oil from redline in my transmission and its still working just fine, along with 75w-90 GL5 redline diff oil. But again you will only be able to make this decision for yourself to see what works best in your eyes.

 

wonder does it have a drain plug on the diff? when I did the diffs on my Wrangler I had to drop two covers.

 

Drain on both...easy job

 

READ POST FROM NOOB UNSURE ABOUT FLUID CHANGE

RECOMMEND THAT HE DISASSEMBLE DIFFERENTIAL INSTEAD

 

/\awesome car thread answer.

-mt-90 works great. make sure the car is level when doing the change.

 

jason your wrangler probably had skid plates protecting it from offroad debris encounters:P

 

the diffs? the diffs are not covered, just part of the transmission and the transfer case.