Just to clarify real quick... I can use the 75/90 in both the tranny n diff correct...and I need 2 quarts for each...

 

Yep. Make sure you buy some new crush washers for both the tranny & diff.

 

Yup, that's the stuff I put in about a year ago. Super smooth.....
Hmm, now I just need to figure out how often I want to change the fluids.

 

I plan to change it out every 3 yrs..include it with the brake fluids at the same time. Guess it depends on how hard you drive it..for those serious trackers, they might change it yearly...

 

alright , where can I get the crush washers at and do u happen to know the specs i need , or are they all the same size.. and thanks

 

get them from the dealer, they are less than a dollar.

 

o alright imma head over there now and get em.... thanks

 

I have recently heard that the LSD additive in the RP 75w90 can negatively affect the syncros' functionality and lifespan. Anyone know if this has any truth to it?

I too am planning on changing my tranny fluid (redline or RP) and can't decide which way to go. Supposedly the Redline MT90 and MTL doesn't have the lsd additive.

 

I have also heard that because of the GL-5 additives, the combo GL-5/GL-4 fluids are not the best thing for syncro operation and they can increase wear in manual trans syncros (GL-5 is a diff spec and GL-4 is a trans spec).

IMHO you are better off using a GL-4 only lubricant. I use BG Syncroshift II. It is a GL-4 only fluid and my trans shifts much, much smoother than before and it almost totally eliminated the syncro whine. While not discussed on this forum much, this is a great product you should consider.

 

http://www.finishlineperformance.com...4-03-1268a.pdf

beers

 

I've been using royal purple on my FC for the last 3 years but only on the diff, for the very same reason. I use the rp synchromax for the gearbox.
...for my 8, I use Idemitsu 75W90, feels so much smoother.

 

Does Mazda use dino as the stock tranny and diff oil? I was going to order Red Line, but got impatient and used Mobil 1 75W90 for the tranny and the 80-90 Valvoline Synthetic Blend for the diff. They were readily available at Autozone. No complaints and both seem to be running smoother than before. May not be as good as RP or RL, but I think I have a better deal than what would be used at the stealership's service dept. Changed mine at the recommended 30k mark at there was alot of gunk on the magnetic drain plugs. Hopefully won't be that way when it's time to di it again.

 

This is the Diff spec, which is and should be a GL-5, such as RP Max Gear, etc. My point before is that manual trans work better with GL-4 only lubricants, not combo lubricants like RP Max Gear, which is both GL-5/GL-4.

 

am using the max gear in both... what it does for the tranny is great.

beers

 

As I understand it, Mazda uses a full synthetic in the diff and a dino in the trans from the factory.

 

I am glad it is working for you. I just had some reservations from what I had learned, so I chose to go a different route and it also seems to work well.

 

Not to revive an old thread. But quick question. I'm looking into changing out all my fluids soon. I need to know, theres the gear box (also called the transmission, yes?) for which I use gear oil or transmission fluid right? Then there is a differential, for which I need to find a 'differential fluid'?

I got 1q of Royal Purple Synchromax intending to replace my gear oil, is the Synchromax equivelent to the Redline 75 90 stuff? Or must I use the Royal Purple Max Gear oil. If so, can I put this Synchromax in the differential? What is the difference between these fluids....

 

If you go with Royal Purple, "Max Gear" is what is recommended for BOTH the manual transmission and differential in the 8, it is a combination GF-4/GF-5. Synchromax is only suggested in cases where an ATF/motor oil is used in the gearbox. For Redline, you use Manual Transmission oil in the tranny (MTL, MT-90, etc. whichever you prefer, I used MT-90 as it meets Mazda weight specs) and 75w90 gear oil in the diff. With redline, the manual tranny fluid is a GF-4 and the gear oil is a GF-5.

 

Wanted to add to clear up your confusion. Technically, both the transmission and differential use a "Gear Oil" on the RX-8. Ideally, the best solution is to find a gear oil specifically for the manual transmission as it would not contain the lsd additives that are in most multi-use gear oils. These additives are there as limited slip differentials need them, but they probably aren't the best thing for the syncros in your gearbox.

Royal Purple makes a multi-purpose gear oil with those lsd additives meeting both the gearbox (GF-4) and the differential (GF-5) standards. Many on here have no problems with it, and RP is certainly a well regarded oil company.

Redline sells gear oil specifically for the transmission without those lsd additives (only GF-4), and gear oil specifically for the differential with those lsd additives (only GF-5). Personally, I liked the idea of having specific fluids for each.

So.. RP Max Gear = Redline tranny fluid & Redline gear oil w/ lsd additives combined. Synchromax is something entirely different.

("Rotary gods", correct me if I've mistaken anywhere on here. This is what I've come up with from searching when I was changing those fluids myself.)

 

Just wanna make sure Im getting this right? If I were to use the Redline I would put the 75w90 NS in the diff. and use MT-90 in the tranny?

Could you use MT-90 in both the tranny and the diff?

 

Also anyone try Lucas gear oil?

 

From reading the threads, I think you want to use MT-90 only for the transmission and 75w90 (not 75w90NS) in the differential. It seems that for Royal Purple, you use Max-Gear 75w90 for both.

Hate to rehash old arguments, but for those that have used both which did you find superior and why? Thanks

 

That is correct.