I've read every transmission gear oil change thread I could find and haven't seen anyone ask or answer this question.

The Red Line website says their 75W90 has polyol ester basestocks (whatever that means) that provides extra slipperiness to reduce friction for hypoid gears of limited-slip differentials. The same part of the website also states that they have other products, namely the MT90 as far as the RX8 is concerned, that have better frictional properties for manual transmission synchros, which require a little more friction for proper synchro engagement.

So why does Royal Purple offer only one product (Max-Gear 75W90) for BOTH transmission and differential? Their website says that Max-Gear has hypoid friction modifiers necessary for certain differentials, much like Red Line's 75W90. It doesn't specify if the hypoid gear friction modifiers are a part of their proprietary Synslide additive technology. But whatever all is involved in Synslide, wouldn't it all just REDUCE friction? And isn't this the opposite of what we want for the manual transmission synchros?

Should Royal Purple ideally offer a different product for the manual transmission like Red Line offers? Did Royal Purple compromise? Or is Royal Purple's single product superior for both (if that's even possible)?

 

The Red line tranny oil has the correct friction modifiers for syncros and their diff oil has some sort of shock modifier. Royal Purple may have done this with just one oil. Most of the post I have seen say to use Red Line or Royal Purple as they are both good prducts.

 

RP does offer two products, both of which I use in my car.

Max Gear in the differential, and SynchroMax in the gearbox.

Synchromax

Love 'em, too.

 

Tony, now I'm really confused. You are the first person that I know of to bring up Synchromax. Everyone else has used Max-Gear 75W90 in the manual transmission as well as differential.

Is Synchromax preferred for the manual trans? What does Royal Purple say? How about Racing Beat, etc? The website says Synchromax is for manual trans that require an automatic trans type oil?!!

How is the shifting, Tony? And how is the shifting and synchronization for the people who just used Gear-Max for the manual trans? Does anyone feel Max-Gear creates undesired characteristics for the shifting?

 

Synchromax is supposed to be for manual transmissions that use automatic transmission fluid. I brought this up in another thread a while ago, but never got a clear answer as to why anyone would use Synchromax in the RX-8 manual gearbox.

jds

 

For what it's worth, I've got RP Max Gear 75W90, and am about to put in both my MT and differential this weekend. I also don't see how Synchromax applies to our application with its listed specifications?

 

I did the Redline MT90, and 75w90. The RP confused me, which is easy to do

 

Thanks for the answers, guys.

So I'll stay away from Royal Purple Synchromax. Bureau13, Sea Ray, and anyone else who used Max-Gear for the manual trans, do you feel the synchro engagement could be better or faster? Or is it pretty damn good regardless?

Maybe I'll just put Red Line MT90 for my trans and Royal Purple for my differential and support both companies. Hmmm.

 

I used the RP MaxGear in tranny and diff on my FD...I was very happy with it and never had any problems. I haven't changed the fluids in my 8 yet, but when I do, I'll stick with the RP stuff. FWIW, I've heard only good things about the Redline gear oils as well.

jds

 

I just talked to a person (forgot his name) at Royal Purple (their phone numbers are 281-354-8600 and 888-382-6300). First, he curtly stated that "We're not Red Line." LOL. Then he explained to me that they have two kinds of additive "packets" in Max-Gear 75W90 such that one optimizes differential performance and the other optimizes manual transmission performance. He said Max-Gear is perfect for the transmission synchros as well as the differential.

 

That sounds great.. So how many quarts should we purchase if we want to replace the diff/trans fluids?

 

Dave,

I just came back from buying Royal Purple Max-Gear 75W90. I bought 4 quarts, which is what all the people from the other gear oil threads said, since the manual trans should take 1.8 quarts and the differential should take 1.4 quarts. These forum members stress that 3 quarts simply won't be enough and you shouldn't try to get away with it.

Hey, you're not far from me. I went all over the place to various Pep Boys, Auto Zones, and Kragen looking for Red Line and Royal Purple without any luck. Red Line and Royal Purple's websites have a bunch of places that simply do not carry their stuff, which is annoying.

I finally called Jackson Napa in Brea and they have both. They have everything you could want. Strangely, the Royal Purple ($8.67 per quart before tax, which is one of the best prices I've seen) was cheaper than their Red Line (both MT90 and 75W90 at $8.95 per quart). Every other place I've looked up, including Ebay, has Royal Purple as more expensive.

Dave, do you have a local shop around San Dimas that you frequent? Wherever you end up buying your stuff, could you please share with us the price you paid? I'm interested to see if you can find lower than Jackson Napa.

 

Hey.. where do you live at?

I too looked at the RP site and couldnt find any dealers located in either the 91766 or 91773 area codes so I had no idea where to even look.

Thankx for letting me know where it is. I'll probably go there this weekend and pick up 4 quarts now. Every time that I get in my car and shift it begs me to change the fluid as it is notchy as heck. I really should do that soon as I am nearing 30,000 miles already and I have only had the car for just over a year now!!! crazy.... nice 2 year warranty..

but anyway.. I usually take my car to San Dimas Auto Racing.. They can be found here...

http://www.sandimasauto.com

They race/prepare/build spec miatas which is their speciality obviously though I am really looking for a true tuner shop. They are very capable people and have done all of my mods for me (pulley's, suspension upgrades, flywheel, etc...)... They are a great shop with curtious and knowledgable people working there... though like I said, I am looking for something more performance oriented.... I have a few shops in mind but still need to do some more research...

PM me if you want to talk some more about it..

later...

 

Manual says 75/90 GL4 for trans and 90wt GL5 (tsb says 80/90 GL5 is ok also) for rear. The weight/viscosity is not near as important here as the GL4 or GL5 spec is. The additive package that makes GL5 a hypoid gear oil is very destructive to bronze bushings generaly used in tranys. While redline and royal purple are great oils i somtimes wonder if they are just trying to sell somthing to make a buck. There is no GOOD GL4/GL5 combined spec oil they are both designed for diffrent types of gear loads and bearings.

 

Hey... I bought my products from here.. Decided to go with the Redline product line....

1 of : Redline - Coolant Additive, Water Wetter $8.79
2 of : Redline - Transmission Fluid [Transmission Oil:MT-90] $15.90
2 of : Redline - Transmission Fluid [Transmission Oil:75W90] $15.90

Order Summary:

Product Subtotal: $40.59
Sales Tax ( 0 %): $0.00
Shipping & Handling: $7.80

Grand Total: $48.39

I purchased it from https://www.paragon-products.com

 

What are you basing this statement on? If RP and Redline gear oils are combined GL4/GL5 (they are..at least RP is and I think the Redline as well) then based on my experience and that of everyone I know who has used it, they're BOTH "good GL4/GL5 combined spec oils." Do you have evidence to the contrary?

jds

 

Hey Dave, good job. Where are you getting your crush washers? May I suggest Super Mazda in West Covina (name changed to Super after the ownership change two months ago). You'll have to order them.

 

Uhh.. my what?

They are not known as West Covina Mazda anymore?

 

For the second time, bureau13 and I seem to be thinking the same thing. I would like to hear more about this from Sig-Sauer. I'm not doubting him at all; I'd just like to hear the reasons because I don't know anything about this stuff.


I thought the Red Line products don't cross over, that the MT90 is GL4 and the 75W90 is GL5, unlike the Royal Purple.


I'd also like to know what exactly is a bronze bushing. Is there only one in the transmission or more? Is it something that is expensive to get replaced if it breaks down from corrosion, wear-and-tear, or whatever?


Something that I didn't mention before about my phone call to Royal Purple was that even before I started asking specific questions, the guy came right out and said Max-Gear 75W90 will not cause corrosion to the gears and bearings (this is also stated on their website), indicating this is a common question that Royal Purple receives and they are ready for it.

So what is the relationship between the gears and bearings AND bronze bushing(s)? If Max-Gear will not corrode the gears and bearings, can we assume it also will not corrode the bronze bushing(s)?

 

Dave,

No they are not known as West Covina Mazda anymore. Earlier this week when I went down there, the new owner was there with his yellow Ferrari F360!

 

Wait haha.. what are crush washers? I guess this is something related to the lube change?

 

Oh no Dave! I thought you were a pro at this stuff. They are just the washers that the four bolts use (the trans has 1 fill and 1 drain washer, the differential has 1 fill and 1 drain washer).

Hold your horses. In a few minutes, I will post a thread in this forum for the part numbers of the four washers as this has caused confusion in the other gear oil threads.

Some people have re-used the washers already on the car with no leakage problems. In general, most people on the forum advise that we do it the right way and get NEW crush washers, since as they say, the existing ones on the car have already been used up. They are after all called CRUSH washers.

 

A pro haha.. not really.. I am still learning... I dont profess to be anymore than a guy who loves his RX8.. takes it to the track.. and loves to have fun... A pro I am not.. what I am though is a pro at these forums haha.. I come on a lot and know a lot about whats going on... I maintain my car but just dont know the intricate details behind it.

 

Evidence No i have no Evidence to prove one way or the outher. I also have no idea of what kind of bearings mazda uses in the trans. I just know about the gear oil (Lots of oil knowlage in general). GL5 gear oil is designed for good shear stability for example the way a ring and pinion mesh. It clings really well. GL4 is more of a a high pressure for example straight cut gears that push directly on echouther. GL4 does not cling or stick to gears well at all. I realize that the manual says ither can be used in the tranny but i can tell you from experience GL4 is what the tranny wants. You have heard of people getting a trans service and the trany was notchy and hard to shift. That is GL5 (really bad when cold). As for the bearing bushing thing ither will lubricate bearings fine BUT if there is any bronze bushings in the trans (not likley because mazda says GL4 or 5) a true GL5 spec oil will eat them up.
GL5 is high in sulfer content for its shear stability. The sulfer eats bronze bushings. So a product designed to meet both specs is giving up protection in some area.

To test this theory anyone is welcome to go get 2 QTS of say anybrand GL5 75-90 and do a trans service. Take the old 8 for a drive around the block you will know in less then a mile that it does not belong there.

If anyone was wondering why i know so much about this crap. 14 years ago i was hired to work at a little place called Minit Lube. They changed to Q-Lube and after about 5 years were baught by Penzoil. We then became the place everyone loves to hate Jiffy Lube. So after changing the oil on around 250000 cars i picked up a thing or 2 about this stuff. BTW save the J-Team horror storys for somone that has not heard them all LOL

 

Sig-Sauer, I have heard those Jiffy Lube horror stories!


Well, I trust what you say and I hope I made the right decision in buying Royal Purple. The store I went to has Red Line as well, and I could actually return two quarts of Royal Purple and buy two quarts of Red Line MT90 for the trans, if I really needed to.


The Royal Purple website states that their "Synslide additive technology is noncorrosive to gears and bearings, including case-hardened gears that are easily pitted by conventional sulfur-phosphorus EP oils..."


So what do ya'll think? Should I go ahead and put the Royal Purple in for the trans? Or return it for the Red Line? Either way, I'll stick with the Royal Purple for the differential.