I wrote to Redline this past Fri night and here is the reply about using the 75w90 in the tranny.

Request Type : Technical Request
Message : Concerning the 75w90NS manual transmission/differential gear oil, I wanted to find out what compatability it has with syncromesh transmissions that use brass or bonze for the syncros. I've read that high sulfur content will corrode these yellow metals at a much more rapid rate in a GL5 than a GL4 lubricant. Could you shed some light on this subject for myself and a few other interested users?


Ethan,

Some GL-5 gear lubes can be corrosive to brass, bronze and copper depending on the EP concentration used. The Red Line GL-5 gear lubes including the 75W90NS don't contain sufficient to be corrosive.

A GL-4 gear lube typically contains a non reactive additive package so wouldn't be corrosive.

He did ask about the application I'm using it for, so I'll write back and see if there are further noteworthy details.

 

All I know is I've used 4 or 5 different lubes for my tranny, including stuff far more expensive than the Redline, and the winner by far for overall performance, ease of shifting, and synchros properly meshing is the Redline MT-90...

(It is MT-, isn't it, lol, it's something-90, anyway )

 

Yeah everybody's been saying MT-90 is the way to go, but I used the 75w90NS. So since everybody freaked on me, and told me terrible things would happen to myself and my unborn offspring 5 generations ahead for using it instead, I decided to ask directly at the source on the compatability issues.

 

Yep thats what i use in both tranny and diffrential and its been great so far. That dreaded 2nd gear grinding has virtually gone away.

 

I don't understand what you point is...

You're buying stuff that's at least $8/ quart.
A transmission flush needs at least 3 quarts of this stuff, so you're spending $25 just in fluids.

Redline makes the MT-90 specifically for this application, and this is what they recommend for it.
Why are you trying to get around the recommendation?

I didn't say you couldn't use the 75W90NS for the transmission.
I said I wouldn't recommend it, and I would consult Redline tech support on it.


-Ted

 

I'm not trying to get around the recommendation. The 75w90 is what I bought and used by reading Redline's site, before reading all the recommendations for using MT-90 here. Since everyone seemed to have bad things to say about the GL-5 usage in our trannies, I decided to ask the techs at Redline to see if it was ok to be using. Like you said, it's nearly $8 a quart, and since I had just changed it, why spend the money on a another complete change if it isn't absolutely necessary. Sorry if my point got lost in translation, I'm not trying to cause people headaches or anything. I just wanted to clear up that it is safe to use, so if you're like me, and already have it in the tranny, don't worry about it and use MT-90 next time. I did get another response from the tech, that he would recommend MT-90, as it will have good all around shiftability and possibly be slightly better than the 75w90NS. Am I cleared of all the trouble I've caused now?

 

I forgive easily, don't know about Ted though, lol

 

Thanks Wayne, I don't want to get on the bad side of people i consider excellent sources of information and help in here. Actually, come to think of it, the main reason I wrote Redline was from a previous post by Ted. See, I do listen and take the gurus seriously.

 

Oh, I wasn't mad.
Do I need to put tons of smileys in all my posts???
I was just being...argumentative.


-Ted

 

you guys qwack me up sometimes

 

The bad rap that GL-5 oils get is mostly related to non-synthetic oils, and that GL-5 oils tend to break down at temps about 250-280F. When that happens the gear oil acid level radically rises causing the eaten brass syncro issue that pops up on this board every 6 months.

As many times as I stress it, the concept of using better quailty oils and lubes just does not sink in.

Better quality oils being used will not allow that tranny temp to get that high where the oil starts breaking down. Oils like MT-90 and Superlight shock proof (which would probably be rated as a GL-5 according to redline) are perfect for our trannys, while oils like valvoline GL-5 gear oils would require constant gear oil changes, so that damage would not occur to the syncros or other brass parts.

 

Thanks for that explaination Mark, that's probably the most informative explaination I've read on the subject to date on what's going on in there. Ted... don't argue with me man.... I hate to argue with anyone, about anything. I had been using the Mobil synthetic and when it started the slight grind to 2nd I decided it must not be good enough. The change in shifting makes me realize how much a difference there can be even between synthetics, yikes.

 

Yup, I agree, there can be differences even between synthetics. I used MT90 in my 87TII, much improved from whatever the previous owner put in, but still a little notchy, and sometimes will not go into 1st very well. Changed it to Royal Purple's Max Gear, and WOW! What a difference!

Not knocking on Redline, I use that stuff in my other cars, but for my TII, the Royal Purple had better results.

 

Kicking Self - when I bought redline they had 75w90 & 75w90ns, but no MT90.

So I got the "suck-@$$ notchy / bogging cold performance" right now from my drivetrain.