I have some Redline I bought to put in mine as well.

 

Redline 75W-90NS doesn't have LSD additive. I don't care what worked for you physics is physics. ATF does not have shock loading capabilities.

 

+1


Well put,

I'm continuing to run Royal Purple in my 87-88 NT trans with amazing results.

 

That's fine. Talking gearbox, not diff.

Royal Purple in the diff.

 

The viscosity of a 50-50 mix of ATF and 75W-90 would be about the same as a 75W-85 oil. Synchromesh series oils are actually lighter. I would not worry about inadequate shock loading protection.

Interestingly, a lot of manufacturers now specify STRAIGHT ATF in their manual transmissions (Borg-Warner, Tremec, and ZF, for example).

 

Those transmissions have tighter tolerances, and even bearing pre-loads in some cases. They are designed to work with the lighter oil.

They also tend to have a type of pump, and smaller orifices within the shafts and gears requiring the less viscous oil.


How do you figure 75w-90 with 50% ATF would yeild only 5 less on the viscosity chart?

 

I won't use ATF in any of my trannies. I did put some once in Percent's tranny because it had bad 2nd gear synchros and nothing to lose. They're still bad, but they don't grind as much now.

 

I know. My point was that lighter oils like ATF are not automatically a bad choice for all manual transmissions because of some sort of lack of "shock loading" capability.

Don't confuse API gravity with kinetic viscosity. 75W-90 is typically around 14.5 cSt at 100 degrees C. ATF is around 7 cSt.

e^(0.5 * ln(7) + 0.5 * ln(14.5)) = 10.07 cSt, about the same as a typical 75W-85 oil.

I mean, if your tranny is working fine running heavy oil, then great. But if it's starting to have problems, the ATF mix works wonders for extending its useful life in my experience. (I understand it's also nice for racers trying to squeeze out those last few ponies, as the lighter oil reduces drivetrain power loss.)

 

As far as I know, I am the one that began propogating this idea on this forum, so I will include the source for this information.

This whole idea (ATF) came from a book I read long ago titled "How to Hotrod and Race Your Datsun". In that book, it was revealed that both of the "major" race teams were running 50/50 gear oil and ATF. They stated the reason as prevention of sludge buildup in the synchros. They also claim that the ATF contains plenty of lubrication for use in this application.

Anyway, just wanted to throw that out there. I now return you to your discussion about how ATF won't work in a manual transmission.

 

I'm currently running 75/140 Kendall Synthetic in my trans. It's giving me the same issues that 75/90 Royal Purple and Valvoline Semi-Synth gave: crunchy second gear on fast shifts when the trans is hot. I spoke with my local transmission repair shop owner about a rebuild, and the owner suggested that I go to a 75/90 conventional. His reasoning is that in a lot of transmissions, even with brand new syncros, if the syncros aren't designed to be used with synthetic, the synthetic is too slippery for the syncros to do their job, causing rough shifts. I have to drain my fluid when I replace my driveshaft this winter, so I'm going to give it a shot for S&G. If it doesn't work, then I'll try ATF to clean the syncros, and if that doesn't help, then I'll just throw some synthetic into it and deal with the crunch.

 

Not saying ATF wont work, as it's been pointed out many are designed for it. Just saying if it calls for gear oil, use gear oil. Can't tell you how many Saginaws, Muncies, T-10's I've rebuild over the years for bearing failures because people put ATF in it.

And like wise later WC-T5's because people put 85w-90 in and torched the 1-2 cone synchros.

I just use what the trans itself calls for, and pick my style/brand of fluid accordingly.

I am a fan of Royal Purple Synchromax for use in place of ATF and GM Synchromesh application.

 

I do run 50/50 ATF & gear oil, but never for more than a week, and I never drive hard on it. I use it to clean out the tranny, then I go back to 75W-90NS. It makes a noticeable difference in driveability.

 

After putting a new trans in as of New years, i put regular junk gear oil in it to break it in. (and was really pleased in the way it shifted to be honest) Then after breaking it in i put some Royal Purple in it, and honestly i'm not that pleased with it. Going to change the fluid in it soon while i fix my speedo gear leak, thinking a bout mixing a bottle of lucas oil stabalizer with a bottle of 5w20. Or going to back to some cheap mineral gear oil.
I'm slowing growing towards liking mineral oils a little better in my car, as before i swore by synthetics but i'm slowly going the other way.
Critizism and opinions appreciated. And i'd like to stay away from ATF, Idk.

 

I've been running Royal Purple for about a year now, both trans and diff.

Initally, I was quite pleased with it, as it shifted easily and it doesn't have the heavy odor that normal gear oil does - - can be an issue as your upper boot seals age.

Last couple of long drives, though, I'm starting to notice some difficulty in 1st-to-2nd shifting, and a bit more gear noise than I remember, especially in reverse.

I don't know if this is just accumulated wear starting to show, or if it's specifically lube-related; I'm going to swap back to a heavy gear oil (used Valvoline for decades), and see if it makes any difference.

 

I love Valvoline, never fails me.
And yeah, i have alot of trouble getting it into reverse.(but that's cause i'm running a 87-88 NT trans with 84-85 12A tailshaft, and a 94-95 Miata Shifter that i've modified to fit the trans which i think sorta contributes to the problem.)
I honestly don't think that should matter though, sometimes it goes in first try.
Otherwise, 1st-2nd up or down is rough sometimes, and i always have to be gentle throwing it into 3rd. I know it's not the condition of the trans, cause it's like new. Syncros and all.
I'm either switching to 80-90 Valvoline Mineral oil or Lucas OS and 5-20. Not sure yet,

 

Our transmissions have brass synchronizer rings and call for a GL-4 gear oil. A trans fluid rated GL-5 has more of the EP (Extreme Pressure) additives in it namely sulfur. Sulfur eats brass and is not 'yellow metal' compliant.

Pennzoil and Quaker State have GL4 and you can go to their sites and read about the yellow metal corrosion. They are hard to find in the store. Redline and Amsoil have a GL4 range because of this. http://www.redlineoil.com/product.aspx?pid=46&pcid=7
http://www.amsoil.com/storefront/mtg.aspx

Every oil I found at the auto parts store is a dual GL4/GL5 fluid. It is supposed to be okay for a GL-4 only brass synchro trans if it specifically says it's "MT-1" but I've read on numerous forums that people trying those later switched to Redline MT-90 or Amsoil and were much happier.

The idea behind a dual GL4/GL5 fluid is to stock less product.

I bought a gallon of Sta-Lube Multi Purpose Hypoid Gear Oil 85w90 GL-4 for $27 at my local NAPA. Non-synthetic. I've read that Rx-8 owners put Royal Purple in their MT Transmissions then they shifted poorly.

More info on GL-4 here: http://www.bobistheoilguy.com/forums...Number=1674043

I have a freshly rebuilt trans with new synchros in my REPU filled with the aforementioned Sta-Lube GL-4 and can't wait to try it out.

 

That makes A LOT of sense.


Thank You!!!

I'm going to go find some GL-4 fluid like you describe.

 

Update: Running 75% Standard Conventional Mineral 80W90 Valvoline GL-5/MT-1 Gear Oil; 25% 5W20 Standard Conventional Valvoline Mineral Oil. Both the cheapest Conventional White bottle Valvoline brand oil.


Shifts the best I've experienced.

 

Bringing this back.
I am having a really hard time finding some gear oil for my transmission that does not have sulfur in it. Looked at the link for Bob is the oil guy and saw a post about Supertech Synthetic Blend 75W90 GL-5. The bottle said prevents corrosion of brass or copper bushings, but the post was from '09. I will check walmart tomorrow to see if it still says that. Anybody on here run that stuff. I am thinking about running it in the transmission and rear diff, diff is not LSD.

 

I use lucas oil synthetic 75w90

 

I'm still trying different stuff even my latest post on this thread.
Royal Purple has given me a lot of headache. Saved up a little cash and put in some Idemitsu Racing Manual Transmission fluid. We'll see how it works.. Otherwise, I will conclude that either a ATF/Gear oil mix(buy the cheapest house brand of each), or the cheapest(like supertech) 80W-90 just like the FSM recommends is the best. I have horrible luck with anything expensive or full synthetic.
If anything I've posted doesn't make sense or contradicts another post, say something and I'll cleat things up. I'm pretty sure everything's been straight forward though.

-Crispin

 

^After months of driving it turned out to be mediocre. Went to Royal Purple 75W-90 and regret it..
Trying Idemitsu as already stated.

 

Funny to see I've posted this.

 

I put the supertech synthetic blend in the transmission and rear diff this evening, only 5.50 a quart. I'll post back and let everyone know the results after i put a couple hundred miles on it.

 

Kentetsu got me started on the 50/50 mix a long time ago. I've always been very pleased with it. Works wonders! Since i'll be making a lot more power soon i'll most likely be going to straight gear oil like hyper4mance2k and clean it every now and then with atf.