View Full Version : GM Syncromesh vs. MT-90 vs. regular 80-90

04-01-2011, 02:00 PM
In the 60 I ran regular 80-90 in the h55f tranny for a long time. Then I switched to MT-90 to improve the shifting... it helped marginally, but it wasn't worth the added cost of the crap especially since I change the oil often. I went back to regular dynoshlog.

Well, I just rebuilt the tranny, or rather took it all apart and threw in new 3rd and 4th gear syncros. I am wondering about the GM syncromesh oil. My brother threw it in his honda and says it absolutely made it shift better.

has anybody tried it? any feedback? I am kinda half tempted to throw it in the tranny right from the start.

04-01-2011, 03:56 PM
Eons ago, in an '82 Datsun Maxima, I ran a pint of ATF along with the 80w-90 in the manual transmission. This helped the shifting nicely.

In my '98 4runner (MT), I run 80w-90, with about 1/2 quart of synthetic with the other 3 quarts of dino-80w-90. I didn't like the way it shifted when filled with full synthetic. I'm happy with the way it shifts now.

So, there are other 'roll your own' options for those who would otherwise run 80w-90.

04-01-2011, 05:21 PM
Yeah I noticed that quite a few folks make their own homebrew fluids. interesting...

Thanks for the feedback.

Dave, you're right, I need to just throw regular 80 90 in there for break in anyways, we'll see how it does..

04-01-2011, 07:52 PM
I don't think it'll hurt anything to try different fluids. My old '84 Mazda had either 80/90 gear oil or ATF spec'd for the 5 speed manual tranny depending on the operating temp. There was a huge overlap for the two temp ranges. I had been running the 80/90 gear oil and decided to try switching to ATF. After the switch, the downshift into second gear was much worse and would grind a bit. I ended the experiment and switched back to 80/90 and the operation of the 2nd gear syncro definitely improved. Try an assortment of lower cost oils to see what works best.