As mentioned, Napa has gl 4... stalube brand.

Correct me if I'm wrong... but synchromesh isnt gl4. Gl rating is a gear oil specification. Synchromesh isnt gear oil. Its a GM transmission product. If anything its closer to the atf family, if anything at all. Not saying its a bad product... want to put it in my mustang and all, just pretty sure its not gl4.

I stand corrected.

PENNZOIL« SYNCHROMESH MANUAL TRANSMISSION FLUID
Pennzoil« Synchromesh Fluid is a manual transmission fluid designed for certain manual transaxles and manual transmissions used by General Motors or Chrysler. Pennzoil« Synchromesh manual transmission fluid is formulated with high-quality paraffinic base stocks, a fluidity modifier, multifunctional performance additives, corrosion inhibitors, a foam suppressor and a shear stable viscosity index improver additive. It provides excellent oxidation stability, low-temperature performance, excellent synchronizer performance and compatibility with yellow metals, such as bronze, brass and copper components found in manual transaxles and transmissions. Synchromesh manual transmission fluid will satisfactorily lubricate General Motors or Chrysler manual transaxles and transmissions from -40 C to +150 C.

I do use it on both my KM145 and V5MT1

ATF works fine too.

Regarding the tsb on gl5 being corrosive. .. Long resolved. No gl5 is damaging to yellow metals anymore. They are all xl8 or something like that certified. Plus the old gl5 recipe from decades ago that was corrosive was only destructive above a certain temp that most transmissions rarely reach. Main problem with gl5 today is that its additive pack makes it, in simple terms, too slippery so it doesn't allow the synchros to mesh and so down, hence poor shift quality.

Regarding synchromesh and atf, they are fine for synchro slowing down. However, my only personal issue is that that atf is on par to a 5w20 oil viscosity and synchromesh only a tad higher. 75w85 gear oil is more on par between a strait 30 or 40 weight oil viscosity. Hence makes feel uncomfortable with the thin stuff. Not saying its bad, just there are no real facts or data to verify the true lube requirements for these trannys.

Off topic, phil... I have a tuff pan of yours, putting it on this week. I want to order a magnetic drain plug. Do you know the drain plug pitch and size off hand? Thanks

There's been guys here who have lunched transmissions because of this. There is NO WAY you could get me to put gl5 in my V5MT1... not now, not ever.

Its the stock size. M18 x 1.5

Not saying that you should use gl5. That stuff's add pack is mostly ment for diffs. I personally use gl4 synthetic only.

All I'm offering is facts. I know there are guys running atf and all kinds of other home brews. Not saying it doesn't work.... however all Im offering is technical data.

Thanks for that phl. Just didn't know what the stock size plug was either and didnt have time to go to a parts store and find out.

so I'm pretty sure the po filled up the transmission with gl5. i have ordered the mt-90 and will drain and refill but here is the thing. my transmission makes a squeal when i first drive in first and second gear. once it get warm its fine. do we thing new fluid might help? I'm pretty sure the transmission is on its way out but maybe i can get some more time out of it, we will see.

holy crap! druid out the old fluid and put in some redline mt-90 and wow! i noticed right away the first shirt that it flat 1 million times better. it used to be real hard to shift from 1st to 2nd but now it just slides into gear. the syncros feel a lot better it only grinds a small amount it third. its totally worth the $50 i paid for the fluid.

ps if you order some order it from jegs because it free shipping and amazon was cray expensive shipping.