That was an incredibly informative read. I read all of it, and while I don't exactly have the time to fact check everything the author, Richard Widman, says he sure seems to take a non-biased fact finding approach to his write up. And sure enough, my '73 manual calls for GL-4 in the trans and GL-5 in the diff. I'm not sure how it will affect the whirr I'm hearing, but it's definitely worth a try. Saving the day again, LeonV. Much appreciated. I'll let you know how it goes.

Hey, LeonV, the label on that GL-5 Wally-World stuff says, "Protects against rust, foam, high temperature and corrosion of copper or bronze bushings." In fact, all of their gear oil branded Supertech are GL-5 and have those words on the back.

Anyway, GL-4 is, as noted in another forum, "as rare as hen teeth." Not sure how I'm gonna get my hands on this crap.

And I'm also doubtful it would stop that whirring sound. But that would be most excellent if it did.

Edited March 16, 201312 yr by DoctorMuffn
"In fact... on the back."

I picked up three quarts of Pennzoil Synchromesh Manual Transmission Fluid (yellow bottle, black top).

On the front it reads: For use in manual transaxles and transmissions requiring GM Part No. 12345349 or 12345577 and Chrysler Part No. 4874464. Meets GM Specification on 9985648 and Chrysler Specification MS9224.

On the back it reads: Pennzoil Synchromesh Fluid is a synchromesh transmission fluid designed for certain manual transaxles and manual transmissions used by General Motors and Chrysler. It provides excellent oxidation stability, low temperature performance, synchronizer performance and is compatible with yellow metals, such as bronze, brass, and copper components found in manual trasaxles and transmissions.

There's no API GL rating. But it's the only gear oil that specifically mentions transmissions and synchronizers that I could find at Autozone.

What do you think?

Hey, LeonV, the label on that GL-5 Wally-World stuff says, "Protects against rust, foam, high temperature and corrosion of copper or bronze bushings." In fact, all of their gear oil branded Supertech are GL-5 and have those words on the back.

Anyway, GL-4 is, as noted in another forum, "as rare as hen teeth." Not sure how I'm gonna get my hands on this crap.

And I'm also doubtful it would stop that whirring sound. But that would be most excellent if it did.

I thought you read that article I posted? If it's a GL-5, it WILL damage your syncros over time.

Whoever said GL-4 is rare is ignorant and misinformed. API GL-4 is not "rare". I use Redline MT-90.

I picked up three quarts of Pennzoil Synchromesh Manual Transmission Fluid (yellow bottle, black top).

On the front it reads: For use in manual transaxles and transmissions requiring GM Part No. 12345349 or 12345577 and Chrysler Part No. 4874464. Meets GM Specification on 9985648 and Chrysler Specification MS9224.

On the back it reads: Pennzoil Synchromesh Fluid is a synchromesh transmission fluid designed for certain manual transaxles and manual transmissions used by General Motors and Chrysler. It provides excellent oxidation stability, low temperature performance, synchronizer performance and is compatible with yellow metals, such as bronze, brass, and copper components found in manual trasaxles and transmissions.

There's no API GL rating. But it's the only gear oil that specifically mentions transmissions and synchronizers that I could find at Autozone.

What do you think?

Buy a GL-4 gear oil. It's not at all difficult to find.

Gotcha'. I guess I was looking for it elsewhere; I didn't want to pay a premium for a name. I'll order some. Thanks.

Gotcha'. I guess I was looking for it elsewhere; I didn't want to pay a premium for a name. I'll order some. Thanks.

You're in Socal, I'm sure you have a speed shop near by that stocks it. I get mine from a local shop (Gotelli's in SSF for anyone on the SF Peninsula). Tranny shifts great...

Great idea. Thanks again, LeonV.