I just read a recommendation by the national T-Bird club's authenticity expert re: lube for standard transmissions. He claims additives in the modern/generally available API service GL-5 80/90 have the potential to corrode the brass syncros, and you should use GL-1 instead. Where would you go to buy GL-1, and wouldn't the other service improvements of modern GL-5 lube likely more than make up for any possible brass corrosion? (though I must admit, when my transmission had to be rebuilt, it was because the syncros had failed!)
Can anyone shed light on this issue?
P.S. He is also still recommending Rotella diesel oil for it's ZDDP content, which Ted claims may corrode your cam.

6 VOLTS/POS. GRD. NW INDIANA

What the T-bird guy said is true. Basically, any oil recommended for differentials contains additives that will corrode yellow metal (synchronizers) in our antique transmissions. This includes any oil recommended for both diffs and transmissions. Modern manual transmissions don't have brass sychros and often share lubrication with the final drive on front wheel drive cars. The final drive requires the hypoid additives. NAPA has access to GL-1, may need to order it. Tractor Supply also has it.

I will defer to Ted on the Rotella. I will say I share his concerns.

It figures, I recently bought 3 gals. of GL-5.  Tossed the receipt, so guess I now have a lifetime supply of differential lube.

6 VOLTS/POS. GRD. NW INDIANA

We've never used GL-1 at the shop, in at least the last 17 years.  GL-5 or the most current spec of the time has been used in everything from brand new to vintage '70s, 60's, 50's and older shaft drive motorcycles.  Never had an issue related to it.

Not saying the claim is wrong.  Not saying you won't have a problem.  I'm just saying I have not observed that problem in practice.  Maybe it is because older stuff just isn't used regularly enough for it to be a realistic issue. Maybe more recent formulations do protect older stuff and the claim is outdated.  I don't know the reason, but I haven't seen it.

Regarding Rotella, since Ted has studied the subject more in-depth than anyone who I actually know, and there are plenty of adequate gasoline engine oil options out there,  I won't use it in any gasoline engine of mine.





Lawrenceville, GA

"Not saying the claim is wrong.  Not saying you won't have a problem.  I'm just saying I have not observed that problem in practice.  Maybe it is because older stuff just isn't used regularly enough for it to be a realistic issue. Maybe more recent formulations do protect older stuff and the claim is outdated.  I don't know the reason, but I haven't seen it."

Amount of use and heat are factors. A rarely driven vehicle may not experience a problem. But most of our cars have passed through many hands before they came to live with us, so there's no telling what's in the trans and diff or how long it's been in there. When I get a new old ride I drain and refill both with the recommended oil for the sense of security. Fool's paradise? Maybe.

I heard the same thing. I decided to stick to GL-1 rated oil just to be safe. NAPA has the GL-1 in there private label brand. Wasn't overly expensive either.

Durham Missouri

I asked a similar question a while back when I filled up my newly rebuilt Ford Toploader 4 speed. GL4 was the recommendation. Don't recall GL1 coming up. I finally found a 2 gallon jug on Ebay or Amazon for what I thought was a fair price. Everything I could find locally was GL4/5. Not what you want. I went with GL4. That would be my recommendation. My local good friend/retired mechanic concurred that GL5 can cause problems. You may be able to find the old thread if you look for it.  

I found GL-1 at my Tractor Supply and the brand is
Traveller
All mineral SAE 90
Ford Tractor
Transmission Fluid  and it has API Service GL-1 on it as well.

I run it in my T85 overdrive transmissions and my 1972 ford granny 4-speed and their doing just fine.


-Gary Burnette-

I normally use a GL4 after seeing many post about the additives in GL5. When I put the T85 in my Ranchero I used a Royal Purple lube that claimed it's safe for the soft metals, it's pricey but how often do you change it, I'll probably never change it again in my life time LOL.. It's been in there 3 years and no problems. 

GL4 would be the go. I use the Penrite one in my early "39" toploader. You U.S. guys are lucky you will have choices, here its Penrite or nothing else as its all GL5 + now.



"Came too close to dying to stop living now!"