VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Yellow metal in Tranny

There are plenty of posts about '40s and '50s Manual Tranny lub. However, let me ask the question in a different way; is there any yellow metal in these trannys?

Jake

I just spoke to a semi-retired tanny mechanic in his late 60s. In his long experience, manual trasmissions did not start using brass until synchro-rings. He had just rebuilt a '51 3 speed, which had no synchro. In these cases, he uses standard GL-5 rated 80 to 90 weight gear oil. In trannies that have syncho-rings, which he says are made out of brass, he uses Redline MT-90, which is specifically GL-4 rated to be yellow metal safe.

The compound in non-yellow metal safe oil is apparently sulfer, which is used as a detergent in modern oils. Sulfer somehow attacks yellow metals.

In my case, my '45 truck has a '54 235 engine and a 4 speed manual transmission. I don't know what the trany came out of. However, my research found a synchro ring on eBay for 4th gear of a '48 - '58 4 speed, and it's definitly brass.

Bottom line IMO; vintage trannies with synchro have brass in them & require a GL-4 rated gear oil. If you don't know if your tranny has synchro, Google synchro rings for it. If it doesn't, you can use GL-5 oils, which have detergents in them.

I agree that many years ago GL-5 oils were not good for "yellow" metals.

Today there are many GL-5 oils which are safe for brass synchronizer rings. You need to look at the application information for the specific brand and weight you are considering.

There are very few GL-4 only rated oils on the market today. Lots of oils are dual rated as GL-4/GL-5 or GL-5/MT-1. Those are intended for use in synchronized transmissions.

Hi Jake

I have always used GL-5 transmission oil in ALL of our transmissions including the ones with brass synchros in them.
Even the transmissions that called for SAE 50 engine oil have had GL-5 75W-90 in them since it was made available.
That's over 40 years of using GL-5's with no problems.

As Rusty said, there were problems many many years ago.
All big brand GL-5's have been buffered to prevent this for many many decades now.

It's a non issue that just seems to keep coming up.

Well, given the above 2 comment, I can definitly see how this can be considered a non-issue. As I said, in looking back thru the VCCA archives, I could find no diffinative answer about yellow metal safe tranny oils. I hope that when this question comes up for guys in my position, who don't even know if they have sychro-rings & are just learning about additives that attack yellow metals, they will find this thread more valuable than any other about vintage tranny oil questions.

Bottom line to lesser educated guys comming here for advice, as is lagely the point of this forum; for vintage trannies anyway, many modern detergent additives have been adapted to be yellow metal safe. Also, there are gear oils that are rated GL-4/GL-5. If all else fails, read the label.

Hopefully advice seakers will have learned you can Google a question like this, tag on "VCCA" and it will take them straight to the complete archive. If they tag on "Forum", it will take then to a whole bunch of forum archives. What an incredible resource!! This tip might be more important than the rest of this.

For those considering following the advice of a semi-retired tranny mechanic (probably kinda Old School), I went to the local Advance Auto Parts store to see if they had any GL-4 90 weight on the shelf. They did. I bought a gallon of Fram Extreme Pressure Gear Oil, SAE 90 for $24.50. That will replace what my mechanic said was gear oil that looked like "chocolate milk".

Jake, rust skills, rusty mind but trying.