VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 '51 transmission/rear end gear oil

This has probably been asked 100 times. I ran a search, but didn't find what I wanted.

It has been recommended to me change the transmission and rear end oil in the '51. Owner's manual says both use SAE90 multi purpose.

Working in a GM parts department, I have access to 80W-90 in both the GL-4 and GL-5 varieties. These are acceptable equivalents, yes? I saw an article online about not using GL-5 in the trans, but didn't read the whole thing. It was rather involved.

Comments, thoughts, suggestions, criticisms...

Thanks

I have used 85W-140 in all my cars in the last 40 years. Being multi-viscosity it covers all viscositys between those numbers.
The 85-140 in the transmission will be a little heaiver than 90 when the oil gets hot. This will reduce some of the usual Chevrolet clutch chatter when the gear oil gets hot. It more or less fills in the clearences in the transmission gears and splines. When these cars were new and owners caomplained about the chatter we we refill the transmission with straight 140 to reduce the problem as there were no multi viscosity gear oil back then.
At one time a gear oil containing sulfur was not supposed to be uesds in transmissions due to the sulfur attacking the brass bushings. The sulfur was used to prevent gear tooth wear in the differentials as it is an extreme pressure lubricant. With todays gear oils there are neutralizers added to prevent this from happening.
Other than that I would just use straight #90 if you prefer.

Gene gives good advice. The only thing I would want to comment on is my notion that the lights oil that will adequately do the job. That is because the lighter oil will do a better job of cooling the heat from friction. I'm probably wrong but just my way of thinking.

I use the 80w-90. Except on the project car I have followed Gene's advice and put in the heavier -140. If it fails I'm sending him the bill for repairs.

I wonder what Chipper has to say about this lighter oil notion of mine.

Charlie

I went to a heavy duty parts house last week asking for GL4 85W-140W and told him that the GL5 attacted the brass in the tranny. He said he had not heard of that, but called his Chevron supplyer and it was confirmed. But they do not have the GL4 and still looking for it it anyone has any ideas.

Chevron havoline gear oil 85-140 list on their site as meeting the requirements of GL-4 and GL-5. Rather than deal with a local supplier (unless a lubricant specialist) try the manufacturers websites. They have some very interesting information. Even though the products do list sulfur as an additive other additives perhaps neutralize its effects. I am not an engineer so have to rely on information from the mfg. which is USUALLY correct.