The Stovebolt Site Forums The Shop Area Driveline Gear Oil for '57 3 speed overdrive

I've attempted to look online for an answer to what gear oil to put in my '57 3 speed overdrive (borg warner). I've read that certain types can damage parts inside the transmission, however I've found direct contradiction as to what type of gear oil will be safe.

Could I get a definitive answer as to what type and weight gear oil to run in the transmission section and in the overdrive section of this transmission? Thanks.

My experience with both the older 3 speed and 4 speed transmissions whether Muncie or Borg Warner dictate that the use of straight SAE 90 weight gear oil is required for these transmissions to operate correctly. The straight 90 weight mineral based gear oil has the proper amount ash content in the lubricant for the synchronizers to engage without slipping. Most of the modern day gear oils are too slick which will cause synchronizers to slip in these older transmission causing gear clash and the need to double clutch the transmission in order for the synchronizers to engage. Slipping synchronizers create excessive wear to both the synchronizers and drive gears. I was able to purchase straight SAE 90 weight gear oil at NAPA or most farm supply stores.

Some of our members don't agree with this analysis, but the Chevrolet/GMC shop manuals state the use of this gear oil. GM engineers must have had a reason to specify this gear lubricant.

Hope this helps.

Tim

As Tim states, there are different opinions on the issue. Since I just finished the rebuild on my R10, I asked this question to my friend (whom I trust completely) about it.

He said, as Tim states, that GM recommends SAE 90. He said that's fine for non-synchronized transmissions. BUT for synchronized transmissions, people may be recommending something else.

Since mine is non-synchro, I'll be using SAE 80-90.

Thank you for the responses. Just to make sure I'm on the right page, when you say non-synchro trans, you mean just 1st gear being on synchro, like the pre 57s, right?

Also, is all 90w the same, or are there particular types of 90w with different ingredients I should be aware of?

Thanks,
Brandon

Non syncro transmissions are much earlier, that unit is considered to be a syncromesh in spite of first gear being non syncro.
The current GO 80/90 is GL5. I believe that a GL4 or lower meets the earlier specifications. This is a subject of much discussion with many opinions as to what to use. Many use the GL5 without any problems.
Fred