Just had my SM318 3-speed transmission rebuilt (synchros bad, possibly from using GL5). I would like to put in the correct gear oil.
The manual states, "Either SAE 90 Multi-Purpose gear lubricant or SAE Straight Mineral Oil may be used". I heard I should stay away from the synthetic and GL-5 gear oils. I also heard I should use GL-4 gear oil. I also read I could use the "Ford Tractor Transmission Fluid Mineral Gear Oil" which is SAE 90 API GL-1.
I was looking to go with the Ford Tractor Transmission Fluid Mineral Gear Oil, which states it is GL-1. I do not know what is currently in the rebuilt trans now and just don't trust it. Good thing the trans has a bottom drain plug for easy draining.
Should I stay away from the synthetics? Is GL-4 better than GL-1?
Any gear oil up to GL-4 can be used. Some GL-4 oils state right on the label that they're safe for manual transmissions. GL-5 oils have additives that mess with the brass components in synchros.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Phil Moderator, The Engine Shop, Interiors and Project Journals
1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes Project Journals Stovebolt Gallery Forum
My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear My truck ....... Respect The Rust If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.
If you don't want to buy a gallon (or two gallons), the SM318 takes a total of 1 quart, 1/2 pint in the u-joint ball area and the rest in the regular fill plug. I have found GL-4 in quarts Sta-Lube Brand and Triax Brand (pics.) I think I got both from Amazon.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
I have found GL-4 in quarts Sta-Lube Brand and Triax Brand (pics.) I think I got both from Amazon.
Thanks Kevin... Nice to know the fluid capacity! So I assume Full synthetic is OK to use in a transmission from 1960 that dates back to the 50's? I might still go with the gear oil from Tracker Supply since I have 2 other old trucks that need transmission service and the 2 gallons might come in handy...
You’re Welcome! Full Synthetic may be too slippery for the syncro's to operate correctly. I would stick with what GM recommended.
Phil Moderator, The Engine Shop, Interiors and Project Journals
1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes Project Journals Stovebolt Gallery Forum
