Topic: Update transmission oil from 80/90 to 140 weight


ThomasT    -- 01-10-2022 @ 11:19 AM
  Purchased a 1951 ford custom with a 3 speed manual trans equipped with a Borg Warner overdrive a couple of months ago and I am considering changing out the trans / overdrive oil from 80/90 to 140 weight as I am trying to slow down oil leakage. Any cons? The car was restored around 2004 and as far as I can tell it sat around for a while. Its in good shape and the trans functions well with no problems. Just leaks a bit more than I am comfortable with. Currently has Brad Penn Multi-Purpose GL-4 SAE 80W/90 gear oil in it now. I live in Florida so all of the driving will be done in warm weather. Looking for some assurance that I am not about to shoot myself in the foot. Regards, TomT.


carcrazy    -- 01-10-2022 @ 1:57 PM
  Be sure to use only a GL-1 Gear Oil in the transmission and overdrive unit mounted to the rear of it. The two units share their oil but they are filled through two different filling holes. One source for the correct oil is NAPA . The correct oil is NAPA SAE 90W API GL-1 Mineral Gear Oil part #65-201. It comes in a 1 gallon container. Another source for GL-1 oil is Fifth Avenue Antique Auto Parts.

Do not use any hypoid axle lubricants in the transmission or overdrive unit as they contain Sulphur additives which can harm the brass or copper components in the overdrive.

Also do not use any synthetic oils in the unit as it can prevent the one way clutch from operating properly.


ThomasT    -- 01-10-2022 @ 3:30 PM
  What are your thoughts about using 140 weight oil?

This message was edited by ThomasT on 1-10-22 @ 3:32 PM


carcrazy    -- 01-10-2022 @ 3:50 PM
  If you can find a GL-1 oil with SAE 140 viscosity, it would probably be OK to use it. I would rather find the source of the leak and repair it properly. If the transmission is just leaking past the rear seal to the driveshaft, that seal can be replaced with the transmission in the vehicle. You just have to remove the driveshaft from the rear of the transmission, install the new seal and reinstall the driveshaft. This is a fairly easy job that will either cure or greatly reduce your leak.


ThomasT    -- 01-10-2022 @ 4:49 PM
  Yep I agree about getting it fixed. That probably wont happen until the summer. I did hunker around and the driveshaft seal is good. Looks like it might be coming out between the transmission and the overdrive. To be honest I am having some difficulty pinpointing the exact spot of where it is leaking. Kind of thinking of going to 140 in the mean time. If there is a risk that it will cause a problem I will hold off.


TomO    -- 01-11-2022 @ 9:22 AM
  Ford recommended mild EP oil SAE 90 ( mild EP oil is rated GL4) in warm weather and i would stick with their recommendations.

I doubt going to a SAE 140 gear oil would slow down the leak much. My trans was leaking from the shift levers and I tried putting in a heavier oil without success.

Did you make sure that the transmission is not over filled? The procedure to fill it is to drain both the transmission and over drive and then fill the transmission with 4.5 pints of gear oil through the transmission fill port.

Try cleaning all of the oil from the outside of the transmission case and then taking the car for a drive around the block. Then examine the case for signs of a leak.

Good luck.

Tom


ThomasT    -- 01-11-2022 @ 10:21 AM
  I was a bit apprehensive about going to 140 weight. I had seen a few posts making that recommendation, but all the books I have for the car state 90 weight oil so I guess I will stay with 90 weight. I did check the fill in the tranny when I got it home as I did notice it was leaking. It was about 3/4" down from the fill so being overfilled most likely is not a problem. I did add a few ounces to bring it up to the bottom of the fill so I should be good for a while. I appreciate your advise. Regards,


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