1959 3100 4 speed gear lube weight
 

Hi, I have a 1959 with a 4 speed manual. I think its an sm420. Iam going on a 5 hour trip and wanted to change the gear lube before I leave. I drained it out. All I need to know is the type of lube and quantity. thank you

Re: 1959 3100 4 speed gear lube weight
 

75w90
should take 5.5 quarts if completely empty

Re: 1959 3100 4 speed gear lube weight
 

Can pick it up fairly cheap at a semi repair shop. I get all my transmission and gear oil at truck shops.

Re: 1959 3100 4 speed gear lube weight
 

85/90 isn't that spendy at the parts house. It takes 6-1/2 pints to fill that trans .

Re: 1959 3100 4 speed gear lube weight
 

Like many old transmissions, there is no input shaft seal some Muncie SM420 four speeds. The design relies on an oil slinger and LH "thread" on the input shaft to direct oil coming through the input shaft bearing onto the inside of the rear of the bearing retainer. From there oil is expected to drain back into the transmission case through a roughly 5/16" hole below the input shaft bearing. Switching to lighter base gear oil can create a fluid leak where none existed previously. Oil can work its way down the bearing retainer then end up on the flywheel and clutch disc creating a slippery mess and a truck with a slipping clutch. Having tried several different gear oils, multi-viscosity and single viscosity, I settled on 140 wt gear oil in the '57 and in my '36 Plymouth.