The Stovebolt Site Forums The Shop Area Driveline Recommended wt oil for rear and closed driveshaft?

Just wondering if the driveshaft (enclosed) and the rear diff share the sMe oil? Also what is a good recommended wt? I have some valvoline synthetic 75 90 and also some 70 140

What year truck? The recommended weight should be listed in the Shop Manual and/or the Operator's/Owner's Manual.

The driveshaft (enclosed) and the rear diff not share back-and-forth the same gear oil, but you usually use the same gear oil in both components.

In an enclosed drive-shaft truck, the transmission oil is "shared" back-and-forth with the gear oil around the enclosed u-joint. However, there is a seal at the u-joint end of the enclosed drive-shaft (torque tube). The torque-tube shares gear oil with the rear end.

Either weight gear oil should be OK. I usually use a 90 wt gear oil in my 1954 trucks rear ends and in SM42 4-speed transmissions (all years).

I use 80-90 Vavoline gear oil in my beast with has a similar drive train.

Don't forget to add a pint of the same gear oil where the u-joint is located!

If the truck has a Hydra-Matic transmission, NO
If the truck has a manual transmission, NO
There is a oil seal at the tranny end of the (enclosed) driveshaft that keeps the tranny gear lube out of the rear axle.
You could say, the tranny gear lube, lubes one end of the (enclosed) driveshaft and the rear axle gear lube, lubes the other end of the (enclosed) driveshaft. Illustration (scroll down) Truck & Passenger car virtually use same(enclosed) driveshaft.
If the truck has manual tranny, the gear lube weight is the same that is in the rear axle.
They just don't share it.90 weight is what is normally used. check manual