View Full Version : The correct lube for a Jeep synchronized transmission

01-11-2020, 07:21 AM
Be sure when you install lube in the transmission/transfer case, that it is for synchronized transmissions. No EP additives should be in it. They (EP additives) have a few bad effects on synchronizer's, especially brass ones. I cannot tell you how many times someone put standard 90wt or 140wt gear oil into a bronze synchronized transmission, only to complain that now it is miserable to shift. Once its in there for a while, it usually effects the synchro's for good.

First and foremost the common UN-spoken concept of the synchro, is not discussed in the "Lube" conversation. The synchro in the T90 is a brass cone clutch. As the shift collar is moved it engages the teeth on the synchro and the inside of the synchro (the cone) presses against the machined surface of the next gear, this pressure spins the next gear up to speed and the shift is "synchronized". Any EP additive impairs the pressure of the cone pressing against the gear to spin it up. This just screws up the shift.

Next is the incompatibility of EP additives and brass synchro's. Most EP additives are corrosive to brass. There is a You Tube Video out there that is not quite accurate so, be careful! There is however some pretty good stuff put out by the manufactures. As always, dropping a line to the Tech Department at your preferred supplier is the way to go if you want to be sure of what you are buying. If they can't answer your questions with fact, buy elsewhere.

The EP additive IS REQUIRED in the differential however!.

01-11-2020, 08:27 AM
Great tip Doc Dana. I'm sure you've seen what happens when the wrong lube is used in a differential.

04-27-2020, 05:20 PM
Would the wrong lube cause the tranny to scream in 3rd gear under load from 20 mph on up?

04-27-2020, 07:23 PM
No, that sounds like there might be some gear damage.