U-Joint Fitting?

i just put my axles back together and noticed that my spicer u-joints came with this small fitting that screws into one of the caps. what is this for? can i put a zirk fitting in it's place? and if i can, should i pump these u-joints full of grease?

 

That's for your Zerk to grease the U-joint. You can grab a fitting for your grease gun at a local auto parts store, or I've been able to use a regular Zerk on the end of my gun if you press into 'em hard enough. Sometimes I'll run the zerk backwards in the grease gun nozzle. Depends.

You'll need to run the low-profile concave fitting for clearance on the knuckle Cs. You can screw in a regular Zerk to lube 'em and then swap back to the low-profile one before you drive it is that's easier.

 

got it!