I was working under my JK today, and I noticed some grease on one of the u-joint caps on the pinion end of the front driveshaft (Coast 1310 with Spicer u-joints).

I confirmed that the u-bolt nuts are torqued correctly to 17 ft lbs. The pinion angle is a few degrees from zero to keep the caster in check, but the shaft runs smoothly with no vibrations. The shaft has about 3,000 miles on it and has been wheeled twice with no issues.

Any idea what would cause this? Is the grease a sign that the u-joint is failing?

 

That's normal. The grease works its way out, and when u grease the joints u want some of the old grease to come out so u have new grease in the u joint. Then just wipe it off.
If u take a screwdriver or small prybar into the joint and pry slightly and u have play then the joint is bad.

 

Is that also true for sealed u-joints like the ones that come with the Coast shafts?

 

Sealed are different. If a sealed joint is failing u will almost always see rust where the little dust boots are or they will be cracked. At least that's what I've seen.

 

do yourself a favor and run these

Spicer 5-1310-1X

cold forged / serviceable

 

Thanks for the recommendation. I actually have some spare 5-1310X u-joints on hand. I think that's the sealed version of the one you mentioned.

 

ur welcome, i run the -1X. hitting 'em with grease once in a while is a bonus