Zerk Basics...

Zerk fittings are supposed to only allow grease to move one way? You squeeze grease in through it but it isn't supposed to let grease out? I realized I have two that are oozing grease but at this late hour I couldn't tell you anything more than "up front" - I guess I should replace those and whatever they are supposed to grease since they are likely letting contaminants in, right?? Or am I making too much of it right now?

It would be a good idea to replace them, though I doubt it's "do-it-today" urgent. The zerk has a little ball with a spring behind it, which acts as a one-way valve. when they rust they don't seat very well, and if the grease is under pressure it will ooze. It still won't let much junk in though. I wouldn't worry about the joints themselves unless they show wear.

Every once in a while one of mine will 'stick' open, I pull it out, clean it in some thinner and put it back, sometimes it works, sometimes it doesn't. biggest problem I have is getting one of the correct size, tried a couple that looked exactly the same size and thread, they went in but would not tighten up, just kept spinning, wtf, threads are not damaged, old bad one goes in fine, go figure.
Wish they had a size/type rating of some kind like 'zerk-1', 'zerk-2', etc so you don't have to guess 'metric or sae', 'what size thread' instead of 'looks pretty close but so do these other two so try all three'... to make matters worse they are not all the same either, my ball joint ones are different than the steering ones....

Zerks come in both SAE and metric sizes, the best way is to a thread gage and measure exactly what came out. The metric ones look exactly like the SAE ones. If a zerk just spins in the hole it is stripped but zerks can also be purchased that are pounded into the hole with a small rubber hammer.

Yes, there is a spring-loaded ball in there to act as a one-way check valve. Rich is correct -- they come with the base threads in both SAE and metric sizes, so you have to be careful when replacing them to get the correct thread. Not sure, but I think all the XJ zerks are metric (and, of course, I have a large stock of SAE zerks left over from my days playing with American iron).

I kind of figured there was a spring behind the ball, thanks for confirming that. I'm also glad it's not "do it today" stuff because that's just not going to get done Will keep an eye out for SAE/Metrics...thanks y'all.

Many times when they screw up, it´s from pumping grease into a dirty zirk. Sand sticks in the grease left on the Zirk and when you pump some new grease in there, you can force some sand in. Sometimes it´s just rust or a bad spring.
If the zirk is on something that rotates, when the grease heats, it will sling it out of there pretty fast.
Remember to wipe off your zirk before and after greasing.