When I had my rear suspension out I greased it really good.
I took the ring off holding the boot on and cleaned it all out really good. The grease still looked ok but there wasnt a whole lot in there. I pumped it full till the boot was plump and put the ring back on the boot. Should be fine for a good while.
Also did this to my tie rod ends but I just couldnt get it to work with the upper balljoints on the a-arms. The boot was really tight and I was worried it would rip. Ive got a spare stock a-arm so if one gets some play in it Ill swap it out. I was able to clean the spare a-arms boot out since it was off the Jeep so it would be good to go for along time if I did need to use it. Only reason those balljoints fail is b/c of the lack of grease..

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LOST KJ'S
Where are you going???
Current Jeep: 2004 Jeep Liberty
-Atlantic Blue
-Air Ride Rear Suspension ; OME/Rustys Lift ; Powertrax Locker ; Moog Lower Ball-Joints ; 245/70/16 Yokohama Geolander A/T-S's on MOABS ; Flowmaster 50 SUV
Lost #007082
http://www.cardomain.com/id/jeepjeepster