98 5.5 short arm lift . 35" tires. Just noticed that front brake discs are always very hot whether I've been on the brakes or not. Wheels turn fine elevated so binding isn't the issue. The bigger issue is a new rotational noise. Seems to be from the left front. I've put in new front driveshaft u joint and a new LF hub/bearing assembly. Drove around with no front drive shaft and noise is still there so it's not a u joint . Axle ujoints seem ok though I've not removed them for inspection. Noise is still there. Just had the gearing changed from 4:10 to 4:88 front and rear. Could it be the pinion bearing ? Should I put it on a lift with wheels running to find the noise ? Please and thank you.

 

XJ's can come with Caliper pistons that are Plastic and Metal, the plastic ones are cheaper but typically with age swell and hang up with the brakes get warm, my daughters did this and ended up getting hot enough to ruin the hub bearings..... this could be your issue.

 

A brake line going bad will do this also (collapse) till it opens back up some mostly on rubber lines.