Calipers Not Letting Go
 

Driving the ‘91 XJ Sport 4.0 home today I realized my front brakes were staying on. By the time I got home they were smoking. Both front calipers arren’t letting go. Indicative of a master cylinder problem?

Thanks!

Or it could be the ever so common grooves worn in the knuckle where the calipers slide not allowing them to slide away from the rotor. A fix for that is to fill with weld and grind flush. Mine also needed a couple applications of sil glyde after because they were still sticking a bit. So maybe the surfaces just need a good cleaning and lube. Also I have heard of an issue where the rubber lines will not allow the pressure to fully release because the inner layer is degrading and acting like a check valve.

As Waynard said, but the fact that they both started at the same time does seem to point to the master cylinder.

Other possible causes are the calipers themselves, or the flexible hoses. The inner lining can collapse and act like a one-way valve.

lift the front end up , pump up the brake so the front tires are hard to turn or spin so the brakes are staying on then open a bleeder screw on let out some brake fluid and see if both front wheels spin free .If it does then I think you have a bad master cylinder .

Whelp, since I hadn’t really even looked at the brakes since I bought this about 1.5 years ago, I picked up new calipers, rotors, pads, SS braided brake lines and a master cylinder. Installed all but the master cylinder and things seem much better. I place fault in the brake lines. I was mistaken about both of them locking up. Rotor wear indicates the driver side was locking up, but the passenger side wasn’t actually engaging fully. Still in the test-drive mode, but this thing rolls much better than before. I’ve been getting poor gas mileage prior to this and I bet this is why. Time will tell.

thanks all!

Sticky calipers are a common problem on XJs. Lucky for us brake part,s even name brand brake parts are dirt cheap so if the calipers are sticking just replace them. you can get loaded calipers with pads and hardwarefor 50 or so dollars less if you turn in your cores.