Brakes Seized?

I have 2 late models with the same problem.

1st: My '98 trail rig
Calipers seized on a trail. I installed loaded calipers. All was good for about 5 miles. Now they're semi seized. (When moving I hear the calipers clunking as 4lo and 4.88s overpower them) When the pedal is depressed, the vehicle stops regularly.

2nd: My '00 DD
Got some serious grinding when braking one day. Tore it down and replaced pads and rotors. I did one at a time. DS first, bled it, then did the PS. When depressing the caliper piston I used a C clamp and cracked open the valve before applying pressure. These are seized BAD. I just spin the rear tires in my dirt driveway when trying to move.

Could I really have blown 2 master cylinders at the same time? Am I doing something wrong? I question my already quasi mechanical abilities! I'll search as well, but does anyone have a quick link to bench bleeding? Never tried it.

Thanks in advance everyone.

A blown master cyl won't seize the calipers. Make sure that they slide back and forth when the pad is pushed off the rotor. Occasionally, a brake hose will develop a "flap" inside which traps the fluid pressure in the caliper.

1. Does anybody really, really, REALLY dislike you? Contaminated brake fluid could account for your symptoms.

2. You buy really, really, REALLY cheap-a** parts?

3. The parts are from Autozone?

4. Coincidence--the source of the problem is different on each vehicle.

winterbeater said:

A blown master cyl won't seize the calipers. Make sure that they slide back and forth when the pad is pushed off the rotor. Occasionally, a brake hose will develop a "flap" inside which traps the fluid pressure in the caliper.

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There's a new "flap" in both hoses? It would seem far fetched... Also, If the master cylinder applies hydraulic pressure to my calipers, wouldn't it also release the hydraulic pressure? What if it's not releasing the pressure? ie something acting as a check valve similar to your flap idea.

joe_peters said:

1. Does anybody really, really, REALLY dislike you? Contaminated brake fluid could account for your symptoms.

2. You buy really, really, REALLY cheap-a** parts?

3. The parts are from Autozone?

4. Coincidence--the source of the problem is different on each vehicle.

Click to expand...

Both vehicles were purchased used from different folks. The DD was owned by a really anal guy that threw money at it. The wheeler, well not so much. I did install SS lines on it years ago. All stock parts I purchased were at Schucks/O'Reilly's. These problems didn't develop at the same time recently, they were in the wheeler last year, but it's "minor" so I keep it in the back of my mind. The DD I obviously can't ignore as it's far worse.

Next time the brakes act up, loosen the master cylinder from the brake booster slightly and see if the problem goes away. This would indicate a pushrod set too long, not allowing the master cylinder's piston to retract far enough to open the compensating port.

Next time have someone else fix the brakes instead :laugh:

Check the sliders on the knuckles that the calipers slide on, My sister's '92 had a notch worn into them that kept the calipers from returning to the correct position. Sadly my '98 has started to do the same thing.

You can fix the notches pretty easily with a little welder and grinder time. Clean any junk out of the notch, throw some weld on it, grind smooth... xjtrailrider did a writeup with some really great pictures, wish I wasn't so lazy or I would find and link it.

Seconding the flap on the hose lining idea also - this happened to one of the employees at my local autozone, he had already replaced both calipers and was complaining that it still stuck, I told him to swap new hoses in and call it a day, now it works great. It's more common than you would think.

Appreciate the help gents. I'll take a better look at things tomorrow. I am confident that the knuckles are good. Didn't see any wear when I was replacing parts. Thanks again.

On you DD make sure that you got the correct rotors. If somehow the parts store gave you the wrong ones from an early model jeep the rotor hat heights are different. I ran into this on a buddys YJ a few years ago. Someone installed a newer setup (hub,rotor,caliper) on one side only before he got it and when we did brakes and rotors we discovered it.

As for your trail rig its possible that the piston in the master is sticking. If I recall correctly some masters use to seperate pistons that are not physically conected to each other but only press against each other when you apply pedal pressure to them. There are springs that make them return to the neutral position that may have broken or the rubber cup seal is dragging and not allowing the piston to return and bleed the pressure off.

wheeling365 said:

As for your trail rig its possible that the piston in the master is sticking. If I recall correctly some masters use to seperate pistons that are not physically conected to each other but only press against each other when you apply pedal pressure to them. There are springs that make them return to the neutral position that may have broken or the rubber cup seal is dragging and not allowing the piston to return and bleed the pressure off.

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Yep, all XJs/MJs/most modern vehicles use this setup. It's the primary/secondary setup that leaves you with some braking ability even if your rear or front brakes go out, there are two pistons in a row and they are separated by springs. When one circuit gets leaky, the spring for that piston collapses all the way and all the force is sent to the other piston+circuit.

For the DD, if I'm reading this right that it won't go at all after doing the brakes, I second checking that the rotors are right. If you could retract the pistons on the caliper, then it's not seized. A flap in the hose will cause drag but you'd be able to get out of your own driveway. Similarly, though you can get hangups and problems from worn knuckles, it's not likely to lock you solid, because all of these things are not likely to occur simultaneously on both sides.

Rotors in this age group are confusing. XJ's switched from cast to composite and then back again some time around 99, and getting the right ones can be a challenge.

For the trail rig, I'd look at hoses and master cylinder first. Hoses aren't that big an expense, so I'd get a new pair, and then flush the whole thing clean. Check those knuckles again. Look for pits and chunks in the ledges that the pads rest on. If the problem persists after that, then I'd suspect the master cylinder.