2000 Cherokee Sport. Front left wheel locks up when I hit the brakes hard and fast. Some say it could be the proportioning valve. Caliper and brake hose is new. Pads look great. Brake disc is fine. Can't find a replacement proportioning valve and where is it located on the vehicle? Please help. Been going on for months and nobody so far seems to be able to correct it. Thanks

 

It's not the prop valve.

Is it possible the other front brake is doing nothing?

 

What means "fine"?

If it's warped that'll definitely lock it up.

Also check for notches in the knuckle where the pads ride.

 

I would inspect the cast arm upon which the caliper slides, and I bet you will find a big groove

This is a common problem with XJ and there are many pics and posts if you search the archives

The brake pad jams and cannot easily retract

It is possible there is some other cause, as typically the brake will stay "jammed", and will get smoking hot

If this is the case, the fix is remove the caliper, heat the casting somewhat, clean up the groove and mig weld it, smooth it out with a grinder

 

I recently replaced the front brakes on my xj. Did you only replace one caliper or both calipers? If you only replaced one there is a chance the other may be weaker and will allow the wheel to spin longer while the new one locks. Or maybe one of the lines to the other one is leaking? I'm just throwing ideas out there. I'm not skilled with brakes

 

Thanks for the feedback guys.
The disc is "fine" since I swopped left and right sides and problem stayed on the left.
The brake does not stay jammed and releases immediately.
I thought the other side might be not braking enough and found the slider pins to be needing clean and lube. But after doing that, no improvement

 

Are you telling me the slider arm the caliper rides on is totally smooth and not grooved?...never seen that on an XJ before

The arm takes the full force of the caliper slamming into it every time you brake, it wears down the metal. special tabs can be fitted to minimise this, but i never seen em

I have had to fix this on all 3 of my XJs

Only a photo will convince me

The proportioning valve can be taken apart, cleaned and put back together, could be the problem, FSM shows, you would need to bleed and reset

Could also be a faulty caliper, piston or seal

 

Thanks awg,

The caliper is new. But I'd love to look at the prop valve. Can you tell me where it is located? And how to go about a rebuild of clean or whatever it might take to take that factor out of the equation.
Thanks man.

Dean

 

Prop valve doesn't control left to right front braking. It proportions front to rear only.

If you must fart around with it, it's on the firewall with the lines from the brake master cylinder going to it.

 

52128420AA



200 bucks assuming you can find one.

 

Yes, it is my understanding that the prop valve only regulates front to back breaking and not left to right.
How would I go about checking of even cleaning/rebuilding the valve if I think it may be the issue?

 

Why would you think the prop valve is an issue based on the info shared with you so far?

The prop valve was never intended to be serviced. Just replaced. I am recommending you leave it alone.

 

If it's any consolation, the front left on my '98 usually locks up first, and I've fixed the grooves and replaced rotors, pads, calipers, and lines. It's no surprise the front locks up before the rear, but why the left tends to lock first, I don't know. It's not egregious, but it is fairly consistent. Otherwise, the brakes work great.

 

OK Guys,

I believe what you're saying. It's just that it's been an irritating issue for so long and have spent a considerable amount of time and money trying to get a diagnosis with zero results.
Most of the time the brakes work fine so I'll just live with it, for now anyway. Thanks for all your feedback, guys.

 

It's not clear if you fully investigated the steering knuckle for divots. Do they look like this (from the awgmobile):