drauch

After driving for 15-20 minutes (home from work) I have noticed that both front wheels seem to start locking up on my 92 cherokee laredo. There is a lot of resistance to rolling and the outside surface of the wheels get HOT. After the car sits and everything cools down, the wheels go back to rolling free. I just recently replaced axle u joints, wheel bearings, brake lines, master cylinder, pads, rotors, tie rod ends, etc on my jeep. I have driven it for about a month since the work with no problem, it is just now having this issue.

Does anyone have thoughts on what could be causing this? I plan on tearing in to this over the weekend and would appreciate any help on things to look for.

Here are my thoughts/suspicions:
1) could be air in the brake lines somewhere. I have already re-bled the system to no avail, but i'll try it again.
2) the front axle seals have been leaking, so the differential might be seizing up when it heats up. I plan on replacing the seals this weekend.
3) the bearing hub nut might have been over tightened, causing the bearing to seize when hot.

Again, these are my suspicions. I would appreciate any advice or pointers anyone has to give. thanks

BatmanXJ

Humm both wheels at the same time. Heat. sounds like an issue in braking system to me.

Some possibilities

Rotors are too deep. Lug nuts tightens the rotor against the backing plate which could lock up the wheels. You could have the wrong part number on the rotors.

Front brake lines.
If they are original, they could have collapsed internally and are not allowing the calipers to release. Easy way to check if it’s the flex hose holding pressure. Just open the bleeder a bit, if it lets off the pressure and frees up the brakes you know that's the problem. Not as likely since you just replaced.

Calipers
The piston seal in the caliper is a square cut o-ring. It causes the inner edge to be slightly angled toward the cyl wall instead of being 90 degrees to it. Now the seal is acting like a one way valve, it freely moves out under pressure, but will not relax due to the increased drag on the inner seal edge. Normally happens when changing brakes when you are pushing the piston in to install the new brakes.


As far as it working better after it sits for a while could be any of the above. to me

Rotors- Heat up and expand- sitting lets them cool down back to have enough clearance to roll

Brake lines- After sitting for a while the fluid could leak its way back down- Not as likely since you just replaced

Calipers-Same as brake lines.

Not your only possible issues, they are easy things to check and rule out.

Have you done anything to the front end latley?

drauch

As far as brakes go- I just did the 96 XJ master cylinder and booster swap (awesome. night and day difference in braking ability) and I replaced all of the old rubber hose with braided stainless line. And replaced all of the pads, rotors, drums, shoes, and bleeder valves.

As far as the rest of the front end- front wheel hubs, u joints, YJ steering linkage upgrade, and ball joints.

All of this work was done about a month ago and I am just now having this problem. I am also thinking brakes and more specifically something in the lines. If it was a caliper issue, would it be coincidence that they are both locking up or would both go at the same time?

Here's how I think i'm gonna test it-
1.drive until it's hot
2.lift a wheel off the ground and try to spin it
3.open the bleeder valve to relieve pressure
4.then try to spin the wheel again.

If the pressure is released and the wheel is still seized, would that eliminate the brakes as being the problem?
Could air trapped in the proportioning valve cause this?

BatmanXJ

Not all the way. That will eliminate brake lines 100%. Calipers 20%. And rotors none. If calipers are messing ul they essentially acting as a 1 way valve.

Are both sides hot when this happpens? And you said around the rim area? Most of the time heat like that produced that fast is from brakeing system. I agreee it would be odd that both calipers went bad at same time.

Just find out more specifically where the heat is coming from.

drauch

Yes, it's both sides getting hot. And the surface of the rims are definitely hot to the touch. Smells like brakes too, but not positive.

Thanks for all the insight. I'm going to try to tackle this issue this evening. I'll try to eliminate the lines by opening the bleeder and the rotor by making sure i got the right part.

If that leaves me with caliper issues, i'll try greasing the slides -> rebuilding -> and if all else fails, just replacing them altogether.

If both calipers went bad at the same time, i'm going to have to start buying lottery tickets cause i must be one lucky guy. Again, thanks for the help.

BatmanXJ

If its your calipers I would replace. They are only around 18 each I beleive. Better to have security of knowing one of your most important braking components work correctly.

drauch

Yesterday, I drove it until they started sticking and got hot, then I lifted the front wheels one at a time and tried to turn them. Both were sticking. I opened the bleeder valves and top of the reservoir to see if there was pressure in the line holding the calipers. This did not relieve the calipers. So i took the calipers off and spun the axle to see if the rotor was rubbing the backing plate. It was not. I replaced both calipers. Now the driver side is pulling when I brake and it was considerably hotter than the passenger side. So, either the passenger side brake is not working at all, or it is fixed. Gonna do some more tests on that one.

The surface of the knuckle where the top and bottom of the pads slide has notches in them. Are these supposed to be there, or could those be preventing the pads from sliding back off the rotor?

BatmanXJ

Not sure what you sre saying about thr notches. Any pictures?. Sounds like you deff have one bad caliper.

Sparkys92XJ

I had major problems on my 91 dodge cummins with calipers. I was buying remanned calipers and I went through about 10 sets on the parts store warranty until they just have me new ones. Once I put the news ones on they worked fine. So it definitely could be your calipers. But let's see those notches on your pads you're talking about

Carl48

The notches you refer to are not supposed to be there ...the sliding surface should be smooth...if it is notched badly enough could be contributing to your problem.

Pelican

I assume OP is talking about notches in the sliding surfaces of the steering knuckle where the pads mount. And no, they are not supposed to be there. Some people get a welder to fill in the grooves/notches and then file them smooth.

Various parts houses offer Crown knuckles (~$114) but they seem to be currently unavailable, at least through the sources I contacted last week, and I ended up ordering an OEM unit -- not cheap.

Edit: I see I crossed with Carl48.

The mail order OEM knuckle (~$178) was still way cheaper than some of the standard parts houses.

drauch

Thanks for all the help guys. I've been driving it all weekend and it seems that the drivers side gets hot and sticks randomly now whereas before it was after a certain amount of time both sides would stick. I think the calipers were definitely bad. Now, i'm going to try filling in the notches with some welding. I thought those notches were supposed to be there, that's how bad they are. Thanks again, I definitely appreciate the help.