I have a 83 Jeep CJ7 with a right front brake that locks up. This a a manual brake system. If I brake the bleeder and relieve the pressure, I’m usually good for the rest of the day. Then it’s the same problem the next time I drive it. I’ve replaced the master cylinder, caliper, rubber brake hose and relaxed the fluid with synthetic. I’m at a loss of what else to do. Any suggestions would be greatly appreciated. The right front is the only one that has this problem.
hmmm … this is a toughie. If it was the rear or you hadn’t replaced the rubber hose and caliper it would be easier… hmmm … what do you mean by “if I brake the bleeder and relieve the pressure”? Do you mean you bleed the right front caliper? And that fixes the problem, but only for a day? I’ve never heard of “relaxing the fluid” with synthetic. Are you sure this is recommended by Jeep? Beyond those queries, about the only thing I can think of is that the rotor is warped, and that is somehow causing this. How? No idea. Maybe have a shop measure the run-out on the rotor, see if it is within specs. Sorry, but other than that I’m clueless. You can always just replace the MC, caliper, and hose again I guess if you run out of ideas. It’s possible on of those is still bad. New stuff sometimes doesn’t work right out of the box. Makes car repair more interesting.
Thanks for your input. Yes, if I crack open the bleeder on the right front caliper or at the master cylinder, fluid will come out relieving the break pads from the disk. I can tell the pedal is getting stiff and it’s starting to load up. Once I relieve it, its good to go for the day. Very, very odd.
I have only seen this happen with a bad hose or master cylinder. If it was a bad hose, cracking the line at the master cylinder wouldn’t help. Therefore your “new” master cylinder is bad or mis-adjusted. That is the plunger length can be too long or short and one of the return ports in the master cylinder is blocked off.
Thanks for the comment. That was going to be next venture. Start replacing the items is already replaced. Starting with the master cylinder. Ugh
Don’t be so hasty. Oldtimer 11 makes a good point about the adjustment of the plunger rod. Make sure there is the proper free-play in the rod before replacing new parts.
The return hole into the master cylinder on any braking system is very small, and can plug up easily. We don’t know the order you did your replacing, but if the master cylinder was done before the lines and slave, dirt from the old system could easily get into the new master and plug that hole. On a system as straight forward as this one do the lines from other wheels join up with this one before they get to the master? If so, the problem is farther down the system, toward the slave end, because the other wheels are not locking. The amount of fluid that moves is very small, and if it can’t shift back when you release pressure, it can lock up a slave fast.
No slave cylinder. The front brake line comes out of the master with an immediate “T” that splits the right and left brakes. The rear comes out of the master and into the adjustable bias controller and splits. I drained all of the fluid and installed new after the master was installed. I think the replacement order was hose, caliper them master cylinder.
Thanks for your input!! This has me stumped.
Instead of just cracking the bleeder, try loosening connections. Start at the master cylinder attachment i.e the master cylinder mount nuts, then the pipe from the master cyllinder, then the pipe leading from the ‘T’, then at the pipe at the entry to the flex hose, then flex hose to the caliper, and finally the bleed screw. When you find the spot where the pressure releases, the component just upstream is most likely the culprit.
I am thinking it might be the pedal push rod is adjusted too long and holding the master cylinder piston extended covering the compensation port. You may ask “Why doesn’t the left caliper also lock?” It could because the left caliper has not been replaced and not moving correctly.
Sorry about the slave cylinder talk - I was reading another post about drum brakes and got my head stuck. Now it’s unstuck. I like the push rod thinking for several reasons, mostly because it’s easy and cheap to fix. Personally, I like to start with easy and cheap, and work up to the big task.
And thats exactly what I did. Fortunately the Jeep parts are cheap, since the same parts was used for many years. I’ll check out the push rod, but I honestly don’t remember there being and adjustment. I’ll get out my manual and see if it says anything about an adjustment. Thanks for your input!!
Reashercher; It relieves the pressure at all of your fore-mentioned areas. I’ll see if there is an adjustment. It started locking up one day and still doing it after replacing everything.
Maybe a bad wheel bearing?
Nope, bearings are fine. Thanks for your input!!
Look for a misplaced up stop on the brake pedal arm or the brake light switch getting jammed. If you can unbolt the master cylinder and the pressure relieves then it has to be in the pedal - pedal hanger - push rod location i.e. under the dash.
My research indicates that you could have a power brake booster on this CJ. Is there truely no power booster? If loosening the master cylinder from the booster releases the pressure, try disconnecting the pedal push rod from the pedal arm. If the pressure does not release with this, you have a problem with the booster. The push rod out of the booster to the master cylinder is adjustable. Its length should be less than the distance into the master cylinder piston i.e. there should be some clearence between the push rod of the booster and the contact surface of the MC piston. Again if disconnecting the clevis from the brake pedal arm relieves the pressure, check the up stop, the pedal hanger, and brake light switch.
I’ll give it a try to see about adjusting it. There is no booster. It is definatly manual brakes. There is no break light switch at the petal. The switch is incorporated into the adjustable bias that regulated the % your looking for between the front and rear brakes. I’ve never seen anything like that before. I couldn’t figure why wires way hooked up to the bias adjuster and called to privious owner and he said it was the brake light switch. Scratching my head, I unplugged one of the wires and pushed on the pedal. Low and behold, no brake lights. Anyway, I just don’t remember there being an adjustment at the pushrod or in the petal. I’ll try to look tomorrow. It’s been really cold here but supposed to get in have 20’s tomorrow. Thanks a lot for your suggestion. I never thought about loosening up the master cylinder from the firewall to see it that unlock the front wheel. When I crack the bleeder or line at the master, quite a bit if fluid comes out. I just can’t wrap my mind around why its locking up and why after that initial “unloading”, it doesn’t load up or lock up the remainder of the day.
Thought I’d let the posters in on what’s happening. I made some shims and shimmed the master cylinder away from the firewall and that did the trick. Thanks for all of the suggestions.
Inspect the brake hose for having a wrap-around style holing bracket. Revlieve the brackets grip on the hose by spreading and retest.
Rust inside a wrap-around brake hose bracket can turn the hose into a one-way valve.
How did you come up with that idea, and why does it work?
@Barkydog, the brake rod was probably not completely releasing the brakes from the master cylinder, and keeping the brake fluid from relieving pressure back into the reservoir. As you drive, the fluid warms and expands, slowly applying the brakes. By adding shims, he let the rod release fully, letting the expanding fluid release into the reservoir. I’m wondering if the peal mount is slightly deformed, taking the rod out of adjustment. Most cars I’ve worked on had adjustable rods to avoid issues like this.