1988 YJ Front Calipers sticking - JeepForum.com

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post #1 of 25 Old 09-21-2011, 07:14 AM Thread Starter
UncleDave
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1988 YJ Front Calipers sticking

I bought this YJ a few weeks ago and am seriously struggling with this issue. The jeep had been parked in a shop for almost ten years so you can imagine things were stuck, including the calipers. I bought a set of new calipers and pads for the front, bled the lines and took off down the road. I didn't get far before I realized the jeep was really struggling. When I got it back to my shop, I put it on jack stands and I could not spin the front wheels at all. They were locked. Took the tires off and the calipers (on both sides) was stuck.

I have bled the lines, check for leaks, check for blockages in the hoses and nothing seems to be working. Last night I took the rubber hoses lose at both ends and blew air (with my mouth) back through to see if there was an obstruction. Nothing. The only thing I did notice was the calipers are not rock solid against the wheel, meaning when the caliper is not stuck I can physically move it back and forth a little.

I'm at a loss. I am not much of a mechanic, but I know the basics. Any ideas would be greatly appreciated.

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post #2 of 25 Old 09-21-2011, 07:21 AM
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Put new rubber hoses on. after years of sitting the inside of the hoses can degenerate. Sometimes a flap will be created within the hose. fluid will flow past the flap to the calipers. But when the pressure is released the flap comes down and acts like a check valve.

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post #3 of 25 Old 09-21-2011, 07:39 AM
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Gunk, rust and wear. I had similar problems with my 1990. After replacing everything; hard and soft lines, calipers, master and wheel cylinders everything works perfect and I think the total cost was only $250 or so.

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post #4 of 25 Old 09-21-2011, 07:41 AM
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I agree with the guys above. Replace the soft hoses and flush the entire brake system for now and see what happens.

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post #5 of 25 Old 09-21-2011, 08:59 AM Thread Starter
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I have to admit I'm a bit skeptical about the hoses being the issue, but I have already ordered them and will try to replace them tonight. I'll follow-up to let you guys know. Thanks for the input.
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post #6 of 25 Old 09-21-2011, 09:16 AM
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i agree with the rubber hoses. the force of the fluid going out opens the collapsed hose when you step on the brake, but since there is less pressure flowing backwards toward the master cylinder (when the pedal is released), the hose stays collapsed - kind of like when you put your finger on the bottom of a straw and then suck in - the straw collapses and closes.

had the problem with the wife's van - replaced rubber section of hose - problem was fixed!

Last edited by fishnic; 09-21-2011 at 09:21 AM. Reason: spelling
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post #7 of 25 Old 09-21-2011, 10:06 AM
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I just had the exact same problem on my xj. New calipers, new pads bled and adjusted. Turns out the rubber lines aren't just rubber inside they are metal also over time they corrode and cause a ton of problems. I replaced those and all the way up to the master cylinder and it's good to go.
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post #8 of 25 Old 09-21-2011, 10:16 AM
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On top of what everyone else says, I would add, to take the calipers and pads off and clean everything real good like shiny clean.
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post #9 of 25 Old 09-22-2011, 08:34 AM Thread Starter
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I didn't get to it last night (teaching a class at church) but will see what happens after work today. I a lot of little things to do to this Jeep, but this is the only major hurdle i have.
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post #10 of 25 Old 09-23-2011, 07:34 AM Thread Starter
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Well, just as I suspected, it was not the brake hoses. Pulled them off and they were good. Replaced them anyway since I already had the new hoses in hand. My buddy decided to do something that I should have done at the beginning (but again, I am not much of a gear head). After getting the calipers stuck again he went all the way back to the master cylinder and cracked the fitting from the front back at the MC. It immediately released the caliper. That suggested to us that the lines were clear all the way back to the MC so it must be something there.

He removed all the fluid, disconnected all the lines to the MC and removed the master cylinder. Using an air hose he flushed everything out. It was when he went to connect it back to the brake booster that he felt the resistance from the brake adjusting rod. It was contacting the MC about 3/8" to 1/2" before the MC was seated flush to the booster. After doing a few google searches he figured it wasn't supposed to do that so he backed it off to where when the MC is fully installed, the adjusting rod is a little shy of making contact.

He filled the system back up with fluid and bled it. He drove it down the road and, though the brake is a little soft right now, it does stop the Jeep and it doesn't seem to be dragging. I will be able to help with it this afternoon so we will be able to fully bleed it and make the final adjustments.

Does all this make sense to you guys? I will be one happy man this weekend if this part of the project is complete.
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post #11 of 25 Old 09-23-2011, 12:54 PM
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I'm always amazed when I'm standing in a parts store looking for brake fittings that such a little adjustment can cripple an entire car. Hope I didn't steer you in the wrong direction. Now get out and drive that beast!
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post #12 of 25 Old 09-23-2011, 01:42 PM
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Quote:
Originally Posted by UncleDave View Post
Well, just as I suspected, it was not the brake hoses. Pulled them off and they were good. Replaced them anyway since I already had the new hoses in hand. My buddy decided to do something that I should have done at the beginning (but again, I am not much of a gear head). After getting the calipers stuck again he went all the way back to the master cylinder and cracked the fitting from the front back at the MC. It immediately released the caliper. That suggested to us that the lines were clear all the way back to the MC so it must be something there.

He removed all the fluid, disconnected all the lines to the MC and removed the master cylinder. Using an air hose he flushed everything out. It was when he went to connect it back to the brake booster that he felt the resistance from the brake adjusting rod. It was contacting the MC about 3/8" to 1/2" before the MC was seated flush to the booster. After doing a few google searches he figured it wasn't supposed to do that so he backed it off to where when the MC is fully installed, the adjusting rod is a little shy of making contact.

He filled the system back up with fluid and bled it. He drove it down the road and, though the brake is a little soft right now, it does stop the Jeep and it doesn't seem to be dragging. I will be able to help with it this afternoon so we will be able to fully bleed it and make the final adjustments.

Does all this make sense to you guys? I will be one happy man this weekend if this part of the project is complete.
The only part that does not make sense is how did it get out of adjustment? I had a similar issue with a bad booster and it took a lot of head scratching to get that sorted out.

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post #13 of 25 Old 09-23-2011, 01:58 PM Thread Starter
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Quote:
Originally Posted by jbolty View Post
The only part that does not make sense is how did it get out of adjustment? I had a similar issue with a bad booster and it took a lot of head scratching to get that sorted out.
Our assumption at this point is that the guy i bought it from replaced the MC at some point while working on the brakes. I'm trying to confirm that with him now to be sure.
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post #14 of 25 Old 09-24-2011, 04:55 PM
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Is it a direct replacement MC or did he upgrade it?
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post #15 of 25 Old 09-26-2011, 07:08 AM Thread Starter
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Quote:
Originally Posted by VirginJeeper View Post
Is it a direct replacement MC or did he upgrade it?
According to him, this is the original MC.

We have now replaced the MC but the brakes are still spongy. The front's bleed out fine but the back is giving us problems. Found a small leak around one of the fittings on the proportioning valve. Gonna use plumber's tape on the fitting and see if that stops the leak, thereby stopping the air from pulling in.

If this doesn't fix it, it's off to the brake shop.
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