Disk Brakes Dragging

I need to start a new thread as I previously piggybacked on another thread and I need help.
Front brakes are dragging, enough to hold be on the profile of the street going into the driveway (2%ish). I started having issues a few weeks ago when the weather warmed up. In the morning they are fine, as I drive for longer periods in cooler temps, or in the afternoon when it is warmer, they start dragging. So, I know it is heat related, and from the brake fluid expanding pressing on the calipers.

About 6 month ago I replaced the stock front brake lines to match my lift with braided lines. Wasn't having and issue, just adding the needed length. They are made by (or labeled) Crown, but packaged by ProComp. This week I replace the MC with a NEW, not rebuilt, MC from Autozone, along with two remanufactured calipers. Same issue persists.

I know there is residual pressure built up from expansion. It can only be any or all of the three components; braided lines, hard lines, or proportioning valve (assuming all new parts working as should). The fluid level in the MC has enough room for expansion, but it has not risen. This to me rules out the MC. I partially suspect the braided lines have delaminated inside, yet find it odd that both do it at the same time.

So upstream from the flex braided lines, besides the MC is the hard lines and proportioning valve. considering the age of the Jeep, I could just replace the line any ways just because. But one question I have is about the proportioning valve.

My understanding that it should not be an issue in holding pressure in the front line. So, could it have a catastrophic mechanical failure that it would hold pressure on the disk brakes? Before I throw more money into her, just trying to see if is a reasonable probability and save ~$70+.

I am almost at a completely new brake system though, and I just might do it to get things all new. But maybe this could help someone else too, that cannot replace everything for financial reasons.

Any thoughts???

 

Thank you for the reply.
Yes cracking the bleed valve releases pressure off of both sides. So, flex lines ruled out.
To me is says proportioning valve (P-valve), or the hard line from the MC to the P-valve.
The P-valve is about 3 inches from the exhaust, and I don't like that. Planned on building a heat shield just to keep its temp down just incase.
But it worked before......

 

I guess that makes sense. Wow, seemed like an obvious now, yet someone had to point it out. Thanks Howard.

Well, I need to go drive it and warm things up to get the pressure built up again. I will report back what I find.

Thanks again Howard.....

 

Ok, drove around a little and got things warm. Brakes dragging again, so I started at the MC and cracked the line. Wheel frees up. To get to the proportioning valve I will end up burning myself on the exhaust pipe. So, from the P-valve to the MC pressure is being built up. I am not seeing an increase in volume within the MC, so I am thinking it is the line between the P-valve and the MC. Nothing looks kinked, bent, or corroded.

Seems how that breaking seal at MC releases pressure, I doubt if it is the P-valve. Therefore I think there is an issue with the curly line coming down to the P-valve and needs replacing. I will order a new line and see what happens.

 

Check your adjustment on your push rod and the brake line attachment. If your push rod is adjust too far in this will occur, you need at least 3/4 free play at the pedal. What can happen, and did happen to me with disk brakes, is the fluid heats up in the caliper, expands and applies the brakes. If this is the case, then your rear brakes should hang up first since they should be applied first in braking. Maybe you need to switch lines on your M/C

Another issue I have had, but dont really believe its yours, is the flex line failing internally and acting like a check valve to allow fluid under pressure in, but not out, locking your caliper. Had that on one side of my chevy.

First thing I would do is back off the push rod adjustment. Then bleed the brakes good. see what happens.

 

Thanks for the reply. Great advice and I have checked that length. I did back it off a little more. I cannot lock up the brakes, which isn't bad, and stops very well. But, what I think is going on is heat from my exhaust pipe is heating up the P-valve and the lines. I can crack the line anywhere (bleeder valve, MC) to relieve pressure, and it goes to normal.

I think it is exhaust from an observation I made today. As I was sitting at a stop light, which has rather long waiting time, the brakes were free and it would rock back and forth. After a few minutes, they started dragging and the Jeep would not rock freely. This was after about 2-3 minutes at the light, ambient air warm, and the Jeep all warmed up. My exhaust I believe is rather close to the P-vavle at about 2 inches. Most of the drive time I did not need brakes, and it acted normal.

The front line may have some issues as it looks buggered up from previous owner, and it may be enough to create a check valve situation. I am going to try to build a heat shield around the area and see how that resolves this.

 

Sounds like you got it figured out. Maybe just make some new lines to get away from the heat all together.

Good luck!

 

Well, I thought I figured it out. There is only one thing left that can be wrong. The combination valve is doing something wrong. Either the metering side or the the switch is tripped (light isn't on, but may not be working) and locking the fluid up front. Thinking back now, a few month ago I remember backing up and the brakes grabbed funny. I thought the rears got stuck on the self adjusting part as they locked up when I gently applied my brakes. It did it once only. I opened the rear up and cleaned the brake area and dabbed a little anti-sieze were the shoes rub. Everything worked fine until a few weeks ago.

So it would seem that my valve went bad after all. Since everything else is new, might as well replace that also and be done with it all and have a new brake system.

So, one question. lines are 9/16 rear and 1/2 front on MC. I am assuming they are the same at the valve. Does anyone know the tread pitch?? Summit has a GM one (same style that my jeep came with) for $49. The one from Morris you need to adapt (stated on their website), but I am not sure about the fitting sizes so I want to make sure. A few of the reviews had conflicting reports, and several said that they leaked too.

Does anyone have that answer??

Thanks for the help.

 

Even though it was a little while ago that I figured out what the issue ultimately was, I thought I would update this incase someone else has the same issue in the future. In the end, I have a completely rebuilt brake system, which is good, right?

The jeep originally came with manual brakes. The manual M/C needed rebuilding, so instead of rebuilding it I converted to a booster brake system. Easy peasy, I have done this before. New power M/C and new booster, and it worked great for 6 month. Then the brakes began to drag. After replacing parts that I could see had issues, no resolve. Even replaced the M/C figuring there was something weird going on.

The culprit was the booster. If I removed the vacuum line, it would release the brakes. I don't think it was the spring inside, but more than likely a valving issue. Doesn't really matter though. It would not release to ambient pressure once brakes applied (brake system warmed up after driving a little bit). So, resorted back to manual brakes and contacted the distributor about the booster. They asked me to return the booster and they will send me out a new one without a charge.

I will keep the manual M/C just incase I run into this again. Hope this helps someone in the future.