Forgive me if there is already a thread for this but i cant find it.

My front brake calipers won't disengage sometimes. I will be driving and all of a sudden my truck will slowly start fighting the brakes without me pressing them and get to the point where i have to downshift to drive downhill. I have replaced both calipers, put in new pads, new rubber lines and new master cylinder and it got better for a while buy now it's happening again. Could it be my back brakes and lines causing my fronts to keep holding like that? Any help would be appreciated!

 

I had a brake booster to do the same thing on me. The higher the rpm, the faster it would apply the brakes without me touching the pedal.

 

Did you replace the booster? And did that fix the problem?

 

I did have to replace the booster. What you can do is remove the vacuum line from the booster that goes to the intake. You will want to plug the hose off with a bolt or something similar so your motor will not have a huge vacuum leak.

Only do this is a safe area as you will only have about 50% braking power. You can stand on the brakes but will be unable to lock the tires up with the booster disconnected. You will still be able to safely to stop the truck with it disconnected just something you don't want to do in a high traffic area.

With the booster not having any vacuum assist, find a rural road and see if your brakes stop engaging without you touching the pedal. That is how I went about troubleshooting mine. Just idling or low rpms may not create enough vacuum to cause the brakes to engage. I was driving 55 mph to get mine to start activating with the booster attached but unattached, I had no further problems and knew I had a faulty booster.

Currently as you are describing your brake situation, depending on how much you are driving it, you may need to replace the pads again. The hubs are getting extremely hot and the heat will extend to the rim and hub assembly when mine did it and if I remember correctly.

When my truck did it, at first I thought I was having a power loss in the motor. When I pulled over to check it out, I tell it was basically stopping on it own and when I got out of the truck it did not take long for me to see I was having some brake issues from the sound of heat of the disc and such.

 

Thanks, I'll give that a shot next time I drive my truck

 

When you replaced the master cylinder did you adjust the the push rod that goes into the piston. You will need a special tool that measures the depth into the master cylinder piston then turns around and measures the distance from the mounting face on the booster to the end of the push rod. you need about a mm clearance.

 

For what ever reason the hydraulic pressure is not bleeding off the calipers .

Could be as simple as a crushed line.

Two bad rebuilt calipers having pistons hang up. In this day seems to happen all to often.

Bad Master Cylinder but that most often would effect all 4 brakes

. Then the front doing most of the braking one might not notice the rear brakes or they could be out of adjustment.

Bad Booster or the linkage out of adjustment .

 

Thanks all for the replies, I took off the vacuum hose to the booster and that seems to be solving all the brake issues, so I guess that means a new booster for me? Or is that just a faulty check valve?

 

It could be a check valve but in my experience, I have never had a faulty check valve but have dealt with 2 bad boosters in the past on different trucks. It is an easy check as air can only flow one way but my bet is on the booster just from experience. Valve would be so much cheaper, boosters are kind of pricey.

 

I'll probably just replace the whole booster so I don't gotta worry about it as much. Thanks for your replies!

 

Been off, computer died. If the push rod is not adjusted correctly and is in too deep the piston cannot return enough to bleed the pressure and will cause the brakes to stay on and the heat generated will create more pressure. this will warp the rotors as well as keep the brakes on. Good luck.