I thought i had this problem fixed last year bu i guess not. When my truck is sitting in the garage ideling and start to gets warm i notice that the front brakes grab. This is before i touch the pedal it happens. If ya let everythin cool down it spins freely. There is no problem with the rear ones. The front is a Heidts 4 piston aluminum caliaper. It has 4 wheel disc with 2 pound residual valves. I have checked and everything was instaled in the right direction. The headers are on the outside of the frame and they are wrapped. The frame does get pretty warm where the collector is. The brake line from the frame to the caliper is about 7 inches from header. Master cylinder is from speed way same as booster. I have disconnected the brake pedal just to rule out the adjustment. When i crack a line it is instant release of brake pressure, but i believe it is there because of the heat. I have tried beat shields but didnt want to spend to much time until i get more opinions. Any help would be great if ya need more pics let me know. Thanks Tony Sent from my SM-G930V using The H.A.M.B. mobile app
Should be nothing that holds or "grows" pressure with the pedal released or off as in your case. How about the adjustment between the booster and master cylinder.
X2 the rod between either the pedal and booster is too long or the rod between the booster and master is too long.
Yes on return spring. Pedal is disconnected from booster. When cold no problem when there is heat that is when the Problem starts. I believe if it was a adjustment problem the rear would have the same problem and it does not. Sent from my SM-G930V using The H.A.M.B. mobile app
I disagree. Sounds like the booster is putting slight pressure on master cylinder just blocking off ports in master. Unbolt master and see if it still does it. Sounds like you have plenty of clearance from exhaust. The brake lines should be able to heat up. The increase in pressure should be released inside the master if there is no input pressure. Sent from my iPhone using H.A.M.B.
Winner winner, just loosened the master and no problem. I have been adjusting rod between the pedal and booster. I asume there is adjustment on the rod from booster to master. I will know in a few minutes. Sent from my SM-G930V using The H.A.M.B. mobile app
disconnect the hose to the booster . i got a bad booster from speed way . it was building pressure while driving and applying the front brakes
The clearance between the booster and master cylinder should be checked with full vacuum applied to the booster, or about 20" Hg. In my experience .040" was the target, but check your booster's requirement if possible. Make sure the pedal can move back farther than necessary to ensure full return of the booster input rod.
I had the basic same problem on my 40 and finally figured out that the booster when it got hot from engine heat/fan that the diaphragm became more pliable if that makes any sense. Put a little extra clearance between the booster and master...…...problem solved.
My thought as well. If it only does it when the engine is running the valve in the booster may be bad, applying pressure to the pistons in the M/C.
Thanks to everyone, I have been trying things all day and it was fixed in 9 minutes on the H.A.M.B. I will monitor it from here on out. I should be able to pick up 2 tenths in the quarter now that the brakes aren't sticking. Tony