Ok Hambers. We need your expertise here. My buddy Jeff has a mysterious brake problem on his 31 hiboy pickup. His brakes lock up every now and then, no telling when this will happen. If it sets for 20 minutes or so it's fine and run great the rest of the time. When it happens the brake pedal won't move/depress, the brake lights come on and it won't roll As I said it just happens occasionally so there's no way to replicate it in the garage or just a trip around the block. Any ideas would be greatly appreciated.
Are any of the wheels getting hot. Maybe the rubber lines are collapsing internally or as stated above incorrect freeplay.
it is the adjustment on mc rod gets hot locks up cools down and releases adj so there 1/4 to 1/2 freeplay I used to be brake tech back inmy much younger days but I found this the hard way on mytruck good luck tom
I had an unusual brake problem like this once. It turned out to be the rubber hoses. They were old. It seems that the tube inside was loose and would knot up in side and restrict the return fluid acted like a check valve. Replace all the rubber hoses. Mike.
If all 4 wheels are locking I wouldn't think it was a bad rubber hose (one wheel locking sure). Would lead more toward the fluid heating up/expanding locking all the wheels & activating the brake light switch (assuming its pressure & not mechanical). Look for lines too close to the exhaust system.
Make certain there is some free play in the push rod. Install a stronger return spring. As the car goes down the road the pedal bounces against the cylinder and it pumps up the system.
Your master cylinder push rod is set up wrong. I dont know if you are running manual or power brakes, only difference is how you are going to fix it. The piston inside the master is not being allowed to return all the way back to its proper rest position. This causes the compensating port in the master to be blocked not allowing all of the fluid to return to the resevoir. Eventually, depending on how much it is blocked, the pressure in the system builds up to the point where the brakes are completely locked, pedal becomes hard and if running a press switch, the brake lights stay on. Let it sit for a while and the fluid will slowly bleed back into the master and release the pressure. If you are running manual brakes, the adjustment is easy, just adj the rod so there is some free play in the pedal. I have seen lots of people over adj there master push rod because there brake pedal is too low but the real problem is usually drum brakes that are not properly adj. If you have power brakes and you have pedal free play then you need to remove the master and measure where the booster rod is sitting, it maybe too long. It should be adjustable or you may have to modify it. Hope this helps.
Heat alone can't do it. If the brake pedal/master cylinder is adjusted properly then expanding fluid will just raise the level in the master cylinder. Must not be enough clearance at the pedal. Thats where I'd look first anyway....
I doubt it is a hose, they are usually clogged period and if its up front you get a bad brake pull. I'll also go with free play. I doubt its heat-related. I had a brake line too close to a header tube and it actually caused the pedal to go to the floor. The fluid actually came out of the tube itself where it got too hot.
The reason the hoses can clog "one-way" is because when you brake there's hundreds of PSI pushing, when you release there's only the springs pushing the fluid back.
Swollen brake hoses wont trigger the brake lite. They'll only lock up/drag on whichever wheel that has the swollen hose. He's got some other problem that is affecting whole system. I'm with the guys that are looking towards the booster/master/pedal issues. -rick
Woodz above absolutely,positively has the answer to your problem. Guarantee it. Had the same thing happen to me and adjustment was the cure. Ralphie
Had a master cylnder once with the "bleed off" hole at the very back of the stroke pluged,.....if you look into the mc. And stroke the pedal you should see a tiny "geyser " effect ripple the fluid surface, if no geyser the push rod is too long as has been pointed out or the bleed hole is pluged Posted using the Full Custom H.A.M.B. App!
I'd check the pedal free play cold, make sure it's good. Then drive it with some tools handy. When the brakes start to lock, unplug the booster vacuum supply, see if it changes. Boosters can have issues and apply brakes with engine vacuum. If that isn't the issue, loosen the master cylinder from its mount and see if the brakes release. If it isn't one of those, which would be surprising, loosen a bleeder screw front or rear and see if it releases. A residual pressure valve could be causing an issue as well, this will test for that. Post back once you sort it out. Posted using the Full Custom H.A.M.B. App!
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