brakes seizing up on older motorhome.

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If the master cylinder is not releasing all the way back, the system will build pressure and apply the brakes..especially if the brake lines go anywhere near the exhaust. You need to make sure that the pedal is coming all the way back and you can feel looseness in the linkage. I have seen brake light switches keep the pedal from coming all the way back and then I have seen where the brake light switch has been adjusted too far into the pedal linkage so the pedal could not retract all the way.

The brake pads have to move freely on the pins holding them in, and the caliper needs to retract slightly after the pressure is released. I'd start by pulling each pin, wire brush the rust off and lube with white lithium grease. Are the calipers new or rebuilt? If rebuilt, I've seen the reman guys just blow them out and reassemble with new seal without honing the cylinders out. When the new seal scrapes across the ridge it starts leaking and could bind.

Also check brake pedal free-play. That should be adjusted/checked with installing a new master cylinder. Make sure there IS some free-play before the master cylinder piston is activated. A seized pivot point can also cause the master cylinder piston to stay activated.

If I read it right you get less and less brake pedal travel, which is the opposite of what would happen if your brake fluid boils. Dragging brakes usually causes the fluid to boil and the pedal go to the floor. I would guess that your problem is caused by too much pressure being developed in the master cylinder that prevents the pedal from being pushed down.

I have a similar problem with my '84, but it appears to be limited to the right front caliper which causes the stiffening of the pedal. It came on out of the blue and I haven't been able to figure it out. New calipers, rotors, pads, MC and soft hoses. If it were all brakes I'd suspect something in the Hydroboost system but it's just the right front. I just live with it. It never locks up completely and frees up after a little bit of non-braking travel.

Sorry I don't have an answer but subscribing for replies....

jplante4 wrote:
The brake pads have to move freely on the pins holding them in, and the caliper needs to retract slightly after the pressure is released. I'd start by pulling each pin, wire brush the rust off and lube with white lithium grease. Are the calipers new or rebuilt? If rebuilt, I've seen the reman guys just blow them out and reassemble with new seal without honing the cylinders out. When the new seal scrapes across the ridge it starts leaking and could bind.

there are no "cylinders" to hone out on disc brakes and the OP put in pads and calipers so there no chance of rusty pins and rusty pins don't cause the brakes to work properly for a while and then slowly tighten up and get hot
Based on assuming all the work done was done correctly and all pertinent ajustments made correctly I would say that maybe the
proportioning valve is faulty but that's a rare condition
it does sound like the MC push rod is not set correctly
Is it the front brakes or the rear sticking on? have you checked that out?

I recently had a master cylinder go bad and it was locking all my brakes on my 2006 Silverado in exactly the same way. It's possible that the master cylinder, although new is defective. There's a proper sequence to bench bleeding the master cylinder, being careful not to push the plunger in too far which can cause damage to a new master cylinder causing it to stick in the compressed position. Also there is an adjustment rod that pushes in the master cylinder at the booster that some times requires adjustment to achieve the proper amount of slack.

It's not likely that this happened but another mistake some people make is putting power steering fluid in the reservoir instead of the proper brake fluid. It looks clear like brake fluid but will swell all the rubber components and end up locking your brakes.

It's not likely it has anything to do with the calipers unless you find it is only locking up on one wheel.

I remember that certain brake pads can swell after heating up . I don't remember what kind.