so I am out driving today, in stop and go traffic, went to the local Harley dealer party. Truck ran and stopped like a champ (I did just install a new master, rear brake line and new pads/shoes a couple weeks back) disk/drum setup out of early 70s Ford). So I get to the show, engine temp never went out of the 180 range, pulled into the parking lot, put it in reverse to swing into a spot (wheels turned to the right) and all the sudden.... the pedal hits the floor (nothing, no brakes!). I pump them and get enough get it parked. I let it sit for an hour, got back in, pumped cold (booster is working), turn the key, pedal falls like it should.... pumped a couple times and off I went. Drive the whole way home in the same stop and go traffic, same heat, etc and the brakes worked fine, no issues at all. I am climbing under now to check everything, but it just makes no sense. The only thing I am thinking is that my exhaust sits close to the booster and master so I wonder if heat played a factor? WTH? Any ideas?
If the pedal went to the floor and you can find no leaks... get a new M/cyl. It sounds like the seals in the M/cyl are going bad and occasionally not sealing in the bore. You got a warning. I'd take heed.
Look over everything for brake fluid leaking. If there are no fluid leaks I'd ***ume there's air somewhere in the system and rebleed the whole system back to front. Kinda scary problem, but you already know that. I'd replace the master cylinder if it happens again after checking for leaks and bleeding the system.
The master is byp***ing internally, you have no fluid leakage. When it byp***es it spits the fluid back into the reservoir. Cure, replace the master. Bob
On a long shot, if the brake line gets way hot, it can act like a byp***ing master. But you should have seen it right away. How much space is between the master and exhaust? Bob
This problem I'm familiar with. Let's look at what you did, you were turned to back in. I would check the front brake calipers for interference with the suspension pushing the piston back in. I had a customer vehicle do the same thing, the steering stop was broken and the caliper hit the suspension on a hard turn forcing the caliper away from the rotor. The first two pumps of the brake pedal was all that was needed to force the caliper back to the rotor. I welded a steering stop on to remedy the problem.
thanks Crusty and everyone else. I think Crusty is on to something..... another thing that occurred to me... could be a cracked brake line whichwould explain why I lost all brakes, but then got them back after a few pumps (when not at full lock) but no the nrakes are not like they were before this happened, I have brakes, but as good as right before this happened.... I introduced air into the lines. no leaks that I can see| drove the truck around and they seem to be working as they should..... but I know the problem is not gone. I am less likely to think master since I just replaced it, but since it, and the booster, are frame mounted and really close to my exhaust, I am probably going to order a firewall booster/master kit tomorrow.
I believe Crusty nailed it .I have seen this before.Banjo bolt will hit the spring an push the caliper back.Mustang ii with 11 inch brakes.Before you buy parts try to duplicate the hard turn backing up.
Crusty is a genius! and correct too I climbed under and went lock to lock and noticed that at full lock (so to speak), the calipers are running into the axle. The pop before I lost my brakes at full lock would have probably have been the caliper fighting the axle and getting pulled way from the rotor, just like Crusty said. Impressive! The only thing I am not sure I understand is why do I have less brake pressure then before this happened? Could this have caused air to get into the system? So now I know what happened (more than likely) and a full system bleed should give me my pressure back (more than likely) and I owe Crusty lunch. I am still going to make a heat shield for my master, but that is probably not related.
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