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 there aren't any leaks it sounds like a messed up master cylinder to me.

 

Is the new MC a dual? Check your front hoses for leaks at full right lock.

 

X 2 on front hose. My Jeep had a leak in hose and only seemed to show when it was turned at full lock.

Paul

 

that would 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.

 

I had a very similiar problem with my ****** coupe years ago.
I would suspect you will find it only happens going backwards, and is knocking the pads away from the disc for some reason.
Try it in reverse with just a small amount of pressure on the pedal, and then again without your foot on the pedal. If the pedal doesnt drop with your foot on it in reverse but does without i would start looking at why the pads are knocking back.

May not be the answer but worth a try. John