Hey guys. Last fall,all new brake lines, hoses, wheel cylinders and a new master cylinder were put into my 53 truck. This spring, the truck was stopping great! I had a very small leak coming by the copper washers by the master cylinder. I had a shop try to stop the leak for me. They did but I don't know what they did to fix it. I drove my truck back to my house about 17 miles. I noticed when I pulled into my garage, some smoke was coming out around my driver's side wheel. The next day, a couple of time while driving, I noticed when braking the truck was pulling a little bit to that side. Well, twice now, I have been stranded by my brakes locking up (basically the brake pedal is completely hard with no give up or down). One time, I had to be towed. I took it to a shop and they could not find the problem telling me that everything appeared to be working fine. The one issue is that the truck seems fine on short trips. It seems to take a bit of a drive to get them to basically lock up. Today, coming back from a show of about a 27 mile drive, they were very bad. I was able to get it back home, but I had smoke coming from the driver's side back wheel and driver's side front wheel. The truck was locked up in my garage. Even if you put it into neutral, you cannot push the truck forward or backward.

What is going on? Thanks for any assistance.

 

To offer up a general summarization of what is happening, the truck builds up pressure while driving to the point of almost lock up. After this, If the truck sits for an hour, it will "leak down" and basically goes back the normal.

Any idea of what would cause this?

 

maybe the relief valve in the master is not working? don't know how it would be related to repair unless it was defective from start and the leak at the master was bleeding the extra pressure until you fixed it?? i had a sim problem and when miles away from home, my redneck solution was to bleed a little fluid (and pressure) off one of the bleeder screws and then head home. not a good general practice but in an emergency? only prob i had with it was at a lumber yard, i got down under the back, bled the pressure and the truck rolled away, put it in gear with e brake on?? hopefully you'll get more expert advice than mine.

 

I had an identical behavior pattern on the brakes. Changed the master cylinder and the problem went away. I think that the residual pressure valve was seizing upon warming up.
And, yes, I would have to pop a bleeder to limp home once it warmed up and locked up.

 

Hey Jim,
Our brakes would be fine then after about a mile we'd get total lock up. Then wait 30 to 40 minutes & everything would be fine - then lock up again down the road. Very frustrating. In our case it was the rod from the pedal to the master cylinder was 1/8 inch too long & never fully released building up pressure.

Good luck over there. You'll find it.

Ben in Austin
1950 F1

 

Jim, this may sound really silly but is the master cyl cap venting like it should? The cap should vent and allow air to get in to system while brakes are in use. If you remove the cap does it go away, Cover master with something to stop fluid from rushing out first cause brake fluid on everything. This is why brake fluid get moisture in it and needs drained/filled/bled every now and then. The pedal rod may be to long but when you get it figured out give it a full system bleed, if the fluid got that hot in could break down and also give you problems. The master itself could have issues as well.

 

Also make sure that the shoes are adjusted correctly before condemning the master cylinder.