The Stovebolt Site Forums The Shop Area Driveline '51 3600 brakes hold pressure due to exhaust heat?

I have read this before but can't seem to find the post that I read it in earlier. So I have rebuilt my entire brake system . New hoses, lines master, shoes the whole thing. I haven't had a problem until now. I was driving the other day and getting around so to speak. Doing errands and such about 4 hours of on off driving. About an 82 degree day. Right when I get home, luckily, my brakes start smelling and the pedal gets real stiff to the point were I can't press it . The brakes are not locked up the truck still rolls with drag from the brakes. Truck sits for a bit and brakes/pedal are now fine. Drove around today no issue. I have read (or at least I think I remember reading) some time back that the exhaust can heat up the master cylinder and cause this to happen because the heated up brake fluid will apply pressure. Is that accurate? Has anyone had this experience? Thanks .

Paul

Paul,
I have had the master cylinder cause the brakes to drag by not releasing all the way. The brakes heated up the fluid and the brakes came on until the truck sat and cooled off. Replaced the master and problem solved.

Maybe time for a bit of heat shielding in just the right places. At least then you will know if heat is the cause or not.

Another thing to consider is the type of brake fluid, I believe the silicon .5 fluid can cause brake lines to swell. When the brakes are applied the pressure is forced thru the swollen lines but cannot return.
I use .3 synthetic, thats what your system was designed to use.

The master cylinder is about 4 months old ,when I did the brake system, so I'm gonna hold off on that. Yeah I think I'll purchase some sort of heat shield and give that a try. Not sure which silicon brake fluid I have but I will check and see what it is.I never thought of that. Thanks for the thoughts.

Make sure when the pedal is released the master cylinder is returning all the way so there is no pressure on the system. It is adjustable.

Also, the shoes might be too tight against the drum. They get hot and hold sometimes.

Ditto on the adjusting the master cylinder rod.
Make sure you have some free play in that MS rod.

If your exhaust is running to close to the MS and/or brake lines, you can fab up a cheap heat shield from some scrap metal and band clamps.

Good luck
Dave

The easiest way to temp in some heat shielding is to simply wrap the item you want protected in aluminum foil. Wrap it loose and crumpled. The reflectivity of the aluminum will deflect the heat the crumpled part will create air voids to keep the heat off the lines/etc.

Obviously, this is a temporary/testing purposes solution so you can find out where you need to fab up something permanent.

If all brakes are dragging it all most has to be the master cylinder is not adjusted to return all the way, or assembled wrong.
If one or two brakes are dragging then they are adjusted to tight.
Heat can cause the fluid to boil causing air pockets making the pedal spongy.

The pedal was definitely not spongy that is for sure. MC rod is good. I didn't check brake shoes yet as I assume I set them correctly(LOL).Thanks again for the input. Not sure if all were dragging or just one drum. It did smell particularly around the RR wheel.Like I said before it's fine now but I haven't probably drove more than an hour or so per day since that day and it's a bit cool now here in WI.

Paul