Odd brake problem with the 25, Any ideas?

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That 25 Guy.
Dec 3, 2002
I rebuilt the stock brakes on the 25 (no booster, single reservoir master cylinder, single cylinder at each wheel). Now I have this heat related problem. When the motor gets hot (not necessarily the brakes) the brake system builds up pressure and applies the brakes.

Here's an example:
Last night (70 degrees) I took it out for a test drive. Everything was fine (with the brakes ::) ) during the drive. Parked the truck and a few minutes later the brake lights came on (pressure switch). The brakes were rock hard at the pedal and were dragging. The brakes slowly loosened up as the truck cooled down.

Things I've suspected and tried:
1- Air in the line that runs behind the valve cover heating up and expanding. Bled the system repeatedly and haven't got any additional air out.

2- The actuating rod between the pedal and the master cylinder has plenty of free play.

3- Master cylinder check valve. Initially I thought this wasn't supposed to be in there, but it is, and it looks and works fine.

So any ideas? Wild theories? This is all stock 1950's technology which I once thought was very simple.

I had the same problem with my 25 before I wised up and did a mini disc conversion :D.

The culprit turned out to be the check valve not operating properly. Make sure you're putting it together how it was originally. I nearly pulled my hair out trying to get that thing to work properly, and I don't have much hair left.

Unless you're looking to keep it 100% original, I would upgrade to dual circuit at the very least.
Thanks Cruiserman,

I'll pull it out and check it again. I thought I understood how it was supposed to be working. ??? I don't have much hair left anymore either - and it's not because of the kids.

Change to discs and spoil all this fun? Maybe on the next one....
I've got some spare 25 hydraulics if you need any. A couple of master cylinders and rebuild kits in various states as well as a new rear brake hose, etc. I'm going to take a complete rear end to recycler pretty soon. The wheel cylinders are rebuilt.

Anyway, if you can't get it to work, let me know, and I'll break down the last master cyl I was using and see how it's put together.
Cruiserman, you've got mail.

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