I had to drive my postwar truck into town today. There's no free play in the brake pedal, and when I got home I smelled brakes. My guess is that there's air in the lines which has expanded so much that it applies the brakes continuously. Am I on the right track here?
I would pull the wheel cylinders and get ready to hone them, but first look for leaks. Air can be compressed but liquid can not .
Could the problem be in the master cylinder? If the piston cannot fully retract it could leave residual pressure in the brake lines that increase with every brake application.
We had a civilian model Ford stake body in our motor pool that would do that stunt at the most inopportune time and place!
Tony
You need to find out if heat expansion or seized wheel cyl pistons, crack off a bleader, if holding pressure then it's the master, piston valve or not enough peddle free play, if not holding high pressure, then slave pistons not returning, seizing up. Also check breather hole on master cap.
parking brake on ?
or the adjusters turned out? (rear wheels)
both will give pedal hieght and brakes will drag
air in line will not hold the brake on and will give low pedal hieght
Check out the park brake system.Something is not releaseing.
This would give hard pedal and smell.Did you notice if the smell was stronger at the back than the front by chance?A bad caliper can drag the brakes on the front but you would feel a brake problem in the front by it's pulling to 1 side or the other.
Park brake? when steve mentioned a post war truck I'm thinking still old, chev, dodge, inter or? park brake on the gear box?
Had that happen to my old Chevy truck a number of years ago. I checked everything. Turned out being a flex line. They get old and swell on the inside blocking return fluid.
Yes, I have had the rubber lines go bad and collapse inside holding slight pressure on the wheel.
Sounds like the master cyl. or the pedal linkage is freezing up and not allowing the pressure to release. There are 2 holes in the master cyl. resivour. One feeds fluid to the cylinder to apply the brakes the other is a vent. If the pedal or piston isn't retracting enough to clear the vent the brakes stay on. You said "prewar" so I'm assuming it's an older single master cyl. system. That's how they operate. It's not air. If anything air would give a spongy pedal not lock the brakes. Second assumption: It's all 4 wheels, right? If so only one thing would affect them all at once and it's described above.
Here's Steve's 1951 Dodge BC pick up:
There's one problem with old hydraulic systems not yet mentioned (but I don't think it's the case now) ..old rubber hoses can swell internally so the return springs can't pull back the shoes - the hoses stops the flow of brake fluid so brakes won't release on one wheel - or the rear axle. All brakes smoking indicates the pedal linkage / the master cylinder being the problem as others have suggested.
Yep, that's the truck. It just got new hoses last year, so that's not the problem. I'll check the MC.
I had the same problem with my '49 Chevy truck on the way to a parade. The left rear wheel locked up and would not release, until my wife pump the brake hard and it went to the floor after that cylinder leaked the fluid out.
I had a new master cylinder, but I ended up replacing all the wheel cylinders, flushing the brake lines,new brake shoes and two brake drums. They don't build anything to last you know.
Now, Willby stops on a dime.
Joe R.
Been a while for me, but weren't the war era and post war era of Dodge Trucks prone to sticking brake cyls if not used near daily and continuously?
Feeble recollection here, but something caused a spark of memory on that.
My sons old 42 Chev army truck had that problem... We found the return port in the MC was clogged with old brake crud and rust. We drilled it out and flushed the system... problem solved.