The Stovebolt Site Forums The Shop Area Driveline Weird braking problems

I'm looking for some help on this one fellows. My 49 is pretty much restored to original. When I spend a few miles on the freeway I have to pump my brakes a couple of times for them to come up. This doesn't happen when driving around town, or even if it's been sitting for a while. This only happens after high speed (55-60 mph) for 5-10 miles. The first time it happened I got the pucker factor when I was coming to my exit, but I just pump it a couple of times and it firms up. There is no leaks I can find anywhere and the master cylinder stays full. Any thoughts?

Was the master cy replaced? If not it may be leaking inside. That would be my first guess if the brakes are all adjusted correctly.

Good looking 49. I was wondering how beauty rings would look w/baby moons on a 49, I can see a set on my 49 one day

As GWW mentioned, is the MC new or rebuilt?
I recently rebuilt my brake system, MC, WC's, all the lines and shoes. I rarely go over 50 and mainly cruise at 45 and haven't had any issues of having to pump up enough pedal to stop at those speeds.
In the approx 2k miles since I rebuilt the brakes I've had to readjust the fronts twice and the rears only once.

Things I'd check are:
Proper shoe adjustment.
All the shoe retaining clips are present & tight.
Jack the truck up, have someone apply the brakes w/1 pump then go around and check that all 4 wheels won't spin. Troubleshoot any that will.
Make sure the exhaust isn't too close to a brake line which could heat it up. If so reroute or shield the line.

Good luck
Dave

Check and make sure that the return spring is connected that holds the brake pedal up. Also make sure that the push rod going into the master cylinder has free play when the pedal is up.

It does sound like it could be a heat issue.

If it doesn't happen after sitting or local driving (assuming you go 5 minutes without hitting the brakes)it doesn't sound like a leak or leakby.

Exhaust too close to a line or the master cylinder or a wheel cylinder heating up due to brake drag would be the common causes.

I have stock brakes on my '49 daily driver. I installed Speed Bleeders a few years ago and life has been simple brake-wise.

I would:

-Install Speed Bleeders

-Bleed in this order, rear drivers, rear pass. front drivers, front passenger

-REPEAT Abo^e

-Adjust brakes carefully

Notes and thoughts:

The Speed Bleeders are a one way valve so you'll be eyeing the master for a full or nearly full reservoir, brake pedal to floor by hand one or two times, check master reservoir, repeat. Labor intensive. Adjusting the brake shoes after you've successfully bled the system is critical, adjust to the sound and feel of slight drag on the shoe(s). Plan on spending a few hours on this task, take your time. I do this procedure once faithfully EVERY year, purging the system of 'old' hydrophilic brake fluid, and replacing with fresh. I buy the one quart NAPA Gold brand.

Let us know how it turns out.

Regards,

Cosmo

Best guess - At highway speeds it's running a little hotter than around town and the M/C is heating up just enought that you are getting blow by on the seals in it. Rebuild or replace the M/C should cure it.

Best guess - At highway speeds it's running a little hotter than around town and the M/C is heating up just enough that you are getting blow by on the seals in it. Rebuild or replace the M/C should cure it.


Disagree w/ heat at highway speeds as my original brake '49 daily driver summer trip 1k miles is indifferent to heat. I do agree with checking the status of the MC, I had mine resleeved in brass.

Oh, and if you're running bias ply, drive alone and not with any loved ones and of course NOT WITHOUT SEATBELTS. Bias plys on that truck were meant for dirt roads at 30 mph, not 65 in modern traffic.

Thanks for all the help guys. I will try your suggestions and see what happens. Cosmo, I've got radials on there.

When you have the problem is it a low pedal, pedal to the floor or spongy pedal?

Low pedal.

When you get off the highway, do the brakes go back to normal after the first slow stop?

Yep, they work fine. Pump back up and no problems just driving around the city streets.

The question should be imediately off the highway do they work fine. A) Pump them up and then they are normal until next time out on the Highway? Or B) does the problem linger for a while and then go away?

A) Air in the lines is heating up, expanding and pushing the fliud back into the MC.

B)The MC is heating up and the piston is leaking.

My bet is still on "B".