My car has a factory vacuum brake booster that was recently repaired by White Post Restorations under warranty because it leaked. Great service, no complaints. Yesterday, while checking for a power steering leak the brake lights lit up. I hadn't applied the brake pedal. My immediate su****ion went to the booster but even after I shut off the engine the lights stayed lit. I cracked the bleeder screw and the lights went off. Today I disconnected the vacuum hose and hooked up a gauge. 18 inches at an idle, drops to 15 or 16 when the engine revs and jumps to about 22 when the throttle is released, then back to 18. That seems OK to me. Here is the weird part. With the vacuum hose disconnected during my check the brake lights came on. I jacked one front wheel off the ground and the brakes were, in fact, applied. I waited a few minutes and they went out. I reached into the window and started the engine again without touching anything except the key. In a couple minutes the brake lights illuminated again. Anyone care to take a crack at what would cause the brakes to build pressure while the engine is idling with the vacuum hose disconnected?
Was the master changed before or after the booster change? Is there inline residual valves that weren't there before? What the combo isn't all original drums all around?or updated to discs upfront? mags you are getting a stuck wheel cylinder or the master is getting stuck. Not moving smoothly. But self applying? Give info on all that has been done. But if they did the work on the booster, removed the master and rebled the system. They should have road tested it and then gave it back.
The MC was rebuilt and installed several years ago along with the booster. The booster started leaking and was repaired under warranty. Pure stock brake system. I've come to the conclusion that the MC piston is not fully retracting after the brakes are applied. There is over an inch of pedal free play, no way to adjust it out using the eccentric mounting bolt. There isn't a "they". I do all the mechanical work myself. No way to road test the car yet. I just installed the last piece of the restoration puzzle in Dec and have been chasing gremlins in the brakes and charging system since then. Once it is road worthy it will get appraised, then insured for actual value. Thanks for the input.
I had the same problem with my '54 Mercury (with Treadle-Vac PB booster) and it turned out to be that the adjustable push rod was too long so that was solved with an adjustment. However, I believe from memory that the stock Ford master cylinder push rod is not threaded like the one used in the Treadle-Vac so there is no length adjustment. Sounds to me like you need to rebuild or replace your master cylinder which is sticking.
I concur with the MC sticking. I've removed, dis***embled, cleaned and re***embled it. Waiting for the paint to dry so hopefully have time to get back to it soon. The Treadle-Vac is a lot different than the one I have.
Yes, Ford used the remote PB booster made by Midland whereas Mercury used the Bendix Treadle-Vac. I have the correct Midland booster on my Ford Skyliner.
Perhaps if you have drums all around they are adjusted on the cusp of locking up? It might not help it if they are too tight. Just a thought.
Time to put this thread to bed. I had three malfunctions which really confused the issue. The first was a faulty brake light pressure switch. It finally failed in the closed position which made it obvious. Problem #2 is an eccentric washer that is mounted behind the secondary shoe. It limits the amount of travel and the manual instructions of how to adjust it, in a word, ****s. I backed it off entirely and cured the just the one brake that locks up. The primary problem was the master cylinder which I had professionally (and expensively) rebuilt. I ordered a rebuild kit from Rock Auto (Raybestos) and took it apart. The piston was wrong for one thing, and all the parts were not installed. Installed the kit, bled the brakes, all is working. Next step is detailing and photographing for Hagerty.
If you want to tell us who the did the MC overhaul it may help others. I have alway rebuilt my own with a kit and hone for cleaning up the bore. I have never found one rusty. Pressure Brake light switches from Harley Davidson are very good replacements for our Fords using that style. Thanks for sharing your finds.
White Post Restorations in VA sleeved and rebuilt it. The MC itself was in pretty poor shape when I sent it to them. I'm happy with the rebuild they did on the power brake module.
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