Packard Forum Index » V-8 (1955-56)

What could be causing my brakes to stay applied in my 55 Patrician? The master cylinder and wheel cylinders have all been rebuilt the TL works great, new brake shoes front (non silicone brake fluid) rear shoes OK and adjusted per the book (resistance then seven clicks down). After the car has driven for about thirty minutes starting and stopping in traffic, the brakes seem to lock and the rear brake lights stay on and she welds her five thousand pound self to the ground. After about 90 minutes the rear brake lights go off and off you go for another thirty minutes. The engine is now quiet, good oil pressure and the temp good. I believe to have uncovered another 29 minute car, please no pushing gents you will all be able to place your bids.

I would guess some type of residual pressure problem.

First thing I'd check is to make sure there is nothing preventing the TreadleVac from returning fully to the off (up) position, for example restriction on the upward movement of the pedal itself. If in doubt on this aspect, disconnect the pedal from the TV unit; if the problem goes away your problem is in the pedal movement. Give an upward tug on the TV actuating rod to insure it's fully retracted. Hopefully the TV was installed promptly after rebuild, they don't take well to sitting on the shelf for months at a time.

If that's not it, then the problem is probably in the hydraulic portion.

vacuum or atmospheric?

Thanks Owen and BigKev The residual pressure not venting seems to describe the problem. I was also wondering if a lack of vacuum or an issue with the atmospheric port could be part of the problem? Brake travel also returns with the pressure is off.

Power brakes were standard equipment on the Patrician, were they not? But a good question, the car could have been mongrelized.

Power brakes and power steering were an option, she has both and fortunately not AC (something less to fix). .

Morgan -

The Brake section of the 1955-56 shop manual, which is archived here, contains an excellent text on theory of operation and proper servicing of the Easamatic Power Brake unit (aka - the Bendix TreadleVac).

You should take note of the proper operation of the compensator port valve in the hydraulic section. Failure of this valve to open upon release of the pedal will cause execssive residual pressure in the system. This can be the result of improper installation of the valve during reassembly; that can result in a broken lower stem.

However, I suppose it could be that the piston assembly in the vacuum section is not releasing completely - perhaps due to a sticking poppet valve. In turn, that could prevent the piston rod from moving to the fully released position, and the compensator port might not open.

I bring up the vacuum section because you noted that the "master cylindler" was rebuilt, but not by whom or to what extent. You see, most kits available to the public these days contain only those parts needed to remove and overhaul the hydraulic section - nothing for the vacuum section. It's my undertsanding that parts for the vacuum piston have been reproduced by rebuilders, but it's been my experience that they won't sell these parts except as part of a complete rebuild service for the Treadle-Vac unit.

Yet, another part that was never provided in any overhaul kit - even those supplied by Bendix - is the compensator port valve spring for the hydraulic section. Though that doesn't appear to be at the root of your problem, it should be noted as another part that is (presently) only available through complete rebuilding service.

I'll still be surprised if anything other than compensator valve and it's activation is the problem. If you can time it so it fails where you can get into a friendly place and remove the fill cap, you can see if it is the issue.

In the relaxed photo, you can see it tipped a few degrees and uncovering the vent port. In the applied photo it is straight up and down and port closed. If you can access it when stuck, you can put your finger in and GENTLY push the stem toward front of car and see if pressure releases. If so, then either the valve is faulty or something is preventing the piston from traveling far enough for the lip on the end to catch the lower stem and activate it. If it is tipped, then the only other possibility is something has happened to the residual pressure valve.

Have you tried pulling back on pedal when things stuck?

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BH. I have entire shop manual on my laptop next to the car plus on a USP zip key fob. The overall was done locally with the standard ordered parts and yes there were a few that were not available but still looked good. Using the manual as a guide everything seemed to go back together. I will run the diagnostics as recommended however someone once said on the forum that the stock Bendix TV works betst as a museum exhibit and another was strongly recommended, do you remember the name of the unit? .