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Brake lights stay on
#1
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Dan Marrin
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I have a '58 Packard Hawk and am just getting it prepared to go off to the body shop; it is one of the rare models that has a manual transmission with overdrive. I notice that when I pump up the brakes, the brake light stay on. I thought I might have a defective brake light switch, so I loosed it and discovered that the system was holding brake fluid pressure even after the brake pedal has been released. Once I relieve the pressure, the lights go out, so I assume the switch is OK? After some research in the shop manual, I see that my car may have a hill holder. Can anyone confirm this? I suspect that the hill holder might somehow be related to the fact that the pressure does not drop off when the pedal is released. I am afraid to drive the car because I assume that the shoes are being held against the shoes. Is there anything else that may be causing this condition?

Posted on: 2017/2/24 20:30
Dan Marrin
Breezy Point, MN
'40 120 sedan, '41 Rollson "high hat", '48 Sup8 conv, '48 Sup8Del LWB sed, '58 Hawk
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Re: Brake lights stay on
#2
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Owen_Dyneto
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Though I suppose it could be the hill holder, the most likely cause is insufficient brake pedal free play. The pedal must have some free play to insure that the internal port is uncovered so pressure can return to zero. Should be covered in your shop manual.

Posted on: 2017/2/24 20:38
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Re: Brake lights stay on
#3
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HH56
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What O_D said. If the Stude master is similar to those Packard used the internal port referred to is almost directly under the fill cap. The brake free play must allow the piston to move back past them so they are open. Packard cylinders had two of the ports -- one in the rear which is fairly large and and one in front of that which looks large but is actually a chamfer and only has a very tiny hole thru the middle. That port was prone to rust or debris filling the depression and blocking the tiny hole. You might check out yours and see if it has a tiny orifice that is blocked.

Believe the hill holder was an option so no way of knowing if the car was equipped without seeing the car or the build slip. You should be able to visually locate it yourself. If present, it is a roundish cylinder with a lever on the side and brake lines connected to one end. It is mounted on the inside of the frame rail directly opposite the master cylinder. The master is mounted on the outside of the rail. The lever on the side will have a rod connecting to the clutch pedal and linkage.

If the unit is working properly it should not come into action unless the car is on an incline with the rear down about 5 or so degrees and the clutch is depressed. As the clutch is released, the rod should move the lever which pulls the mechanism that provides the fluid block away from the brake lines so fluid can return to the master and free the brakes.

If your car has the Hydrovac power brake booster a problem there adds another layer which could add to the puzzle but not sure if hill holders were used with those.

Posted on: 2017/2/24 21:14
Howard
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Re: Brake lights stay on
#4
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Dan Marrin
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Thanks guys for your suggestions. I will try to get over today to get a closer look. Howard, I do have the power booster; how might that tie into the equation?

Posted on: 2017/2/25 8:29
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Re: Brake lights stay on
#5
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Owen_Dyneto
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I do have the power booster; how might that tie into the equation?

Unless the booster if faulty, it really doesn't. Regardless of how the master cylinder is actuated, the linkage must allow the piston in the master cylinder to return fully to it's "at rest" position to allow the hydraulic pressure to bleed off back into the reservoir.

Posted on: 2017/2/25 9:05
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Re: Brake lights stay on
#6
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HH56
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The Hydrovac that Stude used on the 57- 58 Packards has a hydraulic seal arrangement and leather around the power piston configuration much like the Treadlevac units which Detroit built Packards used. As we have found with the Treadlevac units, years of neglect, a faulty seal, or failure to change fluid can cause problems.

Upon release of the brakes, the power piston is returned to its home position by a large spring. Any fluid which may have leaked past the seal into the vacuum side combined with old and possibly hard or contaminated lube can cause the leather seal around the power piston to gum up and stick to a point where the spring is unable to return the piston to the full release position.

In a different arrangement but much the same principle as the Treadlevac, failure of the piston to return fully home leaves in this case, a check ball rather than a valve closed and a thru port inside the slave or secondary master piston assembly is blocked. With fluid trapped inside that secondary master cylinder and piston being unable to return to the main master and reservoir, some pressure can still be applied to the wheel cylinders. Results in effect would be much like the hill holder failing to release its intentional mechanical block.

Even if the power piston side is OK and releasing properly, if the old fluid has managed to congeal or even crystalize as has been found so often in the Treadlevacs after long periods of sitting, the inner valving of the slave master piston can be prevented from working with the same result being trapped fluid.

Posted on: 2017/2/25 11:00
Howard
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