Packard Forum Index » V-8 (1955-56)

For those interested, there is a old stock Minor Kit on ebay. I would rather user new stock. But it way be good just for comparisons:

cgi.ebay.com/ebaymotors/1952-53-54-55-56 ... ssPageNameZWDVWQQrdZ1QQcmdZViewItem

Fredrickr,

There is no place for the fluid to go except on the ground, into the vacuum cylinder, back into the fluid reservoir, or into the brake lines where it's supposed to go (and come back from!).

The theory of the vacuum cylinder vaporizing the brake fluid and sucking it into the engine is plausible, but the vacuum is applied to the vacuum cylinder only while the brakes are applied...there is no constant partial vacuum sucking brake fluid away. So it would take a long time for this to occur. I seriously doubt much fluid lost from the reservoir just "disappeared" and got ejected through the exhaust pipe.

If the reservoir is full and the pedal still goes to the floor, you probably have a faulty compensator valve that is permitting fluid to escape back up to the reservoir when the brakes are applied. Take the cover off and look for evidence of fluid return at the valve seat while a helper is applying the brakes hard. Any fluid flow in there tells you the valve is leaking fluid back to the reservoir instead of into the brake lines.

If the reservoir is empty, fill it back up again and have a helper apply the brakes hard while you look under the car for leaks. If the pedal sinks under pressure and there is no evidence of leaks on the ground or around the wheel cylinders (like on the tires), then it's either leaking back up into the reservoir (again, a bad compensator valve) or the leather piston seal is leaking, in which case you will have fluid in the vacuum cylinder, but also you will probably see it around the bottom of the Treadle-Vac, especially where the master cylinder mates with the vacuum cylinder.

The unfortunate typical response these days when dealing with brake failure in a Treadle-Vac system is to blame the power brake unit. But to be fair, you may very likely have had a failure in the brake lines, one of the wheel cylinders, or a brake hose popped on you. These things could have just as easily have happened with a standard master cylinder or an "upgraded" power brake system. The Treadle-Vac is not the only possible failure on a brake system over 50 years old, and by my experience, it is a dependable unit. As with any old car, drive conservatively, and have a good, operating back-up braking system, your emergency brake.

Gauss of the Edsels

Actually, the power unit is under constant vacuum, which is why you can step on the brakes right after the engine is shut off and still have limited power for a stroke or two, there is a reserve of vacuum made possible by the check valve in the system. It couldn't work any other way.

Actually, in a properly functioning TreadleVac unit, NO vacuum is applied in the space between the vacuum piston and the hydraulic section UNTIL the brake pedal is applied. In fact, with the pedal released, that space is merely at atmospheric pressure.

Power assist is applied, when the pedal is depressed, by closing an atmospheric poppet and opening a vacuum poppet in the vacuum piston assembly, to create the necessary pressure differential to help move the piston down into the vacuum cylinder.

Thank you, Brian. You have it quite right, of course.

Although the power brakes vacuum canister assures that a reserve of vacuum is always available to the unit should the demand arise, the vacuum is not applied, in any case, beyond the input port, connecting hose, and vacuum piston, until the brakes are applied.

That means any brake fluid that has managed to leak into the vacuum cylinder section of the Treadle Vac is not subjected to a partial vacuum from the engine manifold unless brakes are applied.

Thus, the time duration for any of the leaked brake fluid to be subjected to engine vacuum is limited to the periods during which the brakes are actually applied.

Brake fluid leaked past the hydraulic piston seal into the vacuum cylinder is not likely to be sucked into the engine in any significant quantities, as far as I can determine.

Gauss

the T/V must operate completely different from modern boosters, as I know when you remove the check valve from a modern booster, even if it's sat from some time, you can hear the air being push into/sucked into the booster. I just assumed that the T/V would work on the same principle. If it doesn't, it's a bigger POS than I originally thought.

The actuation of the TreadleVac vacuum system follows the pattern of the earlier Bragg-Kliesrath (later bought by Bendix) system used on senior Packard Eights, Super Eights and Twelves from 1933 thru 1939, whether on the mechanical system (thru 1936) or the hydraulic system. These systems were pretty much bullet-proof as many still work today 70+ years later with little or so service required. A similar B-K system was used on many heavy duty over-the-road trucks thru the 50s and perhaps even later. In these sytems, vacuum is held in reserve in a vacuum storage tank, and when the brake pedal is actuated the vacuum enters the chamber of the booster. I believe the distinction you're thinking of is that in most modern units of later design, the vacuum reserve tank is actually part of the booster body.

Owen, I am a bit confused. Since a vacuum is an absence of air how does vacuum enter the booster from the storage tank? Do you mean the air in the booster is drawn into the vacant space of the vacuum storage tank ?

Yes, but probably more correctly, since the reserve tank and booster is connected via a check valve to the intake manifold, the air in the booster is evacuated to the intake manifold when the engine is running, from the reserve tank when it isn't.

Owen, Thanks. I understand.