The brake unit on the 1953 Buick Skylark was a Kelsey-Hayes design . . . not Bendix and not Moraine. That's the one that had the problems described in the Nader book.

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

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

Ain't it the truth, Peter.

That's what made me shy away 25 years ago from attempting to procure $500 worth of new leather piston seals from Albert Trostel and Sons, the manufacturer of the replacement seals found in Bendix repair kits...the originals were made by Chicago Rawhide.

That and the $500 minimum order!

But that sheared compensator valve poppet and stem of yours might be used to refurbish an old stem with a bad seal. If you take a close look the part's design, there is a flange on the stem and a spring-steel speed nut that holds the rubber seal against it.

I seems to me, just from looking at the part, the speed nut could be removed (preferably by breaking it, and eventually replacing it with a new one of the same size), and the old rubber seal with the indentation, slid off the stem and replaced with the good seal from the sheared stem.
It's possible the old spring steel nut could be salvaged off the sheared stem by cutting the broken tip off right at the nut.

Keep the parts anyway...you never know when something stuck in an old Band-Aid tin will be useful!

Gauss of the Edsels

Good for you, Brian.

Sorry, I'm replying to your messages in reverse order...I just discovered the earlier one!

I think most, if not all, of the rampant discontent with Treadle-Vacs is based on poor rebuilds by either incompetent or disinterested rebuilders. It's amazing to me why a rebuilder of brake components would risk his livelihood through negligence toward doing the job right. Although, when it comes to Treadle-Vacs, the repair parts are dwindling, so it may be in the best interest of the rebuilders to do a sloppy job...using some perverted way of looking at it!

I'm glad there are others, like you for instance, interested in keeping old cars old...I mean in design, that is! Why bother showing your old iron if it uses modern guts? I still run generators, electro-magnetic clocks with balance spring and escapement, tube radios, and R-12 air-conditioning. It's so much part of the fun and challenge.

And I'm with you on the doing it myself. If I want something done right, I only depend on myself. If I mess it up, I'll go back and figure out why and do it again. Then, if something I fixed messes up on the road, I feel somewhat competant in getting it fixed.

Also, a failed Treadle-Vac is only a tragedy if you don't know to use the emergency brake...remember, they used to call it that...not "parking" brake! Or your emergency brake is not functional...shame on you!

Gauss of the Edsels

Brian, if you can find the kit you bought, post the part number, and I can probably look up the contents for you, and also the application.

No doubt, NOS kits are the cat's pajamas as far as really, really fixing up your Treadle-Vac, but I always, always keep the old parts in an old Band-Aid snap-top tin for emergency use in case I run out of NOS!

Still, certain parts, like that lousy compensator port spring, do not come in any kit.

I recently scored a couple of major kits, and a complete piston packing kit for Hydraulic Reaction Treadle-Vac (the type used in 1957-59 makes and models) from an AMC source.

Buying kits is so often like getting a pig in a poke, whatever that means. Don't ever buy unless you can see the entire contents. I have a FoMoCo piston packing kit that I bought at a swap meet that is short the curved hose!
I didn't know the Ford kit included the hose until I looked it up in the Master parts catalog. Crap! I bought a short kit!

That's all right, though, the hose is usually OK as long as you twist some single strand copper wire around the ends after slipping them onto fittings to hold them in place. I've also heard of using nylon tie-wraps, but you'd better have one of those tie-wrap "guns" that get the fit real tight.

Gauss of the Edsels

I replace it with a compensator spring from another Treadle-Vac...they are all the same at the compensator port. It's good to keep a lot of spare Treadle-Vacs around for spare parts. I always dissassemble and clean them thoroughly of any old brake fluid to help preserve what's not already ruined.

But I have often wondered if there might be an appropriate substitute: perhaps made of more corrosion-resistant material like stainless steel, rubber or plastic.

It's not a complicated part, just a little gentle compression spring to help close the port when the tip of the valve stem is allowed back to vertical by depressing the brake pedal. Once released from the open, tipped state, hydraulic pressure helps to keep the compensator tightly closed against the valve port seat which is part of the threaded fitting.

I've more often wondered what might be done to repair a old compensator poppet valve and stem with the most common malady, an angled flat spot on the sealing surface from sitting open too long. This can happen to any fully assembled Treadle-Vac, even in a plastic bag on a shelf. I make a habit of removing the compensator assembly, and leave it loose on the bottom of the reservoir until installing in it the car. That way, the any flattening will be even over the entire sealing surface, and will not adversely affect the function of the compensator poppet and stem.

You just have to remember to push in a little on the input rod before re-installing it!

Gauss

Sorry moderator. Like I said, it is inches thick, and I would wear out several scanners putting all that data on line. Don't ask me how I know that! Cheap scanners ain't that hot.

Peter, I'm sorry you sheared off a perfectly good compensator valve and stem...I know how expensive they are to get, not because they themselves are expensive, but because you have to buy a whole blasted $75 kit to get another one!

I hope others in the group have benefitted from your experience. Push the pedal in before installing the compensator assembly, for Pete's sake (sorry, couldn't resist).

Lastly, I'd like to correct one small mis-statement...lie?...I made. You only have to buy *three* of the four Bendix kits to get all the parts they provide in them. And you still don't get the lousy compensator spring. The major kit has all the parts the minor kit has.

Now, if some group member could kindly reveal where he bought his three Bendix kits, I would find my business here complete and satisfying.

Gauss of the Edsels

Peter Packard, the compensator stem tip was sheared off because you probably didn't assemble the unit properly.

When installing the compensator fitting in the bottom of the reservoir, it is necessary to apply the pedal or, if not mounted on the car, push the input rod in a bit first. Then release the pedal or input rod and verify the visible portion of the compensator valve stem tilts forward, indicating the port is open to allow fluid return.

When the pedal is applied, the stem is released, and the compensator port closes allowing the application of hydraulic pressure to the slave cylinders. Then, when the brakes are released, the valve stem is pushed aft from below (indicated by the upper part of the stem tilting forward) again allowing the brake fluid to return to the reservoir.

Contrary to what was posted here previously, the residual check valve is there to maintain a minimum of about 10 psi in the brake lines which "preloads" the system a bit resulting in higher pedal and quicker brake response. Also, an old-style slave cylinder will tend to "gulp" air from the atmosphere when pressure is relieved. The 10 psi residual prevents air gulping at the slave cylinders.

Gauss

Read with great interest everybody's comments on the Treadle-Vac. I've been rebuilding these things for myself and a couple of friends for almost 30 years. I drove my rebuilds reliably in two cars for fifteen years to and from work in Fresno and Long Beach, California, and across the country to the east coast and back, twice, as well as other trips to Fort Worth, Portland, Las Vegas, the central California coast, etc.

Many years ago I was blessed with the good fortune of locating a Bendix power brake technical binder containing extensive parts listings and procedures. I found it at "Acres of Books" in Long Beach, and paid a goodly sum for it, since "Acres of Books" charges by the inch.

Having this resource at my fingertips allows me to confirm the contents of repair kits for Bendix Power-Vac, Master-Vac, Hydro-Vac, Treadle-Vac, and numerous other Bendix products of the 1940's and 1950's.

For the group's benefit, I list here the complete contents of the four repair kits that Bendix made available for 1955-56 Packard Treadle-Vac:

Minor Repair kit:

Guard - Push Rod (boot)
Gasket - End plate (the triangular cork gasket)
"C" Washer - Compensating Valve
Seal - Compensating Valve Fitting
Poppet and Stem - Compensating Valve
Seal - Hydraulic Outlet Fitting
Cup - Residual Check Valve
Gasket - Cover, Fluid reservoir
Cup - Hydraulic Plunger
Washer - Hydraulic Plunger (fiber)
Seal - Hydraulic Plunger (leather)
Seal - Master Cylinder End (rubber)
Gasket - Flange (the large roughly square one)
Gasket - Air cleaner screw (a small rubber washer)
Gasket - Plate and tube (for the vacuum inlet fitting)

Major Repair kit:

All of the above plus:
Seal - Push rod
Seal - Tube plate
Atmospheric Poppet
Vacuum Poppet
Clips (for Vacuum poppet) Quan. 2
Gasket - Diaphragm

Don't expect a new push rod guard (boot) with kits you buy today...that is an extra-cost item (around $15).

Note also the "C" washer that retains the compensator spring was included in the minor and major repair kits, but neither contained the spring itself. Today, expect to have to re-use *both* parts from your old unit, as neither part is provided in new kits.

Piston Packing and Diaphragm kit:

Tube - Vacuum (the short curved rubber hose)
Spring - Piston Packing Expanding
Wick - Piston Packing
Packing - Piston (Leather)
Seal - Tube Plate
Diaphragm
Gasket - Diaphragm

Poppet Replacement kit:

Diaphragm - Vacuum Poppet Compensator
Atmospheric Poppet
Spring - Atmospheric Poppet
Vacuum Poppet
Clips (for Vacuum poppet) Quan. 2
Snap Ring
Gasket - Diaphragm

Notice with the Bendix kits, you really didn't get everything unless you bought all four, and even then you still didn't get that lousy compensator spring.

On DOT5 fluid, have not used it myself, but I've heard generally negative comments about using it with Treadle-Vacs. Would like to hear any positive experience from someone who has used it successfully over an extended period.

The only things I've ever had fail on my Treadle-Vac were the leather piston seal and the compensator valve and stem, and in both cases they simply began to seep a little...nothing sudden, nothing catastrophic.

BTW, the book recommends the 1956 Packard unit (P-4) as the service replacement for for 1955 early (P-2) and 1955 late (P-3) Packard Treadle-Vacs.

The identification numbers can be found stamped into the vertical end of the Treadle-Vac master cylinder.

Wish I knew more about this Craig Henderickson fellow, and what the nature of his brake failure was.

Hope this helps someone.