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A forum member sent in his Treadle Vac which was failing. We've offered to investigate and rebuild a unit to document what the problems were.

First step is to remove the reservoir cover to see the conditions there, see photos.

Photo 1 There is an extensive amount of crud caused by long term storage and not flushing the brake fluid once in a while

Photo 2 And I mean EXTENSIVE!!

Photo 3 As indicated by the white pointer, the bypass return port is blocked with crud and had to be unplugged using a drill bit by hand This port routes fluid that leaks by the primary seal back into the reservoir. If the bypass return circuit is blocked the fluid is then sucked into the vacuum section and the reservoir level goes down. If it goes down too far the brakes will fail.

Instead of cursing the Treadle Vac unit, all ire should be directed to the previous owner who did not maintain the system by flushing and refilling it......... or to the current owner.

It is not the Treadle Vac unit that is at fault, as a manual system will eventually fail also if not properly maintained. The best comparison I can think of is a water pump. If a system with antifreeze is not flushed and refilled periodically the water pump lubricant in the fluid gets depleted, then rust/scale form and get embedded in the seal. Then a leak happens. Nobody curses the water pump as everyone knows that they eventually fail, especially sooner if proper procedures are not followed.

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Photos 4 & 5 Booster can

See the rust and gunk at the end of the can, there was also 3 oz of rust colored brake fluid down there... DOT 3 brake fluid does no cause rust, only water causes rust. A DOT 3 brake system which is open to the atmosphere absorbs water over time and if the car is not used the water collects and rusts the wheel cylinders and master cyl if it is iron. In the master cyl reservoir there was gunk caused by water/oxygen and brake fluid

Photos 6 & 7 Vacuum piston.

There is rust/gunk on the lower (5 o'clock to 7 o'clock) portion of the vacuum piston caused by water

Photo 8 "Tipper "valve/ seat.

The rubber sealing portion of the valve is in perfect condition as is the stainless steel seat. There was no debris under the valve and no indication that there was a leak bypassing the valve

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Diagnosis:

The unit sat a long time without being used and the DOT 3 fluid absorbed water. The debris was drawn into the system and some blocked the return circuit. The fluid that leaked by the inner seal could not return to the reservoir as designed so it was sucked by the outer leather seal and into the vacuum booster

Failure by the owner was the cause of the failure of the unit. When we received the unit we placed it on the Bendix testing bench and it gave appropriate boost and did not leak for the 25 seconds it was actuated. The owner said he experienced non-operation, this can be caused by the fluid being sucked in and the reservoir going dry. On a manual brake system the same thing happens if there is a leak and it is not topped up.

On a manual system the leaks can usually be detected by inspecting the outside of the master cyl or looking at the backing plates. On a Bendix Treadle Vac the leaks are almost always internal thus not easily detectable. Part of routine maintenance is to check all fluid levels, failure to do so can cause engine overheating/failure; Transmission failure; Internal engine failure (lack of oil) or rear axle failure. The brake system is no different.

FOOTNOTE We purchased a 53 Patrician from the dealer in Jersey Shore PA many years ago. The car drove home but it was hard to stop. Treadle Vac tested just fine, then we removed a wheel cylinder, it was frozen almost solid as were the other 3. Two were Wagner brand and two were Delco.

We did not curse at Mr. Wagner and Mr. Delco, we realized that the car had been stored for many many years and that with practically no use frozen cylinders are common. This happens on Packards, Duesenbergs and Fiats too.

Fred in photos Booster10 & 11 were those screws found in the bottom like that?
Wes

If we had found loose parts in the unit we would ahve noted so and their effect on performance. Those are the 3 bolts that attach the vacuum housing to the triangular base of the master cyl portion. In order to disassemble the unit it is necessary to remove the bolts.

Thanks for your question

With the water and rust inside the vacuum portion I would wonder about the condition of the poppet valves or sleeve valve and if any of the crud might have been sucked up inside.

All sections of any unit whether it be a transmission, fuel pump or Bendix TV etc. are disassembled, cleaned and necessary parts replaced when performing a proper rebuild.

Would DOT 5 be any better for use in these? John

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Glad to hear that. I think we have established that some "rebuilders" do nothing but clean up the power piston and don't go inside that end at all. I remember several have mentioned they were still having issues with the assist after a rebuild. I think Ross has mentioned he runs into hardened or split poppet valves that won't seal properly quite often.

I wouldn't think DOT5 would be better, because my understanding is brake fluid is design to trap moisture and keep it from pooling. Then by changing out the fluid every so often removes the mixture (water and dirt) trapped in the fluid and keeps corrosion to a minimum.
Besides that I think DOT5 was designed just for higher temperatures.
Just my two cents.
Wes