Bendix Treadle Vac, Myths, Fiction and Facts

Posted by jfrom@kanter On 2017/2/21 12:21:33

Bendix Treadle Vac, Myths, Fiction and Facts
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Since the start of the internet and the formation of forums there has been a spike in talk and discussion of the BTV and how dangerous this unit can be. There has been posts stating that if one continues to use a car that is equipped with a BTV you are not only putting the lives of other at risk but your own as you will never know when it will fail. But what is interesting is the amount of vehicles that could have been equipped with the BTV during the 1950's and early 1960's. Conservatively speaking 10,000,000 vehicles:

Buick 1957
Cadillac 1956 &1958
Chevrolet 1954-58
Edsel 1958-59
Hudson 1954-57
Lincoln 1953-60
Mercedes 1952-62
Mercury 1953-58
Nash 1954-59
Oldsmobile 1953-56 and early 57
Packard 1952-56
Pontiac 1954-58

We decided to perform a study on the failure of the Bendix Treadle Vac not only to discover the problems that owners have, but in hopes to educate ourselves and others on the unit itself and put to rest some of the myths that have been put out on the internet. We offered a FREE rebuild to any of the members of the Packard forum with a BTV that had recently failed to analyze the causes of failure.

The study that we performed was done across five different units. Three came from customers for analysis and two from cars in Fred and Dan's private collection that had been in long term storage( 40 years). All units that were received where either working at the time of removal with the pedal not returning/sticking or non operational due to non use. Prior to disassembly the units were tested. All held vacuum and produced hydraulic pressure.

All units experienced similar problems. Firstly the brake fluid had crystallized within the hydraulic section in and around the bypass port. Secondly the hydraulic plunger seal had failed allowing fluid into the vacuum section, which then was later sucked into the running engine not showing a physical loss of fluid. In the units that experienced stuck or sticking pedals. DOT3 brake fluid is hygroscopic meaning it absorbs water from the atmosphere. The brake fluid which is prone to water absorption had been allowed to lie in the vacuum section creating rust build up. The friction between the leather seal of the vacuum piston and the vacuum can lead to the stuck pedal. The vacuum sections were in good working order, only needing cleaning and a new leather piston seal.
The crystallized brake fluid:

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The buildup of rust that causes the sticking pedal:

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