Re: New Member - Help with disassembly of Power Brake Unit

Posted by BH On 2007/4/7 10:26:23
Boro -

I've never had a big problem with the TreadleVac unit, myself, and concur with Owen_Dyneto's position that they were used successfully for many years and on many cars.

The NUMBER ONE thing to look out for on these decades-old units (especially from cars that sat, unused, for extended periods) is a pitted hydraulic plunger. Because the seals are held in a fixed position, and the plunger moves through them, a pitted surface will act like a cheese-grater and cause a failure of the seals in short order. A hydraulic failure in ANY single-chambered master cylinder could be catastrophic, but such an event unlikely in a brake system that has been properly gone-through and is properly serviced.

One thing I feel that has often been overlooked in rebuilding these units is the compensator port valve spring. That valve is CRITICAL to hydraulic operation, but the spring is not included in the "minor kit" - not even in an original from Bendix. I have seen this delicate spring corroded in two in a couple of units that I disassembled - cars that hadn't been used in decades. I suspect this happens, over time, because DOT3 is hygroscopic (draws moisture right out of the air) and the reservoir is NOT air-tight (like more modern designs).

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