Re: Bendix Treadle Vac Diagnosis

Posted by fredkanter On 2016/8/10 13:58:17

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.