Re: Bendix Treadle Vac, Myths, Fiction and Facts

Posted by HH56 On 2023/2/21 20:25:44

I think of the two staying with the Bendix unit would probably be the better choice. Not only is it stock but the Moraine unit has its own issues. As far as operational feel and braking assist ability they are probably comparable.

From what I have read and been told, the Moraine unit was made by GM under license from Bendix and used many of the same operating principles and designs Bendix developed for the Teadlevac but also went off on their own in some areas.

Outwardly, the units look very similar but internally there are some differences. The Moraine hydraulic section is quite different. Some have said the biggest issue with the Moraine is due to how it is laid out, if a hydraulic or vacuum side seal starts leaking the fluid is all but guaranteed to be sucked into the vacuum side because there is no relief passage connecting the seal chamber to atmosphere so there is nowhere else the fluid can go.

In the Treadlevac there is a relief passage with a port opening above the fluid level in the reservoir. Fluid going into the vacuum side is not as likely to happen unless the relief passage or port has been blocked in some fashion. With the port open and functional any leaking fluid can go back to the reservoir and any vacuum leaking thru will only pull air.

Unfortunately when Kanter did teardowns of some failed Treadlevac units it was found that apparently some rebuilders were purposely blocking the relief port with silicone. It would be interesting to know why unless they were imitating the Moraine unit or there was a design change on the more advanced Treadlevac models made after Packard went away. Since the repro castings also do not have that port that could be a reason.

A port issue specific to Packard was the flat reservoir cover when combined with a cover gasket designed for a different "bubble" style cover also blocked the port. If either has happened and a seal leaks then the Treadlevac is also prone to fluid being pulled into the vacuum side. As long as the relief passage is not purposely blocked with silicone the cover issue can be easily corrected by adding a small slot where the gasket and port opening meet.