Re: Brakes went potty

Posted by BH On 2012/10/17 9:14:59

Your BTV may have a different design of plug than what's shown in the photos provided by HH56. There are no moving parts in that plug that I know of in that plug; the vent path need only be kept open.

The moving part that you need to be concerned with is the compensator valve - located in the bottom of the reservoir. However, there's no maintenance - except to periodically top off the reservoir with clean fluid. It's when brake fluid condenses (gels) and parts begin to dry out or corrode (typically after years of non-use) that problems occur.

The spring-loaded compensator valve is normally held open, with brake pedal released, by a washer at the end of the hydraulic plunger - allowing fluid between the reservoir and the hydraulic chamber, below.

When the brake pedal is applied, the compensator valve is released as the plunger moves forward, and a spring pulls the valve shut. Unlike more conventional master cylinders, the hydraulic seal of the BTV is held in fixed position. The intrusion of the plunger into the hydraulic chamber simply displaces fluid out into the lines - PROVIDED the compensator valve is closed.

If the compensator valve fails to seal, fluid gets pushed back into the reservoir, rather than the lines - perhaps out the vent in the cap.

Of course, the compensator valve seal can wear over an extended period time, requiring replacement of the stem valve. The stem valve is included in rebuild kits, but reports of quality seem to vary among suppliers. The valve must be removed and installed EXACTLY as described in the shop manual - else it could be damaged.

The relief port has no moving parts, but is simply a passage in the m/c casting for excess fluid. There are some differing opinions as to which way fluid moves.

The 51-54 manual offers nothing on theory of operation of the BTV; for that, you need to download the PDF of the "Brakes" section from 55-56 shop manual, available from this article in the site's in the archive:https://packardinfo.com/xoops/html/modules/article/view.article.php?119