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I also very much like the idea of a retrofit-cap with a low fluid warning switch/lamp. The single circuit brake system in my 53 clipper (manual brakes) has had me worried for years. A bolt in dual circuit MC would also be a safety upgrade I wish I could find. This is one of the few modifications we are allowed to do to historic cars in Germany and maintain original/collector car status. -Mike

It's good to see that a forensic analysis of any issues with the BTV has been undertaken. I'm no engineer, but let me toss in my $0.02 on the matter.

I've used two overhaul kits purchased from Kanter Auto Parts, 20+ years ago, to rebuild the BTVs in my '56 Packards and had no problem, but each of those kits had the original style compensator port valve. I've been into a few other BTVS for minor inspection/repair and to reorient the cover for better access to the fill plug. It seems odd to me that some people have experienced failures after a rebuild, when my father drove a brand-new '56 Executive equipped with the power brakes for nearly 75,000 miles over the course of 7 years and never had a problem with the BTV.

Still, reports of failures so soon after a rebuild in recent years are troubling. The hydraulic section of the BTV is easier to rebuild than a carburetor. IMHO, as someone who's been "tinkering" with various brands and eras of vehicles for decades, I feel that the design of the Treadle-Vac is as sound as any other single-chamber master cylinder of the same period. Surely, the BTV should be able to give as reliable service now as it did when new - provided available parts, at a minimum, meet OE specs.

However, I am concerned about the lack of availability WRT the compensator port valve spring.

Pictured below is a view of the reservoir of the hydraulic section that was sent to me some 20 years ago, as part exchange for the purchase of a good used body for the hydraulic section. The buyer's concern was with the casting, which their (unspecified) rebuilder advised had deteriorated to a point beyond reuse. However, it needed a bit more than just that. The parts as I received them, had been washed cleaned, but after years of sitting in unheated storage, additional corrosion has occurred. The compensator port valve spring was clearly broken, then, but there's not much left of it now - not sure where the rest of it went.

That's not the first broken compensator port valve spring I've seen. Yet, I've also seen one of these springs which was not yet broken, but had weakened at a point where the wire had become discolored; I presumed that was the beginning of corrosion. Thinking back, the spring in my second rebuild exhibited some discoloration, but seemed sound enough to reuse, as the car was (and still is) a work in progress that doesn't see regular use on the road, and was refilled with DOT5.

About 15 years ago, I found a NOS Bendix major overhaul kit for these units at a swap meet, and purchased it just for reference. My recollections were that the major kit included the compensator port valve spring, but someone else said, at another forum, that it was not. Alas, I have been unable to lay my hands on that kit - located somewhere in my offsite storage. However, a Wagner Lockheed Power Brake Replacement Parts catalog from 1960 showed the spring as included in their major kit - in addition to being serviced separately.

While this spring has only a small amount of work to do, it is critical to hydraulic operation of the brake system. I would replace this spring in each of the BTVs in every one of my cars if a proper replacement were avaiable.

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I've read or heard somewhere, can't verify from personal experience, that the compensator port spring, at least the OEM one, was stainless steel. Some things but not many attack stainless steels, in particular acidic halides (chlorides, fluorides, bromides). The same types of chemicals would also be very aggressive on aluminum and ordinary steels.

Stainless steel (steel with 10%-ish chromium) will corrode if it is in an anoxic environment. Corrosion protection in SS comes from corrosion! The chromium on the surface reacts with oxygen in the atmosphere to form a very thin layer of chromium oxide, which prevents oxygen from being able to interact with the iron in the steel.

Does brake fluid have any free oxygen in it? If not, or not much, then SS wouldn't be of much benefit.

Tom, I was thinking more of the possible conditions in storage that might have furthered the damage to the piece pictured, not what might have occurred in service. Sorry for not being clearer about that.

Fred, thanks for all your hard work. I just finished helping a friend of mine rebuild his 1955 Clipper Bendix unit this morning. We were aware how important the spring is and ours looks and works perfect. The unit bench tested very well. Packard did make the brake fluid reservoir kit that lets you monitor the fluid level of your unit without having to crawl and remove the cap. Of course no warning light etc.... Also thanks to Ross for his tutorial on this site on rebuilding the units. I have done 20-30 of them over the years and I always know that I can't learn too much.

I am still of the belief that a spring should be made available to totally eliminate any doubt whatsoever. There is probably one already made that is close if not right on. Reid supply has one with all good dimensions otherwise but the wrong height so surely there are other spring companies that might have a stock spring that would not need set up costs.

I am also believing that if one of the vendors would put together a top tier super deluxe complete rebuild kit consisting of not only the current rebuild kit but also add any and everything that could be replaced in the hydraulic section it would also go a long way toward resolving some issues. In those instructions also mention that in addition to replacing everything with the new pieces in the kit to check the casting for any pitting on the seal surfaces. Maybe even have a picture or two of the seal surface and what is good and what is not.

Market and price it accordingly and I think it would sell. I think there might be some validity to another posters question on who actually does the work. Someone who does not see these things regularly might not necessarily know whether something is good or questionable. If it was in the kit with instructions to use the kit in it's entirety, no ambiguity.

It is the owners responsibility to ensure they take the unit to a knowledgeable rebuilder. If the rebuilder has not seen many of the units and can't tell if a part is defective, run as fast as you can the other way. Owners also need to take responsibility for the decisions they make. There are several good rebuilders of these units and if someone takes it to "a friend of a friend" then they will be responsible for their own decisions and safety.

Couldn't agree more but we both know there are lots of people who get in over their heads or for other reasons -- pride, price, time, whatever -- won't go professional. A full kit would at least give a starting point.

After hearing the story of the one professional already mentioned here, and one on another thread, just wonder how many more have also had those experiences. There used to be a large "rebuilder" of parts here that many local garages and stores did business with. Turns out their version of a rebuild was mostly cosmetic. That was found after there were so many comebacks and then complaints that the state BAR got involved. Rebuilder closed up here but probably just moved to a state or country that didn't care as much. They were "professional".

Might work for some things but the only problem with that approach with BTVs is there is not a large supply to keep coming back for and the first one can be a disaster.

I consider myself reasonably handy with things mechanical and have taken a few TreadleVacs apart over the years out of curiousity but not with the idea of rebuilding for my own use. With something so critical, I'll entrust that to someone with a good reputation that does several hundred of these units a year - really for two reasons. He makes or has made those parts which may be needed that are not ordinarily included in kits, and his experience in looking at hundreds of cores makes his judgement about what is required and what is useable and what is not, far better than my ability to do same.