Re: Bendix Treadle Vac Study- Serioius Business!!
Posted by BH On 2010/12/2 10:40:42
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.
Attach file:
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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.
Attach file:
(113.65 KB)
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