Re: Bendix -Treadle Vac - Failure and Fix
Posted by BH On 2010/10/4 11:57:12
Man, you guys post too fast-n-furious for me to keep up with, but let me try to provide of summary of my perspective.
From the site's Photo Archive (and the 48-54 parts book):
This also shows the same passage, but I wouldn't infer from the cross-section that it is sealed off by the cover gasket.
The cover gaskets on the BTVs in my V8s all had the style of gasket as shown in the image of MMs major kit for 55-6 that HH56 provided, earlier, but the original was made of leather. Could there have been a design change so minor that it was only noted as a lettered revision to the engineering drawing, with no change in part number?
Next, keep in mind that this is an "illustration", but the compensator valve stem as shown, here, looks flatter. Could that have been an earlier design? I'm starting to wonder if whoever produced the repro kits exercised due diligence WRT to some parts. Did they find an unused stock of that one, without questioning why it wasn't used.
Meanwhile, the compensator port valves from my V8s looked exactly like what is shown in Keith's images.
As for the port valve design, it worked without failure for over 7 years and nearly 75K of use in my dad's Exec. It's only been within the last ten years that I've heard of sudden and complete loss of hydraulic action in these car. Yet, I don't think any automaker or supplier intended for their products to be in use THIS long.
I should add that the badly deteriorated compensator port valve springs that I've found have come from cars that sat unused, and improperly stored, for extended periods. Had Bendix made the spring of a more corrosion-resistant material, the valve's seal would probably last at least as long as the rubber cup piston.
I'd expect any wear-related leakage through the compensator port to first manifest itself as a soft pedal, but you should still have sufficient hydraulic action to stop the car. I'd like to think that people who drive cars would be smart enough to notice the change in pedal feel and have it checked out immediately. After all, they sure do complain when they encounter a hard pedal on a power brake system.
From the site's Photo Archive (and the 48-54 parts book):
This also shows the same passage, but I wouldn't infer from the cross-section that it is sealed off by the cover gasket.
The cover gaskets on the BTVs in my V8s all had the style of gasket as shown in the image of MMs major kit for 55-6 that HH56 provided, earlier, but the original was made of leather. Could there have been a design change so minor that it was only noted as a lettered revision to the engineering drawing, with no change in part number?
Next, keep in mind that this is an "illustration", but the compensator valve stem as shown, here, looks flatter. Could that have been an earlier design? I'm starting to wonder if whoever produced the repro kits exercised due diligence WRT to some parts. Did they find an unused stock of that one, without questioning why it wasn't used.
Meanwhile, the compensator port valves from my V8s looked exactly like what is shown in Keith's images.
As for the port valve design, it worked without failure for over 7 years and nearly 75K of use in my dad's Exec. It's only been within the last ten years that I've heard of sudden and complete loss of hydraulic action in these car. Yet, I don't think any automaker or supplier intended for their products to be in use THIS long.
I should add that the badly deteriorated compensator port valve springs that I've found have come from cars that sat unused, and improperly stored, for extended periods. Had Bendix made the spring of a more corrosion-resistant material, the valve's seal would probably last at least as long as the rubber cup piston.
I'd expect any wear-related leakage through the compensator port to first manifest itself as a soft pedal, but you should still have sufficient hydraulic action to stop the car. I'd like to think that people who drive cars would be smart enough to notice the change in pedal feel and have it checked out immediately. After all, they sure do complain when they encounter a hard pedal on a power brake system.
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