Packard Forum Index » V-8 (1955-56)

Looking at the '51-'54 service manual in the Brakes section shows the exact same master cylinder as the '55-'56 one, port and all. I'm starting to wonder if the gasket that blocks the hole is incorrect, and is from a GM or the like rebuild kit which may block it off. (for whatever reason)

If true, then that means that someone rebuilt my BTV in the past using a generic kit. We need more pics of the gasket on as many old untouched units as possible. I'm not saying that my BTV should be taken as factory correct, but it was rebuilt a long time ago if it was rebuilt at all.

Quote:


Hmm, you may be quite correct on that assumption. I'm thinking it was either Buick or Oldsmobile that mounted the BTV like Packard, but no one else.

Quote:

Not according to Motors or Chiltons. The pictures are the same and depending on the car, those books just reference you to the particular section your unit is.

There were two types of BTV, the hydraulic reaction type (HRT) which looks the same but is quite different internally with the plunger being hollow & a membrane on the end pressing against a rod & actually feeding back info to the vacuum side and the poppet valve type (PVT) we use. Several cars used the HRT type but no BTV listed has a piston & cup. There were other Bendix units that did.

Looks like Buick and Oldsmobile mounted it like Packard (and Pontiac as well). Trying to find an un-molested Tri-5 Chevy is like a needle in a haystack.
Here's a couple of pics of a '56 Buick. Cadillac mounted the BTV unit clear up on the fenderwell near the radiator, away from the manifolds and used what had to be a 3' long rod to actuate it.

Attach file:

---

  (35.11 KB)


  (36.24 KB)

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.

Quote:

That's the problem, it's the "here one stoplight, gone the next" nature of the failure that has everyone concerned.

Quote:
Since I've never experienced that in any of my V8s, even after rebuild (though accomplished over a decade ago), I'm thinking that it's not the OE design, but the part used in the repro kits that's the problem. Specifically, I'm wondering about proper fit and durability of the valve stem and quality of seal material.

Any idea how high up the Buick pedal goes. It doesn't appear quite 1:1 as Packards.

Looking closely at this pic:




It looks to me like the lid has a small "bubble" above the port, something that's missing from the later ones.

There's still nothing that anyone can say that will convince me that this thing is safe enough for anything more than a piece of garage art, and even then, knowing the unpredictable nature of these things, which could fall and hit you in the head at any moment...

Quote:

That still doesn't change the fact that depending on a fragile spring and a moving rubber valve to seal braking pressure has got to be the stupidest idea anyone has had since Eve ate the forbidden fruit.