Packard Forum Index » General

If we were to go back to the original purpose of this thread, Fred is putting together a survey. He would like to hear from anyone as to what happened and also is asking for any help in finding some recent units that have failed to see if we can get to the bottom of it. He has offered compensator valves to anyone who suspects a faulty one but until some get evaluated, all we can do is keep guessing. Anyway, an opportunity that we really should take advantage of and if anyone has a recent failure taken out of service they could help with, I think we would all benefit. There must be a few from those who have replaced with modern recently. The details on how to get it returned were posted on another thread but I think we can find them again if anyone speaks up.

Until we find some corroborating evidence on all the extra numbers, probably useless speculation to keep guessing as to what they are and will serve no useful purpose and just confuse the issue further. It does seem that the units were the same over the V8 and earlier years so doesn't look like any particular version can be faulted.

As to KevinAZ's unit, I'd say that's a P2 so would fit early production 55. The cap is interesting and I think bears out the theory that Bendix had a different one they sold as part of a complete newer unit or for other customers. I suspect Packard had a stock or had a bid spec from the original P unit they started with. Since there is only the one number listed in manuals from 52 on for the one we are used to, they kept those to the end and probably because of the thinness for going under the steering column.

If you turn that later cover around 180, I suspect it will be the type designed for that later gasket we have been commenting on and the tube will line up with the bleed port. The early gasket as shown on the other thread is for our covers.

Unfortunately, that cover is probably too thick and the fill port would be directly under the column and not removable if used as it's designed. That's most likely why it is reversed on this one. Could be any number of reasons why it's there, but doubt it came with the car.

More info on Bendix Treadle Vac numbers for serous study:

BTV # 376038 - 1952 - Early 1953 Packard (Vehicle ID Symbol P)
BTV # 376355 Late 1953-554 Packard (Vehicle ID Symbol P-1)
BTV # 377141 Early 1955 Packard (Vehicle ID Symbol P-2)
BTV # 377529 Late 1955 Packard (Vehicle ID Symbol P-3)
BTV # 377697 1955-56 Packard (Vehicle ID Symbol P-4)

As I've read the Bendix catalog from 1957, it is very clear that they were always changing or upgrading their units. I wonder why and what changed, especially as it relates to the units we all have in our Packards? I have no experience with such things, but I am wondering also if anyone could recommend a source for Bendix historical data? I've struck out thus locating anything close.

Were there any difference is the compensator valve between the 54 and prior model vs the 55/56 models? It appears the the majority of folks reporting a sudden failure are 55/56 owners. So that would make me think there is something related to the design of the 55/56 BTVs as opposed to the previous units.

Kev, see post #38 for some data on the differences between 52-54 (slider valve) and 55/56 (poppet valve). What I don't know is if this relates to the vacuum section or the hydraulic section, but if someone here doesn't already have that answer, it should be easy to determine with a call to one of the rebuilders.

It sure would help to have some detailed historical engineering data, but I've nothing like that at my disposal.

As I mentioned, a couple of moths ago, another thread/post, past, the terms "sliding valve" and "poppet valve" refer to the vacuum section - namely, the vacuum piston assembly.

The hydraulic section of the BTV is an elegantlty simple design. Put simply, there ain't that much to it, and it works.

As such, I can only suspect that most of the changes represented by the progression from one unit ID symbol to another, within the same alpha class, have more to do with the vacuum section, but I couldn't completely rule out any changes in the hydraulic section without engineering drawings.

However, the catalogs do show same P/N for the compensator port valve for all Packards from 1952 through 1956 - though that doesn't preclude minor, yet backwardly-compatible, revisions to any component parts along the way. It's interesting that Packard only serviced that valve as an assembly - that is, valve, spring, retainer and fitting.

Yet, that specific compensator valve was NOT exclusive to Packard applications. In fact, previous review of my Wagner-Lockheed catalog showed that the compensator port spring and valve stem in the 55-56 Chevy was the same as used in 52-56 Packard.

While the residual check valve parts that came in my kits from Kanter were of a different design than what came out of my master cylinders, I doubt if anything changed very much in the design of hydraulic section until the BTV progressed to the hydraulic reaction type plunger, in 1957. Yet, don't simply take my word on that; be sure to study the details of the application listings for various parts of the hydraulic section.

It's troubling that the V8 cars seem to suffer from more problems of late, but I still have this nagging gut feeling that it has as much to do with design and/or quality of modern substitute parts - lest we forget the defective valves reported by more than one of our members.

We've seen some valves that appear to be of the original shape, but with insufficient amount of sealing material above the "cup". Then, Fred Kanter provided a comparison pic of three valves (one OE and two different types of replacements) in another thread/post, past. Valve #3 troubles me a bit, in that it appears to be of a large diameter. While the original valve is a relatively loose fit in the bore fitting, could this new one get hung up in there? Personally, I would prefer to have valve #2.

While the compensator port valve spring may not be at the root of all failures, I still think it is important that a replacement spring be made available.

The compensator port, valve and spring are certainly the major concern for the BTV. Fluid loss into the vacuum power unit is a commonly reported problem too.

Is it reasonable to conclude that any compensator port problems are independent of any fluid loss into the vacuum unit problem????

i.e. They are two independent problems. One does not cause the other.

Keith,

If the compensator port doesn't seal when you step on the brake pedal, the brake fluid displaced by the hydraulic plunger goes back into the reservoir. As the resevoir becomes full, some of that fluid would follow the passage, to the rear, down to the bore for the seals, which terminates between the hydraulic and leather seals.

All other things being in good repair, I believe only a small amount of brake fluid could get into the vac shell, in that case.

Ahhhh! Good point BH. Would also expect fluid to exit the entire system thru the filler cap vent too. No???

If the comp port doesn;t seal and fluid is pushed back into the reservoir it would occur under little or no pressure. Since little or no pressure is involved i would expect the seal in the end of the master cylinder to do it's job and not allow any fluid out thru the seal.

Yes, under pressure, fluid will follow path of least resistance.

I don't know the specific working pressure for the BTV, but would guess not much more than 1000psi (likely not enough for disc brakes). Let's juts say that the fluid would have to be under considerable pressure to apply the brakes at the wheels. However, that passage in the casting is quite small where it enters the bore for the seals and the displacement event is rather short-lived.

Although we no longer have the 56 Clipper, my 56 Olds Holiday 98 also has BTV with the same compensator port/valve and I wonder if data from the far more numerous GM cars out there could assist in elucidating an answer to determining the most common failure mode?