Packard Forum Index » V-8 (1955-56)

From Motors Manual, Second Vintage Car Edition.

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Sorry, I can't answer the question about the BTV stainless steel liner but will try to find out. I know my ignorance is showing but the reason I had a US brake business rebuild a BTV for me was because I know bugger-all about them and wanted someone experienced with BTV's to do the job. Also, thanks for the heads-up about personal account details - I didn't understand I could/should do that and now have done so (hopefully). Cheers, John

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Keith, you need to lay your hands an old brake parts catalog and do a little research.

In fact, a Wagner Lockheed Power Brake Replacement Parts catalog from 1960 shows that the same minor repair kit, P/NA FC26869, fits the following models:

58 Mercury (late)
54 Nash Ambassador 60
53-57 Oldsmobile 88, 98
52-56 Packard
53-56 Pontiac

That those vehicles all use the exact same minor kit to service the hydraulic section strongly suggests that the BTV used in the Packard was NOT of an exclusive design.

Major overhaul kits are a whole 'nuther matter; only the 55-56 Pontiac uses the same major kit as the 55-56 Packard. That would seem to indicate that most of the differences lie in the vacuum section.

Meanwhile, the same catalog shows that 55-56 Chevy used the poppet valve BTV; 54 Chevy used a sliding valve BTV (as did 52-54 Packard). The terms "poppet valve" and "sliding valve" have NOTHING to do with hydraulics, but refer to the design of the power piston plate in the VACUUM section.

If I'm interpreting the catalog correctly, the hydraulic valve design, which involves the HYDRAULIC section, didn't appear until 1957. WRT to Chevies, the hydraulic reaction type BTV was used in the 57 models, but only with Powerglide trans; those equippped with Syncromesh models got the Hydrovac.

I don't have time to conduct a full audit, but while there are many different unit numbers for BTVs used over many applications, a random sample of the detail parts shows that many of the hydraulics part were shared among many of them. For example, the cover gasket and compensator port spring and valve stem in the 55-56 Chevy is same as was used in 52-56 Packard.

So, no one has shown me any need for redesign or any remedial efforts - just quality parts that meet OE specs for proper rebuild of the BTV. I still say the devil is in the details that might only be found on an engineering drawing. However, I have too much on my plate as it is. I'll get to the bottom of it, myself, when I am ready to rebuild the BTVs in my own Packards.

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"The terms "poppet valve" and "sliding valve" have NOTHING to do with hydraulics, but refer to the design of the power piston plate in the VACUUM section."

YES! That is what i originaly thot too and still believe until i was accused of some kind of guessing a few posts back.


1. Several months ago HH56 or someone posted pics of the Chevy BRAKE PEDAL assembly. It appeared to be a 3 or 4:1 pedal ratio. Or maybe i saw it in some place else.

2. Motors Auto Repair Manual 1956 (original not a reprint) on page 477 of the Chev brake section indicates All 53-56 Chevies have 1-1/8" front WHEEL cylinders, 1" REAR WHEEL cylinders and 1" master cylinder.

3. the PAckard FACTORY manual ERRONEOUSLY indicates a 1" Master cylinder for the 55-56 POwer brake Packards. IT is not 1". It is 5/8".

--*-- SO, IF the CHEVY has 3:1 pedal ratio and chevy wheel cylinders = Packard wheel cylinders then how is it possible for the Chevy to have a hydraulic unit with a 5/8 Ram equivelent to the Packard unit?????

LEt me make my point another way:

IF the CHEV wheel cylinders AND the HYDRAULIC part of the Chevy BTV is the SAME as the 55-56 Packards then how does chevy get away with a 3:1 pedal ratio and Packard can use a 1:1 pedal ratio???

I'll even state it a 3rd way:

IF everything HYDRAuLIC between chevy and Packard are EQAUL then how does the chevy get away with a 3:1 pedal ratio WHILE Packard has a 1:1 pedal ratio???

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They probably mean the hole that the 5/8" rod fits into, not the rod itself. Logical?

I measured that a month or so ago. It's more like 1-1/8 or maybe larger.

Isn't it tapered? Maybe they just used an average.

In the beginning or the actual chamber where the piston slides in?