Packard Forum Index » V-8 (1955-56)

Vented cap and copper ring washer is (or was) the correct original equipment. Unless you fit a remote filler on the firewall, the cap must be vented to allow the fluid level to rise and fall as the brakes are applied and released.

HH56 gives good advice on testing for fluid seepage around the cap. Most likely what is happenign is that when the brake pedal is suddenly pressed OR when a lot of pressure is on the cylinder the fluid is spurting upwards thru the compensater valve toward the top of the reservoir. This same spurt of fluid can often be seen even on conventional design master cylinders BUT ONLY when the pedal travels the first 1/16" or so.

Sounds to me like a bad compensator valve. Perform the test as HH56 has outlined above. Also note that there is a recent thread about 6 months ago indicating 3hree different compensators used by various rebuilders. IIRC only ONE of them is correct. It is easy to inspect/replace.

Good advice. I'll get that o-ring out of there and go to copper. Re: compensator, I did replace it last time. Is there a source for the correct valve? I thnk the replacement valve presently in the btv is from Midwest powder products (my rebuilder). I may have another here from Fred Kanter. I just want this car to stop as necessary.

I never had a chance to inspect the BTV on my dad's old Exec, but none of my other Packards had any sort of gasket on the cap (and each was a bugger to get off). My dad seemed to think they were made of leather and rotted away over the years, and the average mechanic never realized they were missing. (The gills on the underside of the cap/plug are dead giveaway that it was intended to be vented to atmosphere.)

Since I wasn't able to track down an NOS example, and a rubber o-ring just squeezed right out, I thought I'd try making my own. A washer cut from rubber gasket stock split in relatively short order. I made another washer from a scrap of reasonably thick polypropylene sheet stock and it has worked well.

I've heard that the original was a copper washer, but in the absence of anything in black-n-white, I decided to do a little more sleuthing.

The parts books, both 51-54 and 55-56, show the filler plug gasket, in Gr. 1.337, as P/N 436369. Now that doesn't tell you much UNLESS you happen to check out the hardware listings in the "Utility Items" section; Gr. 50.660 offers a variety of "annular" gaskets. Listed among them is P/N 436369, which is of fibre material. The difference between O.D. and I.D. doesn't leave much meat, which may account for their disappearing act, but consider that the mating surface is only an upturned edge of the sheet metal cover.

Howver, this is not likely the cause of the mushy event.

I bought several appropriately sized copper crush washers that approximated the original. I think I got them from Restoration Specialties.

Some 6 months ago Fred Kanter posted pics of the 3hree different comp valves in service and indicated the correct valve. I've not been able to find the thread in which the pics were posted.

As for the filler cap gasket i would use a lead washer. Not sure where lead washers can be found anymore. However i'm not sure the gasket is of much consequence one way or the other since the cap is vented anyway.

Note that the filler cap KevinAZ has with no vent hole probably had the vent hole soldered closed.

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This way please.

Of the three shown, I believe Valve #2 is closest to original.

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...or simply obscured by decades of rust.

Dear Kevin:

Sudden loss of braking with BTV means the unit needs to be removed and serviced. It could be the compensator valve or the unit could be leaking into the vacuum booster.

As far as brake fluid shooting out the fill cap that is an indication of either air in the system or a problem with the residual check valve. Although the resovoir should not be filled to the brim because some turbulence in the resevoir is normal.

When brakes have to be pumped after a period of storage the residual check valve has leaked and probably let some air into the system, thus the excessive turbulence. So it is a good idea to go out and step on the brake every now and then to keep the system pressurized.

Hope this helps.