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I recognize that piece from under the plug. I wondered what it was for. Will double-check. Also, before I do any more speculating, I am going to crawl under there and inspect things for myself. It could've been a couple of other things that would cause pressure loss, including just low fluid (and where it's going is probably underneath the cover around the plunger rod) or it could've even blown a line. The fluid trail was not on the left, but rather on the right. The smoking, who knows? Could've been unrelated, could've been fluid blowing up on the manifold from a broken front brake line.

I will try to do some plain nuts and bolts looking around, probably Thursday at the earliest if I have time. and someone to help me push it out of the garage and into the driveway so I can jack it up. Owen will be happy to know that I'll probably use jack stands.

I recognize that piece from under the plug.

If you mean the compensator valve which is the stalk with a spring around it, that is the suspected cause of most BTV complaints of stop at one corner but not the next sudden failures. That little blob of rubber is the only thing holding the fluid in when brakes are applied. If it doesn't seal for whatever reason there is pedal to the floor and no brakes.

The relief port & gasket issue is shown in the following photos borrowed from an early discussion.

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OK, we're getting somewhere. I just checked the brake fluid and it was down, as it was before. I looked at the disk at the bottom of the plug, and the holes around it. I cleaned it with brake cleaner, but still could not move it with finger pressure. Is it stuck? And, if so, how do I unstick it?

It is amazing that this can come down to a little relief port and valve, which would be so easy to keep freed up with just a tiny bit of regular maintenance.

I filled the MC with fresh brake fluid-- probably about a third of a cup, then pushed the pedal slowly to the floor and let it up. Heard some gurgling. Checked and added just a couple of tablespoons more to fill it up. Pressed the pedal down, firm pedal now, and let it slowly up. Level stayed the same, maybe a bit of overflow.

I did all this with the plug out of the MC. Will now try replacing the cleaned up plug and see what happens. Will "prime" it with a bit of brake fluid into the relief holes, or whatever they are.

Let me know if I'm on the right track. This is my last little "fix" for the night. Then move it back into the garage.

BTW, I started it, and no smoke this time. Runs fine. Oil level is as it was.

Don't forget to make sure the little vent hole in the cap is clear. Probably on a corner of one of faces of the square.

Your BTV may have a different design of plug than what's shown in the photos provided by HH56. There are no moving parts in that plug that I know of in that plug; the vent path need only be kept open.

The moving part that you need to be concerned with is the compensator valve - located in the bottom of the reservoir. However, there's no maintenance - except to periodically top off the reservoir with clean fluid. It's when brake fluid condenses (gels) and parts begin to dry out or corrode (typically after years of non-use) that problems occur.

The spring-loaded compensator valve is normally held open, with brake pedal released, by a washer at the end of the hydraulic plunger - allowing fluid between the reservoir and the hydraulic chamber, below.

When the brake pedal is applied, the compensator valve is released as the plunger moves forward, and a spring pulls the valve shut. Unlike more conventional master cylinders, the hydraulic seal of the BTV is held in fixed position. The intrusion of the plunger into the hydraulic chamber simply displaces fluid out into the lines - PROVIDED the compensator valve is closed.

If the compensator valve fails to seal, fluid gets pushed back into the reservoir, rather than the lines - perhaps out the vent in the cap.

Of course, the compensator valve seal can wear over an extended period time, requiring replacement of the stem valve. The stem valve is included in rebuild kits, but reports of quality seem to vary among suppliers. The valve must be removed and installed EXACTLY as described in the shop manual - else it could be damaged.

The relief port has no moving parts, but is simply a passage in the m/c casting for excess fluid. There are some differing opinions as to which way fluid moves.

The 51-54 manual offers nothing on theory of operation of the BTV; for that, you need to download the PDF of the "Brakes" section from 55-56 shop manual, available from this article in the site's in the archive:

https://packardinfo.com/xoops/html/modules/article/view.article.php?119

Quote:

Owen,

That's the next step. After I put the plug in, I looked again at the Relief Port drawing that HH posted, and noticed a little "dot" on the side of the plug and wondered, hmmm. Thanks for confirming that.

Since a radiator cap cured my "cooling system" problem, wouldn't it be interesting if some maintenance on the MC cap "cured" my brake problem. It's the little things, I guess.

Fun to look at all the engineering details and realize that good intentions were there, but they depended on careful maintenance.

Brian, the Compensator Valve will be the step after cleaning up the vent on the plug, which, for those who don't know, is on the side of the square "nut" on the top of the plug. I know the rest of it is clean, and yes, the plug does not seem to have any moving parts.

Thanks All

BTW, I have found that a 7/8" 12-point socket will fit on the plug to R&R it, if it is not too tight to remove. Fortunately, mine is all loosened up. If the socket slips when you try to take the plug out, it is better to get down there with a knuckle-bustin open end wrench. With the socket and a long extension, it's a piece o' cake.

Quote:Yes, that is an interesting story and a great place to share it - the Registry! for including it, those little touches are the icing on the cake.

Quote:

HH:

No, I haven't been able to actually see the compensator valve. I think the cover of the reservoir would have to be removed to see it. My question now is, since the dang thing is still eating brake fluid with no sign of it anywhere on the garage floor. . .

How do I get at that "little blob of rubber" and fix it?? Is it accessible without removing the whole MC? If it's stuck, can I unstick it? I'm tempted, as a last-ditch before going to a rebuild, to spray a bunch of non-chlorinated brake cleaner down into the reservoir through the plug hole, let it sit for a while, and see what happens.

If that won't make things worse, I might try it as a final experiment. Otherwise, I'm open to any last suggestions for home-repair. I have no capability of any major R&R in my cramped, cold quarters.

Pretty much everything but this has been sorted out in short order, and I'd really like to get more seat time in the car this fall, but I was pretty sure the BTV would give me a problem to overcome in this car. It's nice to have PB and PS... when they WORK! (No problem with the PS, though.)

I hope this thread helps some other people who have this situation to deal with.

If the fluid is clear you can see the top of valve right in the center of reservoir by shining a flashlight and looking thru the fill opening. A small piece of wire stem surrounded by a conical spring. The blob of rubber is under the threaded plug which contains the assembly and won't be visible from the top.

The compensator valve or blob of rubber is not the cause of eating fluid. If the valve fails, you have no brakes period. The pedal goes all the way down to the floor because the fluid instead of being sealed in the master under pressure to go to wheel cylinders leaks back into the reservoir instead.

If fluid is disappearing and any external leaks ruled out, it is most likely being forced or being pulled into the vacuum side. There are two seals surrounding the piston. Apparently they have hardened, worn or cracked or else the casting surface or piston shaft has developed pits in the area where the seal normally sits and fluid is leaking around them. To replace will require complete disassembly of the unit.

Some months after I had got my Clipper, I experienced brake malfunction. I took the BTV apart - and boy am I glad I did - the fluid (or rather water) was brown and most of it sucked into the vacuum side, piston had rust pits, the seal thus leaking and the reservoir gasket covering the return hole.
I ended up replacing all wheel cylinders, lines and the BTV.

Tom