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Pardon my ignorance but I do have a recently rebuilt BTV bought from Max Merritt and would like to know. I understand the advantage in having a single master cylinder versus a double master cylinder but presuming the single master cylinder works and just the power unit fails, is it like most power brake units in that you can brake but it takes a lot more force on the brake pedal? Or are the brakes totally gone?
Ken

Takes more pedal push, same as you'd have in a modern car without the engine running, once the vacuum reserve was depleted.

Perhaps I should clarify my previous question by stating that I understand that a dual master cylinder can be safer than a single master cylinder as the dual has a backup brake system.

Thanks Owen!

Brians51 wrote:
Quote:
<p>One would have to question who is the idiot here. Red herring in a message board context obviously means hijacking the thread, which is what you did. Randy Burger correctly started a new thread on the subject, which is what you should have done in the first place.</p>
<p>Learn message board protocol before talking smack.</p>
<p>Craig</p>

kens53 writes: "that a dual master cylinder can be safer than a single master cylinder as the dual has a backup brake system."

The dual or tandem MC as used on MOST modern day cars since late 60's does not incorporate any form of a "backup system". The dual is more precisely described as a SPLIT master cylinder where front part of cylinder operates REAR brakes and rear part of cylinder operates FRONT brakes. (some variations)

So the dual or tandem or split brake system is still dependent upon the power unit. It's not like there is somekind of 'backup system' that kicks in if the power unit itself fails.

There maybe somekind of such system in production and most likely in only very recent years of a 'back up' brake system. I don't know. But the Dual or tandem or split systems we speak of here or is generaly construed in the automotive world is as i have described above.

A dual-ciruit MC has two chambers, each operating a "zone" of the car, one for the front that is large in capacity, and another for the rear, which is smaller in capacity than the front due to the needs/demands of the system. There is also an apportioning valve, which, in the event of a failure of the integrity of either front or back hydraulic circuit will toggle the valve over to only apply braking (hydraulic) pressure to the "good" remaining circuit. The most common cause of a problem would be a rusted hard line, or a cracked, aged flex line. I make it my business to know every inch of a vehicle's lines, the condition of the clyinders, the linings, and the master cylinder.
These days you can get the lines pre-bent in stainless steel, and new flex lines and cylinders, and it's a pretty simple swap-out.

Let us consider all years that Packard and Clipper used the BTV. ALSO IN THOSE YEARS standard or manual brakes were offered.

Has there been as many manual brake failure reports as there has been BTV failure reports???? I don't think so.

SO, if the BTV failures are due to owner neglect or backyard bubba mechanics then why arn't the manual brake equiped cars also suffering at least in proprtional numbers????

Quote:
I believe there were only two mfgs that ever made the type design used on BTV--Bendix and Delco.

The master "cylinder" is not a conventional type. Instead of a piston with a cup which pushes fluid ahead of it, BTV is essentially an approx 3/4" closed tube filled with fluid which a rod or "piston" pushes into. The piston almost but never actually touches the sides of cylinder. It just displaces the fluid forcing it out to the brake cylinders. The stroke is direct and long & the rod, by squeezing the fluid out, obtains a considerable mechanical advantage. The volume is made up by length of stroke. The conventional cylinder has a fairly short stroke so needs a bigger diameter for the volume. Because of the diameter, it has to have a greater mechanical advantage to start with hence the 3, 4, or 6:1 mechanical ratio provided by pedal linkages. Therein lies the issue with just bolting something on.

I believe the failure mode of the BTV is in the sealing of the tube or cylinder. There is a single lip around the rod which prevents fluid going into the vacuum portion and the valve which closes the port that supplies or replenishes fluid into cylinder is nothing but a big blob of rubber which covers a hole. That rubber valve is held in place by a spring which can fail or any loose debris in the cylinder can float & catch on the rubber and prevent a seal. No seal, no way to force pressure out to brakes. The conventional cylinder closes off the hole as soon as piston and cup move past so no way for fluid to escape. The hole and lip seal in BTV is under all the pressure developed and any leak will result in no brakes.

"BTV is essentially an approx 3/4" closed tube filled with fluid which a rod or "piston" pushes into..."

Minor correction: It is 1-3/16 inch diameter. The plunger is 0.655 diameter.