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Well I rebuilt the treadle-vac, fabricated some new lines, bled the brakes and still-TOO WEAK. after I bled the breaks the pedal was nice and hard but the minute I fired up the engine-my pedal went down to the floor. The brakes were able to stop the car while I took a test drive around my street but way too weak too take it anywhere of any distance. Does anyone have a suggestion as to how to solve my problem? (and yes I am considering replacing the treadle vac with something else).

Adjust brake shoes.

Remove lid from Master cylinder. start engine. step on brake. whatch for fluid turbulence or rising of fluid level in mc reservoir.

EDIT: I'm really reluctant to comment, the TreadleVac is such a contentious issue and strong feelings both ways abound.

Assuming your problem is with the TreadleVac itself, buy a professionally rebuilt unit or have yours rebuilt by a recognized expert. Some parts which should be serviced are not contained in the kits available to us; the better rebuilders have these parts manufactured for their own use.

I'm only interested in trying to determine what the problem is rather than to just give up and unconditionaly do a conversion or buy a new one. He has a lot of work/resources in this project. Maybe it's just a matter of replacing (a single part) or adjusting.

I'm not ready to crusify the BTV. At the same time i'd rather not spend ANOTHER 12 years of analysis. Maybe Wauhop has enuf mechanical experience and perserverence to diagnose this problem. Perhaps to a simple end fix. Which is exactly why the BTV debate rages on. THere is no reason why the BTV can not be rebuilt by ANY experienced mechanic with the same positive results that any other master cylinder is often rebuilt by ANY experienced mechanic. THus far, that has not been the case routinely enuf. No one wants to do any diagnostics.

Provided the master cylinder is in good operating condition, I've been able to stop these cars, at low speeds, on just the front brakes, provided the feed to the rear is plugged off - and vice-versa.

If pedal travels smoothly and fully, following PackardV8's advice will help you determine whether problem is at the master cylinder or one or more wheels.

Report back and we can direct you to the next step.

Meanwhile, you say that you:

Quote:
Hmm, I would have gone ahead and replaced them all - including the three rubber hoses. It's not uncommon for a leak to appear in some old lines, hoses, or even wheel cylinder seals after a rebuilt m/c or some new lines wer installed, thanks to renwed line pressure.

Dear Wauhop:

Okay, the question here is whether you have air in the system or brake fluid leaking out of the Treadle-Vac.

In the old days I saw lots of BTV's rebuilt because the guy I knew happened to have NOS Packard parts on the shelf. Those days are gone. If the ram is pitted that will cause leakage and thus sponginess (when running). Also, I have seen the seal put in backwards as well as damaged by not using a seal protector (I hope this comes with the kit). The compensator should be the same shape as original. If not, don't use it. As well, I assume there is nothing spraying out of the brake lines anywhere.

For air problems you can go to NAPA and order two sets of Part Number 675-1565 Speed Bleeders. This will get the air out if that is your problem.

Good Luck.

All the brake hose have been replaced this year and the wheel cylinders were replaced in the last couple years-and the system is not leaking fluid. I've bled the brakes and with the engine shut off the pedal is nice and hard just the way I like it, but the minute I fire the old girl up the pedal sinks to the floor.

Check the area where the master cylinder mates to the power unit. IS there any seepage of fluid there???/ Mite not be alot but just some.
Check the brake fluid reservoir!!! Note that in many cases the brake fluid has been sucked from the master cylinder into the vacuum power unit. It sucks it maybe 1/8 teasppoon at a time.

The condition u describe is that the compensator port valve is bad or not seating.

If this were a hydraulic issue with m/c compensator port valve, I would think that the brake pedal would sink to the floor (with your foot on it) regardless of whether the engine was running or not.

What happens if you disconnect the vacuum supply hose from the fitting at the back of the carb (and cap that fitting off) and then fire up the engine?

Also, did you remove the master cylinder cover, as PackardV8 suggested, and watch what's going on with the fluid in the reservoir while someone else operates the pedal?