Customs dual master power booster upgrade not working

I do have someone I know who has a pedal assembly from the manual version of my car which had a master cylinder with a 1" bore like the new one I have now. Theoretically speaking, I'm assuming this would have a better overall ratio than the existing pedal and give me better leverage on the pushrod. Even if I eventually go with an OEM booster/master assembly from a late-model GMC truck or van, like Cosmo mentioned because I know he doesn't care for aftermarket systems like the one I have, the manual pedal would still be helpful. I'm thinking it's a good start.

 

The manual pedal for your car, even if you end up using it with a booster, is a much better bet than the one from the Treddle-Vac system.

The original booster does not work the same way as a modern, diaphragm one, hence the remarkable different pedal assembly, master cylinder bore, and the issues you are having now.

 

On my channeled 34 Vicky. The drive-line, axle, steering, motor, trans, brakes etc. were from a mid 50's Olds. They took the Olds lower firewall (toeboard) and installed that to the upper portion of the Ford Firewall, they ran the Olds brake pedal assy. with the Treadle Vac.

When I got the car, someone had installed a 1" remote master cyl with a booster from an import car, they ratio was 1 to 1. On paper this should not work but the car stopped fine.

I'm currently mechanically restoring the car and installing a 1" bore dual remote master cyl from A.B.S. Brakes in Orange. I installed it the same way with the 1 to 1 ratio for testing only, if this does not work, I have been looking into modifying the pedal ratio by lowering the pivot point at the top of the assy. It is a swing type pedal and that will increase the ratio, I should have the car ready for a shake down by Nov. Well see is it works.

 

If it really was 1:1, you'd have crashed it, on the test drive.

 

According to the original service manual, the brake pedal adjustment height for the manual assembly is 8" vs the power assembly, which is 5 1/2" - I'm assuming that speaks to a much different ratio and pivot point on the manual which will work better with my current setup hopefully. Can't wait to get my hands on that and mount it.

 

Update...I went through the original service manual even further and pulled up a wealth of information. It shows a diagram of the manual pedal assembly, which clearly demonstrates the pivot points are much different. (photos attached below) The brake pedal height is 8" vs 5 1/2" on the power pedal assembly. It also confirms the brake pedal ratio for the POWER pedal that I am using is 1.5:1 and the one for the MANUAL pedal is 6:1. It mentions "the only linkage adjustment possible is the pedal height adjustment."

Further it describes how the pedals work and they do NOT have a 'stop' as previously insisted by someone on the board: "The brake pedal is suspended from a bolt between two mounting brackets. As the brake is applied, a pedal lever extending upward operates a link rearward. This link in turn transmits motion to a lever on an idler, causing the idler to rotate. This rotation causes a second idler lever to push forward on the brake cylinder push rod clevis and push rod. Because there is no pedal stop, the pedal will be stopped in the "off" position by contact of the push rod with the stop plate in the master cylinder."

So would a 6:1 ratio be too much? I know it would better than my 1.5:1 I have now. I'm cautiously optimistic that if this works I won't need to do much fabrication on a universal pedal assembly because this is designed to mount on my car. Again, I posted illustrations below from the manual including the manual and power pedal diagrams, as well as the pedal height adjustment...

MANUAL ASSEMBLY (6:1 ratio - note the pivot points vs the power one below it)


POWER ASSEMBLY (1.5:1 ratio)


PEDAL HEIGHT

 

So would a 6:1 ratio be too much? I know it would better than my 1.5:1 I have now. I'm cautiously optimistic that if this works I won't need to do much fabrication on a universal pedal assembly because this is designed to mount on my car.

The 6:1 ratio should be fine. The manual pedal assy. should be a relatively easy bolt-in. When these came down the the assy. line and it was time to install the brake pedal there was no one standing there with a welder and other tools to modify parts. The installer merely picked up the correct parts according to options being installed on that particular car.

Here is a pic of my 56 Nomad which was converted from treadle vac system to a diaphram booster. You can see the hole in firewall where the old treadle vac was mounted. The new booster/master cly. is mounted in the same place as where a manual master cly. would have been mounted.

 

Sweet! And did you change the pedal assembly?

 

Yes, the pedal assy. was changed to the factory manual brake set up. 55-57 chevy pedal set ups are relatively easy to find. 58's are much harder to find and can be pricey. If I were you I would snag the one you have access to in a heart beat.

 

I think your on the right track now. I forgot that the old treadle vac had the bellcrank setup so my suggestion to move clevis was no good. As I said, the old treadle vac had way more power than the repop item you installed, so with the bigger master cylinder and the low pedal ratio you would really have to stand on it to stop.

With a manual pedal setup and a master cylinder close to original in size the repop booster should get it done. That's a big bitchin' piece of Detroit iron you got to stop. You got to figure if it worked for manual brakes adding the brake booster should make it just that easier. And if it's too touchy you could always put the bigger master cylinder back on to tone it down.

 

I just got the manual brake pedal in. Took a short video of it in operation. Most of the literature and the manufacturer for the booster/master says that the ratio needs to be 4:1, so is it possible the 6:1 on this pedal will be too much? If so, is there a way to knock it down?

 

Try it first.

 

For sure, just curious if it's easier to knock a ratio down or lessen it's effects as opposed to my old pedal with too little ratio.

 

I would try it first, I think with the 8" booster you have a pedal ratio a little more than 4:1 will be ok. It would be pretty easy to reduce the ratio if necessary. Doing a little hillbilly reverse engineering from the drawing you posted of the manual pedal assy., you would only need to relocate one hole aprox. 1/4 to 5/16 of an inch. This should reduce the pedal ratio from 6:1 to 4:1. You would need to weld up the old hole before redrilling the new one. Of course you need to do the actual measurements but I believe I am pretty close.

 

I'd probably just run it as-is.