Packard Forum Index » V-8 (1955-56)

I have a question about changing out my Treadle Vac and replacing it with a dual master with power booster setup. I know this topic has been discussed many times in the past, but I want to be sure everything will work before I make the change. I personally don't have anything against a Treadle Vac when they are working, since mine stops decent. However, it is going on 20 years since the previous owner installed this one when the car was restored in 2002-2003, and I'm looking to change to something I can trust more since where I live has a lot of mountains to go up and down as well as a lot of traffic. I found a rear wheel cylinder leaking a few days ago, and want to change to a dual master and booster while I'm already redoing part of the brake system.

In one thread on here, I saw where someone used a dual diaphragm booster and a Volkswagen remote master cylinder and attached them with a fabricated an adapter plate join the booster and master cylinder.

Link to thread: Volkswagen Power Brake Setup


I also looked at Craig's Panther project before the site went down and saw how he used a remote fill master and a dual diaphragm booster. He also changed his pedal setup.

Link to Craig's site in Web Archive I found: Craig's Power Brake Conversion


I then researched some more and found a thread on an Oldsmobile website of a 55 Olds that had an original BTV unit installed in the same location as the Packard with a 1:1 ratio pedal. He did basically the same conversion that Craig did. He used a dual remote master cylinder, single diaphragm booster instead of dual booster. He converted to disc brakes on the front, but I would probably leave mine drum since it is not easy to change a Packard to discs. He also used a proportioning valve, but I don't think I'll need that either since I would be staying with drums. I might need to 10 lb pressure check valve, but I'm not sure. The guy with the Olds originally altered his factory brake pedal like Craig did, but he went back to the original pedal after not liking the setup of the pedal he made. He said it stops well even with the 1:1 ratio that the Olds has in common with the Packard.

Link to Olds brake thread: Oldsmobile Under Floor Power Brake Conversion


My car is a 56 400, so I don't think my brake pedal is the same as a 55 like Craig originally had. I'm thinking about following a similar process to what the Oldsmobile guy did. One question I had would be what I would need to do with the brake light/torsion level switch?

On another note, I saw where the VW master cylinder I referenced had the ability to use the factory switch. I researched and saw a dual VW master cylinder listed on eBay. Can this VW master be used with the original switch? It says it is a 3/4" bore instead of the 1" that Craig and the Olds person used. Would this be better or worse? Also could this dual VW master be used with a booster to adapt it to the plate in the floor of the Packard?

Link to VW master on eBay: Remote Dual VW Master Cylinder

Another VW Master: VW Dual Master Remote Fill


Does anyone have any suggestions, or has anyone completed any of conversions that are similar?

The 55-6 brake switch is located in a junction block bolted to the Left frame rail below the air vent tube and positioned roughly under the battery. Unless you are totally revising the lines along with the master/booster you will still retain the junction block so the switch will be unaffected. If you do remove the block, there are inline adapter fittings that can go somewhere in a line to provide a port for the switch. There are also proportioning or metering valve assys that can accommodate the switch. If you wanted you could also convert to a mechanical switch operated by the stock pedal arm and totally eliminate the hydraulic switch.

One caution before committing to keeping the 1:1 pedal ratio. With absolutely no mechanical advantage I suggest after you install the new unit you disconnect the vacuum and see how the brakes work with no boost. I think in spite of how the person who did Olds conversion might have been satisfied you will find the stopping process fairly scary. Even the BTV was not all that great with no boost assist but at least the BTV had the advantage of a small diameter ram moving a fairly long distance to squeeze or displace the fluid out of the master. The larger diameter short travel pistons in modern masters which push an equivalent amount of fluid in front of the piston with no mechanical advantage requires some tremendous force. Brake mfgs of power boosters recommend at a minimum 3.5 and most say around 4:1 to have enough force to stop a car with no assist.

Being able to increase the ratio is the main reason so many have opted to locate the modern units a bit higher up in the air vent area in order to keep a stock pedal look. It is possible to modify a stock 56 pedal arm to get a higher take off point to use the vent area but that does have some limitations with stroke length. Most have found it easier to adapt a pedal and mount bracket from another car that already has a higher pivot and connection point. Done with a bit of attention to detail by modifying the arm to use the original pedal pad and cover, from inside the car you can hardly tell something was modified. Of course you do give up the Left air vent but with it positioned to scoop and blow the exhaust from the car in front directly at you, IMO, that might not be a large sacrifice.

As to if the VW with the 3/4 bore would be better I don't know if anyone ever tried it and reported back after using it for awhile. It was speculated that because the BTV ram is fairly small a smaller piston might work with the lower ratio providing the stroke is long enough to deliver an adequate amount of fluid to the larger wheel cylinders but that needed to be proven.