1956 Packard Panther Project

Packard Conversion Projects

"Easamatic" Power Brake Conversion

Easamatic power brake was an option from 1952-56. It was actually a generic system called Treadle-Vac manufactured by Bendix mounted on the floorboard directly under the brake pedal. The Treadle-Vac was also available for various years on many other cars of the 1950s (all GM, Edsel, Lincoln, Mercury, Hudson, Nash and even Mercedes). The Treadle-Vac was superceded in 1959 by the familiar Delco-Moraine power booster mounted high on the firewall.

I believe that there was a good reason why the Bendix Treadle-Vac was superceded by the Delco-Moraine power booster: The Treadle-Vac was failure prone! I personally have had three failures of professionally rebuilt Treadle-Vacs. One failure was without warning and total, i.e., NO BRAKES while driving in traffic! Fortunately, I didnít hit anything and got my 1955 Patrician (slowly) stopped with the parking brake. I know of five other Packard owners who had the same kind of failure. Also of concern is the expense of having the Treadle-Vac rebuilt (several hundred $$$).

These reasons are more than sufficient motivation to find a better solution! However, telephone calls to several aftermarket manufacturers all resulted in the same "NO" answer to my question, "Do you have a replacement for the Bendix Treadle-Vac?" I decided to pioneer this conversion myself during my Panther Project!


Preliminary measurements indicated that the 7" diameter Street Rod booster from Master Power Brakes (MPB) would probably fit. Also needed would be the Remote Fill dual master cylinder from MPB in order to clear the steering column and allow check and fill of the reservoirs. The salesman at MPB also explained their 30-day satisfaction guaranteed policy...I could return the unit for a full refund if it didn't work out. I ordered the parts.

As soon as the MPB components arrived, I did the trial fitting. Fortunately at that time, the entire front end (clip, engine & trans, suspension, steering, etc.) as well as the entire interior (seats, dash, steering, etc.) was stripped off the Clipper, making the trial fit easily accessible.

I carefully measured the stock Easamatic power brake mounting panel and the MPB booster. I determined that the MPB booster must be mounted 1/4" lower than the Treadle-Vac so that its booster diaphram case will clear the top of the recess in the mounting panel. Fortune must be smiling upon this conversion because it turned out that the center hole in the panel is exactly 1/2" larger in diameter (1/4" per side) than the rod bellows and central hump on the MPB booster! Also, the four existing attachment holes are 4-3/8" center-to-center, which will not conflict with the four new holes at 3-3/8" center-to-center for the MPB booster. I measured everything twice and laid out the hole pattern offset 1/4" lower than the central hole center point. I used a 1/4" drill for the pilot holes, followed by a 7/16" drill for the final mount holes.

I fitted the remote mount cups to the master cylinder and then attached the master cylinder to the booster. I then attached the booster to the mounting panel. I trial installed this assembly in the stock location using just two screws to hold it in place. I placed the steering column back in it's stock location.


Everything cleared, although the front of the master cylinder is just touching the frame. However, there's up & down adjustment available in the mounting panel to floorboard attachment, so the final fit will have 1/4" to 1/2" of clearance.

MPB Brake installation in my 1955 Patrician (August 2002)

After the professionally rebuilt Treadle-Vac in my 1955 Patrician failed AGAIN recently (luckily no damage done), I installed the MPB booster and master cylinder I had earmarked for the Panther in my Patrician (I'll buy another for the Panther). It's basically an R&R per the service manual except for the following.

The brake pedal attaches to the MPB booster rod end just like stock IF MPB's #PR101 "Push rod w/Eye" is used as an adapter. You have to ask for this part specifically and it is a "hand-picked" item from their warehouse.

The stock rear brake line screws into the rear outlet of the master cylinder with a little bending IF you have MPB's 1/2-20 adapter or the equivalent from your local auto parts store. The stock front line cannot be used (too short and bent the wrong way). I bought an 18" 3/16" steel brake line at the local auto parts store and bent it into a 270-deg loop on the M/C end (see picture below) to fit into MPB's 9/16-18 adapter (or auto parts store equivalent). I left the "T"-fitting to the stock vacuum tank in the inner fenderwell even though the MPB booster has its own small vacuum tank in order to get extra vacuum force.

NOTE: flex duct and firewall air vent removed for access.

The remote fill reservoir is mounted on the radiator overflow tank bracket, since that was the most convenient place.

Parts used from MPB:
#BS10017" Booster
#MC1001PZRemote fill master cylinder & kit
#HS4001KVacuum hose kit
#HS4006M/C 1/2-20THD brake adapter
#HS4007M/C 9/16-18THD brake adapter
#PR101Push rod w/Eye
Total cost including shipping: $361

Drive report (September 2002)

My 1955 Patrician has the front disc-brake conversion, but stock 12"x2" rear drum brakes. No proportioning valve or residual pressure valves are used. My Pat stops straight, level and true as before with just the front disc brakes converted. However, the foot pressure required to effect a certain stopping force is noticeably more than originally. The foot pressure required is about like manual brakes with drums (which are self-energizing, of course, whereas disc brakes are not). The pedal pressure with the original BT-V was very light; lighter than modern brakes for sure.

Changing Pedal Leverage (February 2003)

I finally got frustrated with the excessively hard foot pressure required with the MPB Booster and the stock 1:1 pedal leverage. MPB recommends at least 3:1 and prefers 4:1 pedal leverage with this booster.

The best way to achieve 3 or 4 to 1 pedal leverage and retain the stock brake pedal position is to REMOUNT the booster higher up on the firewall. This is difficult on a fully assembled vehicle like my Patrician. I needed a BOLT-ON solution, So, here's what I did:

I used the brake pedal from my 1956 Exec 4dr parts car. Here's a comparison between the 1955 and 1956 Power Brake pedal assemblies:


I cut the 1956 pedal and pad to the same width as 1955.


I fabricated a pair of "L" brackets which attached to the toe board using the existing two upper booster retaining bolts. I drilled two holes in the 1956 pedal lever so that the ratio between the "L" bracket pivot (upper) hole to booster rod attach (lower) hole and the ratio between the upper hole and the pedal center is about 3.5:1. Here's a mockup:


Here's the final install:

The pedal is somewhat longer and higher than the stock position, but is quickly adapted to. The required pedal force is now totally satisfactory.


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