Packard Forum Index » Modification Discussion

I come back empty handed. The closes thing I could find in the local reliable junkyards were a couple of '78 Cutlass. They were different.

I will have to branch out to other yards farther away. It's too rainy here anyways.

Chek the year range of application. Since it chevy there is probably aat leadt a 10 year range that parts fit.

I'd like to suggest some broadening of your power brake horizons. My 56 still has its BTV system (I am told that it was rebuilt once, years ago) and it's working well. So I have no immediate plans to replace it. One pedal to the floor will quickly change my mind, if I am that lucky. But all the discussion about later model GM master/boosters got me looking around the family fleet (14 trucks/cars) to do some imagining.

From this thread, some of the bigger problems appear to be fitting in the booster diaphragm assembly. The family fleet includes both gas and diesel trucks (some with upwards of 600K miles) and those with the GM Hydroboost caught my attention. Hydroboost uses the belt-driven power steering pump to provide hydraulic push to the master cylinder, replacing the lack of vacuum inherent in diesel engines. Since the 1980s, we must have had dozens of vehicles with this system and I cannot remember ever replacing the booster portion (but do the regular master cylinders). Of course, the system adds a bit of plumbing and length to the MC assembly. Whether or not the GM pump would be a match for the Bendix or Monroe steering parts would be for better Packard mechanics than I. But the width and clutter of a vacuum booster would no longer be an issue. Besides, there's a good supply of Hydroboost parts in salvage yards, waiting for a good home and they don't require a computer connection either.

Biggest problem with any conversion is the pedal ratio. With the stock Packard location, the ratio is 1:1 because it is at the bottom of the pedal. Just about any modern system wants a minimum of 3:1 and even more in some cases. In an emergency situation with engine off and no power assist be it vacuum or hydraulic, any modern system with a low ratio would be unable to stop the car in any distance close to what would be acceptable.

The BTV gets around this low ratio by the unconventional construction of the master cylinder. It utilizes a rather small ram with a long travel squeezing or displacing the fluid rather than a modern cylinder using a large surface & short stroke piston to push the fluid out. Even with the differences, the BTV still makes for an interesting experience if the power assist portion quits -- but not as interesting an experience as that when the moving mass of rubber called a compensator valve fails to seal.

Craig's two replacement approaches have addressed the ratio problem by either modifying the pedal if a new master is in the original location or by moving the master up in this latest job to have the actuation point higher on the lever.

One thing I have found interesting is location. While some cars followed Packard in placing BTV's toward the bottom and had low ratios, other cars (Chevy, for one) placed it differently and had a high ratio to start with. Near as can be determined, other than possibly some later refinements in the pedal feedback and sensitivity, the basic units were of identical hydraulic construction and functioned equally well at either spot. Because of the placement choice, there is a direct modern bolt in BTV replacement for Chevy but it won't work on a Packard.

Without changing the ratio, I'd be concerned about any modern replacement including the Hydro-Boost or the Electro-boost being able to stop the car in an emergency. The Electro system would at least not be compromised if the engine alone quit but since people have been installing it in the original location, I would be just as concerned if a short should occur or something happened to the battery and the accumulator pressure reserve was all used up.

If the Hydroboost system is the same or similar to that on some buses I've driven then there is an electric backup pump to provide hydraulic boost in the event of an engine stall.

Here's a digipic of the 1979 Chevy brake parts. Match up this with your local Pic-a-part yard.



More digipix of the install to follow...

Craig

The original hole in the BTV toe plate was covered with a piece of sheet metal and bolted in place. The existing vent hole will also be covered and then drilled for the Chevy pushrod.



Craig

Here's some digipix of the Chevy pedal assembly mounting. The fuse box edge was trimmed slightly and vent hole cover plate fitted, but otherwise bolt-up and go.







Note that the Chevy mechanical brake light switch will not be used.

Craig

Holes were drilled in the firewall and vent hole blocking plate, but are not shown here -- see previous inside views for location. The Booster/MC fits like it was meant to be there except for a little interference problem with the neutral/backup light switch shown later.



Craig

We had to custom make some brake lines of course. A coupler was used to connect to the rear. We took that line off and pulled it out to make connection easier, but you should be able to figure that out. The front line connected to the existing brake block noproblemo. Previous to this part of the install, Lance had gone to the local NAPA store to get a couple of brass adapters (shown). After measurement, we both went back to the NAPA store to get the correct length brake lines with preformed double flare lines.





Like I posted before, CAKE (as in piece of).

Craig