Re: BRAKES: Easamatic Power Brakes aka Bendix Treadle-Vac--Change or Not??

Posted by HH56 On 2019/8/1 14:25:09

Welcome to Packards.

As you said, this is a very hotly debated subject and there have been many approaches and thoughts. Some will argue the TreadleVac or BTV for short was used by many cars of the era and was reliable then and if properly rebuilt and maintained will be reliable now. Just as many will argue the BTV is an accident waiting to happen because it is an old technology single line system and prone to sudden and complete failure if neglected, badly rebuilt, or if a single but vital rubber part fails to seal.

The big issue with Packards and changing the BTV to something modern is pedal ratio. The way the BTV operates with it having a long stroke narrow ram displacing fluid as the ram inserts in the cylinder, the Packard mounting position and 1:1 pedal ratio is acceptable. When trying to go with anything modern such as a master with a wide short stroke piston pushing the fluid ahead of it, the pedal ratio needs to be upped to somewhere between 3 and 4:1 -- ideally around 3.5. That alone requires a new or completely revised pedal assy because there is no way to increase the ratio and maintain a stock pedal.

I would be curious what complete kit you found or were thinking of. Am assuming that you are talking disc brakes when you say complete kit?? To the best of my knowledge there are no power brake kits that will directly drop in the original space with the original pedal which is why so many variations have been tried. Any of the brake kits will probably require a relocation of the unit to somewhere higher on the firewall. That can be problematic on some models due to space or location of some hard to move components and definitely visible as a mod. The BTV may not have enough volume for discs so something modern will probably be needed.

Some have thought under the floor might work as far as minimizing visible change but due to space limitations fitting a large diameter vacuum booster under can be problematic. Possibly it could be positioned in a place where the floor could be cut out then lifted and boxed in to raise the booster a bit so as to not have something vulnerable hanging below the frame. Don't know if anyone has tried. There is another approach being contemplated for under the floor using a smaller manual master with a remote and out of the way power booster but anything under the floor also requires a pedal change. Even with the stock 51-4 manual system it is problematic to go to a dual master because of the original master mounting location and method. 55-6 might be more doable because of the different master location but I don't believe any of those ideas have gone to much more than contemplation yet. There is one fellow who is adding discs on a 52 and I believe is planning a conversion to a manual firewall mounted dual master with suspended pedal and a remote power unit for power to the front discs. That is still in the planning stage so details may change.

The ElectroBoost has been used by a few who have dropped it in the stock location in place of a BTV and upped the boost of the power unit to compensate for the low pedal ratio. In my opinion, that is a recipe for disaster. If the power unit fails you still only have the 1:1 ratio which with a 1" diameter unboosted master piston is barely enough to slow the car, not stop it in an emergency. The ElectroBoost is also 12v which would require a voltage conversion on pre 55 models.

At the least, I would go for new lines, hoses, cylinders etc for sure. If you have the BTV rebuilt by a competent rebuilder or get an exchange unit from Kanter or Max it should be good for several years and you keep the stock look but only if you are keeping drums. The competent rebuilder part is the key. The BTV is not that complicated but knowing where failures happen and what might be marginal and need replacing but is not part of a kit is important. Some of the big well known multimake places and chains have been found to be less than advertised when it comes to the BTV.

After the BTV rebuild if you still feel more could be gained then you can think about the approach you want to go toward installing a modern unit because you could research and do it without as much pressure.