Packard Forum Index » V-8 (1955-56)

I decided to give myself a Christmas present and have my mechanic put new brakes on my car-I also asked him to bleed the brakes as the pedal was slightly low. Well I came to pick up the car and he was kind enough to follow me to the garage where I store it-I needed a ride home. As I am travelling down the road, all of a sudden my engine surges and NO BRAKES! luckily I was able to avoid the two cars in front of me and make a sharp right turn, bringing the car to a stop using the parking brake and placing it in neutral. I get out of the car and I can smell brake fluid-I look under the car no leaks-I think some of the brake fluid must have been sucked into the engine. My mechanic figured something went wrong and asked me what happened-A minute later I get in the car and the brakes are FINE! Im dumbfounded-I even tried to panic stop on them and they applied fine-I am wondering if this has ever happened to anyone else out there and how do you keep it from repeating-By the way I have all new wheel cylinders, master rebuilt by White post as well as new hoses.

Believe you have power brakes so did the brake pedal suddenly become rock hard and you really have to stand on it before something happens or did the pedal just go straight to the floor and no brakes?

Going rock hard could indicate a complete loss of vacuum assist but you still should have a bit of pedal and brakes. Going to the floor is the typical symptom when the compensator valve suddenly fails to close. Having it work again right after a failure usually indicates some kind of debris floating in fluid down inside the ram portion of cylinder which moved and lodged under the valve and prevented complete closure.

If the fluid did get all the way to the engine, it would indicate the vacuum canister portion had quite a bit of fluid inside it. Pushing the pedal down could have met the fluid and the resistance could have stopped pedal movement and brake application. It could have also forced fluid up high enough in the canister to reach an opening on the piston where the vacuum could suck it past the piston and into the vacuum valving and on to engine. That much fluid inside would mean a badly failed seal and the fluid reservoir should have been in need of constant refilling -- or with the drive home, almost empty by now.

I do have power brakes-the notorious BTV unit. The pedal did go to the floor.

You mention you were on your way to where you store the Packard. How often do you drive the car? More to the point, how long does the car sit between "drives"?

During the winter it usually sits for quite a while.

Cheque the fluid reservoir of the master cylinder to see if it is significantly low on fluid.

I can almost guarantee you are going to find a chunk of something floating around in the reservoir. It held the valve open.

Well Ross I know and respect you as someone who just knows about EVERYTHING that can go wrong in these cars, One thing that has always mystified me-why did Packard mount that thing in such an inaccessible place (under the floor right below the steering column)?

Short version, NOT Packard specific but general US auto production:
The BTV was one of the first WIDELY used PRODUCTION powerbrake units. It had to fit to a PREwar PLATFORM that was not ever developed with power in mind. A prewar platform that was carried over well into themid 50's. Not until about 58 or 59 did the general platform of the US automobile become redisigned for low, wide stance necessary to accomodate the Interstate hiway system that was just barely in the planning stage mid 1950's. By 58 or 59 WIDE V8 engines, 70 to 120 mph SUSTAINED speeds etc etc etc. that did NOT exist nore was necessarry for the prewar carr and its carry over into the early 50's.

So the BTV was a "get me thru the nite" kind of make shift, shoehorn SOMETHING into an OLD design until we can do better.

The BTV is a short service life, high maintenance (or in plain english a piece of shit) very early attempt at power brakes.

THe Compensator valve that Ross speaks of above is the sore spot of the BTV. Unless one has disassembled a WIDE variety of master cylinders from a WIDE VARIETY of mfg'ers over a WIDE raange of years then one can not understand the shortcomming of the BTV.

THe BTV master cylinder is a PECULIAR desiggn of unorthodoxyy in the world of automobile master cylinders taaken from the midd 1920's TO DATE!

Scroll to the bottom and read the second from last post by Jalapeno about the BTV:

http://www.trifive.com/forums/archive/index.php/t-22857.html