Packard Forum Index » Post-War (1946-54)

HH56. By 'check valve' u mean the check valve INSIDE of the vacuum cannister or the power brake unit or on the back of the carb????

Scottie. Did pulling the emergency brake give any significant braking effect or none-at-all????

It stopped, but by that time I was stopped by striking the vehicle ahead of me as well. Afterwards, I tried both regular brake and emergency brake and they both stopped the car RIGHT NOW, just like usual.

Well, that sounds like brake fade, as speculated by earlier posters. (Front) Disc brakes totally solve that problem. Certainly better shoe material will help. Also, does a 53 Cavalier have 11 or 12-in drums?

Craig

The check valve back of carb with hose attached. Isn't hard to check and would do just for peace of mind but am starting to agree with others that fade is a good possibility.

Dear Scottie:

Nothing worse than a runaway Packard. However, I have the service manual open and there are a few likely suspects:

There is a whole list for Treadle-Vac and topping the list is the vacuum check valve.

For fade issues the manual never sites fluid boiling. However, I would suspect heat expansion and gas fade especially for worn drums. Brake drums are a total headache.

I have even heard of this type of fade occurring on mechanical systems.

To avoid running over somebody in the future I believe if you slam an automatic into reverse it will lock the wheels. Given Ultramatic is PNDLR I would rehearse this maneuver. A friend of mine was almost killed standing near a Treadle-Vac car in a garage when the brake failed in close quarters. It smashed into a restored car!

Now this is not good for the transmission, but that can always be fixed.

I have even heard of this type of fade occurring on mechanical systems.

Sure thing, "fade" is a change in the coefficient of friction (for the worse) between the friction material (lining or pads) and drum (or disc) brought on by heat, it really doesn't care what mechanism was used to put the surfaces into contact.

Fortunately, the last Packards with mechanical brakes (thru 1936) had large 14-inch drums, power boost, and almost exclusively open (spoke) wheels which helped keep the drums cool. The brakes on my 34 Eight, though a bit of a pain to equalize after a reline, are terrific brakes, far superior to what the 56 has.

scottie -

If the pedal travel became "stiff as a board", I'm not so sure that it was from a loss of vacuum.

The vacuum section of the Treadle-Vac is a only a power "assist". In the event of a total loss of vacuum, all you lose is that assist. With else everything in proper working order, the pedal should still move the push rod and plunger, which will quickly bottom out against the vacuum piston plate, which is in direct contact with the hydraulic plunger. Granted, it does take a bit more more effort to stop, then - even compared to a vehicle with standard (non-power) brakes. Pump the brake pedal several times in your car with engine not running, and you'll get a comparative feel for it.

Not long after I purchased my first '56 Patrician, I lost power assist one day, but had no trouble coming to a complete and safe stop. Turns out the internal vacuum hose had slipped off the fitting that passes though the shell, but that wasn't the whole problem. Someone had previously replaced that hose with a piece of common fuel hose. A core from offsite storage provided an original formed/molded hose, which was more like vacuum hose on steroids. Never had the problem again.

In the case of your '53, I have to wonder if something prevented either the push rod, vacuum piston, or hydraulic plunger from moving through its full range of travel. What's weird is that it was a transient event.

Of course, it wouldn't hurt to check the vacuum supply hoses, reservoir, check valve, and even the pedal assembly, first, but you're probably gonna have to look deeper.

Hi all! I highly appreciate everyone's response. At least I have a good idea of what to look for. Right now I have to be patient, it's just too damn cold to fart around on my ol' girl. Boy, do I ever wish I had a garage instead of a carport! It does seem odd that I haven't been able to duplicate the problem. Thanks again!

Brake fade is going to happen even to the best F1 car brakes. Drums are just quicker to fade because they can't get rid of the heat as quickly as a disc, and most if not all the high performance discs are cross drilled to get rid of the heat faster. If you really want the best brakes possible for any car I'd go with Brembo ceramic discs, about $10,000+ for a 4 wheel set.

For those of us in the real world, drum brakes will work just fine for 90% of driving. Now, if you're driving in a large city with a bunch of idiots on their cellphones I'd wholly recommend at least putting discs on the front and moving up to a dual line master cylinder. At least you'd have a fighting chance to stop when you need to.