Weird brakes

[ajwolf]

Hello everyone. I finally got my car saftied. However the brakes keep doing strange things. The garage does6want to give the car back till they are satisfied the brakes are correct. I have all 4 wheel cylinders and hoses replaced, treadle vac rebuilt, new hose from that replaced. Still the rears tend to lock up quite easily, or the car oulls hrd to the left if the rears are not locking up. I know about the articles about how sensitive these brakes were when the car first came out, but this is a big issue. Any ideas would be good. Thank you all.

[Barry Wolk]

Do you have a poppet-valve or slide valve T-V?

[ajwolf]

Hello Barry. Thank you for reading my post and replying. Right now I'm not sure what I have, I'm not sure how to tell the difference. The treadle vac was completely rebuilt professionally by a place that does this service. So the treadle vac was rebuilt four new wheel cylinders the correct ones four new hoses, and the system was completely bled and refilled with new fluid. The place where I had the treadle back rebuilt is closed until Monday, I can ask them on Monday if they remember what it had inside of it that's the best I can do. The car was safety finally and I got water through the steel tube up to the windshield washers nozzles but they were still plugged, so in order to get the car safety that I bypass those nozzles and put some exterior nozzles on temporarily just to get it to work and pass the safety. But the garage just doesn't like the way the brakes are locking up so they're not giving me the car back for safety reasons.

[Barry Wolk]

There were two types of T-V's used during the production of the Mark II. Apparently unbenownst to Continental, the supplier changed the engineering of unit. There is a valve attached directly to the brake shaft that turns on the flow of vacuum from the manifold vacuum source. Putting vacuum to the booster moves a 6' shuttle that adds additional force to your foot pressure. The original slide valve is a perfect design, if there was no wear. It starts losing vacuum containment from the first time it's used and only gets worse. The valve itself was a simple bronze allow that was too sort. It was meant to be sacrificial, but they quickly wore out leaving you with less stopping power without realizing it as it was gradual. You never lost your brakes, as often reported, they simply reverted to non-power assistant.

The T-V was redesigned and T-V delivered in the '56 calendar were a new style. It operated in the same way, but the method to turn on and off the vacuum to the booster changed to a poppet valve, which by automotive standards is far more complicated. Instead of a worry slide valve it has rubber stoppers that are jammed into place with a mechanical linkage. Frankly, they work too well. People I know use the term "grabby" because the cars want to stand on their nose, but it's usually the fronts that grab because the front shoes are 25% wider. 2.5 vs, 2". That, and the diameter of the bike cylinders is how brake bias is designed into the system. They work great when everything is stock.

With hydraulics the pressure at the exit of the master cylinder it is the same at all brake cylinders, so that eliminates the master cylinder because only one side locking eliminates that. I think this has to do with your brake drums being two different sizes, inside, while new shoes are arced to fit new drum. If a new shoe is unmatched to the larger OD of a worn drum you will have a very small contact patch on the new shoe. That overheats it and glazes the small patch, making it less efficient every time you use it, to a point where it offers no help at all. That's a condition that will lock the side with proper brakes.

I grew up in a shop that did brake arcing on every set of shoes installed. Nothing grew in the alley behind the station from the grinding dust. Matching the shoe to the drum allows maximum contact from day one. No "wear them in" nonsense. That can work with new drums and new shoes, but it's best to use a drum caliper and have the shoes curved to fit. The problem is that there are very few of those grinders left. The shop owner were rewarded for getting rid of the machines. Our local auto supplies had machine shops or venders that provided that service, but those shops have closed.

The last thing I'll mention is the pads that the shoes ride on can have grooves from previous wear. A shoe can get stuck in those grooves and not allow hydraulic power to move them until you apply lots of pressure, making it seem like that side is grabby. As a rule of thumb, always replace the brake shoe hardware with a shoe change. The springs are the only thing that pushes brake fluid back to the reserve, so they are a weak link.

Oh, if the MC was bled in the car it will never bleed all the air out of it. It must be bench bled to tip the T-V to get all the air out.

Hope this helps.

[tluke]

When I received my car it pulled to the left quite dramatically when braking. The brake line that goes from the M/C where it branches out to the front left, front right and rear, that line to the right front wheel was plugged. I had to replace it. Of course, when bleeding the brakes you would notice that no brake fluid was coming out of the right wheel cylinder or if not completely plugged, at least a diminished amount to the right front wheel cylinder. Mine was completely plugged so it was obvious. I understand that line often get plugged because of the way it dips down following the frame, moisture tends to corrode it.

[ajwolf]

Thank you Terry. Yes the entire brake system has been emptied and refilled as all the hoses and wheel cylinders were replaced. I will keep all informed. Thanks for your input.

[ajwolf]

Update: Thank you everyone. Brakes are working great. The rears just needed more adjustments until they stopped locking up. The fronts were completely replaced with new shoes,mounting kit, return springs and the drums were turned. New seals and new grease. Minimal adjustment and they work great. Patients is necessary with these cars. I am glad i stayed all original with this car.

[Mickey]

I replaced the shoes to stop the sliding of the rear tires and i had also put in new wheel cylinders