Re: 400 treadle-vac failure

Posted by Tim Cole On 2015/5/11 15:32:57

This thread has become pretty run down.

Let me say this about Treadle-Vac. Back when we had off the shelf NOS parts the thing was great. Some of the engineering in it is not what I would think of as first class stuff (read compensator method and lack of secondary vacuum seal in the booster) but at least the darn thing could be made to work. The situation with Chrysler products (Bendix Hydro-Vac) was impossible, so in those days Treadle-Vac was a much better situation to deal with.

I don't understand some of what that White Post place said they did. I don't understand why someone would sleeve a BTV because the ram displaces the fluid the same way as a fork lift. Of course that place would tell someone like me to get lost, so I can only fathom what goes on down there.

To whit, if the compensator port is clogged the darn thing wouldn't bleed in the first place because that is the only way fluid gets into the lines in a BTV so maybe this car has a regular master cylinder.

Blocked compensator ports is cited as a standard cause of brakes self applying, but if the car does have a booster on it, and the brake pedal is not adjusted properly, the booster can be on at all times. That is easy to diagnose. Disconnect the brake pedal and if the brakes release that is the problem source.

Next, if drum brakes lock up on the road the adjusters can be backed off with a brake spoon so that is a worthwhile item to have handy.

I've never experienced a stuck residual check valve on a drum brake car, but if that starts sticking the brakes will not fully release. If they managed to put it in backwards that should certainly cause a problem (is that even possible? I suppose you can put wheels on backwards). As well, when properly adjusted there should be no brake shoe drag when released.

So, given that the front and rear wheels are locking up on this car I would look at the master cylinder as the most likely cause.

Hope this helps.