Brake frustration

[ALLAN]

when I first got the 70 Polara the brakes were nasty,lot of pedal travel then everything happened..so I have just had the whole system replaced, new cylinders all round,including master, new linings and flexies. now the pedal travel is nice and firm but braking action is lacking, on a test rig the brake action is spot on but driving it can require both feet if you need to stop quick( I tend to drive with extra distance anyway but its still scary ) its a power four drum setup,3" front 2" rear. Could it be I'm expecting too much??

 

[Ross Wooldridge]

Check the fit of the shoes in the drums. Shoes need to be arced to fit the drums - an old practise not done very much any more.

If the curve of the shoe doesn't fit the drum then you reduce the contact area or swept area greatly, resulting in way less brake power.

Also check the master cylinder bore and wheel cylinder bores are correct for your application - too large equals teduced braking power.

It should lock up easily below 30 mph and be decent above that. If not something's off.

 

[70bigblockdodge]

2 feet = no good
Only problems with drums are fade and grabby, neither of which you seem to have.
Something's wrong, sounds like booster is not working properly.

 

[Davea Lux]

when I first got the 70 Polara the brakes were nasty,lot of pedal travel then everything happened..so I have just had the whole system replaced, new cylinders all round,including master, new linings and flexies. now the pedal travel is nice and firm but braking action is lacking, on a test rig the brake action is spot on but driving it can require both feet if you need to stop quick( I tend to drive with extra distance anyway but its still scary ) its a power four drum setup,3" front 2" rear. Could it be I'm expecting too much??

As noted in one of the other posts, you probably have a bad brake booster. Often, if a master cylinder was leaking, this causes fluid to get into the internals of the booster and the rubber parts inside the booster go south. Before replacing the booster, remove the vacuum hose from the manifold to the booster and replace it. These hoses sometimes seperate which causes the inner liner of the hose to collapse, this starves the booster for vacuum and poor braking is the result. Be sure to replace this hose with vacuum rated hose, fuel hose or transmission cooler hose will not work and a lot of parts jockeys do not know the difference.

Dave

 

[traintech55]

With yhe old drum brake set up your booster should require very little pressure to use. Kind of like stepping on an egg without breaking it.

 

[Ross Wooldridge]

I didn't see in your original post that you had not replaced or rebuilt the booster. Definitely check it in addition to the other suggestions.