Very Firm Brake Pedal

[tdangle]

I recently replaced both the vac booster and M/C on my C20 with drum brakes front and rear. The booster went out making it very hard to stop. It is now better but I feel the amount of pressure on the brake pedal is a little higher than it should be. Stock 350 with plenty of vacuum, no kinked hose, and bleed the heck out of the system. Seems to stop ok especially when I stomp on it, just hard to get used to the higher effort required.

Doesn't encourage confidence in the brakes.

[NorCalC20LWB]

Am interested in what others have to say also. I have the same thing, 72 lwb c20. Replaced the mc and booster, new front pads, turned the rotors, bled the whole thing with fresh fluid. Still very hard pedal with not a lot of travel. Sound familiar?

[mike16]

when you say they dont have alot of travel do you mean before they lock up, and do they lock up or do they work normall in every other respect but the firmness.

Not alot of travel may simply be cause by having a set of new pads, new pads are pretty thick and typically requir less travel but its not normally noticable.

hard pedal may be caused by the master cylinder choice ( piston diameter) or maybe the booster does not work. Its possible that a brand new booster could fail. also is your trucks engine producing enough vacuum to support the booster. Cam carb and vacuum leaks may cause this.

I recall that GM products with all drum brakes used a 15/16ths inch diameter master cylinder piston. When they went to disc/drum set up the diameter went up to 1 inch diameter on the MC piston. and the all disc set ups on mid sixties corvettes and the mid seventies eldoradoes were 1 and 1/8th or one and 1/16th inch diameter mc pistons. My own experieces, several of them, installing an MC with the wrong diameter piston will dramatically change pedal effort.

The increase in diameter had more to do with the increased brake fluid volume requirments of typical disc brakes systems rather than any issues with brake pedal effort.

there is a book published back in the early 80's by HP books.on brakes swapping to improve braking. I cant recall its name or the author. but it shows up on ebay and amazon occasionaly. well worth it at any price .

maybe some one can chime in with more info

[toolboxchev]

When I first did my brakes 7 years ago I recall having the same issue. But that was a good thing due to this being a work truck at the time hauling 4-5k.

I just replaced the lifetime Cardone booster for the 3rd time. Where did you get yours from?

[Derek.Matirne]

I just purchased 71 with new mc, vac, and brakes already done, and I was thinking the same thing, it sure takes a lot of leg to get this thing to stop. Years ago when I had my 62, I had a booster out of an S10, and it worked great..... That being said, would a smaller dia booster require less vacuum?

[CUSTOM/10]

Another possibility is you may need to adjust the length of the push rod between the master cylinder and the booster. On my 72 this rod is threaded and can be adjusted. If it's too long you could have too little free play, and a hard peddle, and just depressing the peddle slightly causes the brakes to make contact. If too long the MS will not release the fluid pressure causing the brake to stay partly engaged.

Gary

[NorCalC20LWB]

On mine, vacuum pressure is good, 20+. As mentioned above just seems to require a lot of leg pressure with not much travel in the pedal. Brakes will lock, at least one or two wheels anyway. I have read that the hoses can swell internally, would this cause these symptoms? Or could it be that I'm comparing the feel of a 72 3/4 ton truck to my 07 Acura brakes??

[tdangle]

Funny you say that NorCalC20LWB. I was thinking the same thing, Am I just comparing the pedal effort to an 09 Acura or 15 Challenger (which has the most touchy brakes in a car I have ever driven)

I do remember from the past though, my mom always complaining about driving the truck that the brakes would throw you thru the windshield if you were not careful.

I have good vacuum going to the booster, the rod is adjusted correctly per the factory service manual and it has the correct M/C diameter. Starting to think maybe I have a stuck wheel cylinder.