[glh]

My 1970 Challenger R/T came with manual drum brakes. I mounted a power booster to convert to Power drum brakes. My brake peddle goes all the way to the floor before the brakes start to work. I have new brake shoes installed and adjusted and the system bled at a brake shop.
What do I need to make my brakes work right?

[RedRaven]

Hi there and welcome aboard.

Well first of all lets get your thread to the correct section on the board and we can take it from there eh.

The guys will be on soon so they can give a hand with your brakes issue they are very good with this type of thing so hnag in there its probably something simple.

In the mean time tell us about you and your challenger?

[dave-r]

Did you fit just the booster to the drum set-up or did you fit all the diferent brackets and pedal linkage (in particular the bell crank lever) that the fitting of a booster requires?

Did you use your original master cylinder?

I will move this thread to the correct area of the forum when I get time. So look for it in the brakes section in future.

[glh]

Here are more facts about my brake converssion attempt. I put on a new master cylinder for drum brakes. I put on a booster with the bell crank like it shows in the Dodge service manual. Everything is hooked up right but I have to pump the brake peddle three times and the peddle goes to the floor before the brakes start to work. It will stop the car if I am going slow but I would never take it on the road the way it is now. I have been restoring this car for five years. This is the final problem before I can drive it. Gary

[drewcrane]

If you have to pump them several times before you get a solid pedal than you might still have air in the lines

, pump them up with the car started and until you feel the pedal firm up, shut the car off , open the master cylinder and see if you have bubbles in the fluid,

if so you have air in the lines as well,making for a soft pedal, it seems like you have hooked everything up right ,

you just need to bleed the brakes I use and prefer the gravity method, do not pump the pedal with this procedure ,go to the right rear and start there it takes time but open the bleeder valve and let it drip,and be sure to keep an eye on the level of the master cylinder let it go down about 3/4, NEVER let it drain all the way , you will just add more air, and repeat this with all the other wheels and see what happens.i will keep an eye on your thread just to let you someone is watching

Also make sure the vacuum assist hose is hooked up and does not leak,use hose clamps but not to tight as you will crack the plastic connector that hooks up to the power assist

[dave-r]

Did you bench bleed the master cylinder? If not you need to do that to get all the air out.

[glh]

I bench bled the master cylinder before I instaled it. The brake shop bled the entire brake system when they instaled new brake shoes and wheel cylinders. I did the brake peddle pumping while they bled them the second time. Even when I pump the peddle three times the peddle still goes to the floor before the brakes grab at all and they don't do much to stop the car. The booster works fine. The vacuum hose is tight. The brake peddle at rest is 3 inches off the floor. The peddle in my 71 Challenger is 4 inches off the floor. Do I need something longer to get more throw on the peddle? Gary

[dave-r]

If there is nothing wrong with the master cylinder (good seals etc) and nothing wrong with the rest of the braking system, then there are a couple of factors that determin how the pedal sits and how much it needs to travel.

First the pushrod length determins how far off the floor the pedal starts. I think the manual and power pushrods are indeed different lengths. MP do an adjustable length version which I used on my car.

Another factor is how far the pedal has to travel. This is determined by the diameter of the piston in the master cylinder. Manual brake versions tend to be a smaller diameter so your foot can apply more pressure. However this means the length of travel has to be longer for the same volume of brake fluid displaced.

Power barke cars tend to have a wider piston. This means the pedal has to travel less distance to displace the same volume of fluid but it makes pressing the pedal harder. Not a problem with a booster though.

[glh]

Thanks to everyone who tried to help figure this out. I removed the booster and replaced it with a manual brake rod and reenforcing plate from my 1970 S.E. Challenger project. The breaks work fine now. I got the car on the road for the first time in 20 years. Now I need to find an other manual reenforcing plate and pushrod for my S.E.. I guess the power brake rod was just too short or it was for disc brakes. I will just sell the booster and parts some day. Gary