Hi Guys. I have a 72 dart with stock power disk brakes. My problem is twofold.

When I brake at a light I notice that if I press hard on the peddle while stopped the idle lopes and gets rough as if the engine has sprung a vacuum leak. If I ease off the pedal the idle turns normal again.

Second, I had to brake hard on the freeway the other day and everything was working great until I had to really step on it. It seems once I passed a point in the pedal travel the brakes became rock hard and would not give me extra stopping force. Scared the $*#@ out of me.

Thoughts??

Thanks

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1972 Dart Custom

You may have two problem areas.

Probably you have developed a small vacuum leak in booster diaphragm that under light braking doesn’t open up enough to be noticed. Once brake pedal travel moves diaphragm enough causing a larger leak you get the loping idle, and little to no assist under hard braking simulating lack of braking power. Also listed in FSM are; faulty vacuum check valve, collapsed or leaking vacuum hose.

In addition to defective booster, one or two stuck pistons out of the eight found on KH disk brakes will make for a rock hard pedal, and greatly reduced braking power during harder breaking that won’t be felt with light pedal pressure.

You will need to test booster to determine its ability to hold a vacuum, and inspect caliper pistons for freedom of movement.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Try the faulty check valve first to see if it is leaking. They are cheap and maybe replace the hose. Then you will know if it is the booster or not!

Nothing like having a vacuum leak......
been there and done that many times...

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Guys Thanks for the responses. I will go through all of the parts. I sure don't want that hard stop problem to come about again.

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1972 Dart Custom

Where can you purchase a booster check valve? Is this the white plastic round valve with two ports on the brake booster. I am having an issue with my 87 D-100. When you start it up the brake pedal goes to the floor and the brakes at that time are being applied. I removed the boost line going to the brake booster and drove the truck. I had to brake hard to stop but realize I did not have the assist from the vacuum line. This really has me confused!! Also is the plastic vacuum manifold on the back of the intake manifold a replaceable item? One of the nipples is broken off and I am not able to plug it. This is where the brake booster line gets it's vacuum from along with the cruise control and ac/heat controller.

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!987 D-150 Short Bed,Slant-6, RWD,A-833,2007 Ram Mega Cab 3500 RWD Cummins 5.9

Any Auto Parts store, look in the Doorman section. All the packaging cards are orange, and sometimes on the wall or a circular display. They are only a couple of bucks.

If you live in a town that has poor selections, go to a NAPA Auto parts. They have it.....

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Well shortly after the original post I experienced complete failure of the unit in traffic. Not fun. I have since replaced it with an aftermarket chrome dual diaphragm unit with master cylinder I found on ebay. I only required a little bit of massaging to install it and it works phenomenal.

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1972 Dart Custom

Glad to hear nothing major happened due to failure!! I am still gathering information on my situation. I am trying to find out where the check valve is and some of my vacum hose routing. Frustrating when you don't have an FSM available. I have looked into a complete booster and master brake replacement on Rock Auto. Not terribly expensive but may solve my problem if the check valve thing has failed.

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!987 D-150 Short Bed,Slant-6, RWD,A-833,2007 Ram Mega Cab 3500 RWD Cummins 5.9