TJefferson2020

Since last we chatted on this superhighway I still am experiencing power brake install hell.

Problem: Super hard pedal with very little travel

I've replaced my booster (MBM mfg) 2X and neither has worked (I'm waiting on a third) I've swapped my manual style master cyl (vendor sent wrong one) for a power unit - no change.

Question: Brake pads seem very thick - I know they are supposed to touch the disk but these buggers are givin' quite a squeeze - Should I just drive and wear 'em down? Are they causing the minimal travel and hard brake pedal?

Thanks, again. I'll keep you posted.

BayRay

pjmonfre,

I'll take a stab at it.

How about checking your brake pedal free travel. If your brake pedal doesn't have the correct amount of free travel, the pedal could prevent the master cylinder piston from returning far enough to release the brake fluid pressure. If your brakes seem like they are applied all the time, this could be your problem.

I had this happen to a truck we replaced the master cylinder on. After a few pumps of the brake pedal, the brakes wouldn't release. After banging our head against the wall for a few days, we realized there wasn't any free travel. Actually the pedal was adjusted so tight it was positioning the piston forward in the master cylinder housing. Everytime we would bleed the pressure off at the wheel cylinders the brakes would release until we applied them again.


I hope this helps
BayRay

DansYellow66

I went through some of this converting a Plymouth GTX to power brakes. As noted above you have to be very careful that the pushrod is correctly adjusted so that when released the master cylinder piston will retract past the compensator port and relieve line pressure. Otherwise your brakes are always under pressure. If I remember right the test to check booster operation is to run the motor a few minutes at fast idle to fully build vacuum. Then with the brakes released turn the motor off. Step on the brake pedal and release it. You should be able to do this about three times with the pedal getting hard at a higher point each time. When the vacuum is exhausted, the pedal will be high and hard. Then holding the pedal down, restart the motor. the pedal should immediately fall again to it's normal point when braking. If it doesn't function like this - its supposedly bad. You could also have an old style drum brake master cylinder on the car. I believe all drum brake masters had residual valves in them that maintain several psi pressure in the lines to keep the drum linings close to the drums so pedal travel wouldn't be excessive. On a disc brake car, this in addition to the springs in the caliper pistons may be applying too much force to the pads. Good luck - I know its frustrating. :seeya

One other potential problem is old rubber brake hoses. Sometimes they break down inside and collapse when the pedal is released, preventing the line pressure at the brake to bleed off. This can cause dragging brakes and a hard pedal.


[Modified by DansYellow66, 12:21 AM 3/28/2004]

TJefferson2020

When you say free play - you mean the travel right before any resistance is felt?

pm

TJefferson2020

BayRay - I checked the pedal travel - the AIM says 5" =/- .25" from the floor - mine is about 7" - When I checked the free play - there was none. The pedal was hitting a badly adjusted back up light switch so it couldn't release all the way - I took a few twists off of the clevis too - This should aleviate the brake pad issue - I won't know until I drive it tomorrow.

Although I'm positive that I'm not getting any boost. I'll be calling the mfg of the booster on Monday to see what's up... :mad :confused:

BayRay

pjmonfire,

To adjust free travel, the service manual states:

1. Brake pedal clevis should be adjusted to give barely perceptible end play between main cylinder piston and the brake push rod.

2. Loosen check nut on the clevis.

3. Turn push rod in proper direction to secure the proper adjustment, barely perceptible movement of pedal before contact of push rod and main cylinder piston(1/8 to 3/8 pedal movement should be felt).

4. Tighten check nut on clevis.

I typed it out in case you don't have the service manual. This was on page 5-13.

BayRay