CAN"T get a hard pedal...need suggestions.

[BobbyK]

No Viagra jokes please.

I'v been chasing this problem since I've owned my 71 Blazer(2.5 years now).The brakes have never been good,very poor brakeing performance.

I've done the following to this point:
1-new front calipers with premium pads.
2-Rotors are within specs so I just scuffed the surface with a medium sanding disc on my drill.
3-made sure rear brake cylinders were moving freely.Lots of pad left on the shoes so I left them alone.
4-adjusted rear brakes so there is only a slight drag felt when I turned the drum by hand.
5-I adjusted the e-brake and that actually works great!
6-new brake booster(there WAS a leak in the old one).That only made the brakeing easier(less pedal effort).Didn't improve performance though.
7-new master-cylinder.bench bled it 1st before I installed it.(TSM states stock M/C provides enough pressure for 4 wheel disc.)
8-new prop. valve. (for 4 wheel disc.)
9-bled the brake system umpteen times.Pressed the pin on the prop. valve while doing this.Also bled the brakes in the proper sequence.Started from the farthest wheel and worked to the closest.
10-adjusted the rod that's inbetween the booster and the M/C.
11-checked my vacume lines and checked how much vacume I had going to the booster.All is o.k. there.
12-new stainless flex hoses(all 3 of them).

What's worse is I just converted to rear disc brakes (used the TSM kit)and now the pedal is even worse. I did adjust the rear disc e-brake and the pads are real close to the rotor.
I'll post pic's of the rear disc install on another post.
Help me,I can't figure it out!
Thanks

[Zurbo]

I ended up having to have mine power blead to get all the air out so the pedal was no longer spongy. Since you have rear disks though, I would think they require more fluid volume than the ol drums. I assume the conversion kit comes with a different master cylinder and proportioning valve which it sounds like you installed.

[tom hand]

Oh I feel your pain. I went thru this problem with a 72 vette. After countless trips to have it pressure bleed, talks with hundreds of so called brake experts, I finally found the problem and it was so simple. In order for a master cylinder to operate properly it must return to the end of it's stroke each time you push the pedal. The first thing to check is your brake pedal linkage. It should have a small amount of freeplay much like a clutch pedal. The second place to check is where the master cylinder bolts to the booster, if it is starting to push the master cylinder plunger when you tighten the bolts it will never work. It is rare to have these problems, but when they crop up it will drive you crazy.

[BobbyK]

Tom,I adjusted the rod between the booster + M/C so it was just touching the cup in the M/C.
I know the brake pedal can be adjusted but I can't see any reason why anyone in the past would have done such a thing.
I'll recheck the booster/M/C rod and double check the pedal like you said though.
Also it looks like I'll get the system power bled next week.
Thanks

[Gordo]

Curious,,,is the peddle low and hard, high and hard, low and mushy or high and mushy?

[BobbyK]

Low and mushy

[ckhd]

If you're a "do-it-yourself" kind of guy, go buy this month's Car Craft. Page 74 shows how to build your own pressure bleeder.

[Slammed67]

I just looked at the pictures in your other post. I can't tell for sure, but it looks like the bleeder screw isn't at the highest point of the caliper the way it is mounted. Seems like most calipers are mounted vertically, not horizontally, like you have them. You may have some air still trapped in the caliper, ablove the bleeder screw. A fellow board member told me about how he was having problems too...... I think he had to pull the calipers off and hold them at the correct angle in order to get them bled properly. Just an idea.

[BobbyK]

Yea I did that when I bled the Brakes.Bent up a coat hanger and hung the rear caliper so that the bleeder was faceing up.Tapped the caliper to help expell any bubbles as well.

[roger0080]

My first thought was what Tom Hand suggested. I had that exact problem also. A mis-adjusted brake pedal to master cylinder.

Q: Does the "brake" light come on/stay on? Is the bulb/circut working?

The pedal stays mushy when you don't "pop" the presure switch back in the proportioning valve causing the system not to have equal pressure between the front and rear. When that happens the "brake" light is suppose to light.

That's all I can think of.

-Roger

[BobbyK]

Brake light comes on for about a second at startup then goes out.It does not come on at any other time.