Need help! No Brake Pedal

[68BBC]

Hey guys I have got to get some brakes on my truck so I can move on. Here is what I have, and what I have done so far.
4-wheel disc brake set-up, with correct prop valve. All new lines and hoses. The master cyclinder is good. When you block it off the pedal is hard as a rock. The push rod on the booster has been adjusted to the correct length. I have no air in my lines, nothing but solid fluid coming out each caliper. Ok so here is the kicker. I can take a pair of vise grips and clamp off the center rubber hose that connects the two rear lines, and I have a pedal. I can also clamp off the two hoses that go to the caliper and I have a pedal. I can open one side of the bleeder and push the opp side caliper piston in and fluid comes out the other side. When you push on the pedal the pistons move on the caliper so it's working, but I can't get a pedal it still goes to the floor. I need help. I have been working on these brakes for about two months, and I am about to give up.

[cdowns]

to me it sounds like you're exceeding the fluid capacity of the master cyl in the back

[68BBC]

Cdowns, what would that mean exactly? I have the correct master cyclinder. Is there something that I can do to fix that? Could my prop valve be bad? Thanks for your help!

[cdowns]

Originally Posted by 68BBC

Cdowns, what would that mean exactly? I have the correct master cyclinder. Is there something that I can do to fix that? Could my prop valve be bad? Thanks for your help!

if you have somehow been given a disc/drum master cyl there isnt enogh brake fluid for the rear brakes to work properly due to insufficent fluid volume

if you look at the master cyl both compartments should b about the same size for 4wheel discs

[68BBC]

That is correct. Both of my reservoirs are the same size.

[QKENUF4U]

are all your bleeders on the calipers at the high point of the caliper ??? (not upside down/mounted on wrong side of car)

[68BBC]

They are all just past the 12 o'clock position. I have took the rear calipers off, and placed a c-clamp on the pistons so I can move them around to see if any air is trapped. Nothing but fluid comes out. What is so wierd is when you clamp that center hose it has a great pedal, so I would think that this would eliminate anything from that point foward being bad. I have had a few mechanics come by and check it out, but they can't figure it our either. This shouldn't be that hard. I know it's going to be something simple that I am just over looking.

[QKENUF4U]

only reason i ask that question was this........

YouTube- Brakes hard to bleed

sounds like youre on the right track... sorry i cant help more.... good luck

[68BBC]

The you tube video didn't show up, but I even went and bought new calipers to see if the ones that came in the kit were bad. I get the same results with the new calipers. It is vert consistant whatever it is.

[68BBC]

I see the video now!

[cparman]

What kind of rear disc brakes? If you are using the GM style calipers with a mechanical E Brake thru the caliper MAKE SURE the rear calipers are adjusted. Pull the wheels, and see if the rear brake pads are sloppy as they sit mounted in the caliper. If they are, and you have the kind of calipers I am talking about, there will be a lever on the back side. Take a pair of channel locks, and manually move the lever thru it's range of motion several times. Then see if the pads are more snug as the sit in the caliper

IMO that is the first step

The threaded rod adjustment under the dash is to adjust the brake pedal height only, and has nothing to do with when the brakes are applied

the second step is to check the clearance between the booster and master cylinder. The redneck/Chip way to check the clearance is to unbolt the master cylinder ( not the brake lines ) from the booster, and get a small ball of clay 1/4" , and put in the back of the master cylinder piston. There will be a small depression in the M/C piston. Bolt the M/C back to the booster. Then unbolt the M/C again. See how much the clay is compressed. There only needs to be a tiny bit .010" of clearance. Some of the rods coming out of the booster are threaded, that makes it easy, If it is not threaded, see if you can remove the rod by pulling it out of the booster, and weld a bead of metal to the end, and then clean up the weld. Repeat the steps above until you get a PEDAL, and then go drive your truck. I will caution you that there can be some ' gain ' in the pedal after driving it the first time or two. What I do is drive the truck a short distance, and confirm that I am happy with the brakes, and find a side street, and put the truck in neutral and see if it will coast to a stop. If so, then you are ready for a 3-5 mile ride doing the same thing. If you feel brake drag, then grind a bit more off.

[68BBC]

cparman, Thanks for your advise, and I am open to anything at this time. The kit has mid 70's gm car calipers with no parking brake. The booster that I have has an adjustable rod. I have adjusted it to just almost touch (.020) the plunger on the master cyclinder. One mechanic told me to just get in the thing and drive it down the road, and let the fluid heat up, but my pedal will not even pump up or firm up. I hate to take the truck for it's first ride and it be the last, and loose 25k.

[cparman]

Hey Brother, you have nothing to loose by taking all of the clearance out between the booster/MC. I would just to prove a point. The fact that your booster has a threaded rod makes this easy to do, and if you use my redneck method of measuring clearance you will know fore sure. IMO .20 is too much. I would want you to think about the pivot point ( where the brake pedal mounts ) and the booster mounting point ( the fulcrum ) this ratio should be 4 to 1. SO if you have .020 between the booster/MC that equates to .80 at the pedal. Tighten that baby up and get a pedal. Then drive it around the short block and check to see if you have it too tight. Don't out smart your common sense !

I did a Disc conversion on a 70 Barracuda. I did all my usual stuff, and bleed the brakes with the help of one of my guys. I was the bleeder. I saw a good stream of fluid come from all 4 wheels. I asked my guy if he had a pedal. He said it was all the on the floor. I said no problem. He looked at me like " he aint real bright " I move the car around the building, and new it would stop. Took all of the slop from the between the booster/mc and got it a bit too tight, one more adjustment, and my customer loves his disc brakes

Originally Posted by 68BBC

cparman, Thanks for your advise, and I am open to anything at this time. The kit has mid 70's gm car calipers with no parking brake. The booster that I have has an adjustable rod. I have adjusted it to just almost touch (.020) the plunger on the master cyclinder. One mechanic told me to just get in the thing and drive it down the road, and let the fluid heat up, but my pedal will not even pump up or firm up. I hate to take the truck for it's first ride and it be the last, and loose 25k.

[panhandler62]

I think cparman is on to something here.

Since you can clamp the line and get good feedback that suggests that your front brakes and proportioning valve are OK.

Since you can bleed all four corners that suggests that fluid pressure does go to the back brakes.

I would pull a caliper off and push the piston all the way back in. Have someone step on the brakes and see if it moves. If it does then push it back all the way again and have someone hit the pedal. Now; see if you can get the pad to wiggle or get a feeler between it and the disc.

It's possible that your calipers don't match the rotors. They may be working but running out of push before they clamp down.