Need help with brakes (new lines/system)

[BruthaMan]

Hey guys,

We're just about finished with the restoration of Pancho and having some trouble with the brakes.

Here's what we have:

1) New brake booster

2) New Master Cylinder

3) New Prop valve

4) New stainless lines front and rear

5) New calipers all the way around

Everything is new on the system with a rear disc brake conversion.

Symptoms:

1) With motor off, we have manually bled, hand pump bled, and power bled with air compressor. After a two pumps, it starts getting stiffer like it should, but can never get it on the first pump. Brake pedal returns normally.

2) More troubling, with the motor running and the booster hooked up to vacuum, pedal goes to the floor quick and then "squishes" back up slowly. No amount of pumping the brakes, WITH the motor running, gets anything at all. Just straight to the floor and slowly comes back up.

Things we have tried:

1) Bench bleed the master cylinder. No problem.

2) Hand bleed, hand pump bleed, power bleed with air compressor based bleeder tool.

3) Recenter the prop valve.

4) Rebleed the system.

The most troubling part is, with the motor running. If we disconnect the vacuum line, it goes back to described above, but the pedal returns normally. With vacuum line on, the system is a no-go. Straight to the floor, slow return on the pedal.

This is a brand new system, new lines, new everything. Spent two days on it so far and even had a bud from Mieneke come out a look at it (before we knew how it reacted with the motor running).

We're missing something, but I'm not sure what it is. Any of these symptoms seem familiar? Sure could use some advice! Once we get the brakes working, will be time for a test drive and you can imagine how eager (after a year of restoring) we are to do a test drive!

[cableguy0]

the first thing is just because you have new parts doesnt mean they are working properly. with the pedal sinking to the floor and if theres no external leaks anywhere i would lean toward the master cylinder being bad. if your getting good fluid out and no air on the bleed.

[BruthaMan]

Thanks CG.

One more observation. I had backed it out today (first time drive in over a year!). Went to pull back in the garage, press brake and we have brakes. But it still goes way down, but they did work a little.

Another thing we did, that I had not mentioned...we disconnected the lines at the master cylinder and blocked them off with bolts to test for any leaks. No leaks at all, pedal was instantly hard with little effort on pressing the brakes.

We're going to try another bleed tomorrow. If anyone else has any suggestions, would be much appreciated!

[87Bob]

Originally Posted by BruthaMan

Thanks CG.

One more observation. I had backed it out today (first time drive in over a year!). Went to pull back in the garage, press brake and we have brakes. But it still goes way down, but they did work a little.

Another thing we did, that I had not mentioned...we disconnected the lines at the master cylinder and blocked them off with bolts to test for any leaks. No leaks at all, pedal was instantly hard with little effort on pressing the brakes.

We're going to try another bleed tomorrow. If anyone else has any suggestions, would be much appreciated!

Did you bleed the system in order of the farest away from the master to the shortest? Meaning RR-LR then RF-LF. If you don't do it in this sequence you can be pushing air around in the system and not know it. Engine on or off it should be rock hard at the pedal. Also you mentioned you put disks on the rear do you have flow controls in the rear system? If you don't the natural siphoning effect can make the pistons in the calipers withdraw into their housings and then you have to extend them all the way back out before they come in contact with the rotors. Also did you get a new purportioning valve for rear disks? It's different then the one you'd use for disk/drums.

[menace121978]

Wade,

i agree w/ these guys. if you bled the brakes like 87BOB said it sounds like a problem with the master cylinder. hooking the booster up and the engine running will usually magnify the Symptoms. good luck bro, i know your anxious!!

[BruthaMan]

Guys, thanks for all your help and suggestions.

I'm happy to report that we have the brakes working flawlessly now! In fact, for the first time in almost a year, I drove her to the exhaust shop (with *some* brake, but not where it should be) and had the Corsa mufllers installed.

Now, it is with great humility that I come back to report the problem. Doh! Felt like a fool!

We're at Custom Exhaust in Amarillo (great guys btw, did a fantastic job!) and was telling them about the truck and what we had left. Expressed that had *some* brakes, could drive and stop, etc, but wasn't were it needed to be.

The truck was up on the lift and the guy turns around, walks to the front and said "this is your problem right here," as it places his hand on the caliper, then walks to the other side and places hand on the other caliper.

I'm thinking "oh no, don't tell me...I paid a fortune for those polished calipers from Online Performance..." Nope.

Know what it was? Take a guess!



We had them on opposite sides with the bleeders pointing to the bottom. Said "switch those out with the bleeders on top...they'll never bleed from the bottom right." Felt like a fool...we knew better and it never even occurred to us.

After the exhaust was installed, took the slow back roads back to the house, switched the front calipers out (we had the back ones right and I even recall us talking about it when installed those...the bleeders need to be on top!), re-bled the system a few times and brakes are perfect!

So I thought I'd set aside my humility and post an update/solution, in case there might actually be someone left in the world that doesn't know the bleeders have to be on top!

[cableguy0]

hey at least it turned out to be a cheap and easy fix. and a lesson learned

[87Bob]

Hey do do happens! We all have made mistakes along the way.