Major brake issues, help please

[88Stanger]

I have been fighting a brake issue for far to long. I have little to no pressure at the rear, here is what i have and here is what i have tried:

1969 C10 complete rebuild from ground up with LS conversion
all new brake lines installed, front to rear
Disc conversion on Front and Rear
new POL Wilwood power booster, dual master cylinder and Disc to Disc prop valve

I am trying to bleed the brakes and the rear bleeders have only a small amount of fluid coming out, with little to no pressure. This is after an hour of bleeding the brakes the good ole way with buddy on the brakes and me bleeding.
The master cylinder does have the plug installed where the warning light goes
no leaks to date

i have checked the distance the rod is extending from the booster when the brakes are depressed fully. there is full travel on the brake pedal also

i did pre-bleed the master cylinder also with a bleeder kit

So thats where i am. I am just frustrated. i have searched and tried what i know of so far other than connecting the rear line directly to the master cylinder and seeing what pressure i have then. i do have an adjustable prop. valve from SSBC valve that i also plan to try after the direct connection.
I am open to any and all ideas at this point.
Thanks in advance for any help.

[saxart]

If it were mine, I would disconnect the brake line going to the junction at the back and see if fluid comes out strong when your buddy presses on the pedal. If you're getting fluid there, keep working your way toward the rear brakes and see how the flow is at the brake line going into the rear caliper.

It may not be the fix, but it will give you information to help diagnose the problem.

[HO455]

Originally Posted by saxart

If it were mine, I would disconnect the brake line going to the junction at the back and see if fluid comes out strong when your buddy presses on the pedal. If you're getting fluid there, keep working your way toward the rear brakes and see how the flow is at the brake line going into the rear caliper.

It may not be the fix, but it will give you information to help diagnose the problem.

2X this. You may have a bad hose at the axle. I would start at the top of the hose. Then you have divided the system in half. Depending on whether you have pressure or not decides which direction you go next. Either way Saxart is spot on. Trace back to see where the first place pressure is present.
In my world the hose is more likely to be defective from the factory than the rest of your new components. That being said I have had several new master cylinders not work out of the box. Mostly due to debris in the bore preventing the seals from trapping fluid to make pressure.

Good luck

[67 chevelle]

Originally Posted by saxart

If it were mine, I would disconnect the brake line going to the junction at the back and see if fluid comes out strong when your buddy presses on the pedal. If you're getting fluid there, keep working your way toward the rear brakes and see how the flow is at the brake line going into the rear caliper.

It may not be the fix, but it will give you information to help diagnose the problem.

great advise

[AussieinNC]

All good suggestions from others...lots of very knowledgeable folk here....

I suspect the proportioning valve has sensed the bleed process, tripped over and blocked off the rear brake circuit...

Did you use the tool to stop the prop valve from tripping over? Like

https://www.classicindustries.com/pr...2.html#reviews

If the rear hard line before the flex hose has little to no pressure, the prop valve has tripped over...

Remove all switches from the prop valve and master cylinder and jump on the brake pedal once real hard...the trip valve will usually reset itself.

Also, try bleeding the system using a pressure bleed canister tool with and adapter to fit the top of the master cyl...

Constantly pushing the pedal only aerates the fluid and causes more issues.

Finally...hope you are not using DOT 5 fluid...its is silicon based and not suited to most aftermarket systems...stick with DOT 3 or DOT 4....

[88Stanger]

Ok, well i decided to order all new hard brake lines from classic industries, pre-bent for my truck.
Got them in and went ahead and installed them. Damn, its nice to use stuff already pre-bent.
So now here is what i have:
from POL i ordered their Power booster, Wilwood 1" piston master cylinder and disc to disc prop valve. I bench bled the Willwood master and got all the air out of it. Then installed the brake bleed tool into the prop valve (Like the one AussieinNC posted). I did need to remove the piston and re-install it to a position that is correct and allow the tool to be installed correctly, into the v notch as it should.
Then i installed all the brake lines from front to rear, front and rear systems including across the rear axle. The only items left not changed out is the rubber hose from the frame to the axle, which is brand new, but i checked it out and it appears to be working fine, not blocked.
After all this, i vacuum bled as much as i could, then had a buddy over and do the you push the brake, hold it and i open the bleeder. We did this and still at the rear, little to no pressure and the pedal does not go all the way to the floor, like the fronts do.
Now im really frustrated!!
So, i started the pressure test from the rear towards the front. I still was not getting the pressure i should, so i worked my way forward, still nothing.
So, what to do now. I took off the master cylinder with the prop valve attached and thought, i want to do a test, basically a pressure/bleed attempt with the prop valve attached, and dang, lots of air came out, so i kept bleeding it until all the air was done.

Could the air in the prop valve cause the issue?

This weekend im going to re-install the master and prop valve after i bled them both and give it a try.

[67 chevelle]

Originally Posted by 88Stanger

Could the air in the prop valve cause the issue?

This weekend im going to re-install the master and prop valve after i bled them both and give it a try.

Yes absolutely yes

[geezer#99]

Did you change the pedal ratio?
Does your prop valve have a reset button in the front like this one (black cap)?
https://leedbrakes.com/i-19296666-pr...isc-brass.html

[davepl]

x3 for a collapsed or degraded rear axle hose (just a guess though!)

[88Stanger]

I thank each of you for the responses!! I really appreciate it. So frustrating.

So with anticipation of this, I ordered a brake pressure kit. I completely agree with find where the pressure is first, then find where it is not and addressed it then.

[Chris_oz]

Is the master cylinder returning all the way back? I have seen it many times the pushrod is too long, not allowing the piston to return all the way, it can stop the flow of fluid into the body of master cylinder bore.
Bench bleeding it and all is good, on the car no flow.
Check that you have free play when the pedal is at rest.

[88Stanger]

Chris_oz
I measured the distance your asking about and used some clay to check distance and it's all checking out.
Out of just raw frustration I order the adjustable Wilwood prop valve and bracket that goes together.
Thanks for the thought, any others?

[67 chevelle]

Originally Posted by Chris_oz

Is the master cylinder returning all the way back? I have seen it many times the pushrod is too long, not allowing the piston to return all the way, it can stop the flow of fluid into the body of master cylinder bore.
Bench bleeding it and all is good, on the car no flow.
Check that you have free play when the pedal is at rest.

This is another great point , the majority of aftermarket brake systems have this issue , and it is hard to diagnose , kicked my butt for a year on a chevelle

[RichardJ]

Which Wilwood adjustable prop valve and how did you plumb it? Would really like to see a clear picture of the plumbing.

[88Stanger]

Originally Posted by RichardJ

Which Wilwood adjustable prop valve and how did you plumb it? Would really like to see a clear picture of the plumbing.

I bought stock replacement lines from classic industries. The master and adjustabke prop valve and booster are the all black kit offered by POL. They plumb together with supplied lines. Then I installed the stock lines for a 1969 short fleet side. My 2" drop spindles and such came from CPP.

[HO455]

That's a clean looking proportioning valve. I like it!

[88Stanger]

Originally Posted by HO455

That's a clean looking proportioning valve. I like it!

Thank you sir. Been a long ride, but almost done. Fully rebuilt LS motor is just waiting to go to tuner, but need brakes 1st. Lol these just showed up for the front replacements, rear shows up today.

[RichardJ]

>>from Chris_oz
Is the master cylinder returning all the way back? <<

>>from 88Stanger
I have checked the distance the rod is extending from the booster when the brakes are depressed fully.<<

I tried to reread all the posts and I'm not sure how the booster pin length was checked. The retracted pin length is what is important and must be checked.
Loosen the MC and space it away from the Booster with a couple of thick washers or anything that will temporarily separate them. Try bleeding again.

[88Stanger]

Mike,
I did check that depth. I used depth gauges and a micrometer, I also used the putty idea and it checks out to spec that wilwood requires.
Really appreciate the idea though.

[Mike (Asheville)]

Originally Posted by 88Stanger

Mike,
I did check that depth. I used depth gauges and a micrometer, I also used the putty idea and it checks out to spec that wilwood requires.
Really appreciate the idea though.

I appreciate what you're saying but having done it several times I've found it almost impossible to "measure" the length since the master cylinder recesses into the booster by about a half an inch. Feel is a more reliable indicator. This may be one of the only times where "you can be too short but can't be too long."

[AussieinNC]

This might be a silly question...but have you screwed down the knob on the proportioning valve prior to bleeding the rears?

Rotate the knob clockwise at least ten turns, then try bleeding the system again...

Also, I assume you are using the old "have a buddy press the pedal down then crack open a bleeder" technique? I stopped doing that a while back...I now use a power bleeder with a plate attachment that covers both master cylinder reservoirs....pump it up with a full load of fluid, then starting at rear open each bleeder until a full stream of fluid comes out.

Makes bleeding a one man process...

If this gets your brakes functional, back off the proportioning valve knob conterclockwise 8 turns...then give it a little test drive....

To increase rear brake pressure turn the knob clockwise until the rears lock up a little too easy, then back it out one turn at a times until it feels good for your driving style.

[88Stanger]

Originally Posted by AussieinNC

This might be a silly question...but have you screwed down the knob on the proportioning valve prior to bleeding the rears?

Rotate the knob clockwise at least ten turns, then try bleeding the system again...

Also, I assume you are using the old "have a buddy press the pedal down then crack open a bleeder" technique? I stopped doing that a while back...I now use a power bleeder with a plate attachment that covers both master cylinder reservoirs....pump it up with a full load of fluid, then starting at rear open each bleeder until a full stream of fluid comes out.

Makes bleeding a one man process...

If this gets your brakes functional, back off the proportioning valve knob conterclockwise 8 turns...then give it a little test drive....

To increase rear brake pressure turn the knob clockwise until the rears lock up a little too easy, then back it out one turn at a times until it feels good for your driving style.

May I ask where you got the power bleeder and the MC lids?
I have the adj. Prop valve all the way open. I know this is open because i used a pressure gauge 1st on the MC, each port, then on the prop. Valve and both had same # of about 1000lbs without vacuum ti the booster.

[88Stanger]

Originally Posted by Mike (Asheville)

I appreciate what you're saying but having done it several times I've found it almost impossible to "measure" the length since the master cylinder recesses into the booster by about a half an inch. Feel is a more reliable indicator. This may be one of the only times where "you can be too short but can't be too long."

Mike, I went and tried your idea. After putting in couple washers the space at the pedal before you feel it against something is now further down then before.
I understand your concern about the pin being recessed into the booster. I took a machinist flat ruler and laid it against the booster wall, then took a depth measurement to head of pin from a the flat surface of the booster, then did the opposite (sort of) to the MC. Did a little math and have 1/8th inch gap. Then I tested this with the clay on the booster pin and attached the MC fully, it too showed about 1/8" gap.
With your idea of the washers doing what it did makes me think it is ok. What you think? What I'm feeling at the pedal what it should be if it is done correctly?

[Mike (Asheville)]

Originally Posted by RichardJ

>>from Chris_oz
Is the master cylinder returning all the way back? <<

>>from 88Stanger
I have checked the distance the rod is extending from the booster when the brakes are depressed fully.<<

I tried to reread all the posts and I'm not sure how the booster pin length was checked. The retracted pin length is what is important and must be checked.
Loosen the MC and space it away from the Booster with a couple of thick washers or anything that will temporarily separate them. Try bleeding again.

Almost certain to be this ^^^^.

Remove the nuts that secure the master cylinder to the booster. Then slowly push the master cylinder along the mounting studs until it's seated properly in the booster. If you feel any pressure at all the pushrod is either too long or not fully seated within the booster.

[dbm52]

with 1000 to 1500 psi at the rear brakes you should have plenty of brake. is it possible you have mounted the calipers upside down, ie the left caliper on the right side & the right caliper on the left side this would put the bleeders on the bottom. the bleeders must be at the top of the caliper