[chevyrestore]

Ok I borrowed a booster adjustment depth tool, I guess I still had it out a little too much, adjusted it as per the tool and test drove, when I SLAM on the brakes it throws me forward more but still no wheels locking up.

The only other thing I had time to do was throw a one person bleeder bottle on the rears, looks like there a good squirt out of there but not a lot of fluid in that squirt.

What would cause that? Its like if someone was holding the pedal and I cracked the bleeder it would squirt out but not as much fluid as what the fronts would have.

[aosborn]

I have seen this many times. If the fluid at the front calipers is running clear you are probably good there. As for the rear not flowing as much fluid, there still might be air trapped in the system, or you haven't moved the rear caliper pistons out enough to allow much fluid in the calipers.

With a helper pumping the pedal, start bleeding the rears right at the outlet of the master cylinder, then at the outlet of the combination valve, and then back at the wheels. See if that helps.

Also, activate the parking brake levers on the rear calipers and see if the parking brake mechanism moves the pads.

Lastly, test the brakes as I have described in an earlier post while the truck is jacked up off the ground.

Andy

[chevyrestore]

the truck has been bled atleast 5 times, should have gotten all the air out, should I bleed AGAIN at the MC? I recently replaced the line going from the PROP valve to the MC and rebled twice again, same amount of fluid coming out.

I pulled the e-brake lever and its just a pure mechanical piston that pushes the pads out and no way affects the piston on the caliper. Ill try the thing with the brake pedal and spinning the wheel when I get a helper out here. Im by myself most of the time.

[thinwhiteduke]

Originally Posted by gearheadslife

crack the line for the rears, and see if the pedal now is easier.. I'm guessing here that the rear brakes are in the master port nearest the booster, if the rubber line is failing internally, it block flow under pressure and make it hard to move the piston in the master.. as will a stuck propotioning valve that closed off the rears..

How old are those rubber lines in the rears?

They do close up internally over time, restricting the flow.

I had a similar problem with my land rover . Put a new flexible rubber hose it , and bingo! Problem solved.......

just a thought, hope you sort it soon,

Duke

[chevyrestore]

I bought the rear end from a friend that said he ripped it off a junkyard car, I assume they are the original rubber lines, theyre super short rubber lines but I see how it could still cause that, so should I just replace those or do some more checking?

[thinwhiteduke]

Well, if you replace them, at least you can take that questionable part out of the equation.
They may, and are most probably good, but if your flow is shy at the rear??? put new ones, then you know for certain that they got full flow and you won't have to touch em for a while. Maybe you can take one off at a time and check them, but just as easy to put a new one back on,can't be that expensive, plus, then they're new!
I only had one on my truck, cost about twelve bucks.
You can test by have the rear up on stands, then have a helper apply the brakes normal/hard for a bit, release the pedal, and your rear wheels should be instantly 'free'. If they still got some resistance still, then the flex lines could be partially blocked.

Hope this helps

Duke

[chevyrestore]

should I have 2 lines from the prop valve going to the rear or is it ok have it with 1 line going to the pumpkin and splitting into two?

[thinwhiteduke]

Mate, you got me there,

I live in Australia

Just make sure that any flexible lines are not blocked - free flowing

All I'm saying is that they can become blocked 'progressively ' over time!!

You should be sure that they are flowing as they should, and not restricted through 'swelling' and closing the 'hole' off......

I'm not familiar with your particular application , just be certain that your flexible lines are in good condition!!

Let know how u go!

Duke

[cobalt327]

One line to the rear split at the rear end is fine.

Have you verified there's no rear brake proportioning valve in the MC? Is there an added-on adjustable prop valve?

[aosborn]

Originally Posted by cobalt327

One line to the rear split at the rear end is fine.

Have you verified there's no rear brake proportioning valve in the MC? Is there an added-on adjustable prop valve?

The valve in the master cylinder would be a residual pressure check valve which does not provide the same function as a proportioning valve.

The residual pressure check valve in a drum brake application keeps the return springs on the brake shoes from retracting the shoes away from the drum, and keeps the seal on the wheel cylinder pressed out against the bore.

As to the re-bleeding of the brakes, what I am attempting to determine is whether the amount of fluid coming out at the various points is constant. Example, good flow right at the MC, good flow at the output of the combination valve, poor at the calipers. It can help to determine problems.

Also, it isn't surprising to find air trapped in a brake system that has been thoroughly bled. It won't hurt to go through it again starting at the MC. If it is indeed thoroughly bled it won't take but a couple of pumps at each point to confirm it. Also, make sure you have a helper working the brake pedal and don't just depend on a vacuum bleeder or pressure bleeder alone.

Another thing to keep in mind, is that until your brakes are bedded in, you won't get maximum stopping performance. Also, unless you are moving pretty fast you may not get lock up on dry pavement when you have wide grippy tires. That is why trying them on gravel (if you can) or wet pavement is a good indicator of what is going on.

[cobalt327]

chevyrestore- Is there a combo valve on it? I recall somewhere you saying there was. Or an added-on proportioning valve? If you have a prop valve already in the system (in the combo valve not MC- so sorry), and have added another one, you have cut the pressure to the rear brakes too much.

[chevyrestore]

no internal MC valves from what I can tell, I added a classic perform disc disc proportioning valve, no other valves in the system.

[cobalt327]

The following explains what I'm getting at: http://www.classicperform.com/Instru...structions.pdf. If this hasn't been done, the pressure to the rears will be insufficient. A stock-type combo valve is modified in a similar manner.

[chevyrestore]

I see what your getting at, I was told by CPP if there is a 2 stamp its for a disc drum and if theres a 4 stamp its a disc disc valve and there is a clear 4 stamp so I shouldnt have to modify anything correct?

[cobalt327]

Originally Posted by chevyrestore

I see what your getting at, I was told by CPP if there is a 2 stamp its for a disc drum and if theres a 4 stamp its a disc disc valve and there is a clear 4 stamp so I shouldnt have to modify anything correct?

In a defect-free world, no you shouldn't have to do anything.

The only other thing I had time to do was throw a one person bleeder bottle on the rears, looks like there a good squirt out of there but not a lot of fluid in that squirt.

What would cause that? Its like if someone was holding the pedal and I cracked the bleeder it would squirt out but not as much fluid as what the fronts would have.

This is what prompted me to bring this up. If nothing else cures the problem- I think you should look to be sure.

The last statement above could also be taken to mean there was insufficient volume as opposed to pressure. Like if the MC were a disc/drum unit, having less volume for the rear drum brake cylinders than a disc brake caliper requires.

Who knows- when all's said and done, you may just need a bigger booster.