47-55.1 Pressure bleeding

[dsraven]

my thoughts too. something just needs a little adjustment tweak, a metering valve reset, check of the prop valve operation and flow test, and/or spec info to see how the master cyl in place is supposed to be connected. not a fan of the small boosters but thats what we have to work with, don't wanna re-invent the system, just get it working.
if the master cylinder is getting a stroke of some kind then there must be fluid going somewhere. it would be good to know where it is going and how far down the pipe is it getting. is there a restriction inline for the rear brakes, like the prop valve or a metering valve that won't flow? if he is power bleeding the brakes at 12 psi and isn't getting much out of the rear then there seems to be a flow issue out back.

it seems he has s10 front brakes and second gen camaro rear set up. s10 has 2 types of front brakes. single and dual piston calipers. just as a comparo for fluid requirements here is some info on these. not sure of the master cyl size that came with the brake booster kit.

s10 single 2.5" piston front disc brakes used a 10.5" rotor, a master cyl with a 0.9448818898 bore
the same truck used a rear wheel cylinder with a 3/4" bore and a 9 1/2 x 2 rear brake set and a 10.8" booster

s10 dual 1.8" (3.6" total) piston front brakes used a 10.5" rotor, a master cyl with a 1" bore
the same truck used a rear wheel cyl with a 3/4" bore and a 9 1/2 x 2 brake set and an 11" booster

a second gen camaro, say from '75, used an 11" rotor, a master cyl with a 1.125 bore, a single piston caliper with a 3" piston, a rear wheel cyl with a 7/8 bore, had a 9 1/2 x 2" rear brake set and a 10.8" booster

[burnin oil]

Originally Posted by mr48chev

I'm pretty well positive that he has all new brake parts on the truck just as almost every mechanical part on the truck is new or rebuilt. I don't think that is the issue

That is true. My point was that I have a similar issue and the parts are new on my truck. I just didn't install them but could put them back in the box and return them. They are that new. It was more of a reminder to double check parts since they are not what they used to be. We have seen alot of new part failures over the last couple of years. Everyone is giving great advice here and I am soaking it up also, especially since I am doing the same thing on my truck. 30 years of experience and you are making me feel like a teenager!

[dsraven]

Haha, if you start lopping everybody off you better not check the thread for a few days. Let it settle, lol

[dsraven]

Sorry, I meant lipping everybody off it auto corrected twice..

[72Mountaineer]

Its been a while, though I have not given up, made a few changes, none seemed to matter, still a pedal that goes almost to the floor. I removed the rear residual valve, talked with the folks where I bought the new MC, they said a natural 10lb valve in included in the fitting for the rear. No change. At the urging of a buddy I installed a 2nd front line, changing from a T to both front calipers, along with it own 2lb valve. No change. I am trying to include a few pics that may answer some questions of people who have posted in this thread, which I appreciate a lot, but this hasn't worked yet. Next step (maybe) is to adjust up the rear shoes kinda tight, giving the new shoes/drums some bedding time.

[dsraven]

ok, try this:
adjust the star wheels so the brakes are tight and you can't turn a wheel by hand
adjust the park brakes so they are tight, then apply the park brakes, if possible, to be doubly sure they are tight
now step on the brakes a couple of times like usual. is the pedal height more like it should be after a couple of applications with time in between each pedal step? if so then something in the rear brakes would seem to be the issue.

questions
what do you have for rear brakes? used that came with the rear axle and are assembled like they were when you got it? all new parts assembled on the rear axle? machined stock drums and regular sized stock shoes? machined stock drums and oversized shoes to go with the oversized drum diameter after machining? have you looked at every part in that drum set up to ensure it is all up to spec and operating?
are the backing plates in good shape and flat where the brake shoes rub? sometimes backing plates can get grooved out and a shoe will fall into that groove so it doesn't self centre properly and this can affect adjustment because the new shoe drags on the drum when not centred
do you have a park brake, is it adjusted properly?
does the master cylinder move a complete stroke when the pedal has moved a full stroke, in other words, does the pedal and linkage adjustment allow a full master cylinder stroke before the pedal runs out of travel? the pedal should bottom out the master cylinder and come to a hard stop before the pedal hits the floor. it should also come to a stop at the top of the travel with some free play at the master cylinder/booster end of things. this allows the master cylinder to refill and also lets the fluid back into the reservoir after a brake application or after the fluid has expended due to heat generated by the brakes.
is your prop/metering valve centred and allowing fluid to go to the front and rear brakes? if the system was apart and then bled the metering valve has the chance to move the piston inside it one way, like you had a brake failure, because when the system has been emptied and then you start to bleed the system, the first circuit you bleed will start get pressured up as the air is bled out. this pressure on one circuit, with no pressure yet on the other circuit, will move that failure/isolating piston in the metering valve. when this happens it is not going to allow fluid to go to the other circuit until the piston is centred again. that is the reason for the "metering valve bleed tool". that tool keeps the piston from moving when the pressures in the 2 circuits are different. when done the tool is removed and the brake failure indicator sensor is screwed back in. possibly that is a reason why you have had trouble getting fluid from the bleeder screws out back?

like mentioned previously, the drum brakes require a park brake to be operational and adjusted properly. the star wheel adjusts one end of the shoe to fit the drum, and the park brake (backed off prior to and then re-adjusted after the star wheel is done) adjusts the wheel cylinder end of the shoe to fit the drum properly. this adjustment separates the shoes at the wheel cylinder end so the return springs don't bring the shoes (and wheel cylinder pistons) all the way back against the anchor stops. with no park brake, or a non adjusted park brake, the wheel cylinder pistons are fully retracted so the master cylinder has to move enough fluid to get the shoes against the drums first before any brake application happens. sometimes this can be almost a full stroke of the pedal.
if you can remove a drum and snap some pics of your rear brakes that would be great. maybe something got overlooked or is/was missing? you can also see if the shoes are fitting the drums by the contact pattern on the shoes. maybe we can also get the bore size of the wheel cylinders?
anyway, keep feeding us info and we will keep trying to help you figure it out. I understand how frustrating it can be when it is supposed to be "all good" but doesn't work.

[dsraven]

have you burnished the brakes?

[72Mountaineer]

Sure would like to show some pics but something about a security token will not let me. I have messaged the admin. lets see what happens. The rear brakes are stock 10 bolt variety, actually for a 2nd gen Camaro, worked well for me for 23 years on my '81, I figured they would work on this truck. Shoes and hardware kit were from Advance a few years ago, I just finished and started driving the truck this summer, it has about 125 mi. on it. Drums, lines (steel and flex) are new also. Explaining things would me much easier with pics.

[Rickysnickers]

I am one of the mods in this forum. Try posting one picture at a time. Sometimes, posting multiple photos at a time creates issues. If that doesn't work, send me a PM and we'll get it worked out.

[72Mountaineer]

[72Mountaineer]

[72Mountaineer]

Spring bracket idea courtesy dsraven, shot of the brake arm stopper (which is literally a stopper)

[72Mountaineer]

[dsraven]

Any results from the rear brake and park brake adjustment theory? Better pedal travel, same?

[dsraven]

have you done the "step on the brakes and see whats happening in the fluid reservoir" check? are there 1 little fountains that come up when the pedal is first stepped on?

[dsraven]

sorry, 2 little fountains should appear in the fluid when the brakes are stepped on. I fat fingered that.

[dsraven]

you could run the lines closer to the bottom of the frame so they are lower than the master. that would allow any air to "go to the top" and out into the reservoir. should still work the way it is though, just harder to bleed.

[dsraven]

I see you have the "brake failure" switch on the prop/metering valve. if you use a test light on the switch, power the test light lead instead of grounding it then touch the switch terminal, and the light turns on then the metering valve is not centered. it's a quick test for the metering valve to see if it is centered. just make sure the metering valve is grounded.

[72Mountaineer]

I did the adjustment thing, maybe a little more pedal, but not much. Never did the fluid check, I'll try the switch thing. Today I adjusted the backs with the star wheel, took it a ride, things feel slightly better since I bled them traditionally this weekend. I brought it home after about a 10mi ride with a few stops and a couple "jams". When I got home I quickly did a temp check, both drums were at about 195 deg., both rotors were about 110. Just wondering if things were getting real hot, seems they aren't. I adjusted the drums 2 clicks (yes just 2), drove about 15 mi, more stops, etc., drum temps after were 215 each, slight brake smell coming off the wheels. Tomorrow I'll pull the wheels/drums and check things, I guess I'm waiting for the shoes to bet bedded in. Maybe when the new shoes and drums get a coarser surface, things will get better.

[dsraven]

If you have stuff apart snap some pics and post them.
The auto adjusters should work when brakes are applied in reverse could try that too.
If you have it on stands anyway, and plan to remove the drums for a check, maybe crank the adjusters up tight (after you have done your initial analysis and then stuck the drums back on) and see if the pedal height is better.
Smooth drums are what you should see and want. That is the purpose of burnishing, the friction material on the pad or shoe heats up and the resins cure and make a material that works better but also some of that material binds to the drum or rotor and fills/smooths the surface for a better bite on the 2 surfaces.
Also check slack in the linkage. You dont want too much but you also need some so the master/booster can return fully.
Does the pedal height change if you pump the pedal a couple times?

[1project2many]

Originally Posted by joedoh

just a note, on most GM the front reservoir is the REAR BRAKES. and when I say this, some people have shown me examples of like 50s corvettes that are front/front rear/rear but every s10 swap i have done with every booster/master i have reused the front reservoir is the REAR brakes. it has the larger hose which some people equate to the discs, but hydraulics dont really work that way.

so if you have a disc/drum master, this could be your whole problem. not enough pressure to the front.

just something to check, cant say thats what it is, but i would sure check.

The reservoir closest to the firewall is the primary reservoir. This is because the booster (or pedal for manual brakes) directly actuates the piston for the primary reservoir. As pressure builds in the primary brake system the secondary piston is applied. Since front brakes do most of the stopping, the front brakes are often connected to the primary port. This arrangement causes the front pads to apply first while pressure builds to apply the rear brakes. Connecting the lines to opposite ports can result in the driver having to apply more pedal pressure to stop. In my experience drivers often report that a pedal travels to far when they are experiencing the need for increased pedal pressure.

[mr48chev]

I'd say about half the problem with aftermarket master cylinder setups is that the sellers are extremely vague with their instructions and assume that the person installing the unit is well versed in brakes in general. I've searched for online instructions on installing these units from the sellers in the past 20 years a number of times and it never gets any better. Not much for actual instructions and not much as to which end of the cylinder goes to what end of the truck.

That goes opposite of what we usually do if we snag the brake system off a donor rig, Then you usually check to see what line goes to the front and what line goes to the back and try to remember for later.

[dsraven]

yeah, I'm of the same mind with 1project and mr48. without any instruction as to which port is front/rear it is a guess and hope thing. like said though, maybe worth it to swap the ports/lines and see if that fixes it. those are short lines from the master to the prop valve so possibly a couple of new slightly longer lines could be installed and bled at the prop valve through gravity with those fittings left slightly loose till no bubbles then torqued up. that way you don't introduce air to the rest of the system if done quickly. if you don't know what the master came from it would be hard to figure out.

[72Mountaineer]

Wow, this opens up a whole new can of worms. I hooked up the lines for everything as per the instructions from Tuff Stuff, makers of the whole MC/booster/prop valve system. I consulted their tech guy as per the correct system for my truck, and this was suggested and purchased. I did a little research (the Google style) today and it seems that when the reservoirs are different sizes and the front reservoir is the larger is when the lines from the prop valve go to the front closer to the firewall (in my case the booster). Correct me if I'm wrong here. I've got the instructions for the prop valve and this is what it shows.

[dsraven]

If you have the instructions that came with the unit and connected it as they advise then it SHOULD be good. It might be worth the call to recheck to ensure the unit you received was actually the correct unit. maybe it got boxed wrong or something.