Manual Brake Help

I converted my truck over to manual brakes from power brakes because my engine doesnt create enough vacuum for power brakes. Here is how it is made up...

72 Camaro Master cylinder with a 1 inch bore.
72 Camaro front calipers
79 Camaro rear end with drum brakes.
1988 s10 proportioning valve from a manual brake truck. Front disk, rear drum setup.
My pedal ***embly is from the same 88 truck, and I had to use universal pushrod, it is in the top hole of brake pedal for the "manual" leverage.

Heres my problem. I bench bleed the master, bled the rest of the system with nearly no pedal pressure after an hour of bleeding, and no seeing any bubbles. I then bought a vacuum pump and bled the master again, and bled the entire system. I have pedal pressure about 3/4 way down in pedal stroke, and I cannot push it to the floor because of pressure.

Think I have to large of master cylinder? Can I adjust my pushrod out further? Any suggestions??

Thanks!

 

I am in the process of installing brakes. Go to mark williams on the web and he has a chart to tell you what to use. I picked up a 1" bore master cylinder because 1 1/8 would give me a hard pedal according to the chart.

 

can you hear the rear brake shoes moving ? tighten them up if you can.

 

What happens if you "pump" the brake pedal? does it not move so far on the last couple strokes? if so might be loose rear brake adjustment, as he suggested.

Did you carefully check every connection in the system for leaks? If air leaks in somewhere, it won't bleed completely.

 

Rear drums have been adjusted to almost to tight just to be sure it wasnt anything to do with adjustment in the rears. I just put this system together so its possible that their might be a leak in a line somewhere, but all the fittings are dry so I doubt it.

If I pump the brakes it never does "pump" up. It stays a consistent pedal pressure.

It feels just as soft as power brakes, and then gets hard around 3/4s to the floor, but I cannot touch the floor with the pedal, that may be because Ive ran out of stroke..?

I read the Mark Williams site and I think I am dead on about the 1in bore size, so I think either a bad master cylinder or I still have air in the lines somehow.

 

Are the bleeders on the calipers at the very top?

 

When the pedal is all the way up, there should be 1/16 inch free play between the pedal linkage and the piston in the matser cylinder. If not, the piston may not come back far enough to uncover its fill hole.

 

What about residual check valves?

Do you have any?

 

Since you're using all Camaro master, calipers and rear wheel cylinders, then I wouldn't think there's any issue with the size of the master. I would wonder about the condition of the master. Was it new when installed or off a donor vehicle?

 

if you have firewall mounted m/c shouldnt need residual valves as the fluid wont run back to m/c

 

I disagree.
What's gonna keep the shoes next to the drums?

http://www.mpbrakes.com/technical-support/troubleshooting.cfm

 

With the master culinder located on the firewall, the fronts discs do not need a residual. The '72 master might have an internal residual valve for the drum rears, but the '79 rear drum brakes do not need a residual, as they became obsolete by the mid '70s. However, installing a 10 lb inline or using the factory internal valve is a good idea for any drum system, as it will provide slightly less pedal travel.

 

Trusting in MPB isn't a wise decision!

 

Bleeders are on the top of the calipers. The front calipers are the only thing that hasnt changed since the change over to manual. The only used part I have is the prop valve from the 88 S10 that had a disc and drum setup.

I do not have any residual valves. I considered them but if it was a flow back issue I would be able to pump the pedal a few times and have a hard pedal. My pedal is consistently spongy.

Master cylinder is new from your favorite Chinese auto part store. I may do a warranty exchange just to be sure I guess.

Ole don - Right now my push rod is just touching the piston, are you suggesting I use the push rod to push the piston in a 1/16 of an inch?

 

Heres my problem. I bench bleed the master, bled the rest of the system with nearly no pedal pressure after an hour of bleeding,and no seeing any bubbles. I then bought a vacuum pump and bled the master again, and bled the entire system. I have pedal pressure about 3/4 way down in pedal stroke, and I cannot push it to the floor because of pressure.

Ok what's the problem? Do you not have breaks at 3/4 pedal?
If you stoke the master too far you'll **** it up. If it doesnt return all the way as in no free play it won't pump fluid.

Now does your statement above mean "A" that there were no more bubbles after an hour or "B" that there never were any bubbles and you gave up after an hour.

 

Their were no bubbles after 15 mins, i kept bleeding it because of pedal pressure. I do not no if truck will stop because its not ready for a voyage yet. So really do not know at what point in pedal travel breaking will begin but I can say that I have very little resistance on the pedal until 3/4 the way down.

 

MPbrakes is TOTALLY wrong about the purpose of residuals. They DO NOT, CANNOT, and were NEVER designed to "counter" return springs ( how's a 10 lb check valve counter 75-100 lb or greater return springs?), or "keep the shoes close to the drum" (that's what the heck adjusters do!) Never mind the fact OE residuals disappeared in the mid '70s.
MPB probably provides great parts/service, and does have good overall tech support, but on this subject they're wrong.

 

My foot isn't on it so I can't tell if you have a hard mechanical & physical stop in pedal travel at 3/4 of the way or building pressure.

All you have to do is stroke the master 1 time all the way to it bottoming out and its junk.

What needs to be known is donor pedal travel to floor vs your pedal travel to floor

 

Alright, I will try and replace the master and see where it goes from there. Thanks for your time 31 Vicky. Probably wont have time until next week, but I will report back in.

 

From my own experience with them both of those statements are a wrong ***umption

 

Proportioning valves don't "center", that's the pressure differential switch (that is part of a "combo" valve, which can include a prop valve) that sometimes has to be centered. The "diff" switch cannot/does not cut off pressure to either axle-it simply turns a light on in the dash when there is a pressure differential of about 400 psi or so.

 

http://www.thebrakeman.com/valvetechi

 

"All you have to do is stroke the master 1 time all the way to it bottoming out and its junk."


Not trying to start an argument here ... but

I always bottom the master cyl piston (several times by hand ... slowly) when I am bench bleeding. I actually just bench bled a used master a couple of weeks ago and that master is still in the car and working fine ... (I am NOT in the habit of using used master cylinders, I just had a couple lying around, still attached to the boosters from some cars I had s****ped a while ago ... I was having trouble diagnosing a brake issue and thought I would bench bleed one of the old ones and toss it in to see if the master was my problem, turns out my problem was a faulty "brand new rebuilt, fresh from the box" caliper. Mid eighties GM G-body ... front disc/rear drum).

How is a person supposed to bench bleed without bottoming the master?

 

First of all I'm not sure that the 75-100 lbs of spring pressure and 10 lbs of hydraulic line pressure aren't apples and oranges.

And secondly I think that the 10 lb residual valve is only supposed to overcome some of the 75-100 lbs of spring pressure..........not all of it. If it overcame all of it, wouldn't you have brake drag?

 

As for the residual pressure issue ... I am running 1980 Camaro rear drum brakes, GM G-body calipers, and a mid eighties GM Blazer (the smaller S10 based Blazer) master/booster/pedal ***embly, and factory proportioning/combination valve. Due to the fact that I used all factory parts (from different cars though) AND installed the master/booster on the firewall (as GM did on the Blazer) I felt no need to (so therefore didn't) install an residual pressure valves. My brakes work flawlessly.

My understanding is that aftermarket residual pressure valves are only needed when the master is installed lower than the calipers/wheel cylinders (like when the master is installed under the floor.

 

Thanks unkledaddy... I've actually read that a while back. Good information..

Here is the prop valve I'm using. Anyone see any problem with it? I don't have the bleed tool though, I guess that could be a problem?

 

I think you're right concerning disc brakes, not drums.

 

I can guaranty you that you came up against the springs at its designed stroke length on the bench before you bottomed out the master. Hook it to a 5,6,7 to 1 ratio manual pedal and bottom that master out with your foot. Different designs have different issues, some times it rolls the seal if you get it past the sweet spot.

On a used one, its a **** shoot. In the bore, along its normal stroke range, the bore is likely to be clean. Beyond that is where all the dirt and **** would be if there is any. Push the seals past that dirt and you'll have problems.

 

The best way to test a master cylinder.
Make sure its bled, and then put plug fittings the ports.
The pedal should be rock hard at the top.
If its not rock hard at the top or gets harder lower in the stroke you have a problem someplace between the plugs in the ports and your foot.

 

Chevy Venture minivans and their ilk use residual pressure valves, one in each rear hard line. The master is well above the rest of the hydraulic system.
That said, I do not believe they would help in this case.
It sounds like a caliper that refuses to slide, and of course, even this idea is provided the system as built is properly matched.