Brake system fiasco, I'm at witts end! I need a guru!

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  #1  
Old 01-25-11, 07:05 PM
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Brake system fiasco, I'm at witts end! I need a guru!

1977 Monte Carlo braking system on a hotrod, front disc/read drum, aftermarket booster and master. Original master worked for 10 years so its a proven system. I now have a brand new master again, 4th one but that is another story. Master and booster have been professionally bench tested and proven good.

After replacing the master, my pedal is 1/2" from the floor with the engine running, and high and hard with the motor off. I bled all 4 wheels starting with the furthest, I tried bleeding with the motor running and not running. I carefully measured the actuator rod and adjusted it. Counting the slop in the pedal linkage I have 1/2" free play in the pedal with the motor off.

In the past I tried reverse bleeding and it didn't help. I have no combo valve, the front has a TEE in it and I have a manually adjustable rear valve. The rear drums are working and the front pads are pushing in. I have no air coming out when I bleed.

I have been working on this for longer than I care to admit and I have posted this before, I appologize. I'm trying to get some new ideas from some new blood before I take a sledge to it!
 
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Old 01-25-11, 07:08 PM
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Vacuum boost issue?????

Mike NJ
 
  #3  
Old 01-25-11, 07:16 PM
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Troubleshooting

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Step 1: Check the Brake System Fluid Level - Check the level of fluid in the brake master cylinder. It is natural for fluid to be a low if the front or rear brake pads/shoes have worn down, but if they are in good condition and the brake master cylinder reservoir is empty you might have a brake fluid leak somewhere in the system. Inspect front brake calipers, rear wheel cylinders (drums) or rear brake calipers and flex hoses front and rear of vehicle and look for any sign of fluid leakage. Also check the rear of the brake master cylinder for fluid leaks, if brake fluid is present the master cylinder seals have failed and the master cylinder needs to be replaced. Replace any parts that are leaking or show signs of previous leakage. Refill and bleed the brake system as needed. (Note: if brake fluid has contacted the brake components i.e. brake pads or brake shoes the brake lining material is contaminated and must be replaced) If the brake fluid in the reservoir is full proceed to the next step.


*

Step 2: Brake Master Cylinder is Full of Brake Fluid- If upon inspection the brake master cylinder is full of fluid, the brake master cylinder may be bypassing internally. This means the seals inside the master cylinder have failed allowing the fluid from the front of the master cylinder plunger to slip through to the rear of the plunger and back into the fluid reservoir. Allowing the brake pedal to go to the floor with out pressurizing brake fluid into the system. Replace master cylinder with new unit and bleed system as needed.
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Step 3: Failing Axle Bearings - The vehicle axle bearing holds the wheel true to the axle shaft while allowing the wheel to rotate. If the bearing fails it will allow the rotor to move back and forth, forcing the brake pads inward into the caliper. Then as you apply the brake pedal it will go to the floor as the caliper fills with fluid. In this case it may take one or two pumps to the brake pedal to regain normal operation. Inspect and replace failed axle bearings as needed, finish by bleeding and adjusting the system.
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Step 4: Air in Brake System - When brake calipers or rear wheel cylinders fail they can allow air into the system when the brake pedal is released. Bleed the brake system by loosening the air bleeder, if air is observed from the bleeder replace the caliper or wheel cylinder and re-bleed system. This condition is rare but it does happen.
 
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Old 01-25-11, 07:19 PM
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Diam.f the master is the problem.bore and stroke of the M/C determines how far the pedal must go to actuate the calipers
 
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Old 01-25-11, 07:37 PM
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All good replies.. . here are more details

New master, front brakes, front calipers, new front rotors, new front brake hoses, new rear shoes, one new drum, one new wheel cylinder, booster tested by a professional brake shop, removed combo valve and replaced with TEE and a manual for the rear, one new brake line.

Old master was 15/16" bore and worked fine for 10 years, the next 3 masters (the 1st 2 had the wrong lid and leaked but the brakes worked) were the exact same, this master is a 1 bore. Once replaced I am now 1/2" from the floor instead of 1/4" from the floor.

I'm not losing fluid anywhere.. no leaks and the master is staying full. The only thing that hasn't been replaces is one rear wheel cylinder, and a few brake lines.
 
  #6  
Old 01-25-11, 09:25 PM
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What is the adjustment on the rear brakes?? If they're loose, this will cause pedal travel... Did you remove the proportioning valve??? This device keeps 3~4 psi in the system to help keep the seals seated & the springs tight,, You HAVE to have this,, not a "T"".. I'm assuming this is a dual resivoir type Master??/ Roger
 
  #7  
Old 01-26-11, 05:56 AM
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The rear adjustment of the drums is not loose, tight if anything. Before the seal in the master started to leak I would hear the rear drag a little when I pulled it out of the garage. The vehicle only gets driven a few hundred miles per year and I assumed the noise was because the drums got a little haze of rust from sitting. I confirmed that the front pads and rear shoes are close to the braking surfaces.

This is a GM dual reservoir. It is very common on these hot rod projects to remove the combo valve. I did have this exact problem before I removed it. If I were to buy a Wilwood kit as we used on another project, it has no combo valve.

We confirmed that when the pedal is depressed only 1/2" the front brakes are tight enough that I can only move the rotors if I put a bar thru the studs and try and spin it. It seems as though the brakes move right away but there is no hard feel at the pedal. I have run literally a gallon of fluid thru this system and I gen NO bubbles. I can't imagine any air trapped in this thing but that is how it acts.

BTW, yes I bench bled the master before I installed it.
 
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Old 01-26-11, 03:41 PM
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Roger, you may just be onto something. I have never heard about residual brake line pressure before you mentioned it, today I heard it again! As many brake systems as I have worked on, I never knew that there was a pressure valve as part of a combo valve.

I hear that there ia a 2.5# and a 10# unit, I'm wondering which way to go. My master is not under the floor but I'm wondering if 10# is the way to go. Based on my symptoms, I'm thinking this may finally be it!

If anyone else can chime in, or if Roger doesn't mind further enlightening me, please do so. It is my understanding the this only applies to drum brakes and it keeps 2.5# or 10# pressure in the rear line so that the master doesn't have to supply as much volume on the next press of the pedal. In my case I may be having to push so much fluid to the rear that the master is internally shifting the spring and therefore has nothing left to give to make the front work.
 
  #9  
Old 01-26-11, 05:49 PM
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hotrod, i am confused on the issue now.

Old master was 15/16" bore and worked fine for 10 years, the next 3 masters (the 1st 2 had the wrong lid and leaked but the brakes worked) were the exact same, this master is a 1 bore. Once replaced I am now 1/2" from the floor instead of 1/4" from the floor.

you had brake pedal stop at 1/4 inch from the floor with old mc, and now you have 1/2 inch?

anyhow..

look, it's a pretty simple thing, hydraulic brakes. i have to 2nd wrench 47. it's your aftermarket mc. you have blow by leak internally.


Step 2: Brake Master Cylinder is Full of Brake Fluid- If upon inspection the brake master cylinder is full of fluid, the brake master cylinder may be bypassing internally. This means the seals inside the master cylinder have failed allowing the fluid from the front of the master cylinder plunger to slip through to the rear of the plunger and back into the fluid reservoir. Allowing the brake pedal to go to the floor with out pressurizing brake fluid into the system. Replace master cylinder with new unit and bleed system as needed. that your mc "benchtested" as good means nothing. there's much more pressure under load conditions on the car. if i were you, i'd have put the old one back on, and see what happens.

also, there's a weird one for you. do you have any lengths of your brake lines made out of reinforced rubber hose? those expand over the time and take extra fluid pressure into them.
 
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Old 01-29-11, 02:17 PM
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My comparing 1/2" and 1/4" from the floor is between master cylinder 3 and 4 after the issue occurred. The 15/16" bore gave me 1/4" and the 1" bore gave me 1/2" of pedal. The current master is a GM dual reservoir and is new.

I ordered a 10# residual pressure valve and I will install it in the rear line close to the master. After Roger brought this up I started to read on the subject. I'm hoping that this is related to my problem. Apparently the combo valve incorporates this into the drum brake line and when I removed the valve I may have introduced this issue. Most of the guys that I know that removed the combo valves did so because they were going to 4 wheel disks which I do not have.
 
  #11  
Old 01-29-11, 02:48 PM
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Thought your thread was interesting. If you don't have a combo valve any longer it could cause you problems but not the sort you have now.

But since it is a hot rod and you have a bunch of new parts, let me suggest something to think about. I'm guessing the calipers are off a GM type product. Seen this a lot with other types, but are you certain that the bleeder valves on the calipers are at the top of the caliper piston? Some can be installed on perches where the bleeder won't line up on top as intended.

Much easier to do with old Chrysler systems but harder to do with something off a GM product. I've seen folks with 2 left calipers and they did get them to bolt on. Have to take the caliper off and bleed it with a block of wood in between the pads or get the correct part.

Based on what you are saying there is air in the system or space between the pads and rotors or shoes and drums. Pretty simple overall but it can be frustrating. If you are really stuck, back up and go back to basics.
 
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Old 01-29-11, 04:48 PM
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new is new it doesnt mean its good, ive gotten plenty of parts, new and reman, that have failed right out of the box
 
  #13  
Old 01-30-11, 11:32 AM
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I did be sure that the bleeders are on the top. These are new '77 Monte Carlo calipers and the master is a 1" bore, dual reservoir GM. Also keep in mind that I have had this exact same issue before I added anything new, but I do realize that getting a bad replacement part is not unheard of.

I also confirmed that I have no space between the shoes and drums and the pads and the rotors.

We're adding the residual valve today, we'll see what happens.
 
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Old 01-30-11, 02:12 PM
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UPDATE: still nothing great to report!

We installed a 10# residual valve in the rear line before the manual proportioning valve. We re-bled the entire system and got lots of air in the rear as expected. The brake pedal is still very near to the floor.

I then readjusted the actuator rod, I screwed it out until I couldn't mate the master to the booster, I then wound it in until the master mated up. This was a fairly large difference from the original adjustment that I made by measuring with a vernier caliper. I now have about an 1" from the floor but I can tell that all 4 wheels are braking.

The next step is to put the wheels on and drive out into the driveway, if I can get the snow out first. If this thing stops good enough to get it in the trailer I HAVE TO GET IT OUT of my garage!

I am so disgusted with this thing it's unbelievable! My gagare is tied up and I have projects that need to go in. If nothing else I need it out to clean up the mess!

One thing that I don't understand... no matter how I adjusted the actuator rod, it made no difference to the play on the pedal side of the booster.
 
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Old 01-30-11, 04:22 PM
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Originally Posted by HotRod53F100 View Post
My comparing 1/2" and 1/4" from the floor is between master cylinder 3 and 4 after the issue occurred. The 15/16" bore gave me 1/4" and the 1" bore gave me 1/2" of pedal. The current master is a GM dual reservoir and is new.
you know, you seriously got me curious on something. do you have brake pedal that STOPS 1/4'' FROM THE FLOOR, or you have 1/4'' TOTAL PEDAL TRAVEL BEFORE IT STOPS? as if it travels all the way down to 1/4'' FROM THE FLOOR, you like have no brakes at all.
booster diaphragm is not leaking, right?
DID YOU TRY TO PUT OLD MC BACK ON?

something else that keeps bugging me. i simply could not get over idea that there's something in the brake system that maintains constant 3-4 psi pressure, as that means, brakes will be continuously locking, due to that pressure.
fortunately, i am not crazy:

Proportioning Valve
The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.

The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.
 
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Old 01-30-11, 04:49 PM
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Old 01-31-11, 04:38 PM
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My brake pedal is 1/2" from the floor as if I have no brakes. There is brake there, just not much.

I realized that I had not yet replaced the rear wheel cylinders, so just for giggles I am going to change those too.

I can't use the old master since it leaks out the rear seal. I took it to a rebuilder and they disassembled it reporting that it is too pitted to rebuild. I don't know if it would even work now that it had been disassembled.

Ukrbyk... that looks like a lot of valuable info, I will digest that for clues

OBTW, my brake pedal does not have multiple settings. This hasnlt been brought up yet but Ukrbyk's posting mentions it.

The comment about keeping pressure on the read line was foreign to me too. Supposably it takes so much force to overcome the brake springs in a drum sytem,that it is common to keep the line pressurized, It also keeps the seals set right. Second, it keeps fluid pressure on the system so that the master doesn't have to move as much volume and it doesn't suck it all back in upon release of the brake pedal. It is installed and it does not drag the brakes, I'm told that this is a feature that is a little known feature that is built into the combo valve.
 
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Old 01-31-11, 09:48 PM
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Hmmm Mine was green...

http://rds.yahoo.com/_ylt=A0PDoTBRkE...77/77monte.jpg

I had 70 71 74 77 79. All great cars.

Mike NJ
 
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Old 02-01-11, 07:15 AM
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Actually, there are parts that you would recognize, the body isn't one of those parts.



Front frame, brakes, steering column, engine, transmission, and rear differential.

Yours is a sweet looking/clean ride. Don't see many of those any more.
 
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