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  #1  
Old January 6th, 2007, 04:46 AM
XJ Chief XJ Chief is offline
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Default Vette Master Cylinder

Installed it yesterday. When bleeding the master and the brakes it seems like when the rears are bled the pedal drops to the floor but the fronts don't cause it to drop. Plenty of fluid coming out the front bleed screws, just the pedal doesn't drop as dramatically as the backs. Doesn't seem right. Test drive shows the rears will lock up but not the fronts. Even with the weight difference I'd expect the front tires to lock up too. The plan is to jack the truck up and check to see if the front drums are grabbing and continue bleeding the front. Anybody have any thoughts?
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Old January 6th, 2007, 06:50 AM
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sermis sermis is offline
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Is the master drum / drum ********** disk / disk? If it is drum / disk it will push more fluid to the front or rear. I ran all new bake lines and a vet master and no problems. Make sure that the shoes are adjusted right. That will cause one set to catch before the other.
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Old January 6th, 2007, 08:23 AM
robsgp robsgp is offline
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I have the same thing going on except I seem to get more fluid out of the rear bleeders when the pedal is pushed. The rear resevoir is connected to the front brakes. When it's on jack stands the fronts do lock up but when I come in from a drive the front drums are cool. I'm hoping do more adjusting this weekend.
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Old January 6th, 2007, 08:44 AM
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Barrman Barrman is offline
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This is the point in your project where all kind of unexpected problems could be the "one thing" keeping you from being done. I don't know the history of your truck, so I am just going to list out all the things I can think of that could be causing the rear to get pressure but not the fronts.

As written above. Is it a disc/disc master cylinder? Find out for sure.

The line to the front brakes should be screwed into the firewall side of the mc

is the mc piston returning all the way back when you let go of the pedal? If not, no new fluid is going to get into the front brake circuit.

do your brake lights still work? The brake signal switch is now connected to just the front brake pressure. If they are not lighting up, then you are getting no pressure out of the mc to the front brakes system.

If your brake lights are working, yet you are getting no fluid to the front wheels. Then you might have clogged up brake hoses. They are made out of rubber and are made to flex. Chances are they need replacement anyway since they are pretty close to 40 years old now. I would recommend you pull the wheel cylinder end off and see if any fluid flows.

(A good way not to get fluid all over the place while messing with brakes is to get a glass jar. A Mason jar is just about perfect. Put a little bit of clean brake fluid in the bottom. Either stick a brake line into the fluid or connect a hose to reach under the fluid. Then you can sit in the cab, push the pedal while looking under the truck and watch either fluid or air bubbles flowing into the jar. Connecting a vacuum line from the bleeder screw to the bottom of the jar is a great way to bleed brakes by yourself. Just push slowly while watching for bubbles. When the bubbles stop and you still get fluid moving, close the bleeder screw and move onto the next wheel.)

If fluid is flowing fine through the hoses. Then you are looking at gunked up wheel cylinders.

If no fluid is coming through the hose, then pull the other end of the hose off and see if you have fluid at the end of the metal line. IF you do, then you have a bad hose. If you don't, then you have to trace the lines back to the MC and find the restriction.







I hope this made sense. Like I wrote at the top, I don't know your truck so I just threw in everything I could think of without giving you a brake operation lecture.
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Old January 6th, 2007, 09:06 AM
FSJGuy FSJGuy is offline
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Get the littel speedbleeders from the HELP! section of the parts store, too. They work great, along with the previously mentioned hose/mason jar thing. Just make sure the wife knows she'll be missing 4 mason jars PERMANENTLY!

I also found that I had to open a bleeder on both the front AND rear circuits to move fluid.
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Old January 6th, 2007, 09:26 AM
Fastfrankie Fastfrankie is offline
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Quote:
Originally Posted by XJ Chief View Post
Installed it yesterday. When bleeding the master and the brakes it seems like when the rears are bled the pedal drops to the floor but the fronts don't cause it to drop. Plenty of fluid coming out the front bleed screws, just the pedal doesn't drop as dramatically as the backs. Doesn't seem right. Test drive shows the rears will lock up but not the fronts. Even with the weight difference I'd expect the front tires to lock up too. The plan is to jack the truck up and check to see if the front drums are grabbing and continue bleeding the front. Anybody have any thoughts?

I can't believe this. I am having the same problem as I type. I installed all new wheel cylinders (Ford van), new Vette master drum/drum, new brake rubber hoses front and back as well. I even went back with the stock pushrod and now the piston is against the snap ring. The rear line on the m/c goes to the fronts and the front lines goes to the rear brakes. I plugged the block with a plug where the rears used to come out of as well.

When I bleed the rear brakes, the fluid squirts out in a stream and the pedal goes to the floor. When I do the fronts, it comes out but dribbles out...and the pedal does not go to the floor, which is odd.

I had my old man step on the brake pedal and I couldn't turn the rear drums with it on the lift. I tried to turn the front drums, and they still can be turned.

I think what I may do is take the front drums off and bleed it with them off. I want to see it allowing the brake shoes to move more with the drum off will allow me to bleed the cylinders better.

I can't believe someone else is having the same problem as me right now...

I'll post back today or tonight as I keep on scratching my head! LOL
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Old January 6th, 2007, 10:05 AM
Fastfrankie Fastfrankie is offline
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Well I just got back in. My brake lights are not working....I guess I don't have enough pressure. I even took off the front drums and had my dad depress the pedal. They didn't even budge.
I am wondering if the idiots who rebuild these things gave me a disc/drum master cylinder for a Corvette. Trust me, my wife's uncle is Joe Cardone, who owns Cardone auto parts rebuilding. His stuff is crap and they just opened a plant in Mexico. You think Mexicans can tell the difference between master cylinders? They just throw them in boxes and paint them!
Speaking of that, is there ANY way to tell the difference between the drum brake and disc/drum brake master cylinders? Before I take it off and exchange it, I'd like to see if anyone knows a way to just look at it and tell...
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Old January 6th, 2007, 10:24 AM
XJ Chief XJ Chief is offline
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All great replies. I'm wondering if the master is the wrong type. Seems strange to have the EXACT same problem as a person who did the same swap at the same time.
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Old January 6th, 2007, 10:28 AM
Fastfrankie Fastfrankie is offline
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Just got off the phone with Autzone. I questioned him as far as my master cylinder possibly being a power brake master cylinder being rebuilt and put in a manual master cylinder box. He tells me "about 1 in every 5 or 6 are just wrong or have issues/problems." That doesn't surprise me at all since my buddy who is ASE certified REFUSES to install any Cardone auto parts since they always fail or come back and he has to eat the labor. I love breaking my wife's uncles chops about the crap he "rebuilds..."

The number is definitely the 1371, and I even had the guy try a 69 Corvette, 71 Corvette and 76 Corvette....all the same...just double checking since they only list "power brakes" or "manual brakes" - no mention on their computer about drums or discs.
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  #10  
Old January 6th, 2007, 03:14 PM
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WetCJ WetCJ is offline
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All Corvettes from 1964 on were 4 wheel disc brakes so at least that won't be the issue. Biggest difference between disc or drum usage is the check valves in the outlet ports, drum should have them, disc shouldn't. I use a 1970 Impala 4 wheel drum master cylinder on mine, same bore size as original M715 and should have the check valves for drum brakes.
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