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Old 03-03-2003, 08:37 AM
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Post Help! Going Nuts! Mysterious Master Cylinder

I have a '50 Chevy Fleetline, and I have managed to get 11" GM rotors on the front, and I have the stock drums on the back. I re-plumbed all of the brake line with .25 in. steel line, put residual pressure valves (2 on front 10 on back) in line, and strung it all together with the aid of a half dozen adapters.

The '68 Mustang dual cylinder master cylinder is on an R&B pedal bracket adapter, and mounted in the original location on the frame, and runs sans-booster. So I'm ready to roll, right? Wrong.

Now, here's what I did: I used my vacuum pump to suck the fluid through the lines, and thought I'd done a good job, but the pedal went all the way to the floor when I stepped on it! So the next day I get the old lady out there to stomp on the pedal while I man the bleeder screws, and I bleed 'em the two-man way. She can get pressure if she pumps 'em, and I wasn't gettin any air, but as soon as you let off the pedal and push again, it hits the floor!

So I go and dig up the box for the master cylinder, and it says that I should use the enclosed plastic bleeder nozzles and hose to bench bleed the master cylinder while it's mounted in the car. I do, and it's recirculating fluid through the little hoses to the reservoir, so I hold the pedal down and tighten up the brake line, and let up the pedal, repeat for the back line, and bleed 'em again.

Same story! I'm going nuts trying to figure out why I can't get pressure when I hit the pedal. I can get and hold pressure when I pump 'em up, but not when I just press down normally.

I have all of the pads and shoes and drums in place, and I'm not leaking fluid anywhere, so what gives!?!?!?!

Help meeeeeeeeee!!!!!!!!

Stretch

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Old 03-03-2003, 09:16 AM
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Try adjusting your rear brake shoes. If they are presently adjusted loose, they will have to travel too far, thus pedal to the floor.
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Old 03-03-2003, 12:43 PM
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i dont know bout dem damn ferds, but ifn'its a newer chevy, the porportioning valve has a reset button (with a rubber bootie over it, like an electric terminal) did you push de button??? you DO have a porportioning valve dont you? your discs take way way more pressure than the drums.

[ March 03, 2003: Message edited by: bullheimer ]</p>
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Old 03-04-2003, 07:43 PM
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I agree with the other posts. I would also check to see if the master cylinder you have installed now is designed to work with the disc, drum system you have. Second, I would check to see that the brake pedal is coming all the way back thus allowing the piston in the master cylinder to go back all the way when the brake is released. Third, I would try a different bleading method. I don't know why this works but the following method has always worked for me in the most stubborn situations. Get a $6.95 one man brake blead kit from the parts store. This is a clear bottle and a clear hose. Elevate the recovery bottle higher than your caliper or wheel cylinder. (Key to making it work) Open the bleader valve and pump the brake pedal several times, making sure not to let your master cylinder run dry. You do not have to open and close the bleader valve like the conventional method. Start with the longest brake line away from the master cylinder and go to the shortest. You should be able to blead the entire system with less than a quart of brake fluid in 30 minutes using this method.

Let me know what your progress is.
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Old 03-05-2003, 12:16 PM
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Proportioning valve, eh? I don't have one, no. I have residual pressure valves, but no proportioning valve. I didn't think I'd need one if I was using a disc/drum master. I thought that they were only necessary if your back brakes were grabbing too much....fill me in on this..
thanks,
Stretch
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Old 03-06-2003, 03:44 PM
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you got me stumped on that one. my master cylinder was designed for discs in front and big huge honkin full floating drums in rear, so essentially it's okay as is for discs in the rear. but most cars have porportioning valves as far as i know, and they have discs front and drums rear, with the masters to match. i dont work in a garage, i thought you always have to have one
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Old 03-11-2003, 06:54 AM
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Hey Frisco,

You were right on! I moved the shoes out so they were closer to the drums, and got a lot more pedal. I was even able to take it for a spin around the block. It's still a little spongy, but I can work on that. 50 was the last year for the old Huck brakes before Chevy switched to the bendix system we all know and love.

These brakes aren't self energizing like todays drum brakes, so as you lose pad, you lose pedal. I have a disc drum master cylinder, and the proportioning valve would only help if my back brakes were too grabby.

Thanks for all your help guys!

Stretch
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