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Old 03-27-2003, 07:24 PM
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Arrow '49 Chevy Truck-More Brake Problems

I'm finishing up a '49 Chevy truck. It has a Mustang II front end with disk brakes. Mid-Late 70's Mustang II booster and master cylinder. Camero rear with drum brakes. I have replaced the pads and shoes front and back, I've replaced the booster and master cylinder. I've bled and adjusted every thing. The pedal goes down about 2 1/2 inches and then becomes solid but the brakes don't lock up. The truck will stop but it kind of rolls to a stop. I don't have a proportioning valve. I am under the impression (right or wrong) that the Mustang MS is made for disks and durms. I've got the large reservoir (the one closest to the booster) going to the front brakes and the small one going to the rear. I'm using 3/16" lines on the front and 1/4" on the rear. I'm not driving the truck yet, other then around the block.
Do I have the lines plumbed right? Do I need a proportioning valve? What am I doing wrong? Any help will be appreciated.

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Old 03-27-2003, 08:00 PM
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Where is the Master Cylinder mounted? Do you at least have residual pressure valves in the front and rear brake lines? Are the back drums adjust out close to the drum so you can hear a slight drag when the tire is turned? I always keep all the hard lines the same size 3/16.
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Old 03-27-2003, 08:10 PM
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I have the booster and the master cylinder mounted on the fire wall. From what I have read I don't need a residual valve if the master cylinder is above the wheel cylinders. I'm afraid that I've read too much. Sometimes the more I read...The less I know.
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Old 03-28-2003, 05:16 AM
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Himed, sounds like you may be "bottoming out" one your pedal stroke. This is going to creat some work, but you need to remove your booster and master cylinder and take some basic measurements. If the rod to the booster stays in the booster when removed, measure the flull length of the stroke and note it. Now slip a stiff wire into the rod mounting hole on the brake pedal and check that full travel gives you near the same distance as above. Now check the travel of the master cylinder piston to make sure it is close to the other two. I suspect your problem will become obvious by the time you hve finishd this. If not reassemble and reverse your lines, small chamber ot the front and large to the rear. Sound wrong? I have seen lots of disk/drum set ups this way and have had the same poor results when I tried hooking them up the other way. (have the same setup on a 41 Ford Business coupe and I will check it when I go to the shop today to make sure it is set up "the other way".

Trees

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Old 03-28-2003, 06:37 AM
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Thanks for the input. I'll check the measurements this evening or tomorrow morning.
When I got the truck it was plumbed that way. But the brakes didn't work very well. Then I read in a book that the big chamber was for the front brakes and I switched it around and replaced the booster and master cylinder.

[ March 28, 2003: Message edited by: hiimed ]</p>
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Old 03-28-2003, 08:49 AM
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If you have a dual cylinder for disc/drum combination the larger of the resevoirs actuates the discs, the smaller the drums.
A dual drum/drum or disc/disc cylinder has equal sized resevoirs.
The discs require much more fluid volume to activate them.
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Old 03-28-2003, 06:24 PM
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You may be able to get away with not having the 2 lb. residual pressure valve for the front disc brakes with the master cylinder mounted on the firewall but you will need the 10 lb. valve in the rear brake line for the drum brakes. The valve helps keep some line pressure in the wheel cylinders so you don't suck air and also keep some pressure on the brake shoe return springs. The pressure isn't enough to keep the shoes rubbing on the drums.

I have a 1950 1/2 ton Chev with the disc/drum master cylinder on the firewall with the power booster and I didn't take any chances. I have the 2 lb residual pressure valve in the front line going to the disc brakes "using the larger reservoir due to the higher fluid requirements of the larger caliper chambers". The rear line goes into an adjustable proportioning valve and then goes into the 10 lb. residual pressure valve and then splits to each rear wheel cylinder.

Joe
<a href="http://50chevy.freeservers.com/" target="_blank">http://50chevy.freeservers.com/</a>
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Old 03-29-2003, 03:13 PM
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I had a Line lock/Parking brake that was plumbed into the line going to the back brakes. I think that was my problem. I removed the valve and bled the system and everything is better now. "Trees" suggested that I get a control block from a Mustang II. I think after that I'll be in good shape.
Now after I finish the wiring it'll be ready to drive.

Thanks to everyone for your input.
Ed
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