AD Manual Brake Conversion on a 1980 El Camino


Feb 11, 2016
Since being around brakes a lot since I started, sometimes I get a reoccurring question when people are doing the conversion.

What ports do my lines bolt up to?

The ports on all G-body master cylinders have a ½-20 inverted flare port (port closest to the firewall) for the front brakes and a 9/16-18 inverted flare port (port located toward the front of the master cylinder) for the rear brakes. The KIT comes with adapters to mate the stock GM line fittings to the MOPAR style master cylinder’s 3/8-24 inverted flare outlets.

For most GM applicatiosn, remember:
Rear port of master cylinder goes to the front brakes.
Front port of master cylinder goes to the rear brakes.
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Feb 11, 2016
Master Cylinder Bleeding Procedures.

NOTE: DO NOT bench bleed a master cylinder on the car. On a g-body the master cylinder sits at an angle and it WILL NOT get all the air out of the master cylinder. Use a vise to hold the master cylinder level to the ground to bleed the master cylinder of all its air.

I like to use plugs to bleed the master cylinder of air instead of the procedure that uses hoses to recirculate the fluid from the master cylinder ports back up to the reservoir. Why?

When using plugs to close off the ports of the master cylinder, this procedure will let you know if all the air is out of the master cylinder AND if the master cylinder is bad. You don't want to find out your master cylinder is bad after you have it installed and are trying to bleed the rest of the system. You most likely will not get all the air out of the system when your master cylinder is bad. New or rebuilt, it is always good to make sure your master cylinder is in good working order before bolting it onto the car. It will one less thing you have to trouble shoot if you run into other issues when you are trying to trouble shoot braking issues.

Steps to bleeding a master cylinder:

1. Mount the master cylinder in a vise with the bore of the master cylinder level with the ground. Do not use the top of the reservoir as a guide because is may not be level with the bore of the master cylinder. It may be at an angle versus the bore of the master cylinder.
2. Use the appropriate size solid plugs to plug the outlets of the master cylinder so no fluid can escape the ports.
3. Fill the master cylinder with the appropriate amount of brake fluid.
4. Use a rod to SLOWLY cycle the master cylinder piston in its bore. DO NOT use a flat head or phillips heat screwdriver because they have sharp edges and could harm the bore of the master cylinder. I usually use a nut driver that is used for ¼” drive sockets as a rod because the end does not have any sharp edges and there is a handle to hold onto.
5. After cycling the master cylinder piston SLOWLY a few times, the piston should become rock solid and only move about 1/16 of an inch or less down the bore.
6. After the piston becomes rock solid, push in on the master cylinder piston and hold for 45 seconds. If the piston slowly moves down the bore of the master cylinder, you have a bad master cylinder. If the piston says rock solid and does not move, you master cylinder is good.
7. Mount to your car and bleed the rest of your system starting with the brakes furthest away (passenger rear) from the master cylinder and working your way to the closest (drivers front) brake.

Feb 11, 2016
This is from The Brake Man at from his Facebook page. It may make you think a little differently about aluminum calipers and multiple piston calipers.


1. Pad area (volume) has no effect on braking torque. Pad area (volume) effects life and heat management.
2. Caliper clamping force is a function of piston area (on one side of the rotor) times line pressure.
3. The hotter the brake pad gets, the faster it will wear.
4. Deflection anywhere in the brake system will result in a proportional reduction in clamping force.
5. Piston count has nothing to do with clamping force, piston area does.
6. Caliper deflection that exceeds piston O-ring retraction (around .020”) will result in brake drag.
7. Given the same design, aluminum calipers will always deflect more than steel, cast iron, or steel reinforced calipers.
8. If your pads are tapered, your calipers are deflecting.
9. All brake pads perform best in a temperature range. Too cold is just as bad as too hot.
10. The smallest, lightest rotor that will dissipate the necessary heat is the best rotor for the application.
11. A smaller bore master cylinder increases line pressure.
12. Larger diameter caliper piston(s) increase clamping force.
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Mar 12, 2010
Houston, TX
I pulled this information from the CPP website. I include this information on this thread because, during a manual brake conversion, the differential valve in the proportioning/combination valve may be triggered and cause only one side of the system to work resulting in poor braking performance.

The differential valve is built into most GM prop valves. It is for safety. If one side, front or rear, of the brake system looses pressure, the differential valve is triggered blocking off the low pressure side of the brake system so that the master cylinder can still provide pressure to the other side of the brake system. This ensures that there is some for of braking as a way to stop the vehicle. If a differential valve was not part of the braking system, and there is a loss of pressure in one side of the system, the master cylinder would not be able to build pressure. This would result in NO brakes.

Combination/Proportioning Valve Test

Use a test light by attaching a clip to a positive contact on the vehicle and touch the point of the tester to the electrical connection of the combination valve. If the the light does NOT come on, the valve system is operating correctly and no further testing is required.

If the light does come on, this indicates that the pressure differential valve is stuck in the front or rear position.

Bleed the brake system to determine if the front or rear lines are blocked off. Set up one front wheel and one rear wheel for bleeding at the same time. Crack both bleeder screws and gently pump the pedal a few times.

The blocked side will trickle fluid out when the bleeder screw is cracked and the pedal pressed. An unblocked line will squirt fluid out the bleeder.
The lines that are clear must be left open and the blocked lines should have the bleeder screws tight to cause pressure to build up on that side. Be sure to use the standard bleeding procedures to prevent air from entering the system.

Slowly press the pedal with steady pressure a number of times until the light goes out; this will center the differential valve. You may also hear a pop come from the proportioning valve. This is the metering valve returning to its equalized position. When the light goes out, close the bleeder screw. (See fig. below)

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Site Admin
Feb 25, 2005
Inola, OK
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