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#1017823 - 01/02/15 12:51 AM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
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malibudave78 Offline
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Houston, TX
One of the main problems that arise when converting to manual brakes using a 7/8" bore master cylinder is LOW drag calipers.

LOW drag calipers require a step bore (quick take up) master cylinder. In my opinion they are too large to operate smaller 2.50" bore calipers with sufficient pressure, they are harder to bleed, and they have a 100lb residual valve that can fail. My opinion also is to change out to new (NOT rebuilt) calipers to make sure you do not get a set of LOW drag calipers.

To learn a little bit about new stock size calipers, I just purchased a set of left and right AFCO 2.5" bore metric calipers that are a bolt in, stock, replacement caliper for g-bodies, S10s, and most 3rd gen f-bodies. I removed the stainless steel piston and square piston seal to make sure it was not a LOW drag caliper.

SPECS:
MFG. Part #: 7241-9003 RH and 7241-9004 LH
Centerline of Holes: 5.50
Caliper Pistons: Single Piston Diameter: 2.50
Inlet fitting: 10mm-1.5 Material Type:
Steel Finish: Natural
Sold in Quantity: Each

Description:
The 2 1/2" bore steel GM metric caliper is designed to be a used as a stock replacement caliper. The caliper features a stock appearing remanufactured castings, remanufactured grounded 2 1/2" stainless steel piston, and low drag seals (see below) . Each caliper is assembled and pressure tested.

LOW DRAG SEALS
Though the description says "low drag seals", the seals are square with no noticable taper.




The seal-groove in the bore of the caliper are also square with no noticable taper.


When the seal is installed, it barely clears the top of the bore, and because of this, the piston to bore clearance, it seams, to have fairly tight tolerances.

The small end of the piston is what contacts the back of the brake pad. It measures 2.38".
The large end of the piston is what is inside the bore of the caliper. It measures 2.50"


Inside of piston cup, facing the brake pad.


Backside of piston that is installed inside the caliper bore.


I have bought these same exact part numbers a few years back and these new ones are a different casting with, what looks to be, a stainless steel piston. These calipers DO NOT come with pads, but they come with slider pins and slider pin bushings. At this time, they are around $40, and seem to be an improvement over the previous design.

Bottom line is that these should be a good stock replacement, NON low drag, brake caliper that will work with both strait bore master cylinders and step bore (quick take up) master cylinders.

#1028656 - 08/27/15 07:46 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
Joined: Apr 2008
Posts: 75
malibudave78 Offline
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malibudave78  Offline
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Houston, TX
Caliper Update:

I have found a good NON low drag (normal) bolt in replacement brake calipers for stock front brake systems. These brake calipers can be used with strait bore (normal) master cylinders and step bore master cylinders.

It is under the Centric Brand. They are about $33 plus shipping at rockauto.com.

Part number are:
14162066
14162065

AFCO has a brand new replacement brake calipers. They are about $49.99 plus shipping. $100 order are free shipping at Summit Racing, Jegs, and Speedway Motors. These should be NON low drag.

The part numbers are:
6635003
6635004

Last edited by malibudave78; 08/27/15 08:08 PM.
#1032871 - 12/07/15 05:28 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
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malibudave78 Offline
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malibudave78  Offline
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Joined: Apr 2008
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Houston, TX
Manual brake installation with adapter plate painted satin black to match firewall better.


#1035214 - 02/18/16 04:56 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
Joined: Apr 2008
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malibudave78 Offline
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malibudave78  Offline
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Houston, TX
Below is an analysis using the Brake Torque Calculator found on Pro-Touring.com. This calculator will give you an idea of what brake torque is for a certain front and rear setups. I am just going to show the changes from the stock front g-body brake system and compare them to a Blazer dual piston brake swap, a stock LS1 Camaro brake swap, a LS1 Camaro brake swap with Corvette calipers

Page 7, Post #140

http://www.pro-touring.com/threads/10458...-of-KORE3/page7
This entire post is a really good read if you are interested about brakes.


Here are the inputs that are the same for ALL different types of brake systems shown below.
• 6 to 1 pedal ratio
• 26” tall tire
• 100 ft/lb pedal pressure
• Manual Brakes – NO POWER ASSIST
• Pad Coefficient of Friction - .45
• Use of stock type (tandem) master cylinder

____________________________________________________
Stock G-body/S10/3rd Generation F-body Front Brake System
• Rotor Diameter – 10.5”
• 7/8” Bore Master Cylinder Area - .601 sq-in
• Line Pressure – 998 psi
• Front Caliper Piston Area – 4.909 sq-in
• Front Clamping Pressure – 4899 pounds
• Front Rotor Torque – 964 ft/lb
• Tire Forces – 890 lb
____________________________________________________
Stock LS1 Camaro/Firebird Front Brake System
• Rotor Diameter – 12”
• 7/8” Bore Master Cylinder Area - .601 sq-in
• Line Pressure – 998 psi
• Front Caliper Piston Area – 4.931 sq-in
• Front Clamping Pressure – 4921 pounds
• Front Rotor Torque – 1107 ft/lb
• Tire Forces – 1022 lb
____________________________________________________
Stock LS1 Camaro/Firebird Front Brake System with Corvette Calipers with 7/8” bore master cylinder
• Rotor Diameter – 12”
• 7/8” Bore Master Cylinder Area - .601 sq-in
• Line Pressure – 998 psi
• Front Caliper Piston Area – 3.994 sq-in
• Front Clamping Pressure – 3986 pounds
• Front Rotor Torque – 897 ft/lb
• Tire Forces – 828 lb

Stock LS1 Camaro/Firebird Front Brake System with Corvette Calipers with 21mm bore master cylinder
• Rotor Diameter – 12”
• 21mm Bore Master Cylinder Area - .537 sq-in
• Line Pressure – 1117 psi
• Front Caliper Piston Area – 3.994 sq-in
• Front Clamping Pressure – 4461 pounds
• Front Rotor Torque – 1004 ft/lb
• Tire Forces – 927 lb

____________________________________________________
Stock Blazer Twin Piston Front Brake System
NOTE: The Blazer twin piston front calipers have a piston area too large to run a .875” bore master cylinder. These calculations are using a 24mm bore master cylinder.
• Rotor Diameter – 10.75”
• 24mm Bore Master Cylinder Area - .701 sq-in
• Line Pressure – 856 psi
• Front Caliper Piston Area – 5.152 sq-in
• Front Clamping Pressure – 4410 pounds
• Front Rotor Torque – 889 ft/lb
• Tire Forces – 821 lb

Stock Blazer Twin Piston Front Brake System
NOTE: The Blazer twin piston front calipers have a piston area too large to run a .875” bore master cylinder. But to show the differences between the systems, these calculations are using a .875” bore master cylinder.
• Rotor Diameter – 10.75”
• 7/8” Bore Master Cylinder Area - .601 sq-in
• Line Pressure – 998 psi
• Front Caliper Piston Area – 5.152 sq-in
• Front Clamping Pressure – 5142 pounds
• Front Rotor Torque – 1036 ft/lb
• Tire Forces – 956 lb


Rating from best to worst:
1. LS1 Camaro / Firebird stock front brakes with 7/8" bore master cylinder.
2. Blazer Twin piston stock front brakes with 7/8” bore master cylinder. NOTE: This setup will not work with a 7/8” bore master cylinder.
3. LS1 Camaro / Firebird front brakes with Corvette brake calipers and a 21mm bore master cylinder. NOTE: A 21mm master cylinders are fairly rare and hard to find.
4. Stock g-body/S10/3rd Generation F-body stock front brake system with 7/8" bore master cylinder.
5. LS1 Camaro / Firebird front brakes with Corvette brake calipers and a 7/8” bore master cylinder.
6. Blazer Twin piston stock front brakes with 24mm bore master cylinder.

Last edited by malibudave78; 02/18/16 05:13 PM.
#1047501 - 01/24/17 10:13 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
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malibudave78 Offline
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Houston, TX
Since being around brakes a lot since I started manualbrakes.com, 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 manualbrakes.com 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

#1047502 - 01/24/17 10:17 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
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malibudave78 Offline
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Master Cylinder Bleeding Proceedures.

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 Ό” 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.

#1048884 - 03/12/17 02:06 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
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malibudave78 Offline
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This is from The Brake Man at tbmbrakes.com from his Facebook page. It may make you think a little differently about aluminum calipers and multiple piston calipers.

12 RULES YOUR BRAKES LIVE BY:

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.

#1051879 - 06/28/17 05:34 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
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malibudave78 Offline
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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)


[Linked Image]

#1070997 - 06/07/21 06:07 PM Re: Manual Brake Conversion on a 1980 El Camino [Re: malibudave78]  
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malibudave78 Offline
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malibudave78  Offline
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Joined: Apr 2008
Posts: 75
Houston, TX
In a manual brake system, the master cylinder size you choose should be dictated by the total volume of your brake system (calipers and wheel cylinder) and what type of seat you sit in to drive.

What difference does a seat make? When you are putting your effort into pressing the brake pedal to stop the car, the seat cushion does not supply a lot of support. Some of your effort that you apply to the brake pedal is also pushing yourself back into the cushion. The effort you use to press the brake pedal is less effective because some of that effort is waster as your body sinks into the seat cushion. The more effort you apply to the pedal will also sink you deeper into the seat cushion. If you have a racing seat (i.e. Kirkey), it has little to no cushion as it is made of aluminum. A hard back seat like a Kirkey will give you more leverage and allow most of the effort you apply to the pedal tas your body is supported by a hard surface and not a soft seat cushion.

If you have a racing type seat, you can get away with a larger bore master cylinder. Some people use 1-1/8” in diameter and have no issues when using a racing seat.
A larger bore master cylinder will require more effort to stop the car for a given front and rear brake setup. A smaller bore will require less effort to stop the car for the same front and rear brake setup as the larger bore master cylinder.

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