Manual Brake Conversion

[turboz4life]

Would just like to give this thread a much needed bump. Read it start to finish and it answered many questions I had regarding converting to manual brakes and hopefully it will help others too.


Posted from the TurboBuick.Com mobile app

 

[malibudave1978]

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.

 

[87geeinn]

Great info Dave. If you remember from my other post, I cancelled my order of the Afco units because I was afraid they were low drag units based on the description. Looks like you confirmed the opposite and that they are non-low drag units. Guess I could have saved a few hundred bucks over the Wilwood units after all. Oh well.

Not to hijack, but my setup with the 15/16" CJ5/CJ7 MC, Wilwood 2.5" calipers, and Hawk pads works great. Only downside is the Hawk pads do take a little heat to get working good. Until you make 4-5 decent stops, braking power feels significantly reduced. However, once they are brought up to temp, it's almost difficult to tell they are manual. Quite a significant change from cold to hot. I also like the feel of the 15/16" over the 7/8" bore. I simply felt the 7/8" had too much pedal travel for my liking.

 

[RmvBfrFlght]

Interesting about the Hawks pads, maybe copy your post to your other thread. We discussed CarboTech AX6 and the Stoptech High Performance street pads there.

RemoveBeforeFlight

 

[malibudave1978]

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

 

[malibudave]

Manual brake installation with adapter plate painted satin black to match firewall better.

 

[malibudave1978]

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/...featuring-Ron-Sutton-and-Tobin-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 systemwith 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.

 

[malibudave1978]

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)