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The MANUALBRAKES.COM adapter plate and matching gasket are CNC machined by a water jet for a perfect fit. The adapter plate is made from rigid 1/8” thick aluminum with dimensions that covers up the hole in the firewall after you remove the power booster.
Frequently Asked Questions (FAQs)
When using the standard MANUALBRAKES.COM adapter plate without the retention cup, no modifications are necessary for all “G-Body” cars and 1st generation S-10 trucks (1982-1993) and S-10 Blazers (1983-1994). If using the MANUALBRAKES.COM adapter plate with retention cup, then there will be some trimming of the firewall to fit it properly on 1st generation S-10 trucks and Blazers. If done correctly, this will not cause any problems if converting back to power brakes. All vacuum boosted power brake equipped “G-Body” cars and all 1st generation S-10 trucks and Blazers have provisions in the brake pedal for manual brakes. This brake pedal provision is an extra hole drilled into the brake pedal from the factory to allow the use of manual brakes. The MANUALBRAKES.COM adapter plate uses these factory provisions to convert your vehicle to manual brakes.
On 2nd generation S-10 trucks (1994-2003) and Blazers (1995-2005), there is a need to have modifications done to the firewall because these years where never equipped with manual brakes from the factory. A 2” inch hole will need to be cut in the firewall centered between the top two holes that the vacuum booster bolted to for clearance of the master cylinder and the pushrod retention cup.
What is the piston size of a “G-Body” and S-10 caliper?
Stock piston size is 2.38”.
Caliper Specifacations of Aftermarket "Metric" Calipers
Caliper...................................Part Number...........Advertised Bore Size.......Actual Piston Size.....Weight
Wilwood 2" Bore Caliper.........PN 120-9333............2.00".................................1.981"..........................4lb 1.6oz
US Brake / AFCO Caliper.......PN 7241-9004..........2.50".................................2.376"..........................6lb 4.7oz
CCP Big Bore Caliper.............PN CP412526..........2.75".................................2.565"..........................6lb 11.2oz
Wilwood 2.75" Bore Caliper....PN 120-8926............2.75".................................2.704"..........................4lb 8.6oz
What is the bore size of a master cylinder on a G-Body?
Manual brake master cylinders are 7/8” and are cast iron. Power brake master cylinders come in 24mm strait bore and a step bore version with a primary bore of 24mm and a secondary bore of 36mm. Most of the strait bore master cylinders where cast iron, though some power boosted versions where aluminum. The stock step bore master cylinder came in aluminum. Any new step bore master cylinder made today will be made of cast iron.
What is the bore size of a master cylinder on an S-10?
Manual brake master cylinders are a step bore design and have two different bore sizes. The bore sizes are 24mm and 31.6mm and where originally aluminum from the factory. Most power brake master cylinders came in 24mm and 36mm step bore and where originally aluminum from the factory. Any new step bore master cylinder made today will be made of cast iron.
What modifications should be done to the stock braking system?
If using the stock brake components, make sure all parts of your system are in good working order. Vacuum assisted power brakes will mask some faults in the brake system that a manual brake system will not be able to cover up. It would be good to replace old rubber brake lines with good aftermarket steel braided lines. Steel braided lines allow less “ballooning” that can happen with rubber brake lines and will contribute to brakes that feel spongy. Quick take up (low drag) calipers that came on most “G-Body” cars, S-10 pickups and blazers, and the third generation camaros and firebirds will require a step bore master cylinder. Another upgrade would be to a NON low drag calipers and a standard, strait bore master cylinder in a 7/8" bore. Upgrade to aftermarket pads.
What are quick take up (low drag) calipers?
In early 1980s GM introduced the quick take up (low drag) caliper on most of its vehicles. The reason for the quick take up (low drag) caliper was the energy crisis. The quick take up (low drag) calipers were designed to reduce the friction between the pad and the rotor to improve gas mileage.
The engineers at GM found that changing the square cut seal groove on the caliper could cause the caliper piston to be pulled back twice as much as the conventional caliper. The quick take up (low drag) caliper is designed with a 30 degree bevel in the seal groove as opposed to the conventional calipers 15 degree bevel. With twice the bevel, there is twice the seal flex. Flexing the seal two times as much pulls the caliper piston back into the caliper bore 2 times as far creating no drag of the brake pad on the brake rotors.
What’s the problem with using a quick take up (low drag) caliper?
The volume of fluid needed to take up the extra gap created by the quick take up (low drag) caliper exceeds a conventional master cylinder's capacity so a step bore master cylinder is needed. A stop bore master cylinder provides a large volume of fluid initially to take up the gap and then internal bypass valve switches the master over to a high pressure system where it acts as a conventional master cylinder. Quick take up (low drag) calipers require a step bore master cylinder to function correctly.
How do you visually check if your calipers are a quick take up (low drag) design?
“G-Body”, S-10, and 3rd generation F-Body vehicles use the same caliper design. Conventional calipers where used from 1978 to 1980 on the “G-Body” and quick take up (low drag) calipers started where used from 1981 to 2002 in “G-Body”, S-10, and 3rd generation F-Body. Because the calipers are the same design, externally there’s no way to tell because the quick take up (low drag) calipers are mixed in with conventional rebuilt calipers.
How do you physically check if your calipers are quick take up (low drag) design?
To check if your caliper is a quick take up (low drag) engineered, perform the following test. Purchase or rent a pair of brake hose clamps at an auto parts store. Press the brake pedal as it is and then clamp off the two front rubber hoses. If the pedal returns and is high and firm, chances are you have quick take up (low drag) calipers. Be aware that this same of the same symptoms will occur if the bleeder screw is not in the 12 o’clock position when mounted on the spindle or there is still air in the caliper.
Can you use quick take up (low drag) and step bore master cylinder with manual brakes?
Yes. This is how it was done from the factory in the 1st generation (1982-1993) S-10 trucks, but they are not known to be very effective when braking. The stock front S-10 quick take up (low drag) calipers, 2.38” bore, are too small compared to the stock S-10 master cylinder step bore of 24mm and 31.6mm. This will cause a harder than normal pedal and there is insufficient clamping force produced by the system to make the braking effective. The stock S-10 step bore master cylinder is the smallest step bore master cylinder made. A 7/8” strait bore master cylinder is recommended, but can not work with the stock front quick take up (low drag) calipers. Since a more effective 7/8” bore master cylinder is recommended, an upgrade to larger 2.75” bore calipers are also recommended. A smaller bore master cylinder bore equals more brake fluid pressure at the caliper and a larger bore caliper equals more clamping force on the rotor.
What is a "metric" brake caliper?
A metric brake caliper where designed to be used on the GM metric chassis (1978-1988 “G-Body” cars). It is a floating, single piston design with 2.38” piston. The metric brake calipers where used on 1978-1988 “G-Body” cars, 1982-2003 S-10 trucks and SUVs, and 3rd generation F-Body (1982-1992 Camaro / Firebird) vehicles. Aftermarket metric calipers come in bore sizes of 2.75” bore, 2.50” bore, 2.25” bore, and 2.0” bore. Most aftermarket metric calipers are designed as conventional calipers and are not a quick take up (low drag) design. All metric calipers have a slide bolt center to center spacing is 5.50 inches and use a D154 brake pad.
What is a “G-Body” vehicle?
Technically, G-Body vehicles are the GM intermediates chassis designation made from 1981 to 1988. The GM intermediate vehicles from 1978 to 1980 also used the same chassis and are technically “A-Body” chassis. For simplicity and to avoid confusion, the 1978-1980 “A-Body” vehicles are lumped in with the 1981-1988 “G-Body” vehicles.
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