Guide to Successful Corvette Brake Installation

 

Guide to a Successful Corvette Brake Installation

 
In order to get the most out of your Corvette braking system overhaul, it is imperative that wheel bearing end-play and rotor run-out are also brought to within factory specifications. Failure to meet these requirements may cause a "spongy" pedal sensation or complete loss of pedal control in a short time, even with new calipers installed. This condition is due to "piston knock-back" (oscillation), which causes the pistons to act as air pumps at each out of spec wheel.
    These parts were originally machined at the factory as a riveted assembly, so separate machining of the rotor will disturb the relationship between these parts, causing the rotor to become a "wobble plate."  If this condition now exists (see run-out specifications below), the situation may be improved by repositioning the rotor in one of the four other positions on the axle flange.  A new rotor will not necessarily solve the problem, since it probably also will require re-drilling the parking brake adjuster access hole (if desired).  If this does not cure the run-out problem, removal of the axle shaft and re-machining the rotor and axle shaft as an assembly may be necessary.
    Check rear disc run-out and bearing end-play using a dial indicator for the most accurate results. Total allowable end-play plus run-out should not exceed .009" on rear wheels.
    If a dial indicator is not available, rotor wobble can be used as an indicator of an out of spec condition, but not as an accurate measurement. Raise both rear wheels and mount car on stands. Remove wheels, start the engine and run at idle speed, then shift into gear. Rotors will turn slowly, allowing observation of their condition from the rear of car. In addition, the offending wheel can also be identified by the continued recurrence of air bubbles when bleeding the caliper located at the out of spec. wheel.
    Excessive end play can only be corrected by readjustment of rear wheel bearings, which requires that the axle shaft be first removed.
    For front wheels, replacing and adjusting wheel bearings per note 3 (below) is all that is required. After adjustment, the maximum allowable bearing end-play plus run-out should not exceed .010". See below for correct run-out specifications.
 
1965-82 Corvette and 1969 Camaro Z-28
Delco Moraine Type Disc Brake
Rotor (Front & Rear)
    Thickness……………………………………………………………1.250 inches
         minimum after re-machining (1971Later)........................1.230 inches
        Minimum allowable (discard)……………………..............1.215 inches
    Parallelism (note 1)...........................…………………………...0.0005 inches
    Lateral run-out T.I.R. (1965-70)................……………………….0.002 inches
    Lateral run-out T.I.R. (1971-later (note 2)..……………………...0.005 inches
    Surface finish (non-directional) 1965-70)……………......30-50 micro inches
    Surface finish (non-directional) 1971-later)………….......20-60 micro inches
 
 
 
Torque Limits
 
Caliper mounting bolts (front & rear)……………………………………………70 ft. lbs.
Caliper assembly bolts (front)………………………………….………….120-140 ft. lbs.
Caliper assembly bolts (rear)………………………………………………...55-65 ft. lbs.
Wheel bearing nut………………………………………………………………see note 3
 
Note 1:  Total variation in thickness allowed when rotor is measured at four or more locations.
 
Note 2:  Maximum rate of change must not exceed 0.001 inch in 30°.
 
Note 3:  While rotating wheel, tighten spindle nut to 12 ft. lbs. Torque. Back off adjusting nut one flat and insert cotter pin. If the slot and pin hole do not line up, back off the adjusting nut an additional ½ flat or less, as required to insert the cotter pin. Spin the wheel to see that it rolls freely and then lock cotter pin in place (correct procedure can only be accomplished when friction pads are not in contact with rotor).
 
Installation of Calipers
 
Assemble pads to the calipers before mounting on the car. Separate pads with 1-5/16" thick wood block spacer (or 2 red plugs one inside the other), which will pop out when caliper is placed over disc. This approach will greatly ease installation, prevent possible damage to components and eliminate the need for putty knives or clips.  Installation of pads on mounted calipers is best accomplished using the brake pad installation tool from Muskegon Brake, or the equivalent.
    When installing front brake hoses, always remove them from the frame and install them in the caliper first. Next install the free end of the hose in the 12 point retainer bracket on the frame and install the "horseshoe" clip. With both front wheels off the ground turn wheel through a full left to right turn to insure that hoses do not twist or take a double bend.  If hoses do not bend correctly remove them from the 12 point bracket and re-orient them so that they bend with minimum twisting. Failure to complete this part of the installation may cause brake lock-up in service, since the thin wall interior hose may collapse and restrict the fluid from relieving caliper line pressure.
    Rear brake steel lines should be replaced by new parts if corroded or kinked. We suggest purchasing 22"  lengths of 3/16" diameter pre-flared tubing, available at most auto parts stores, and bending them to suit using the old line as a guide. Pre-bent custom rear steel brake lines are available from Muskegon Brake.  
 
Brake Fluid
 
It is advisable to replace brake fluid if the color is brown or muddy. This condition is due to water that has been absorbed by the fluid, which will eventually corrode the brake lines and master cylinder, plus possibly creating a vapor lock under extreme braking conditions. Flush system with clean brake fluid and replace with a good grade of disc brake fluid (DOT 3 or 4 Glycol base) or with Silicone Brake Fluid (DOT 5, also available from Muskegon Brake). This fluid will not absorb water, does not damage paint and maintains its viscosity over a larger temperature range.
 
If you're still using glycol-based brake fluid but are considering switching to silicone fluid, read our guide to Converting to Silicone Brake Fluid.
 
Power Steering Control Valve Centering Instructions
 
Caution: keep arms away from steering wheel; occasionally, the wheel may start to turn by itself because the control valve may not yet be centered (every vehicle is slightly different and it is not possible to exactly preset all valves at the factory).
    A tendency for the car to steer in one direction (no hands on wheel) indicates that the control valve requires further centering adjustment. This assumes that the front end has been properly aligned.   
    If centering is required, disconnect the rod end of the slave cylinder from the vehicle, allowing it to hang loose. With the front wheels off the ground and the engine running, remove the metal cap (located under the 2 hoses that connect to the slave) at the end of the control valve. Adjust the valve by gently turning the screw (under cap) clockwise or counter-clockwise, depending on which way the rod moves until the rod comes to rest. Replace dust cap and reconnect rod to bracket.
 
Wheel Bleeding Sequence and Tips
 
The correct bleeding sequence for 1965-82 Corvette's with disc brakes is as follows:  RR-(outer), RR-(inner), LR-(outer), RR-(inner), RF, LF.
    Pressure bleeding is recommended for all hydraulic brake systems. The bleeding operation itself is fairly well standardized. First step in all cases is cleaning the dirt from the filler cap before removing it from the master cylinder. This should be done thoroughly. Pressure bleeding is fastest because the master cylinder doesn’t have to be refilled several times, and the job can be done by one man. To prevent air from the pressure tank getting into the lines, do not shake the tank while air is being added to the tank or after it has been pressurized. Set the tank in the required location, bring the air hose to the tank, and do not move it during the bleeding operation. The tank should be kept at least one-third full. If air does get into the fluid, releasing the pressure will cause the bubbles to increase in size, rise to the top of the fluid, and escape. Pressure should not be greater than about 35 psi. On vehicles equipped with plastic reservoirs, do not exceed 25 psi bleeding pressure.
    When bleeding without pressure, open the bleed valve three-quarters of a turn, depress the pedal a full stroke, then allow the pedal to return slowly to its released position. Some makers suggest that after the pedal has been depressed to the end of its stroke, the bleeder valve should be closed before the start of the return stroke. On cars with power brakes, first reduce the vacuum in the power unit to zero by pumping the brake pedal several times with the engine off before starting to bleed the system. Pressure bleeding, of course, eliminates the need for pedal pumping.  
    Flushing is essential if there is water, mineral oil or other contaminant's in the lines, and whenever new parts are installed in the hydraulic system. Fluid contamination is usually indicated by swollen and deteriorated cups and other rubber parts. Bleeding is necessary on all four wheels if air has entered the system because of low fluid level, or the line or lines have been disconnected. If a line is disconnected at any one wheel, that caliper only need be bled. Of course, on brake reline jobs, bleeding is advisable to remove any air or contaminants. Master cylinders equipped with bleeder valves should be bled first before the calipers are bled. In all cases where a master cylinder has been overhauled, it must be bled. Where there is no bleeder valve, this can be done by leaving the lines loose, actuating the brake pedal to expel air and then tightening the lines. After overhauling a dual master cylinder used in conjunction with disc brakes, it is advisable to bleed the cylinder before installing it on the car. The reason for this recommendation is that air may be trapped between the master cylinder pistons because there is only one residual pressure valve (check valve) used in these units.
 
(Information From ALLDATA Online)
 
    When using DOT 5 silicone brake fluid, the bleeding process is the same as stated above but the steps must be done VERY SLOWLY, in order to prevent from aerating the system.
 
Brake Pedal End-Play
 
In order to obtain correct pedal height, adjust pedal end-play after bleeding system or replacing master cylinder.
 
1. Locate pedal push rod under dash (std.), between booster and master cylinder (opt.); loosen check nut.
2. Turn push rod as required to provide 1/16" to ¼" end-play at brake pedal. 
3. Tighten check nut and recheck pedal travel and feel.

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