Diagnostic Procedure # 6 - Brake Imbalance

DIAGNOSTIC PROCEDURE # 6 - BRAKE IMBALANCE

1. Spin the front tires to make sure the front hubs are unlocked. If the hubs are unlocked, the axle shaft will not rotate with the wheels (4X4 models only).

2. Check for front wheel rotational drag with warm/hot brakes.

a. Make a series of 10 stops from speeds of 30 mph (48 km/h).

b. Make the 10 stops with no more than 30 second intervals between stops. This generally will induce a maximum pull if there is a drift/pull concern.

c. Raise the front end of the truck so that both tires are off the ground.

d. Rotate the front wheels by hand.

NOTE: FOR ALL 4 WHEEL DRIVE TRUCKS, MAKE SURE THE HUBS ARE DISENGAGED.

Both tires should rotate about the same amount, with little brake drag occuring. Some brake drag will naturally be present for each size of truck.

3. If the truck has excess brake drag, proceed as follows:

a. Open the bleed screw on the affected wheel to check for residual pressure in the brake lines. If there is a squirt of brake fluid out the bleeder screw and the drag is reduced or eliminated, the master cylinder may not be allowing the brake fluid to return to the reservoir.

b. Check the master cylinder push rod adjustment. Refer to the appropriate Truck Shop Manual, Section 12-30 for service details.

c. Check the brake pedal to determine if it is fully returning.


4. Remove both calipers and check piston retraction using a "C" clamp and wooden block. The piston should easily move back into the bore under the force of the clamp. Re-build or replace as needed.

5. If Steps 1 through 4 have not determined the concern, swap rotors and linings from side to side.

Figure 2:

NOTE: INNER SHOE TAB CLEARANCES SHOULD BE RECHECKED AND MODIFIED IF NEEDED. SEE FIGURE 2 AND REFER TO SERVICE PROCEDURE 1.

6. Test drive the vehicle with 10 or more stops from 40 mph (64 km/h) before evaluating for brake drift. This will allow for proper seating of the brake pads. If there is no change in drift while braking, it may be assumed the concern is not the result of the front brakes.

7. Check the rear brakes. Remove the rear wheels and brake drums.

a. Check for contaminates (i.e., grease, axle lube, leaking brake fluid, etc.).

b. Check for broken components, frozen parking brake cables and improperly installed parts.

c. Check the cage diameter using the Brake Adjustment Gauge (D81L-1103-A) or equivalent. If either side is out of specification, check for proper function of the adjusting mechanism and repair or replace as required.

d. Check the rear wheel cylinders by the following method.

^ Replace one of the brake drums.

^ Have another person apply the brakes and watch for movement of one of the brake shoes on the other wheel.

^ Re-apply the brakes while holding in place the shoe that moved. The opposite shoe should now move. If no movement is observed, repair or replace the wheel cylinder.

^ Re-install the drum and repeat the procedure for the other rear brake.


8. If the condition still exists, swap rear shoes from side to side and drive the truck. If the drift is significantly reduced, replace the rear linings. If the drift/pull is not significantly reduced, go to Service Procedure # 7.