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FORD BRONCO -> BRAKE SYSTEM; 4WABS, RABS, Self Test... -> Early Replacement of Brake Components, Rotors & Pads Due to Roughness Concerns, Ford for 82 to present
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Early Replacement Of Brake Components, Rotors & Pads Due To Roughness; All Fords 82-Present, All Mercury 82-Present, Merkur 85-Present; "...Condition: Small changes in braking torque when the brakes are applied creating brake torque variation. *Runout of disc rotor *Rusted rotor surface *Warped rotor due to improper wheel lug nut tightening *Varied rotor thickness around the disc *Transferred patches of lining material on the rotor surface *Uneven tire wear and balance. Repair Procedure: Begin with step 1 and finish with step 6. 1. Check the Condition of the Tires and Their Balance. Sometimes the brake roughness concerns are not braking roughness at all. In fact, some complaints are due to out-of-round and out-of-balance tires or broken steel cord in the tires. The effects of these problems show up at all conditions of driving but may seem worse when braking. That fact can be used to correctly determine that the customer is not experiencing brake-caused roughness. If however, there is a brake roughness problem in addition to tire problems, then both need to be repaired. If the inspection shows that tires are contributing to roughness by vibration during all driving conditions, they should first be balanced and rotated using normal maintenance procedures then follow steps below to correct the brake roughness. 2. Check the Wheel Lug Nut Tightening Torque Uneven and/or out of specification torque on the wheel lug nuts will cause the brake rotor to warp. Up to 0.005-inch rotor runout can occur due to improper lug nut tightening. The first thing to check for is the consistency of torque of the lug nuts on each wheel. Torque readings not within 20% of each other cause brake roughness. Improper lug nut tightening can have the following effect: 1. Rotor runout 2. Rotor thickness variation 3. Brake torque variation 4. Brake roughness Ultimately, the rotor may be damaged and must be resurfaced. Follow the procedure in the Service Manual for resurfacing the rotors. Proper torque must be used when a resurfaced or new rotor is installed. Use of a torque wrench is again stressed, or as an alternative, Torque Sticks may be used. When installing a new rotor, do not machine the rotor on a bench lathe. Any surface contamination can be removed with solvent or with very light sanding. 3. Check or Rust/Contamination on Mounting Surfaces Surface rust or contamination on the wheel-to-rotor and rotor-to-hub flange surfaces should be cleaned with very light hand sanding. Use garnet paper 100A or aluminum oxide150J grit. DO NOT USE HARSH ABRASIVE TOOLS. If the cleaning is not done, it will contribute to the runout of the rotor when assembled, which will cause brake roughness later on. Ford does not approve of removal of rust on the rotor using harsh abrasive tools. The on-car turning procedure is the only sanctioned method at this time to deal with the repair of rusty rotors. Since the thickness of the rotors are manufactured to less than 0.0004 inch tolerance, using hand held tools on the rotor surface can not guarantee maintaining the tolerance. Brake roughness will occur with rotor thickness variation of 0.0008 inch or less on certain sensitive vehicles. 4. Check for Runout of the Front Rotors on the Car and Front Hub Mounts Rotor runout while rotor mounted on the car should not exceed 0.003 inch. With the wheel off, fasten the lug nuts back on to hold the rotor onto the hub. The fastening torque should not exceed 81 Nm (60 lb.-ft) and should be even. With the dial indicator attached to the spindle, slowly rotate the rotor to get the total indicated runout. This value should not exceed the Total Indicated Runout (TIR) as specified in the appropriate Service Manual. If it exceeds specifications, first index the rotor one (1) wheel stud at a time. If the readings still exceed 0.003 inch, than the hub face runout should be checked. Repeat the runout check procedure on the hub face. If the runout exceeds 0.002 inch, the hub must be replaced; otherwise the rotor must be resurfaced on the vehicle or replaced. 5. Check for Rear Brake Roughness Except for the vehicles with separate drum in disc parking brake (e. g., Crown Victoria, Grand Marquis, and Town Car) applying the parking brake can actuate the rear brakes. Attempt to slow down the vehicle from 48 km/h (30mph) with the transmission in neutral using the parking brake. If roughness is present, then the rear brakes need to be serviced. If roughness is not present, than the front brakes need servicing. To service the rear brakes follow the procedure, above for servicing the front brakes. 6. Check for Proper Caliper Operation Inspect the calipers for leaks and brake fluid contamination. Any leaks from the wheel cylinders and seals must be repaired per the Service Manual. Also, inspect for glazing of the brake pads which may indicate a seized caliper piston; frequent severe or unintentional braking by the customer. Repair as specified in the Service Manual..."
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