By Larry Hammer
Technical Services
Mighty Auto Parts
Many years as a technical hotline troubleshooter, clinic instructor and writer have impressed upon me how certain vehicles establish a pattern of failures. Often vehicle manufacturers encounter a problem with a component or system, the engineers work through the problem, and the same condition recurs years later. Often it is with the same vehicle platform. How can this be? The vehicle manufacturer may resolve a difficult issue by redesigning a part or making a system modification. Later, that part is replaced by an original style component or one that doesn’t meet the revised spec, thus reintroducing the symptom. Sometimes the condition is a formulation-related issue which can change sporadically. Many technicians don’t have access to this information. Knowing your parts supplier is the best way to prevent this scenario. Let’s consider some examples of recurring conditions and problems that are impossible to solve without some factory assistance.
GRABBING REAR BRAKES
In 1990, our technical hotline was inundated with rear brake grabbing complaints on Ford F150 trucks. On a cool, damp morning, the rear brakes would grab and chirp the tires. Without the anti-lock assist, the vehicle could skid out of control. The aggressive rear braking sensation occurred any time moisture was present, especially after the vehicle had been parked for a few hours. Replacing the original equipment linings with an aftermarket friction would cure the condition. Here’s why. Unlike the OE lining which was non-asbestos organic (NAO), many of the aftermarket linings were still asbestos and not moisture absorbent. Ford actually replaced some trucks and vans, prior to isolating the formulation as the cause of the braking condition. The first notice we received from Ford addressing this issue was in 1993, advising of a new friction formulation which was less sensitive to moisture. The alternate friction formulation satisfied the brake grabbing condition for a period of time, only to surface again.
Recurring Condition…On 10/01/01 Ford introduced another TSB on the F150, advising that a grabbing condition from the rear brakes may occur during the first few brake applications following an extended exposure to high humidity. This condition was due to the rear brake linings being too sensitive to moisture. A revised friction formula was made available for the 1997–2001 F150 vehicles. Most would assume that once a condition was identified and corrected, the symptom would not be repeated, at least on that vehicle platform.
Sealing the System…On 9/06/04 Ford issued another TSB addressing a moisture-related condition. The bulletin stated that some 2002–2005 Ranger trucks may exhibit a rear brake grabbing condition during the first few brake applications, after the vehicle has been parked for several hours. The condition is due to moisture intrusion into the rear brake linings. The symptoms can be minimized by sealing the backing plate with silicone sealant. Ford recommends replacing the brake linings and checking for loose or missing hardware, especially a missing adjuster plug. Inspect and clean the lining contact area of the drum, and machine the drum if necessary. Reinstall the drums and adjust the brakes. Thoroughly clean the back side of the backing plate to promote adhesion of the sealant. Apply the sealant to the back side of the backing plate in the following areas: axle flange, wheel cylinder, parking brake cable, and hold-down pins.
With pressure from the government to eliminate the use of asbestos, the braking industry basically had to reinvent the friction material. With these new formulations came many challenges. Many brake performance issues had to be dealt with, and we continue to deal with those issues. Wheel lock-up during periods of high humidity was one of those challenges. Caution: Light rust forming on a brake drum or rotor can promote the same aggressive braking condition.
FRONT BRAKE ROUGHNESS
Complaints of front brake roughness or shudder while braking may be encountered by owners of 2004–2005 F150 trucks. Traditional procedures to circumvent the brake performance symptoms will likely be futile. Ford advises that the mentioned vehicles may require a steering and brake assembly modification. A service replacement may be required for the rack and pinion, rotors, and caliper assemblies. The necessary replacement components are based upon the vehicle build date and the current parts installed on the vehicle.
For example: 1) Vehicles built prior to 8/20/03 require a replacement rack and pinion assembly. 2) Determine if the vehicle is fitted with the new or old style rotors (new style rotors contain 47 cooling fins). If the old style rotors are present, replace the front rotors and caliper assemblies. If the new rotors are present and are within the proper thickness specification, machine the rotors and install the new service calipers.
Brake grabbing, roughness or shudder can be a challenge to diagnose. Conventional procedures may not offer the solution or prevent a recurrence. Be aware that some vehicles have received factory modifications. Installing components that are not compatible may re-introduce the problem.
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