Brake Service - Service Tips
Article No.98-5A-52
03/18/98
BRAKES - BRAKE SERVICE - SERVICE TIPS
LIGHT TRUCK:
1986-97 AEROSTAR
ISSUE:
Brake service, including both time and quality, may be further improved if "extra care is taken during brake service. Most Service Manuals do not contain the "finer points" of brake service.
ACTION:
Refer to the following Brake Service "Shop Tips" when servicing brakes.
BRAKE SERVICE "SHOP TIPS"
The following is "food for thought" when an Aerostar is brought in for any brake related roughness/pull concern. We have attempted to supplement the standard Service Manual procedures with aspects that are unique to this vehicle and questions that might not be obvious to ask the customer.
First, make sure that you fully understand the customer's concern. Customers are not trained to diagnose vehicle problems and relay that information in a technical manner. The terminology the customer uses when describing his/her concern may be inappropriate or misleading for the problem the vehicle is experiencing. For example, a vehicle was brought in for service with the customer stating "the vehicle is hard to steer." After the technician spent a lengthy amount of time trying to pinpoint the problem and could not find anything wrong with the the vehicle's steering and handling capabilities, he accompanied the customer on a test drive. He asked the customer to reproduce the problem and discovered the actual problem was brake shudder. The customer had a difficult time "steering" the vehicle during hot brake applications when the vehicle had a tendency to shudder. If you are uncertain that you understand the customer's problem, don't guess, ask the customer to take you for a test drive and attempt to reproduce the problem. In the end, it will save not only your time, but the customer's as well.
It is also a good idea to visually inspect the vehicle before servicing. Note anything that may contribute to or exaggerate the customer's concern, such as bent or distorted rims, the addition of a trailer hitch, or low tire pressure. Not only can bent or distorted rims exaggerate any roughness problem that the vehicle may have, it may also distort the rotor/drum much in the same way that over-torqued lug nuts will (discussed later). This, in turn, may cause brake shudder problems later down the road. If the vehicle has a trailer hitch, ask the customer how often he/she pulls the trailer? How heavy is the trailer? Is the trailer equipped with its own brakes? Pulling a trailer (especially if it is not equipped with trailer brakes) may cause Aerostar brakes to heat up quicker and consequently wear faster. Low tire pressure can exaggerate brake pull. Always verify proper tire inflation when diagnosing any vehicle pull or drift concern. If time permits, check/set the proper tire inflation (tire pressure is shown on the certification label on the driver's side door opening) and then have the customer demonstrate the pull/drift concern.
Once you have a full understanding of the customer's concern and usage cycle (i.e., city driving with hard frequent braking vs. highway driving with moderate infrequent braking), you can begin to service the troubling components. When checking for dragging brakes, check for residual hydraulic pressure in the brake lines. If it is suspected that the residual pressure is being generated by the booster/master cylinder, generally you will find that both front brakes or both rear brakes are dragging as they are connected to the primary and secondary master cylinder circuits respectively. To check for residual pressure, first make three to five brake applications with vacuum on the booster (engine running). With the vehicle raised on a hoist and the wheels free to spin, crack the bleed on the suspected dragging caliper/wheel cylinder. If there is a "spurt" of brake fluid and a noticeable release of brake, there may be residual pressure in that brake.
NOTE:
FLUID SEEPAGE IS NORMAL; SPURTING FLUID WITH A CORRESPONDING RELEASE OF THE BRAKE WOULD MEAN RESIDUAL PRESSURE IN THE SYSTEM.
Repeating this procedure for the other brake in that circuit will verify a problem with the circuit versus just the single brake. If it is determined that there is residual pressure in the circuit and you cannot pinpoint the cause in another component, the booster output rod adjustment may be at fault. The Aerostar brake booster design does not allow for field adjustment of the output rod. ADJUSTMENT OF THE BRAKE BOOSTER OUTPUT ROD CAN ONLY BE PROPERLY PERFORMED AT THE MANUFACTURER. DO NOT ATTEMPT TO ADJUST THE OUTPUT ROD. Consequently, the booster must be replaced if there is residual pressure in the system and the booster is pinpointed as the root cause.
Once you start to disassemble the vehicle, observe and note the condition of the components. Keep track of anything out of the ordinary that might assist you in diagnosing and servicing vehicles in the future. Some things to look for are:
^ If you notice on the front brakes that one pad is wearing quicker than another it would suggest that the caliper is not sliding properly on its rails.
^ While looking at rear brakes, note the wear pattern on the drum braking surface. If it appears to be shiny and glazed, the pads may be contacting the drum. If you can still see the factory turn marks, the shoes may not be contacting the drum which may suggest an under-adjusted brake or a frozen wheel cylinder.
COMPONENTS TIPS
Reference the Aerostar Service Manual, Section 06, for proper brake service procedures.
Rotors and Drums:
Resurface (as necessary) these components rather than just replacing them. Rotors should be replaced only if damaged or below minimum thickness specifications.
Linings:
If you are servicing the rotors and/or drums, you should inspect the linings as well. If there is a generous amount of lining material and it seems to be in good condition, you may reuse the pad assemblies. Linings may be used to a thickness of 1 mm.
Calipers:
Check if the pistons in the caliper seem to be binding or have seized. To understand the force required to push the caliper pistons back, use a set of tongue-in groove pliers. With an old pad in its service position (this will absorb any marring that the pliers may cause to the piston), use the pliers to push the pistons back. This method should help you understand the differences of required force from caliper to caliper.
NOTE:
IF YOU HAVE NEVER USED THIS METHOD BEFORE, IT IS RECOMMENDED TO FIRST TRY IT ON A KNOWN GOOD CALIPER TO GET A FEEL FOR THE "BASELINE" FORCE REQUIRED TO PUSH THE PISTONS BACK.
Rear Brake Assembly:
When reassembling the rear brakes, use the recommended tool (D81L-1103-A) to set the lining-to-drum clearance. This will help assure that the brakes are in proper adjustment when the vehicle is returned to the customer. Also verify that the rear wheel cylinders are fully functional. This can be done after reassembly by applying the brake pedal and verifying that brake torque is being generated on both rear wheels.
SPECIAL MATERIALS
Lubricant:
The specified lubricant used on mating brake components has changed. The new part number is D7AZ-19A331-A. This lubricant has a silicon base and should provide lubrication as well as better corrosion protection than the previous petroleum-based lubricant. It has a better temperature resistance and should stay in place much longer in a high heat area such as brakes. Also, petroleum-based lubricants do not react well with the rubber on the caliper slide pins and may eventually be harmful to the assembly. Some locations specifically require this silicon-based lubricant.
NOTE:
THESE AREAS MUST BE FREE OF ALL DIRT AND CORROSION PRIOR TO APPLYING THE LUBRICANT.
They are:
^ On the knuckle - Specifically in the "V" grooves in which the caliper slide pins will rest, and where the caliper ends butt up against the knuckle (refer to Figure 1).
^ On the caliper slide pins - Lubricate the slide pins as well as the "V" groove to ensure proper lubrication all around (refer to Figure 1).
^ On the caliper - In the "V" grooves as well as the ends of the caliper which butt up against the knuckle to ensure proper caliper movement (refer to Figure 1).
^ On the knuckle where the inner pad rests - This area needs to be lubricated to prevent the pad from rusting to the knuckle which may reduce brake effectiveness and cause rotor wear on only one side, possibly resulting in brake shudder.
^ On the rear brake backing plate - Specifically where the shoe and lining assemblies contact the backing plate. Lubricate here to make sure the linings do not rust to the plate and prevent movement (i.e., when the parking brake is set overnight, if the shoes rust to the plate they would not be able to fully retract once the brake was released).
Linings:
Lining material is critically important to the proper function of the brake system. When diagnosing a problem, verify that the correct lining material is on the vehicle. Remember that the linings equipped on the Aerostar are specific for this vehicle application and any variation can change the stability, performance and control of the vehicle.
ASSEMBLY
All brake assembly procedures should be followed per the Aerostar Service Manual, Section 06.
Remember to check, when assembling the component, the condition of all the mating surfaces such as: caliper-to-knuckle, rotor-to-hub (4X4 only), wheel-to-rotor, drum-to-hub or axle flange, drum-to-wheel, etc. Any foreign material on these mating surfaces can considerably distort the runout and/or roundness of the brake components, or in the case of the caliper, may reduce proper function. If there is any rust or foreign material on these surfaces, clean them with a stiff wire brush or the equivalent.
In addition, remember that over-torquing of wheel lugs may distort brake components and possibly cause excessive runout or out-of-roundness. When assembling the wheel, be sure to use the recommended torque sticks (164-R0314) or an equivalent calibrated torque wrench.
FINAL CHECK
When the vehicle is completely reassembled, verify that the customer's concern has been addressed. Duplicate the customer's driving pattern on the verification drive, being careful not to do more harm than good. For example, if on the drive you have heated the brakes to the point that you can smell the linings, you have driven the vehicle too aggressively and should visually recheck the brakes before returning the vehicle to the customer.
Hopefully, these service suggestions will further improve the service procedure and enhance customer satisfaction. If possible, educate the customer on exactly what was wrong and what was done to service the vehicle. Simple items like proper tire pressure and replacing components with only approved certified materials can save a lot of time and heartache in the future.
OTHER APPLICABLE ARTICLES: NONE
SUPERSEDES: 96-26-17
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 301000, 390000, 703000, 790000