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Caliper Clinic: Rebuilders Not Only Can Improve An OE Design, But They Can Also Improve The Consumers' Opinion

By Paul Schuck

Rebuilders not only can improve an OE design, but they can also improve the consumers' opinion about the rebuilt auto parts business, in general.
Many people still believe that all rebuilt parts are sub-standard compared with original equipment parts. However, most rebuilders are continually working to improve the reputation of rebuilt parts by producing quality parts, and by improving deficiencies in an original equipment manufacturer's design. Caliper rebuilders have opportunities for the latter with the two caliper designs discussed below.
One such OEM design deficiency is on the 1986 through 1994 Ford F250/ F350 trucks, and on the 1986 through 1991 Ford E250/350 vans. This caliper, originally produced for Ford by Dayton Parts, is a two-piston design that uses three different casting numbers. However, one casting number has two different pad gap dimensions. The 1991 to 1994 F250 also uses a different seal than the others due to a change in the seal groove dimension in the piston bore.
Other changes may be due to the following: In May 1990, Dayton issued a technical bulletin (TE000190) which recommended the use of D450 disc pads on newer style calipers with a pad gap of 2.890". The bulletin also advised against using the D120, which is used on calipers with a pad gap of 2.860", in the newer style caliper due to the pad gap change.Using the D120 disc pad in a caliper with a 2.890" pad gap may result in insufficient seal engagement of the pistons when the linings are fully worn. The D450 disc pad includes a constrained layer shim staked to the disc backing plate which reduces noise and may act as a heat shield. See Chart 1 on page 37.
The D450 pad will fit calipers with a pad gap of 2.860", but the caliper will not fit over the rotor unless the rotor thickness is reduced more than .030". This combination is not recommended because reduced rotor thickness or mass will affect the rotor's ability to dissipate heat.
In May 1992, Ford issued a Service Recall Bulletin (92S44) which outlines how to correct a loss of front brake effectiveness experienced on vehicles that are used for heavy duty service. There are two Ford kits involved in the recall. Both kits include piston insulators to be used on calipers that contain aluminum pistons.
One of the kits, however, also includes an insulator jacket for vehicles equipped with 7.5L EFI engines. The piston insulators serve as a heat shield to protect the brake fluid from boiling, and the jacket insulates the driver's side brake line which is routed too close to the exhaust manifold.
In July 1992, Dayton issued a technical paper (TE10001) which recommends replacing all aluminum pistons with phenolic pistons which will further insulate the brake fluid from high operating temperatures.
By February 1995, Ford also was recommending the replacement of the dust boots on heavy service vehicles with a new boot which contains silicone in order to alleviate problems with rubber deterioration caused by high operating temperatures. See Figure 1 on page 36. This new silicone boot is gray in color and will withstand higher temperatures than the standard EPDM rubber boot.
Most caliper parts suppliers now offer these revised parts to the aftermarket and to rebuilders who have recognized the opportunity available. Many rebuilders now supply this caliper with phenolic pistons, silicone boots and the D450 brake pad (on calipers with a 2.890" pad gap) as standard items. When making these improvements to this caliper which correct the problems experienced at the service level, the customer's opinion about rebuilt parts is greatly improved.
Another design deficiency that caliper rebuilders have an opportunity to improve is with the GM "W" Body vehicles. The 1989 through 1993 Buick Regal, Chevrolet Lumina, Oldsmobile Cutlass Supreme, and Pontiac Grand Prix models with rear disc brake calipers experience problems associated with the slide pins. The caliper design incorporates two large slide pins with rubber dust boots at each end that become frozen due to corrosion buildup between the steel pin and the cast iron caliper. See Figure 2.
This corrosion buildup is a result of two dissimilar metals being subjected to contamination, heat and static electricity. Once the deposits build up inside the casting, the pin becomes frozen and no longer allows the caliper to slide or retract as designed. When the slide pins freeze, the rear brakes no longer function properly, which will also dramatically affect the front brake performance and lining life. Caliper rebuilders see this as a problem as well as an opportunity. Although this problem may result in more caliper sales, it also impacts the warranty returns of this caliper to the rebuilder. When the rear caliper problem appears, front caliper performance is affected as well, possibly resulting in both the front and rear calipers coming back to the rebuilder as a warranty.
Many rebuilders have overcome this deficiency in one of two different ways. Some rebuilders utilize an oil impregnated bronze bushing which is press-fit into the cast iron sleeve bore and also includes stainless steel slide pins to eliminate the corrosion build-up. See Figure 3 on page 37. Other rebuilders utilize aluminum slide pins that incorporate a hard coating which interrupts static electricity and prevents oxidation and galvanic corrosion from forming. See Figure 4. Some rebuilders also recommend using a synthetic molybdenum disulfide lubricant in place of the original silicone lubricant. This synthetic lubricant has superior performance characteristics over silicone in metal-to-metal applications, yet it will not affect rubber parts as petroleum-based lubricants will. Both methods are an improvement over the original design and will prevent the slide pins from freezing well beyond the original design.
Whichever method is used to correct the slide pin problems, the risk of the caliper coming back to the rebuilder as a warranty is greatly reduced. Not only do these caliper upgrades improve your reputation as a rebuilder, but they also serve as a clear statement to your customers and to the vehicles' owners that rebuilt auto parts can meet - and in some cases actually exceed - the original part with regard to quality, performance and value.
Just as original equipment manufacturers will continue to improve the quality of the products that they produce each year, rebuilders will continue to look for deficiencies upon which they can improve for the aftermarket.
Most caliper rebuilders are constantly working to improve the reputation of the rebuilt caliper either through quality parts or by improving deficiencies within a original equipment manufacturers design.