Caliper Clinic: Rebuilders Not Only Can Improve An OE Design, But They Can Also Improve The Consumers' Opinion - Engine Builder Magazine
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Caliper Clinic: Rebuilders Not Only Can Improve An OE Design, But They Can Also Improve The Consumers’ Opinion

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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.

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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.

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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.

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