Model MA TOW Tractor. Manual - part 20

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                       p. 5

(b)

Drive tractor slowly and make several slow speed stops.

(c)

Check all brake fluid line fittings and caliper areas for fluid leakage.

(d)

Correct any discrepancies before returning tractor to normal service.

B.

CALIPER OVERHAUL

1.

Delco Caliper

(a)

Removal:

(1)

Removal of the caliper for overhaul is the same as for shoe and lining
replacement except that it will be necessary to disconnect the brake hose.

(2)

First, disconnect the hose from the steel brake line and cap the fittings to
prevent dirt from entering the line or the hose. Remove the caliper, with bore
attached, to a work bench for overhaul.

(b)

Disassembly:

(1)

Before beginning disassembly, thoroughly clean the exterior of the caliper
using clean denatured alcohol. Place the caliper on a clean work surface.

(2)

Remove the brake hose from the caliper, discarding the copper gasket. Check
the hose for worn spots, cracks or other signs of deterioration. Discard the
hose, if damaged, to be replaced with a new hose at reassembly. Drain brake
fluid from the caliper.

(3)

Use clean shop towels to pad the interior of the caliper and remove the piston
by directing compressed air into the caliper inlet hole.

NOTE: Use just enough air pressure to ease the piston out of the bore. If the
piston is blown out,even with padding provided, it may become damaged.

CAUTION: DO NOT PLACE THE FINGERS IN FRONT OF THE PISTON IN
AN ATTEMPT TO CATCH OR PROTECT IT WHEN APPLYING
COMPRESSED AIR. THIS COULD RESULT IN SERIOUS INJURY.

(4)

Use a screwdriver to pry the boot out of the caliper. Extend the screwdriver
across the caliper bore, under the boot, and pry up. Be careful not to scratch
the caliper bore.

(5)

Use a piece of wood or plastic, a plastic toothpick is ideal, to remove the
piston seal from its groove in the caliper bore. DO NOT USE A METAL TOOL
OF ANY TYPE FOR THIS OPERATION.

(6)

Remove the bleeder valve from the caliper.

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                        p. 6

VI .

REAR WHEEL DISC BRAKES (SERIAL NO'S 0128 AND UP)

B.

CALIPER OVERHAUL

1.

Delco Caliper (cont)

(c)

Cleaning and Inspection:

(1)

The boot, piston seal, rubber bushings and sleeves are to be replaced each
time the caliper is overhauled. Discard, do not bother to clean and inspect,
these parts.

(2)

Clean all other parts in clean brake fluid or denatured alcohol. Use dry, filtered
compressed air to dry parts and blow out all passages in the caliper and
bleeder valve.

CAUTION: USE OF LUBRICATED SHOP AIR WILL LEAVE A FILM OF
MINERAL OIL ON THE METAL PARTS. THIS MAY DAMAGE RUBBER
PARTS WHEN THEY COME IN CONTACT AFTER REASSEMBLY.

(3)

Check the mounting bolts for corrosion, breaks in the plating or other damage .
Do not use abrasives in an attempt to clean the bolts - replace them.

(4)

Carefully examine the piston OD for scoring, nicks, corrosion and worn or
damaged chrome plating. If any surface defects are detected, replace the
piston.

CAUTION: PISTON OD IS THE PRIMARY SEALING SURFACE IN THE
CALIPER ASSEMBLY. IT IS MANUFACTURED AND PLATED TO CLOSE
TOLERANCE. REFINISHING BY ANY MEANS OR THE USE OF ANY
ABRASIVE IN THE FIELD IS NOT ACCEPTABLE.

(5)

Check the caliper bore for the same defects as the piston with the exception of
plating damage. The piston bore is not plated and stains or major corrosion
can be polished with crocus cloth. Do not use emery cloth or any other form of
abrasive. Thoroughly clean the caliper after the use of crocus cloth. If the bore
cannot be cleaned up in this manner, replace the caliper.

(d)

Reassembly:

(1)

Lubricate the caliper bore and the new piston seal with clean brake fluid.
Position the seal in the caliper bore groove. Lubricate the piston with clean
brake fluid and assemble a new boot into the piston groove so that the fold
faces the open end of the piston. Insert the piston into the caliper bore, using
care not to unseat the seal, and force down to the bottom in the bore. This will
require a force of 50 to 100 pounds. Position the OD of the boot in the caliper
counterbore and seat with Tool No. J-22904.

(2)

Check the boot installation to make sure that the retaining ring molded into the

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                       p. 7

boot is not bent and that the boot is installed fully below the caliper face and
evenly all around. Otherwise dirt or moisture may enter the bore and cause
damage or corrosion.

(3)

Install the brake hose in the caliper inlet using a new copper gasket.

(e)

Installation:

Installation of the caliper and mounting parts (rubber bushings, sleeves, shoe and

lining assemblies, and bolts) is the same as for lining replacement except for the
following:

(1)

The brake hose must be connected to the steel brake line.

(2)

After overhaul or any time that the brake hose or line is disconnected, the
calipers must be bled. Use either the manual or pressure tank method.

(f)

Check Out:

(1)

Check brake pedal for sponginess or hard pedal.

(2)

Drive tractor slowly and make slow speed stops.

(3)

Check all brake fluid line fittings and caliper areas for fluid leakage.

(4)

Correct any discrepancies before returning tractor to normal service.

2.

Kelsey-Hayes Caliper

(a)

Removal:

(1)

Remove about two-thirds (2/3) of the total brake fluid capacity from the master
cylinder reservoir vhich serves the disc brakes. Do not drain the reservoirs
completely.

(2)

With vehicle raised evenly on a hoist or jack-stands, remove the rear wheels.

(3)

Locate brake line and wipe area aroung fitting at brake with a clean cloth to
remove excess dirt and grease.

(4)

Disconnect steel brake line from caliper. Plug brake line to prevent loss of
fluid.

(5)

Remove the caliper from the vehicle in the same manner as specified for shoe
and lining replacement.

(6)

Remove the shoe and lining assemblies and the rubber bushings in the same
manner as specified for shoe and lining replacement.

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                        p. 8

VI .

REAR WHEEL DISC BRAKES (SERIAL NO'S 0128 AND UP)

B.

CALIPER OVERHAUL

2.

Kelsey-Hayes Caliper

(b)

Disassembly:

(1)

Prepare a clean bench area.

(2)

Open bleed screw and drain brake fluid from caliper assembly.

(3)

Mount caliper assembly in a vise equipped with padded jaws. (Caution:
Excessive vise pressure will cause bore distortion and binding of piston.)

(4)

Remove piston from cylinder bore using compressed air. Use extreme care to
avoid damage to piston or bore. Allow dust boot to remain in caliper groove as
piston is withdrawn.

(5)

Remove caliper from vise and remove dust boot.

(6)

Using a small, pointed, wooden or plastic stick, work piston seal out of its
groove in piston bore. Discard old seal. Do not use a screw-driver or other
metal tool for this operation, because of possibility of scratching piston bore or
burring edges of seal groove.

(7)

Remove bleeder screw.

(c)

Cleaning and Inspection:

(1)

Clean all parts with brake fluid and wipe dry, using a clean, lint free cloth.
Using an air hose, blow out the drilled passages and bores.

(2)

Inspect cylinder bore for scoring, pitting or corrosion. A corroded or deeply
scored caliper should be replaced; however, light scores and stains may be
removed.

(3)

Polish any discolored or stained area with crocus cloth. Use finger pressure
rotating the crocus cloth in the cylinder bore; do not slide the cloth in and out
of the bore under pressure. Do not use any other form of abrasive or abrasive
cloth. Black stains on the bore walls are caused by the piston seals and will do
no harm.

(4)

Check each piston to see if it is pitted, scored or worn. If any of these
conditions exist, discard and replace the piston.

(5)

Check the clearance of the piston in the bore, using a feeler gauge. Clearance
should be .002" to .006". If clearance exceeds this specification, replace the
caliper assembly.