Model MA TOW Tractor. Manual - part 21

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                       p. 9

(d)

Reassembly:

(1)

Dip new piston seal in clean brake fluid and install in groove in bore. Seal
should be positioned at one area in groove and gently worked around the
groove, using clean fingers, until properly seated. NEVER USE AN OLD
PISTON SEAL. (Be sure seal is not twisted or rolled.)

(2)

Coat new piston boot with clean brake fluid. Install in caliper by working into
outer groove, using fingers only. (Boot will seem larger than diameter of
groove, but will snap into place when properly positioned in groove.) Using
forefinger, slide around inside of boot to be sure it is seated, or correctly
installed.

(3)

Plug high pressure inlet to caliper and bleeder screw hole, then coat piston
with a generous amount of lubricant (as specified above) . With fingers
spreading boot, work piston into boot and press down on piston. (The
entrapped air below piston will force boot around piston and into groove as
piston is depressed.) Remove plug, then carefully push piston down the bore
until bottomed. CAUTION: Force must be applied uniformly to avoid cocking.

(4)

Install new bushings, see specific section.

(5)

Install bleeder screw.

(e)

Installation:

 (1)

Examine shoe and lining assemblies for wear damage, or fluid contamination.
If condition is found satisfactory they may be reused. If not, install new shoe
and linings in both brake systems. If old linings are reused, be sure they are
installed in their original positions.

(2)

Install inboard and outboard shoe and lining assemblies in support and caliper.

(3)

Remove plug from brake line and install into caliper. Tighten securely.

(4)

Be sure that bleeder screw is open, then reconnect the brake line at the caliper
housing. Bleed the system (see specific section). Allow the caliper to fill with
brake fluid. After all air bubbles have escaped, and fluid runs clear from
bleeder, close the bleeder screw. Replenish the brake fluid in the master
cylinder.

(5)

"Pump" the brake pedal several times to actuate the piston seals and position
the shoe and lining assemblies.

(6)

Check for fluid leakage at all connections under maximum pedal pressures.
Refill master cylinder reservoir as necessary.

(7)

Install rear wheels and tighten lugnuts to one hundred (100) foot-pounds (135
N-m).

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                        p. 10

VI .

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

B.

CALIPER OVERHAUL

2.

Kelsey-Hayes Caliper

(e)

Installation:

(8)

Remove jackstands.

(9)

Road test the vehicle and make several slow speed stops to wear off any
foreign material on the brakes and to seat the shoes. The tractor may pull to
one side on the first application after service. This is normal until shoes are
seated.

(f)

Check Out:

(1)

Check brake pedal for sponginess or hard pedal.

(2)

Drive tractor slowly and make several 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.

C.

ROTOR

1.

Renewal:

(a)

Chock the front tires and jack the rear wheels off the ground.

(b)

Remove the lugnuts which secure the wheel to the drive axle hub and remove the

wheel.

(c)

Reinstall lugnuts so as to hold the hub against the rotor.

(d)

Remove the cotter pin from the hub nut and remove the nut and washer.

(e)

Remove caliper assemblies. See specific section.

(f)

Slide the wheel hub and rotor off the axle

2.

Disassembly:

Remove lugnuts thereby separating rotor from hub.

3.

Cleaning:

WARNING: NO SMOKING, FIRE OR OPEN FLAME IS PERMITTED IN AREAS WHERE

ALCOHOL IS BEING USED. AVOID INHALATION OF FUMES.

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                       p. 11

(a)

Clean rotor with alcohol.

(b)

Use lint-free cloth to dry.

4.

Inspection:

(a)

Inspect weldments for evidence of corrosion or cracking. Replace if cracked or

severely corroded.

(b)

Inspect rubbing surfaces for evidence of corrosion, pitted or scratches. Replace if

scratched, corroded or pitted.

(c)

Check the thickness and out of plane limits of the rotor. The minimum limit should

be .885 inches.

5.

Reassembly:

Using lug nuts, fasten hub and rotor together.

6 .

Installation:

(a)

Slide the wheel hub and rotor onto the axle.

(b)

Replace caliper assemblies. See specific section.

(c)

Replace axle nut and washer and replace cotter pin.

(d)

Replace wheel and secure with lugnuts.

(e)

Lower rear wheels to the ground and unchock front wheels.

7.

Check-Out

(a)

Check brake pedal for sponginess or hard pedal.

(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.

D.

BLEEDING THE DISC BRAKE SYSTEM

1.

General:

(a)

If the caliper was removed for overhaul, or if the brake hose or steel line was

disconnected for any reason, it will be necessary to bleed all air from the calipers
and connecting lines.

Chapter 3: Overhaul

Dec. 1995                     Section 3-6                        p. 12

VI .

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

D.

BLEEDING THE DISC BRAKE SYSTEM

1.

General: (cont)

(b)

Prior to bleeding the system, it is important to check the master cylinder reservoir.

Use hydraulic fluid, DOT 3, Extra Heavy Duty Brake Fluid to bring the level up to
within one-eighth (1/8) inch of the top.

(c)

Brakes can be bled either manually or with pressure bleeding equipment.

CAUTION: FLUID WHICH IS DRAINED, FLUSHED OR BLED OUT OF A

TRACTOR’S BRAKE SYSTEM SHOULD BE DISCARDED. IT IS NOT SAFE FOR
REUSE FOR ANY PURPOSE.

2.

Manual Bleeding:

 (a)

Manual bleeding requires two men - one to pump the brake pedal and another to

operate the bleeder valves. Make sure that the master cylinder is full. After the
bleeder valve is opened, depress the brake pedal one full stroke, close bleeder
valve, then allow the pedal to return slowly to the released position. Allowing the
pedal to return too quickly may draw air into the system. Continue operating the
pedal in this manner until one cylinder or caliper is bled. Refill the master cylinder
and go on to the next cylinder or caliper.

CAUTION: IN ORDER TO INSURE THAT NO AIR CAN BE SUCKED BACK INTO

THE SYSTEM, THE BLEEDER VALVE MUST BE CLOSED AT THE END OF EACH
STROKE, BEFORE THE BRAKE PEDAL IS RELEASED.

(b)

Since it is desirable to bleed the longest line first, the normal sequence for manual

bleeding at the wheels is: Right Aft, Left Aft, Right Forward and Left Forward.

(c)

Check the fluid level in the reservoir frequently during the bleeding procedure.

3.

Pressure Bleeding:

 (a)

If he equipment is available, the pressure tank method of bleeding is faster, since

the master cylinder does not have to be refilled several times. Pressure bleeding
equipment must be of the diaphragm type. That is, it must have a rubber diaphragm
between the air supply and the brake fluid to prevent air, moisture, oil and other
contaminants from entering the hydraulic system. Install the special bleeding adapter
to the master cylinder. Make sure that the pressure tank is at least 1/3 full of fluid.
Position the tank so that its hose will easily reach the adapter on master cylinder of
the vehicle being serviced, then make the air pressure connection to tank (20 to 25
psi) . Open the tank valve to bleed all air out of the hose before connecting it to the
adapter. After making this connection, open the valve when ready to begin bleeding.

CAUTION: DO NOT LIFT, MOVE OR SHAKE THE TANK AFTER AIR PRESSURE

IS APPLIED. THIS MAY CAUSE AIR TO BECOME TRAPPED IN THE FLUID.