PRINCIPLES OF OPERATION

Released Position (Fig. 11-24 )

In the released position, both sides of the vacuum piston are open to vacuum. This allows the vacuum piston to be held in the released position by the vacuum piston return spring. This is accomplished as follows.

In the released position, the air valve is seated on the. floating valve. Air, under atmospheric pressure, is shut off at the air valve. The floating valve is held away from the valve seat in the power piston. Vacuum, which is present at all times at the forward side of the vacuum piston, evacuates any existing air at the rear of the vacuum piston. This air is drawn through two small passages in the vacuum piston over the valve seat to the forward side of the vacuum piston.

The master cylinder piston push-rod, being attached to the vacuum piston assembly, is also held in the released position by the vacuum piston return spring. In the released position, the compensating port is open and fluid can flow in either direction between the master cylinder and the fluid reservoir. A slight pressure is maintained in the lines by the residual check valve.

As the pedal is depressed, the operating rod carries the air valve away from the floating valve. Further movement allows the floating valve to contact a seat in the vacuum piston, shutting off the vacuum to the rear of the vacuum piston. Air, under atmospheric pressure, can now enter through the air filter, travels past the air valve seat and through two passageways to the rear of the vacuum piston. With vacuum on the forward side and atmospheric pressure at the rear, a force is developed which moves the vacuum piston and the master cylinder piston push-rod in the apply direction.

The initial movement of the master cylinder piston in the apply direction closes the compensating port, sealing off the fluid reservoir from the master cylinder. Further movement of the master cylinder piston in the apply direction increases pressure in the master cylinder, forcing fluid past the residual check valve, through the lines and into the wheel cylinders to apply the brakes.

As the pressure in the master cylinder increases, the force on the end of the master cylinder piston causes the piston push-rod reaction plate to move away from its stop and press against the reaction levers. The levers in turn, pivot and press against the end of the air valve and operating rod assembly. This allows approximately 30% of the load to be transferred back through the reaction system to the brake pedal. This gives the driver brake feel.

 

Holding (Fig. 11 -25)

When the desired brake pedal pressure is obtained, the vacuum piston continues to move forward until the floating valve, which is still seated on the power piston, again seats on the air valve. The vacuum piston will remain stationary until pressure is applied or released at the brake pedal.

 

Releasing (Fig. 11-24 & 11-26)

As the pressure on the brake pedal is released, the air valve spring forces the air valve back until the snap ring contacts the vacuum piston. Further movement of the air valve unseats the floating valve from the vacuum piston. As the air valve seats on the floating valve, it shuts off the supply of air under atmospheric pressure. As the floating valve unseats from the vacuum piston, it opens the area to the rear of the vacuum piston to vacuum.

With vacuum on both sides of the vacuum piston, the vacuum piston return spring returns the vacuum piston together with the master cylinder piston push-rod into the released position. Brake fluid, under pressure, in the lines now flows back through the residual check valve and into the master cylinder reservoir.

DISASSEMBLY OF MORAINE POWER BRAKE (Figs. 11 -27 or 11 -28)

1. Deplete vacuum supply, then clean the outside of the power brake unit. Remove filler cap then empty brake fluid from master cylinder reservoir.
2. Clamp master cylinder in a vise with the operating rod up. Scribe an alignment mark on the top center of the front and rear housing.
3. Rotate the rear housing counterclockwise to separate the two housings. If the rear housing cannot be readily loosened, tap the rear housing lightly with a plastic hammer. (Fig. 11-29 or 11-30)
4. Remove the rear housing and vacuum piston assembly from the front housing.
5. All series except 30, 31 and 32, remove the rubber boot from the-rear housing. Remove the filter from inside the boot.
6. On 30, 31 and 32 series, remove the plastic boot from between the mounting brackets. Remove the retaining ring, clevis and locknut, then remove the filter from the operating rod.
7. Remove the vacuum piston assembly from the rear housing.
8. Remove the seal from the rear housing.
9. Remove the master cylinder to front housing attaching nuts and remove the master cylinder from the front housing.
10. Remove the front housing seal and the vacuum check valve and seal from the front housing.

DISASSEMBLY OF VACUUM PISTON (Fig. 11 -31)

1. Remove the lock ring from the vacuum piston by prying one of the ends out from under the large divided locking lug.
2. Remove the reaction retainer and push-rod, reaction plate, reaction levers and air valve spring. Also, remove the small reaction bumper and the air valve spring seat from the air valve.
3. Install Tool J-21524 in a vise. Position the vacuum piston assembly on Tool J-21524 so that the three lugs on the tool fit into the three notches in the vacuum piston. (Fig. 11-32)
4. Fold the diaphragm away from the support plate so that the hands can grip the steel support plate and rotate support plate counterclockwise until the support plate separates from the vacuum piston. (Fig. 11- 33)
5. Remove the diaphragm from the support plate.
6. Remove the silencer from the neck of the vacuum piston tube.
7. Position the vacuum piston in a vise padded with shop towels. Do not clamp vise on tube, Using Truarc pliers J-4880, remove the snap ring on the air valve. (Fig. 11-34)
8. Place the vacuum piston, tube down, in a press. Using a rod not exceeding 1/2" in diameter, press the air valve assembly from the vacuum piston. (Fig. 11-35)
9. Remove the limiter washer and air filter from the operating rod.
10. Remove the master cylinder push-rod from the reaction retainer. Remove the two "0" rings from the push rod.

CLEANING AND INSPECTION

1. Thoroughly wash all parts in alcohol, blow out all passages and air dry. Place parts on clean paper.
2. Inspect front and rear housings for scoring, pitting, dents or nicks. Small imperfections may be smoothed out with fine crocus cloth. Check housings for loose studs. Replace housings if they cannot be repaired.
3. Inspect vacuum piston diaphragm for deterioration or abrasions. Replace if damaged.
4. 30, 31, and 32 Series-Inspect air valve and operating rod assembly for scratches, nicks distortion or corrosion. C h e c k seat for smoothness. Operating rod should move freely in air valve but should not pull out. Replace assembly if worn or damaged.
5. Check vacuum piston support plate and reaction retainer for cracks, distortion damaged reaction lever seats or rough and uneven floating valve seat. Be sure all openings and passages are clean.
6. Check reaction levers for distortion. Replace if damaged.

ASSEMBLY OF MORAINE POWER BRAKES

For assembly of master cylinder refer to MASTER CYLINDER - ASSEMBLY.

Vacuum Piston

1. Install two new "0" rings, coated with lubricant on the push-rod.
2. Insert the push-rod so that the round end of the piston protrudes from the end of the tube of the reaction retainer.
3. Wipe a film of lubricant on the large OD of the floating valve and on the "0" ring on the air valve. On 30, 31 and 32 series, install a new "0" ring on the air valve.
4. Position a new air valve and operating rod assembly, air valve first, into the tube of the vacuum piston. On 30, 31 and 32 series, install the new floating control valve, so that the flat face of the valve seats against the air valve.
5. Position the floating valve retainer over the push-rod so that the flat side seats on the floating control valve.
6. Using Tool J-21601, press the floating valve until it seats in the vacuum piston. Line on tool will be flush with top of vacuum piston when floating valve is fully seated. (Fig. 11-36)
7. Position the operating rod limiter washer over the operating rod and down onto the floating valve.
8. Position the large ID air silencer over the neck of the vacuum piston. Install the small ID filter inside the neck of the vacuum piston over the operating rod.
9. Install Tool J - 21524 in a vise. Position vacuum piston on the tool so that the three lugs fit into the notches in the vacuum piston.
10. Install the vacuum piston diaphragm on the diaphragm support plate, on the side opposite the locking tangs. The inner lip of the diaphragm must fit over the edge of the center hole of the support plate.
11. Coat the entire inner lip of the diaphragm with lubricant.
12. Position the support plate and diaphragm over the tube of the vacuum piston. The flange of the diaphragm fits into the groove on the power piston. (Fig. 11-37)
13. Press down and rotate the support plate clockwise until the lugs on the power piston rest against the stops on the support plate.
14. Position the vacuum piston assembly in a padded vise, tube down. Do not clamp tube. Using Truarc pliers J-4880, install the snap ring into the groove in the air valve. (Fig. 11-34)
15. Install the air valve spring seat, dished side down, so it seats on the snap ring. Install the reaction bumper into the groove in the end of the air valve.
16. Install the air valve return spring so that the large end seats on the spring seat.
17. Install the three reaction levers in the slots in the vacuum piston.
18. Position the reaction plate, numbered side up, on top of the reaction levers. Press-down on the reaction plate until the reaction levers POP UP.
19. Position the reaction retainer and push-rod as shown in Fig. 11-38. While retaining pressure on the reaction retainer, install the lock ring as shown in Fig. 11-39.

ASSEMBLY OF POWER BRAKE UNIT

1. Coat the rear housing seal with lubricant and install in the rear housing with the large flange of the seal on the same side as the mounting studs.
2. Apply lubricant to the tube of the vacuum piston and insert the tube of the vacuum piston through the seal of the rear housing.
3. Coat the vacuum check valve seal with lubricant and install with the beveled side of the seal toward the inside of the front housing,
4. Install the vacuum check valve in the front housing.
5. Install the front housing seal and the master cylinder on the front housing. Torque mastercylinder attaching nuts 15 to 20 ft. lbs.
6. Clamp the master cylinder in a vise. Position the vacuum piston return spring over the hub of the front housing.
7. Position the rear housing over the front housing so that the scribe marks will be aligned when housings are assembled.
8. Depress and rotate rear housing clockwise until the front and rear housings are locked.
9. All series except 30, 31 and 32-Install the felt filler into the last fold of the rubber boot and install the boot over the operating rod.
10. 30, 31 and 32 Series-Install the felt filter over the operating rod and install the retaining key. Install the plastic boot over the operating rod so that the projections locate in the holes of the bracket. Install the locknut and clevis.
11. Check the push-rod adjustment as outlined under PUSH-ROD ADJUSTMENT.

PUSH ROD ADJUSTMENT (Fig. 11-40)

The push-rod adjustment is important because the compensating port in the master cylinder must be open when the vacuum piston is in the released position.

The push-rod adjustment can be checked as follows:

1. With the vacuum unit assembled and the master cylinder and front housing seal removed, position Gauge J-7723-01 over the push-rod with the legs of the gauge resting on the front housing of the vacuum cylinder.
2. The adjustment is correct if the guage just contacts the tip of the push-rod or if the tip of the push-rod is no more than .010" below the gauge.
3. If the push-rod is not within specifications, and the push-rod does not have an adjusting screw, a new service adjustable, push-rod must be installed and adjusted to specification. If the push-rod, being checked, has an adjusting screw, adjust the push-rod to specification.