TECBRAKE T680B (01) PDF Document

The following special tools are required for installation:

1. Crowfoot wrench- 9/16″
2. Crowfoot wrench- 5/8″
3. Feeler gauge- 0.080 (2.03 mm)
4. Feeler gauge- 0.085 (2.16 mm)

The recommended torque values for the TECBRAKE T680B engine brakes on E7 engines are:

Thoroughly clean the engine before beginning installation. Remove all engine components necessary to permit access to cylinder heads. Remove valve covers. Loosen intake and exhaust rocker lever adjusting screws.

Make sure that there is a minimum of 0.025″ clearance between the top of the valve spring retainers and the underside of the yoke.

The torque for the three rocker bracket hold down bolts on an E7 (680B) engine is 40 lbft (54 N*m), to be tightened in two steps starting at the center.

The required valve clearances are:

Intake valve lash – 0.016″

Exhaust valve lash – 0.024″

Tighten the adjusting screw lock nut to 26 lbft (32 N*m).

The slave piston lash should be set to 0.080″ for 1991 & on models with S.N. 1B0001 & higher.

The slave piston lash should be set to 0.080″ for 1990 models with S.N. listed in the Chart below.

The slave piston lash should be set to 0.085″ for all other 1990 not listed & pre 1990 models.

The housing marked “FRONT” must be installed over cylinders 1, 2 and 3. The housing marked “REAR” must be installed over cylinder 4, 5, and 6. Position housing so that the oil supply bore is located over the oil supply screw. Push the housing down so that is flat against the rocker shaft bracket.

Starting in the center, tighten the brake housing mounting capscrews to 20 lbft (27 N.m), then re-torque to 45 lbft (61N*m) for the T680B (E7).

Check for interference between rocker arm and engine brake slave piston on all cylinders. If binding occurs, reposition housings.

The valve lash must be set while the engine is cold. Do not start the engine before setting the lash. Unadjusted valves may have insufficient clearance between the valves and pistons. Engine damage could result. It is important that the valves be adjusted carefully to assure maximum engine brake performance.

The Master / Slave Piston Actuating Relationship Listed in Engine Firing order Sequence is:

1. Set engine brake slave piston lash using the adjusting screws located above the slave piston. Because the exhaust valve push tube acting on its master piston operates a slave piston on a different cylinder, care must be taken to adjust the proper slave piston. The engine must be rotated to allow the exhaust valve to be fully closed prior to making the adjustment on each cylinder.
2. Figure 3-7 identifies which push tube operates which slave piston. The same procedure for locating TDC for each piston when setting valve lash may be used when setting the engine brake slave piston lash on each cylinder.
3. The slave piston lash should be set as follows:
   • 1991 & on- with S.N. 1B0001 & higher – 0.080″
   • 1990- only S.N. listed in Chart below – 0.080″
   • All other 1990 not listed & pre 1990 – 0.085″

Lock the adjusting screw in position by tightening the lock nut to 20 lbft (27 N*m) torque. The adjusting screw should be held in position while the lock nut is tightened using a crowfoot wrench. Recheck the lash.

For optimum performance and to prevent engine damage make sure that the correct lash is used and care is taken in adjustment procedure. Slave piston adjustment must be performed when with the engine not running. The engine temperature should be cold (below 140°F or 60°C) and stabilized.

Start the engine and let it idle for a short time.

Bleed air from the engine brake housing. Accelerate the engine to about 1800 RPM then release the throttle. Quickly depress the solenoid as shown to cause the brake to operate. This process should be repeated 5-6 times on each brake assembly in order to fill the housings with lube oil. When all of the air has been removed the brake should operate immediately when the solenoid is depressed.

Adjust the clutch switch so that the actuator arm is deflected from 1″ to 1.5″ (25 mm to 38 mm) when the clutch is in the up (clutch engaged) position.

Check the switch by depressing the clutch. The switch should “click” to an open electrical position as soon as the free play in the clutch is taken up. When the clutch is released, the switch should “click” to a closed electrical position.

The foot switch should be mounted on the cab floor to the left of the clutch pedal and should be located so that it can be conveniently operated with the drivers left foot.

The diode on the fuel pump switch is wired for a negative ground electrical system. If the vehicle uses a positive ground system, the diode must be removed and reversed.

Tighten the screws to 55 lbin (6N.m) when attaching the fuel pump switch assembly to the rear of the pump.

Adjust the switch to activate when the throttle lever is in the idle position. Loosen the screws holding the switch to the bracket, allowing the switch to slide back and forth on the bracket. Make sure the throttle is in the idle position when making the adjustment. Re-tighten the screws.

Tighten to 100 lbin (11N*m) torque when attaching the fuel pump switch and mounting bracket to the fuel pump using the screws just removed.

Adjust the switch to contact the actuating arm when the throttle is in idle position. Tighten switch screws. Switch should “click” as soon as throttle lever is moved off of idle position.

Adjust the switch to activate when the throttle lever is in the idle position. Loosen the screws holding the switch to the bracket, allowing the switch to slide back and forth on the bracket. Make sure the throttle is in the idle position when making the adjustment. Re-tighten the screws.

Install the solenoid harness by connecting one end to the solenoid valve and the other to the inside of the terminal in the spacer assembly.

Check system to determine if voltage is present at terminals in engine brake spacer assembly. Voltage should be present when engine is not running, with ignition on, clutch disengaged, throttle in idle position, and all dash switches in the “on” position.

Dry solenoid with low air pressure.

Clean solenoid bore in brake with solvent and wipe dry with paper towel. Be careful not to leave any lint or residue in bore that may contaminate brake hydraulic components.

Tighten solenoid valve to 5 lbft (7 N*m) torque.

When removing the control valve covers wear eye protection. Control valve covers are under load from control valve springs. Care must be used when removing covers to avoid personal injury.

Push on the check valve ball with a small wire through the hole in the bottom of the control valve to make sure that there is spring tension on the ball. The ball should lift freely with a small amount of force and return quickly to the seat when the force is removed. Replace the control valve if it is defective.

Wear eye protection and use proper tools when removing slave pistons. Slave piston springs are highly compressed and can cause serious personal injury.

Check adjusting screw to be sure plunger is free to move in both directions when light force is applied. Internal spring force must hold the plunger in an extended position. Do not disassemble the adjusting screw. Replace screw assembly if defective.

Check master piston outside diameter ground surface for nicks or burrs. Piston must slide in bore without binding. Replace if binding occurs. Check top surface of piston. Replace piston if there are cracks or pitting.

Install the engine brake On-Off switch and Hi-low switch in a convenient location in the dash.

Using cab harness (TJ018132), connect the green wire to a ground stud located behind the dash. Cut the gray wire to length and attach connector and wire you just cutted off, using the butt connector provided. Re-attach the connector to terminal #87 on the relay base. Connect the grey wire to the Hi-Low switch. The two black wires in the harness are not used.

At the rear of the fuel pump, locate Mack wire coded 22-D-0.8. Cut off the connector. Using the TecBrake engine-to-cab wiring harness (TJ018130), splice the blue wire to the wire coded 22-D-0.8.

Run the yellow wire located in the engine-to-cab wiring harness (TJ018130) to the High-Low switch. Connect the wire to the switch then use the cable ties to secure the wiring in position.

Same as Step 1 of CH chassis installation (Install the engine brake On-Off switch and Hi-low switch in a convenient location in the dash).

Same as step 2 of CH chassis installation, plus, also remove the short jumper wire from the two wires that connect to the On-Off switch.

On the outboard dash panel junction box, locate terminal #12 and confirm that the original Mack wire coded 3-H-16 is connected to it. Crimp a terminal to the Blue wire in the engine-to-cab harness (TJ018130) and clamp it to terminal No. 12 of the outboard dash panel junction box.