1988 Mack Truck R688T Owners Manual

The 1988 Mack R688T is a heavy-duty conventional truck featuring a robust chassis, powerful diesel engine, durable transmission system, and advanced cab comfort features. This manual provides comprehensive information on vehicle operation, maintenance procedures, troubleshooting, and technical specifications for the R688T model year 1988. Below are key sections covering safety, features, operation, maintenance, and technical data.

1. Vehicle Overview 2. Safety Information 3. Operating Instructions 4. Technical Specifications 5. Controls and Instruments 6. Maintenance Schedule 7. Engine Systems 8. Transmission & Drivetrain 9. Braking System 10. Electrical System 11. Troubleshooting Guide

Vehicle Overview

Key components: Heavy-duty steel frame, Mack ENDT 675 diesel engine, 5-speed manual transmission, air brake system, hydraulic steering, and premium cab interior.

Feature	Description
Engine	Mack ENDT 675 6-cylinder diesel
Transmission	5-speed manual with overdrive
Brakes	Full air brake system with ABS
Suspension	Heavy-duty leaf spring with shock absorbers
Cab	Steel construction with sleeper option
GVWR	Up to 66,000 lbs
Fuel Capacity	100 gallons standard
Wheelbase	Available in multiple configurations
Axles	Mack rear axles with various ratios
Electrical	12-volt system with alternator

Safety Information

Essential safety procedures for vehicle operation and maintenance.

Pre-trip inspection: Check tires, brakes, lights, and fluid levels daily.
Seat belt usage: Always wear seat belts when vehicle is in motion.
Load securement: Ensure cargo is properly secured and within weight limits.
Emergency equipment: Maintain fire extinguisher and warning devices.

WARNING! Always use wheel chocks when parked on inclines. Never operate with damaged safety equipment.

Operating Instructions

Proper vehicle operation procedures for optimal performance.

Starting procedure: Depress clutch, turn key to start position.
Gear shifting: Use clutch fully; match engine RPM to road speed.
Braking: Apply air brakes gradually; avoid sudden stops.
Parking: Apply parking brake; chock wheels on slopes.

CAUTION! Allow engine to warm up before operating under heavy load.

Technical Specifications

Engine Model: Mack ENDT 675
Displacement: 672 cubic inches
Horsepower: 237 hp @ 2100 RPM
Torque: 860 lb-ft @ 1200 RPM
Transmission: Mack TRTXL107 5-speed manual
Front Axle: 12,000 lb capacity
Rear Axle: 38,000 lb capacity
Brakes: Air-actuated S-cam
Fuel System: Direct injection
Electrical: 12V, 75 amp alternator

Controls and Instruments

Dashboard controls and instrument panel functions.

Main Controls: Ignition switch, gear shift, clutch, brake pedals, accelerator, parking brake.

Instruments: Speedometer, tachometer, air pressure gauges, fuel gauge, temperature gauge, oil pressure gauge, voltmeter. Warning lights: Low air pressure, check engine, low oil pressure, high temperature. Switches: Headlights, marker lights, hazard lights, wipers, heater/AC controls.

Maintenance Schedule

Routine maintenance intervals and procedures.

Daily: Check fluid levels, tire pressure, lights, brakes.
Weekly: Inspect belts, hoses, air system for leaks.
Monthly: Lubricate chassis, check battery condition.
Quarterly: Change engine oil and filters.
Annually: Complete system inspection and servicing.

Tip: Record all maintenance in log book for warranty compliance.

Engine Systems

Mack ENDT 675 diesel engine operation and maintenance.

Starting: Use glow plugs in cold weather; wait for wait light to extinguish.
Cooling system: Maintain proper coolant level; check for leaks.
Fuel system: Use clean diesel fuel; replace fuel filters regularly.
Air intake: Keep air filter clean; check for restrictions.
Exhaust: Inspect for leaks; ensure proper backpressure.
Lubrication: Use recommended engine oil; check pressure daily.

WARNING! Never operate with low oil pressure or high temperature warnings.

Transmission & Drivetrain

Manual transmission operation and drivetrain maintenance.

Transmission: Mack TRTXL107 5-speed with synchronized gears. Clutch: Single plate, dry disc with hydraulic actuation. Driveshaft: Heavy-duty with universal joints. Rear Axle: Mack bogie with power divider.

Braking System

Air brake system operation and maintenance procedures.

System includes air compressor, reservoirs, brake chambers, slack adjusters, and S-cam brakes. Daily air pressure build-up test required. Automatic moisture ejection system.

CAUTION! Never operate with air pressure below 60 PSI. Test brakes before each trip.

Electrical System

12-volt electrical system components and maintenance.

Battery: Two 12V batteries in parallel. Alternator: 75 amp output. Starter: Heavy-duty gear reduction. Lighting: Sealed beam headlights, LED marker lights. Fuses: Circuit breakers and fuses in dashboard panel.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, battery, or glow plug issue	Check fuel level, battery charge, glow plug operation
Loss of power	Fuel filter, air restriction	Replace fuel filter, check air intake
Brake problems	Air leaks, worn linings	Check for leaks, inspect brake linings
Electrical failure	Battery, alternator, connections	Test battery and alternator; clean connections
Transmission issues	Low fluid, clutch adjustment	Check fluid level, adjust clutch

Emergency: Carry basic tools and spare fuses. Know emergency procedures.

Service: Contact authorized Mack dealer for major repairs and warranty service.