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This 146-page New Holland 790 Harvester Service Manual (OEM #40079011) walks you through every drivetrain and electrical system on the Model 790, from the telescoping PTO down to the Metalert II sensor harness. Inside you get full wiring diagrams for the control box and Metalert relay panel, a dedicated troubleshooting section for spout, deflector, and reversing gearbox faults, plus step-by-step teardown procedures for the cutterhead, sharpener, and blower assemblies. Set your blower drive belt to a 6½-inch spring length, and confirm the reversing gearbox belt deflects exactly 1 inch under a 60-lb pull before you button it back up. No more chasing a false Metalert detect with guesswork and a test light. This PDF carries bookmarked, searchable sections, so you can jump straight from the shear bar adjustment to the wiring diagram without flipping through 146 pages by hand.
What's Inside This New Holland 790 Manual
| System | Pages | Key Topics |
|---|---|---|
| Safety | 4-6 | Personal Safety, Machine Safety, Important |
| Telescoping PTO | 7-10 | Introduction, Removal, Disassembly, Inspection, Assembly, PTO Phasing |
| Main Drive Gearbox | 11-16 | Output Shaft, Input Shaft, Gearbox Housing Code |
| Electric Clutch Drive | 17-22 | Introduction, Changing Drive Belts, Adjusting the Armature Air Gap, Disassembly, Inspection, Assembly |
| Reversing Gearbox | 23-30 | Shifting Assembly, Drive Sheave, Feed Roll Drive Chain, Bearing Mounting Hardware, Input Shaft, Output Shaft, Idler Shaft |
| Feed Rolls | 31-40 | Introduction, Top Feed Rolls, Lower Front Feed Roll, Smooth Roll, Parts Inspection, Installation |
| Cutterhead | 41-50 | Specifications, Installing and Adjusting Cutterhead Knives, Number of Knives, Replacing the Cutterhead Assembly, Knife Inspection, Installation |
| Sharpener | 51-56 | Sharpening the Cutterhead Knives, Adjusting the Sharpening Stone, Adjusting the Stone Carrier, Sharpener Shaft, Advancing the Stone |
| Shear Bar and Scraper | 57-64 | Adjusting the Shear Bar, Replacing the Shear Bar, Inspection, Shear Bar Adjusting Mechanism, Smooth Roll Scraper |
| Blower | 65-70 | Replacing the Blower Band, Adjusting the Paddles, Replacing the Blower Belt, Blower Fan, Inspection, Assembly |
| Wheels and Axles | 71-72 | Specifications, Wheel Bearing Repair, Disassembly, Assembly |
| Hydraulic Components | 73-76 | Attachment Lift Cylinder, Hydraulic Swing Tongue Cylinder, Removal, Repair, Installation |
| Normal System Operation & Current Flow | 77-112 | Control Box Components, Circuit Breakers, Switches (Spout, Deflector, Feed Rolls), Metalert Ii Relay Panel, Sensor Assembly, Feed Roll Stopping System, Wiring Diagrams |
| General Electrical Troubleshooting | 113-120 | Spout Motor Troubleshooting, Deflector Motor Troubleshooting, Reversing Gearbox Troubleshooting, Electric Clutch Troubleshooting, Test Tools |
| Metalert Ii Test Set & Procedures | 121-125 | Metalert Ii Test Set, Test Box Functions, Signal Generator, Connecting Test Set, Voltage Check, Pull/drop Test, Sensitivity Test, Noise Test |
| Metalert Ii Troubleshooting Guide | 126-136 | Identifying Major Symptoms, Machine Resets Normally, Machine Does Not Reset Properly, Never Detects, False Detects, In-Field Test |
| Electrical Component Adjustments & Repair | 137-139 | Connector Replacement, Terminal Installation, Sensor Assembly Removal, Solder Terminal |
| System Adjustments & Testing | 140-142 | Sensor Shielded Cable Repair, Stop System Adjustment, Limit Switch Adjustment, Reversing Gearbox Actuator, Test Plug Testing |
| Electrical Labor Guide | 143-144 | Harness Connector Repair, Sensor Harness Repair, Solenoid Replacement, Electronic Panel Replacement, Gearbox Actuator Replacement |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Air blowguns pressure | 35 PSI (2.4 BAR) | p. 6 |
| blower drive belt tension | 6½" spring length | p. 16 |
| reversing gearbox drive belt tension | 1" deflection at 60 lbs. (267 N) pull | p. 16 |
| belt tension | 60 lbs.-65 lbs. is required to deflect the belts 1" halfway between the sheaves on the lower strand | p. 17 |
| hold-down springs stretched | 1/2" | p. 33 |
| 540 RPM PTO Driveline Max Input | 130 horsepower | p. 7 |
| 1000 RPM PTO Driveline Max Input | 150 horsepower | p. 7 |
| Main Drive Gearbox Input Shaft Rolling Torque | 12 in. lbs.-18 in. lbs. (1.36 N·m-2 N·m) | p. 14 |
| Main Drive Gearbox Output Shaft Rolling Torque | 3 in. lbs.-6 in. lbs. (4 N·m-7 N·m) | p. 14 |
| Electric Clutch Armature Air Gap | 0.020"-0.050" (0.5 mm-1.3 mm) | p. 18 |
| Shear Bar Support Clearance | 0.045"-0.065" | p. 58 |
| Blower Paddle Clearance to Band | 1/32"-1/16" (0.8 mm-1.6 mm) | p. 66 |
New Holland 790 Common Problems This Manual Covers
New Holland 790 harvester header plugs on the auger side with wet edge crops, feed rolls won't pull
Check the hold-down spring stretch on the top feed rolls; each spring should stretch 1/2" when engaged (page 33). Remove the roll cover and inspect for bent or worn teeth on the lower front and smooth rolls. Adjust spring tension or replace worn discs so the rolls bite into wet, matted crop instead of pushing it into the auger.
Manual Section: Feed Rolls p. 33Threshing leaves unthreshed kernels behind and grain loss climbs out the rear of the machine
Measure the shear bar clearance at both ends with a feeler gauge; it should read 0.045"-0.065" (page 60). Tighten or loosen the shear bar adjusting mechanism until both sides match spec, then rotate the cutterhead by hand to confirm even clearance. Uneven clearance lets whole stalks pass through unthreshed instead of being sheared and processed.
Manual Section: Shear Bar and Scraper p. 60Drive belts on the electric clutch twist or snap repeatedly during normal harvest operation
Check belt deflection at the center of the lower strand; 60 lbs.-65 lbs. of pull should deflect the belts 1" (page 17). Loosen the mounting bolts and slide the clutch assembly to reset tension, then retorque. Replace any belt showing cord separation or glazing; a loose belt twists under load long before it visibly wears through.
Manual Section: Electric Clutch Drive p. 17Machine drive gets jerky or loses power intermittently under heavy crop load
Check the reversing gearbox drive belt deflection; it should read 1" at 60 lbs. (267 N) pull at the center of the lower strand (page 16). Adjust the idler or mounting bolts to restore tension. Inspect the belt sheaves for wear grooves, since a worn sheave lets the belt ride low and slip before the tension spec even reads correctly.
Manual Section: Reversing Gearbox p. 16Telescoping PTO driveline vibrates hard or shudders violently under heavy crop load in wet corn
Verify driveline load matches the tractor's PTO speed rating; the 540 RPM driveline is rated for 130 horsepower maximum input (page 7). Running above that rating past rated RPM overloads the slip clutch and shears the nylon slide bushings inside the yoke. Inspect the slide collar and bushings for scoring, and confirm PTO phasing is correct before regreasing and reinstalling.
Manual Section: Telescoping PTO p. 7Frequently Asked Questions
How to reset New Holland 790 chopper after plugging?
After a detection event, the sensor assembly automatically resets in 1-2 seconds. However, the alarm horn will continue to sound, and the electric clutch and stop pawl solenoid will not re-engage until the feed rolls are reversed. To fully reset the system after plugging, the feed rolls must be reversed. p. 104
What are the torque specs for New Holland 790 cutterhead knives?
The knife bolt torque for the New Holland 790 cutterhead knives is 175 ft. lbs. to 200 ft. lbs. (237 N·m-270 N·m). It is important not to overtighten these bolts. The knife support block torque is 175 ft. lbs. (237 N·m). p. 41
How to adjust feed roll tension on New Holland 790?
To adjust the feed roll tension, ensure the hold-down springs (Figure 5-1) are stretched 1/2" when engaged. If necessary, adjust the bracket at C (Figure 5-1) to achieve the correct tension. p. 33
When to replace feed rolls on New Holland 790?
The smooth feed roll should be replaced if it is dented or shows deep scratches. For the left feed roll hub and shaft (stub shaft), it should be replaced if there is more than 0.015" (0.38 mm) runout in the shaft. p. 36
How quickly can I access this Ford New Holland 790 manual?
Instant PDF download. You get the full 146-page searchable Service Manual immediately after payment. Open it on your laptop, tablet, or phone right in the shop.
Am I able to print pages from this Ford New Holland 790?
Yes, print as many copies as you want, and there are no restrictions. Many mechanics print the section they need and bring it to the shop floor.
Does this Ford New Holland 790 manual include wiring?
Complete wiring diagrams are included, covering all electrical circuits, harness routing, and connector pinouts for the Ford New Holland 790.
