Taking 18 lawn tractor models apart and back together, from the 805 through the 1720, this 174-page Cub Cadet 1720 service manual PDF (OEM ID 772-3870) handles engine removal, steering, transaxle, hydrostatic drive and PTO work. Wiring diagrams split by serial number (107,999 and below, 108,000 and above) and by 1988, 1989 and 1990 builds trace the key switch and PTO switch circuits, while the theory pages explain engine cranking, engine run, PTO start and PTO run. Transaxle teardown goes down to the differential and Duo-Trak differential, and the hydrostatic transmission chapter handles removal, adjustments and the snow thrower attachment. Retighten spindle pulley nuts to 90 to 110 ft-lbs., and bring Duo-Trak through-bolts to 7-10 ft. lbs. Your job may be a brake adjustment or wheel alignment check. Bookmarks open the serial-number wiring diagram matching your tractor, so you can confirm which key switch or PTO switch version applies before ordering a replacement.
What's Inside This Cub Cadet 805–1720 Series Manual
| System | Pages | Key Topics |
|---|---|---|
| Engine Removal | 3-9 | Battery Removal, Hood and Grille Removal, Cable and Wire Disconnection |
| Installation | 10 | Governor Throttle Linkage, Choke Linkage, Carburetor |
| Electrical System Theory and Operation | 11 | Engine Cranking, Engine Run, PTO Start, PTO Run |
| Electrical Wiring Diagrams | 12-16 | Wiring Diagrams, Serial Number Variations, PTO Switch, Key Switch |
| Engine Removal and Installation | 17-21 | Engine Removal, Battery Removal, Installation Procedures |
| Chassis and Steering Assembly | 22-31 | Steering Assembly, Front Axle, Wheel Alignment, Turning Radius |
| Speed Transaxle Service | 32-47 | Transaxle Removal, Disassembly, Differential Assembly, Duo-Trak Differential |
| Brake | 48-49 | Removal and Disassembly, Adjusting the Brakes |
| Hydrostatic Transmission | 50-63 | Hydrostatic Transmission Removal, Hydrostatic Adjustments, Disassembly/Reassembly |
| Hydrostatic Transmissions | 64-92 | Disassembly and Assembly, Sundstrand, Repair Parts List |
| Service Menu (Model 717-3048) | 93-103 | Brake Adjustment, Trouble Shooting, Differential Assembly, Transaxle Reassembly |
| Hydrostatic Controls and Adjustment | 104-106 | Adjusting the Brakes, Drive Belt Replacement |
| Mower and Snow Thrower | 107-156 | Mowing Deck, Lubrication Guide, Snow Thrower Attachment, Skid Shoe Adjustment |
| PTO Troubleshooting and Clutches | 157-166 | PTO Troubleshooting, VX Series Clutches, Mechanical PTO, Electrical Diagrams |
| Special Torques | 167-174 | Inch Nuts, Bolts, Jam Nuts, Hardened Surfaces |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Spindle pulley nut torque | 90 to 110 ft-lbs. | p. 110 |
| Cap screw torque (5-speed transaxle cover) | 90-100 inch pounds | p. 42 |
| Brake lever top nut torque | 100 in. lbs. | p. 42 |
| Differential hex head bolt torque | 7 ft. lbs. | p. 45 |
| Duo-Trak differential through-bolt torque | 7-10 ft. lbs. | p. 46 |
| Mower blade nut torque | 50 to 60 ft-lbs. | p. 110 |
| Transaxle housing bolt torque | 80-120 Inch/LBS. | p. 103 |
| Standard torque for 1/4" bolt (Type 5) | 9-10 ft-lbs. | p. 167 |
| Standard torque for 3/8" bolt (Type 8, all other applications) | 45-50 ft-lbs. | p. 167 |
| Standard torque for 1/2" bolt (Type 5) | 80-90 ft-lbs. | p. 167 |
Cub Cadet 805–1720 Series Common Problems This Manual Covers
Cub Cadet 805 through 1720 lawn tractor engine will not crank with key in start position
Verify the four start requirements on page 11: operator in seat, PTO switch off, transmission in neutral, key turned to start. Then check the circuit from the battery through the fuse and ammeter to key switch terminals B and S, the neutral indicator switch, PTO switch terminal 1 and the solenoid S terminal. Disconnect the battery cables, negative first, before repairing any wiring (page 171).
Manual Section: Engine Cranking p. 11Electric PTO clutch does not engage when PTO switch is moved to start position
Verify the operator is seated and the transmission lever sits in neutral or forward, never reverse, as page 11 requires. Check for battery voltage at PTO switch terminal 5, then move the switch to start and test terminals 3 and 4. No current at 3 or 4 means the P.T.O. switch is bad and must be replaced (page 158). Disconnect the battery cables, negative first, before swapping it (page 171).
Manual Section: P.T.O. Trouble Shooting p. 158Steering assembly showing worn nylon bearing, worn bushings, broken gear teeth or bent shafts
Clean all steering parts in solvent and dry them, then inspect the nylon bearing and bushings for wear and check for broken teeth, bent shafts and stripped threads (page 27 for pre-1988 units, page 28 for 1988 and 1989). Replace damaged parts, grease the gears, bearings and shaft with Cub Cadet multi-purpose grease, and install with the wheels straight ahead and the pinion centered.
Manual Section: Steering Assembly Inspection and Repair p. 27Front axle play at pivot bar adjustment bolts with front wheels out of toe-in
Check for play between the front axle and both pivot bar adjustment bolts every 50 hours, as the caution on page 31 requires. Loosen the jam nut 3 to 4 turns, turn the bolt counterclockwise until it hits the axle, tighten the jam nut, and repeat on the other bolt. Measure toe-in at approximately 1/8 inch, then be sure all parts are tightened.
Manual Section: Front Axle Inspection and Repair p. 31Hydrostatic transmission not holding neutral with S/R lever linkage out of adjustment
Verify the engine is shut off first; page 95 warns never to attempt adjustments with the engine running. Check the control linkages to the directional control, the oil level in the reservoir on top of the hydro, that the freewheel button is fully released, and the input drive belt. Then perform the neutral adjustment and S/R lever linkage setup on page 54, leaving the cotter pin out until the procedure calls for it.
Manual Section: Hydrostatic Transmission Adjustments p. 54Mower deck out of level side to side, cutting the lawn unevenly
Verify the machine is off, the key removed and the parking brake locked before any adjustment, as the page 108 warning requires. Check tire inflation, then park on a hard level surface such as a garage floor. Level the deck until left and right blade front cutting-edge-to-ground measurements fall within 1/16 inch, per page 128, keeping hands clear of the sharp blades (page 119).
Manual Section: Brake System and Hydrostatic Transmission p. 108Frequently Asked Questions
Why does the PTO or mower deck fail to engage?
If the PTO fails to engage, first check for current at terminal five (5) of the P.T.O. switch using a red wire. If current is present, move the switch to the start position and verify current at terminals 3, 4, and 5. If current is missing at terminals 3 or 4, the P.T.O. switch is faulty and must be replaced. Also, ensure the air gap is set to .017 inches. p. 158
What are the battery replacement specifications for the Cub Cadet 805-1720 Series lawn tractor?
The manual specifies using battery part number 725-3061 for the models listed. When activating a new battery, fill each cell to the top of the plates with diluted sulfuric acid, allow it to sit for 30 minutes, and charge at the recommended rate until the specific gravity is at least 1.250. p. 173
What is the torque specification for the cap screws on the 5-speed transaxle cover of a Cub Cadet 805-1720 Series?
When reinstalling the cover on the transaxle case, the cap screws must be torqued to 90-100 inch pounds. p. 42
What is the correct torque for the differential carrier hex head bolts on a Cub Cadet 805-1720 Series lawn tractor?
When reassembling the differential carrier, the four hex head bolts must be torqued to 7 foot pounds. p. 45
What is the required torque for the transaxle housing bolts on a Cub Cadet 805-1720 Series lawn tractor?
The housing bolts for the transaxle must be retorqued to 80-120 inch/lbs. p. 95
What do I get after purchasing this Cub Cadet 805 manual?
Instant PDF download. You get the full 174-page searchable Service Manual immediately after payment. Open it on your laptop, tablet, or phone right in the shop.
Can I print just the pages I need from this Cub Cadet 805 manual?
Yes. Many buyers print one chapter at a time for their own shop and keep the rest on a tablet.
