10-22-2025, 12:00 AM
Yes, it is possible to access and inspect the C1 and C2 clutch packs on a John Deere 670A motor grader without removing the engine, but it requires careful disassembly of the transmission housing and a solid understanding of the power shift system layout.
JD 670A Background and Transmission Design
The John Deere 670A motor grader was introduced in the late 1970s and became a staple in municipal and contractor fleets due to its robust frame, 8-speed power shift transmission, and mechanical simplicity. It was powered by a John Deere 6414T turbocharged diesel engine and featured a full hydraulic blade control system. The 8-speed transmission used a planetary gearset with multiple clutch packs—C1 through C4—to engage different gear ranges.
The C1 and C2 clutch packs are responsible for the lower gear ranges (typically 1st through 6th), while C3 and C4 handle the higher gears. These clutch packs are hydraulically actuated and housed within the transmission case, which is bolted directly to the rear of the engine.
Terminology Note
To inspect or replace the C1 and C2 clutch packs, the following steps are typically required:
Field Experience and Practical Advice
In one case, a technician diagnosed a 670A with no movement in gears 1–6 but full function in 7th and 8th. The issue was traced to a failed C1 clutch pack. By removing the top cover and valve body, the technician accessed and replaced the clutch without disturbing the engine. The repair took two days and cost under $1,000 in parts.
Conclusion
Inspecting and servicing the C1 and C2 clutch packs on a JD 670A is entirely feasible without pulling the engine, provided the technician is familiar with the transmission layout and has the proper tools. With careful disassembly and attention to cleanliness, the repair can be completed efficiently in the field or shop. This approach saves time, reduces labor costs, and keeps a classic workhorse like the 670A in service for years to come.
JD 670A Background and Transmission Design
The John Deere 670A motor grader was introduced in the late 1970s and became a staple in municipal and contractor fleets due to its robust frame, 8-speed power shift transmission, and mechanical simplicity. It was powered by a John Deere 6414T turbocharged diesel engine and featured a full hydraulic blade control system. The 8-speed transmission used a planetary gearset with multiple clutch packs—C1 through C4—to engage different gear ranges.
The C1 and C2 clutch packs are responsible for the lower gear ranges (typically 1st through 6th), while C3 and C4 handle the higher gears. These clutch packs are hydraulically actuated and housed within the transmission case, which is bolted directly to the rear of the engine.
Terminology Note
- Power Shift Transmission: A type of transmission that allows gear changes under load without disengaging the drive.
- Clutch Pack (C1, C2, etc.): A set of friction and steel plates that engage to transmit torque through the planetary gearset.
- Transmission Input Shaft: The shaft that connects the engine flywheel to the transmission.
- Hydraulic Valve Body: The control unit that directs pressurized oil to the clutch packs.
- Transmission Pump: A gear-driven pump that supplies oil pressure to the clutch circuits.
To inspect or replace the C1 and C2 clutch packs, the following steps are typically required:
- Remove the cab floor panels and transmission top cover to access the valve body and clutch control ports.
- Drain the transmission oil and remove the filter housing.
- Disconnect the hydraulic lines and electrical connectors from the valve body.
- Unbolt and lift the valve body assembly to expose the clutch piston housings.
- Remove the retaining bolts and extract the C1 and C2 clutch drums using a slide hammer or puller.
- The engine does not need to be removed, but the transmission must be partially disassembled in place.
- The input shaft remains connected to the engine, so care must be taken not to damage the splines or seals.
- A clean work environment is essential to avoid contamination of the hydraulic system.
- Replacement of the clutch pack should include new friction discs, steel plates, piston seals, and snap rings.
- Always measure clutch pack clearance with feeler gauges and compare to factory specifications.
- Engine bogs down when shifting into gear, especially in 1st through 6th.
- Machine moves briefly then stalls under load.
- No movement in forward or reverse despite gear engagement.
- Hydraulic pressure drops when clutch is applied.
Field Experience and Practical Advice
In one case, a technician diagnosed a 670A with no movement in gears 1–6 but full function in 7th and 8th. The issue was traced to a failed C1 clutch pack. By removing the top cover and valve body, the technician accessed and replaced the clutch without disturbing the engine. The repair took two days and cost under $1,000 in parts.
Conclusion
Inspecting and servicing the C1 and C2 clutch packs on a JD 670A is entirely feasible without pulling the engine, provided the technician is familiar with the transmission layout and has the proper tools. With careful disassembly and attention to cleanliness, the repair can be completed efficiently in the field or shop. This approach saves time, reduces labor costs, and keeps a classic workhorse like the 670A in service for years to come.
