Description
Product Overview
The KYB MAG170 travel motor friction plate is a critical component of the wet multi-disc brake system in MAG-170VP series hydraulic travel motors, widely used in 20-35 ton class crawler excavators from Kobelco, Sumitomo, Kato, and CASE. This friction disc operates immersed in hydraulic oil within the motor housing, providing reliable parking and service braking for the machine track drive system.
The MAG170 is a shell-rotating, high-torque hydraulic piston motor combined with a planetary gear reducer, designed specifically for crawler excavator travel drive applications. The motor features a variable displacement swash plate (two-speed), hydraulically balanced pistons, dual counterbalance valves, shockless crossover relief valves, and a multi-disc wet brake system with negative brake actuation linked to the counterbalance valve.
Common applications include Kobelco SK200-8, SK210-9, SK230-6, SK250-8, SK260-8; Sumitomo SH200, SH240, SH210A5, SH240A5; and Kato HD700-7, HD1430-3 excavators. The MAG-170VP-3800 configuration delivers 37,300 N-m of maximum output torque at 57.8 MPa maximum operating pressure.
MAG170 Motor Technical Specifications
| Parameter | MAG-170VP-3800E |
|---|---|
| Displacement (High / Low Speed) | 43.2 / 170.0 cm³/rev |
| Maximum Output Torque | 37,300 N-m |
| Maximum Speed | 2,500 rpm |
| Speed Ratio | 1.5 to 2.0 : 1 |
| Maximum Flow | 270 L/min |
| Maximum Operating Pressure | 57.8 MPa |
| Maximum Brake Torque | 7,352 N-m |
| Weight | 420 kg |
| Application Class | 35-ton class excavators |
KYB MAG Series Model Range
| Model | Displacement (Hi/Lo) cm³/rev | Max Torque N-m | Max Speed rpm | Max Pressure MPa | Tonnage |
|---|---|---|---|---|---|
| MAG-12V | 12.5 / 31.0 | 1,176 | 4,000 | 20.6 | 1.5 ton |
| MAG-33V | 33.8 / 47.4 | 5,390 | 3,300 | 49.0 | 6.0 ton |
| MAG-44VP | 44.1 / 55.0 | 23,500 | 2,800 | 80 | 8.0 ton |
| MAG-85VP | 41.4 / 57.5 | 17,700 | 2,500 | 34.3 | 13-15 ton |
| MAG-170VP | 43.2 / 170.0 | 37,300 | 2,500 | 57.8 | 35 ton |
| MAG-230VP | 60.7 / 240.0 | 58,800 | 2,400 | 86.2 | 35+ ton |
Wet Multi-Disc Brake System
The MAG170 travel motor incorporates a multi-disc wet brake system with negative brake actuation linked to the dual counterbalance valve. This design ensures automatic brake engagement when the machine stops and automatic release when travel is initiated.
Brake System Features
| Feature | Description | Benefit |
|---|---|---|
| Wet disc design | Friction plates run immersed in hydraulic oil | Excellent cooling, corrosion protection, long service life |
| Negative brake | Spring-applied, hydraulically released | Failsafe – brakes engage automatically if hydraulic pressure is lost |
| Counterbalance valve linked | Brake release coordinated with travel pressure | Smooth start/stop, prevents brake drag during travel |
| Multi-disc configuration | Multiple friction and steel plates in alternating stack | High braking torque in compact package |
| Integrated design | Brake built into the motor housing | Protected from dirt, water, and debris |
How the Brake Works
- Parked / Braked (default state): Brake springs press the friction disc stack together, locking the motor output shaft and preventing track rotation. This is the “negative” or failsafe condition.
- Travel initiation: When the operator commands travel, hydraulic pressure builds in the counterbalance valve circuit. Once pressure reaches the brake release threshold, the brake piston compresses the springs and separates the friction disc stack, releasing the brake.
- Travel operation: The brake remains released as long as sufficient travel pressure is maintained. The dual counterbalance valve controls speed and prevents runaway on slopes.
- Stopping: When travel is stopped, hydraulic pressure decreases. The brake spring force overcomes hydraulic pressure and reapplies the brake, bringing the machine to a controlled stop and holding it in place.
The crossover relief valve provides shockless deceleration by absorbing inertia energy during braking, reducing mechanical shock to the drivetrain and improving operator comfort.
For additional technical background on heavy equipment hydraulic drivetrain systems, see our final drive system guide and center joint analysis.
Two-Speed Travel Motor Design
The MAG170 features a variable displacement swash plate that provides two-speed operation – high speed/low torque for travel and low speed/high torque for heavy push or steep grade conditions.
Speed Change Mechanism
The swash plate has three working surfaces (a, b, c) with two steel balls acting as pivot points for tilt switching:
- Low speed (high displacement): Pilot valve shifts to low speed position. The two-speed piston chamber connects to tank, and the swash plate is pushed to position “a” (maximum tilt angle). This provides maximum torque at reduced speed for heavy digging, climbing, or pushing.
- High speed (low displacement): Pilot valve shifts to high speed position. System pressure acts on the two-speed piston, pushing the swash plate toward the cylinder block to position “b” (minimum tilt angle). This provides higher travel speed for job site mobility.
The speed ratio is approximately 1.5 to 2.0:1, giving operators flexibility between fast travel and high torque modes depending on working conditions.
Internal Construction and Key Components
The MAG170 travel motor assembly includes several major subsystems:
| Subsystem | Components | Function |
|---|---|---|
| Hydraulic Motor Section | Cylinder block, pistons, swash plate, valve plate, shoe plate | Converts hydraulic energy to rotational mechanical energy |
| Two-Speed Mechanism | Two-speed piston, pilot valve, swash plate pivot balls | Switches between high and low displacement modes |
| Counterbalance Valves | Dual counterbalance valves, crossover relief valves | Controls travel speed, prevents runaway, absorbs braking shock |
| Wet Brake System | Friction discs, steel separator plates, brake piston, brake springs | Provides parking and service braking with negative actuation |
| Planetary Reducer | Ring gear, planet gears, sun gear, carrier | Reduces motor output speed while multiplying torque for track drive |
| Sealing System | Floating seal, O-rings, oil seals | Prevents dirt and water ingress; contains hydraulic oil |
| Bearing System | Heavy-duty tapered roller bearings | Supports radial and axial loads from track forces |
The shell-rotating design means the outer housing (ring gear) rotates while the central shaft remains stationary. This configuration provides excellent load distribution and structural simplicity for high reliability in heavy-duty excavator applications.
Compatible Excavator Models
Kobelco Excavators
- SK200-8, SK210LC-9, SK210-9, SK230-6, SK250-8, SK260-8 (20-30 ton class)
Sumitomo Excavators
- SH200, SH240, SH210A5, SH240A5 (20-25 ton class)
Kato Excavators
- HD700-7, HD1430-3
Other Brands
- CASE excavators with MAG170 travel motors
- Yanmar YB351 series
Note: Always verify compatibility by checking the travel motor model tag on your machine. Different excavator models and serial numbers may use different MAG170 configurations (such as MAG-170VP-3800E or MAG-170VP-3800G). Related Kobelco part numbers include friction plate 2415U154S5 and brake disk 2415U160F2. Kato references include 619-54041001.
Maintenance, Failure Modes, and Service
Recommended Maintenance Practices
- Keep it clean: Regularly clean the exterior of the travel motor to prevent dirt from entering through damaged seals or during service work.
- Use correct lubricant: Maintain proper hydraulic oil level and use the specified oil grade. Contaminated or degraded oil accelerates wear on all internal components.
- Monitor for leaks: Inspect for oil leaks regularly – external leaks indicate seal failure that can lead to internal contamination and component damage.
- Check fasteners: Periodically verify torque on mounting bolts and connections according to the service manual.
- Control oil temperature: Excessive operating temperature accelerates seal aging and degrades oil properties.
- Monitor case drain flow: Increased case drain flow is an early indicator of internal wear and volumetric efficiency loss.
- Address issues promptly: Investigate unusual noises, vibrations, or performance changes early to prevent catastrophic failure.
Common Failure Modes
| Failure Mode | Possible Causes | Symptoms |
|---|---|---|
| Brake disc wear | Frequent braking, contaminated oil, improper adjustment | Reduced braking torque, increased brake travel, brake drag |
| Friction material delamination | Severe wear, overheating, oil contamination | Brake noise, reduced braking performance, metal particles in oil |
| Brake piston seal failure | Age, heat, oil contamination | Brake does not release properly, brake drag, overheating |
| Spring fatigue | Cycling over time, heat | Reduced brake holding force, machine creeps on slopes |
| Valve plate / swash plate wear | Contaminated oil, lack of maintenance | Reduced travel speed, increased case drain flow, loss of power |
| Bearing failure | Heavy impact loads, poor lubrication | Noise, vibration, abnormal travel tracking |
| Seal / floating seal failure | Age, debris, misalignment | Oil leaks, water/dirt ingress, internal contamination |
Our replacement parts selection and maintenance guide provides additional systematic inspection procedures for excavator drivetrain components.
Friction Plate Replacement Guidelines
When to Replace
Replace travel motor brake friction plates when:
- Braking performance has noticeably decreased and the machine does not hold securely on slopes
- Brake drag is present, causing reduced travel speed and increased operating temperature
- Metal particles or friction material debris are found in the hydraulic oil
- Visual inspection during service shows friction material wear approaching limits
- The brake fails to release properly after replacement of other brake components
- Abnormal noise or vibration comes from the travel motor during braking
Inspection Checklist
| Component | Inspection Points | Replace If |
|---|---|---|
| Friction discs | Friction material thickness, surface condition, delamination, glazing | Worn below minimum, cracked, delaminated, or glazed |
| Steel separator plates | Flatness, scoring, heat discoloration, spline/tang condition | Scored, warped, heat-damaged, or splines worn |
| Brake piston | Seal condition, free movement, bore condition | Leaking seals, sticking piston, scored bore |
| Brake springs | Free length, tension, corrosion, cracks | Weakened, broken, or significantly fatigued |
| Seals and O-rings | Hardness, cracks, wear, leakage | Leaking, hardened, or damaged |
| Hydraulic oil | Cleanliness, contamination, level | Contaminated, degraded, or low level |
Best practice: Always replace the complete set of friction discs and steel plates together for proper brake function. Replace all seals and O-rings during brake service. Thoroughly clean all components before reassembly to prevent contamination of new friction material.
Compatibility Verification
Before ordering MAG170 travel motor friction plates, confirm the following:
- Motor model: Verify your travel motor is a MAG170 series (check the motor identification tag)
- Motor variant: Note the exact configuration (e.g., MAG-170VP-3800E, MAG-170VP-3800G)
- Machine model: Confirm your excavator model and serial number
- Side: Travel motors are often left/right specific – verify which side you need
- Brake type: Confirm multi-disc wet brake (standard on MAG-50 through MAG-230 series)
- OEM part numbers: Cross-reference with existing part numbers from your motor or equipment parts catalog
If you are uncertain about fitment, send us your motor model number, machine model, and serial number and we will help verify compatibility.
Ordering and Supply Information
| Parameter | Detail |
|---|---|
| Product | Wet brake friction plate for KYB MAG170 travel motor |
| Motor Compatibility | KYB MAG-170VP series travel motors |
| Machine Applications | Kobelco SK200-260, Sumitomo SH200-240, Kato HD700/1430, 20-35 ton excavators |
| Brake Type | Multi-disc wet brake (negative/spring-applied, hydraulic release) |
| Origin | Made in China |
| Warranty | 6 months |
| Minimum Order | 1 piece |
| Unit Price | Negotiable (contact for quotation) |
| Bulk Pricing | Available for orders of 50+ pieces |
| Lead Time | 1-5 business days |
| Monthly Capacity | 1,000 pieces |
| Packaging | Neutral export packaging / wooden cases |
| Payment Methods | T/T, PayPal, Western Union |
We supply a full range of travel motor components including friction discs, steel separator plates, brake pistons, springs, seal kits, and complete brake assemblies. We also offer repair parts for other MAG series motors (MAG-12V through MAG-230VP).
We ship worldwide from China with multiple logistics options: express courier (5-10 days to Southeast Asia), air freight (7-14 days), and sea freight (15-30 days). Both single-piece sample orders and bulk orders for parts dealerships, repair shops, and fleet operators are accepted.
Browse our complete construction equipment parts catalog or read our guide to evaluating reliable parts suppliers before purchasing.
