Caterpillar 950G Loader Background
The Caterpillar 950G Series I wheel loader was introduced in the early 2000s as part of CAT’s mid-size loader lineup. Built for construction, quarry, and agricultural applications, the 950G features a 3116 diesel engine, a full powershift transmission, and advanced hydraulic systems. With an operating weight of approximately 38,000 pounds and a bucket capacity of 3.5 to 4.0 cubic yards, the 950G became a popular choice for fleet operators due to its balance of power, visibility, and serviceability.
Caterpillar, founded in 1925, has sold tens of thousands of 950-series loaders globally. The Series I variant introduced refinements in cab ergonomics and electronic diagnostics, including a monitor panel capable of displaying fault codes and system alerts.
Brake Pressure Warning and Accumulator Issues
One of the most common issues on high-hour 950G loaders is the persistent brake pressure warning light and audible alarm. This is often linked to a failing or undercharged brake accumulator. The accumulator stores hydraulic pressure to ensure consistent brake response, especially during engine-off conditions.
To test accumulator precharge:

• Start the engine and allow the brake pressure light to go off
  
• Shut down the engine and turn the key to ON
  
• Slowly depress the brake pedal repeatedly
  
• Count the number of full strokes before the warning light and alarm reappear
  

• Transmission selector switch and wiring
  
• Click Box settings near the headliner (used to adjust shift behavior)
  
• Diagnostic codes from the monitor panel
  

• Remove the valve cover
  
• Disconnect the injector harness
  
• Crank the engine while observing each injector
  
• Look for oil bubbling around injector bases
  

• Coolant temperature sensor failure
  
• Alternator charge delay
  
• Injector control faults
  

Overview of the Komatsu PC30
The Komatsu PC30 is a compact hydraulic excavator first introduced in the late 1980s as part of Komatsu’s mini excavator lineup. Its design focuses on maneuverability in tight urban or construction sites, featuring a 3-ton class operating weight, an adjustable boom swing, and a standard 18–22 kW diesel engine. Komatsu, founded in 1921 in Japan, has produced millions of excavators worldwide, with the PC30 series seeing significant adoption in Asia, Europe, and North America due to its reliability and ease of maintenance.

Common Electrical and Hydraulic Problems
Users often report that older PC30 models experience intermittent engine stalls, hydraulic sluggishness, and electrical faults. The key areas to inspect include:

• Battery and Wiring Harness: Over time, insulation can crack, leading to short circuits or open circuits. Ensure all connectors are clean, corrosion-free, and tightly secured.
  
• Control Levers and Micro Switches: The operator’s levers send electrical signals to the hydraulic control valves. Worn switches can cause erratic boom or bucket movement.
  
• Hydraulic Oil Contamination: Milky or discolored fluid can indicate water intrusion, reducing pump efficiency and causing cavitation in the main pump.
  
• Fuses and Relays: The PC30’s electrical system includes multiple 7–15 A fuses. A blown fuse can interrupt critical circuits such as the starter solenoid or auxiliary hydraulic functions.
  

• Visual Inspection: Check wiring for cracks, frays, or exposed conductors. Confirm battery terminals are tight and free of corrosion.
  
• Hydraulic Pressure Test: Use a gauge to verify pump output pressure. Typical PC30 main pump pressure ranges between 200–220 bar under load. Deviations may indicate worn pump gears or internal leaks.
  
• Switch Continuity Test: Using a multimeter, ensure micro switches on control levers register proper continuity when actuated. Replace switches that fail the test.
  
• Fuse and Relay Verification: Remove each fuse and relay individually to test with a multimeter for continuity and functionality.
  

• Wiring: Replace damaged harness sections and apply dielectric grease to connectors to prevent corrosion. Label wires before removal to avoid cross-connection.
  
• Hydraulic System: Flush and replace fluid every 2,000 hours or sooner if contamination is detected. Replace worn seals on pumps and cylinders.
  
• Switch Replacement: Always source OEM or high-quality aftermarket microswitches for control levers to maintain precise hydraulic response.
  
• Preventive Measures: Keep the machine sheltered from rain or excessive moisture to prevent electrical failures. Regularly inspect tracks, sprockets, and undercarriage to avoid cumulative wear that can affect machine stability.
  

• Avoid operating the excavator at maximum hydraulic load for extended periods, as this accelerates pump wear.
  
• Warm up the engine and hydraulic system before heavy digging to maintain consistent pressure and reduce component stress.
  
• When using auxiliary attachments, monitor electrical draw and hydraulic pressure to prevent overloads or circuit faults.
  
• Keep an accurate maintenance log, noting oil changes, filter replacements, and electrical repairs to ensure consistent service intervals.
  

Koehring 466E Excavator Background
The Koehring 466E is a legacy hydraulic excavator produced during the late 1970s and early 1980s by Koehring Company, a historic American manufacturer known for its heavy-duty construction equipment. Founded in 1886, Koehring was once a dominant name in crane and excavator production before merging into Northwest Engineering and eventually becoming part of Terex. The 466E model was designed for mid-range excavation tasks, featuring a robust mechanical structure and a powerful diesel engine, typically in the 150–200 horsepower range.
With an operating weight exceeding 60,000 pounds, the 466E was built for durability and field serviceability. Its hydraulic system powered a multi-function boom, stick, and bucket assembly, with large-diameter pins and bushings at each pivot point. These machines were widely used in infrastructure development, mining, and municipal work across North America.
Rod End Bushing Wear and Measurement Challenges
One of the most common wear points on older excavators like the 466E is the bucket cylinder rod end bushing. This bushing serves as the interface between the hydraulic cylinder rod and the bucket linkage, allowing for rotational movement while absorbing shock loads. Over time, the bushing can wear out or disintegrate entirely, leaving the rod end unsupported and prone to misalignment.
In this case, the original bushing was completely worn away, and the operator was left with a rod end eye that had no clear internal diameter. The bucket pin, which passes through the bushing, was measured at 3.0 inches in diameter, but the outer diameter (OD) of the missing bushing was estimated to be between 4.5 and 5.0 inches.
Fabrication Strategy and Material Selection
When OEM parts are unavailable or undocumented, custom fabrication becomes necessary. To fabricate a replacement bushing:

• Measure the rod end bore precisely using calipers or bore gauges
  
• Confirm the pin diameter to ensure proper internal clearance
  
• Select a bushing material such as 4140 steel, bronze alloy, or hardened nylon depending on load and lubrication
  
• Machine the bushing with a press-fit OD and a clearance-fit ID (typically 0.005–0.010 inch over pin diameter)
  
• Include grease grooves or ports if the original design supported lubrication
  

• Ovality or distortion—if the bore is no longer round, the bushing may not seat properly
  
• Cracks or elongation—these may require welding and reboring
  
• Surface corrosion—clean thoroughly to ensure proper fit
  

• Grease pivot points every 8–10 operating hours
  
• Use high-pressure lithium-based grease for heavy-duty applications
  
• Inspect bushings quarterly for signs of wear or play
  
• Replace pins and bushings as a matched set when possible
  
• Avoid side loading the bucket during operation
  

Background on the 555A Dump Valve
The Ford 555A backhoe (Loader‑Backhoe model) includes a dump valve that’s actuated by an electric solenoid. This valve, when energized, dumps shuttle pressure to the transmission sump — effectively preventing forward/reverse drive.  On some machines, this setup is tied into micro‑switches mounted at the foot pedal and the loader “wobble” (bucket) stick. Those switches send 12 V to the solenoid circuit to trigger or disable the dump function.

What the Wiring Looks Like (Based on Field Experience)
From practical user troubleshooting:

• The dump‑valve circuit shares a 7.5‑amp fuse with the horn and RTD (Return‑To‑Dig) function.
  
• On the loader handle (wobble stick), there is a microswitch that should complete the circuit when pressed; in other words, pushing the switch sends +12 V to the dump‑valve solenoid. One person found their switch was “backwards” — it killed power when pressed instead of providing it.
  
• The green wire is commonly used for power supply to the common terminal of the switch; and a yellow wire often goes to the switch’s normally‑open (NO) contact.
  
• There was also a loose wire found by a user, hanging on the right side of the bucket frame, which became hot (12 V) with the key on and seems to connect to the same fused circuit.
  
• The dump‑valve solenoid itself resides on one of the spools in the loader valve assembly.
  

1. Bad or Miswired Microswitch
   • If the switch is wired backwards or fails internally, it won’t send the correct signal to the solenoid. One user corrected this by re‑wiring the switch: green to common, yellow to NO.
     
   • To test: Use a multimeter to check for +12 V at the switch when the key is on. Then press the switch and verify there is +12 V on the output wire (to the solenoid).
     
2. Fuse Location and Rating
   • The circuit uses a 7.5A fuse (same circuit as horn / RTD). If that fuse is blown or weak, the valve won’t activate.
     
   • Always check the fuse condition when diagnosing the dump‑valve solenoid wiring.
     
3. Unplug and Isolate the Solenoid
   • If the dump‑valve solenoid is getting power unexpectedly, unplug its connector and check if the “drive lost” issue resolves. Some users have reported intermittent drive loss tied to a dumped solenoid.
     
   • If unplugging solves the problem, the wiring or the switches (wobble stick / pedal) are likely at fault rather than the solenoid itself.
     
4. Worn or Missing Switch Hardware
   • One user discovered the wire to the limit switch (“RTD” or Return‑To‑Dig) on the loader frame had been ripped off.
     
   • If the limit switch is missing or damaged, repairing or replacing it is necessary to restore proper dump‑valve control.
     
5. Contaminated Transmission Hydraulic Fluid
   • Milky or cloudy fluid in the transmission (gears) or center housing may indicate water contamination, which can impair solenoid or valve performance.
     
   • It’s advised to change the fluid and filter, especially if water is suspected.
     

• Rewire the dump‑valve switches using the proven configuration: Green → common, Yellow → NO terminal.
  
• Replace the 7.5A fuse if there are signs of fatigue or corrosion.
  
• Install dielectric grease on electrical connectors to prevent corrosion.
  
• Regularly check the loader handle and foot‑pedal microswitches for mechanical wear or misalignment.
  
• Inspect the transmission fluid for water contamination — if present, flush and replace with the correct spec fluid.
  
• Label the wires during inspection so you can revert if needed, especially if the dump‑valve harness has been previously modified.
  

• On older 555A backhoes, wiring insulation can brittle or crack, leading to intermittent shorts or open circuits.
  
• Switches on the loader stick and foot pedal often carry wear over time, especially from vibration and repeated use.
  
• Previous owners or mechanics may have modified or removed parts of the dump‑valve circuit, making troubleshooting more difficult.
  
• Contaminated or degraded hydraulic fluid can impair valve performance — this is more likely in machines that haven’t had regular maintenance.
  

FMGRU 1035 RBI Crane Overview
The FMGRU 1035 RBI is a specialized mobile crane manufactured by FMGRU, an Italian company known for producing hydraulic lifting equipment tailored to industrial and construction applications. The 1035 RBI model, built between 2006 and 2008, features a telescopic boom, hydraulic outriggers, and an integrated control system housed within a shield panel. FMGRU cranes are widely used across Europe and parts of Eastern Europe, particularly in utility maintenance, rail infrastructure, and compact urban lifting operations.
The RBI designation typically refers to a rotating boom installation, allowing for 360-degree lifting capabilities. These cranes are often mounted on truck chassis or rail platforms and rely heavily on electronic control modules to manage boom extension, rotation, and load monitoring.
Importance of the Shield Panel Diagram
The shield panel—also referred to as the electrical control panel—is the nerve center of the crane’s operational logic. It contains relays, fuses, circuit breakers, and programmable logic controllers (PLCs) that govern:

• Boom extension and retraction
  
• Load moment indicators (LMI)
  
• Emergency stop functions
  
• Hydraulic valve actuation
  
• Safety interlocks and override systems
  

• Non-responsive boom controls despite hydraulic pressure
  
• Flickering or inactive display panels
  
• Intermittent power loss to the shield panel
  
• Fault codes with no reference documentation
  

• Corroded connectors due to moisture ingress
  
• Blown fuses hidden within sub-panels
  
• Faulty relays that fail under load
  
• Software glitches in the PLC requiring reset or reprogramming
  

• Contact FMGRU via their official support email
  
• Provide the crane’s serial number and year of manufacture
  
• Request both the electrical diagram and hydraulic schematic
  
• Ask for any software update logs or PLC programming guides
  

• Label all wires before disassembly to aid reinstallation
  
• Use a multimeter to verify voltage at each relay and fuse
  
• Replace corroded connectors with sealed, weatherproof terminals
  
• Document any modifications to the panel for future reference
  
• Consider installing a surge protector to prevent damage during power fluctuations
  

Background on the Kobelco SK135SR
The Kobelco SK135SR is a compact-to-mid excavator widely used in construction, landscaping, and urban work sites. Its hydraulic system uses two variable‑displacement pumps and a pilot‑operated control scheme, typical for its class.  Kobelco offers a “control pattern changer” as an optional feature on this model, meaning the joystick/directional control layout can be swapped.
Why Change the Control Pattern
Operators often prefer different control layouts depending on their background. Two common patterns are:

• ISO / “Cat” style: Right lever = boom + bucket, left lever = swing + stick.
  
• SAE / “Deere / JD” style: Right lever = stick + bucket, left lever = boom + swing.
  

1. Locate the pattern‑change switch: The SK135SR‑2 model supports a 4‑way pattern changer per the parts/option list.
   
2. Swap lines: According to a detailed post, to go from Deere to Cat style: rearrange hydraulic pilot lines—specifically:
   • Swap line 1 and line 4
     
   • Swap line 2 and line 3
     
   • In that user’s machine, line 1 was tan, line 2 was green, line 3 was green, and line 4 was blue.
     
3. Confirm the pattern: After the line swap, test the joysticks to make sure the functions now match Cat / ISO layout.
   

• Be sure to label or document old line routing before changing anything, in case you need to revert.
  
• Work with clean hydraulic fluid: when disconnecting pilot lines, you risk introducing air or contamination.
  
• After rewiring, bleed the pilot circuit to remove trapped air.
  
• Confirm that any software or display-based “mode” (if present) also matches the new physical control layout.
  

• The change is often considered a “user‑modification” rather than a factory default.
  
• Dealers may not regularly perform pattern swaps and therefore lack hands‑on experience.
  So, using community resources (like wiring diagrams shared by other users) can be very valuable.
  

• The SK135SR supports a manual control‑pattern swap using a 4‑way pattern changer.
  
• By swapping specific pilot lines (1↔4, 2↔3), you can convert between Deere-style and Cat-style control.
  
• After the change, testing and bleeding are essential to ensure smooth and correct operation.
  

Cummins 8.3 Engine Background
The Cummins 8.3L engine, also known as the C8.3 or 6CT8.3, is a straight-six diesel engine introduced in the late 1980s. It became a popular powerplant for medium-duty trucks, construction equipment, agricultural machinery, and buses due to its balance of torque, reliability, and serviceability. With a displacement of 8.3 liters and configurations ranging from 215 to 300 horsepower, the engine was widely adopted in both mechanical and electronic variants.
Cummins, founded in 1919, has built a reputation for producing durable engines with global parts support. The 8.3L engine was eventually succeeded by the ISC series, but it remains in service across North America in older fleets and specialty equipment.
Common Applications and Donor Vehicles
When sourcing a replacement 8.3L engine, especially for a boom truck, the most cost-effective approach is to look beyond traditional engine dealers. Several operators have successfully acquired engines from:

• Military surplus trucks, particularly the BMY M923 5-ton series
  
• School buses, which often retire with low engine hours
  
• Municipal auctions, where fire trucks and utility vehicles are decommissioned
  

• A complete BMY 5-ton truck with a Cummins 8.3L engine may cost $4,000–$5,000
  
• These trucks often have fewer than 20,000 miles
  
• The remaining chassis can be sold for parts or repurposed for off-road use
  

• Injection pump: Military versions may use a different model than commercial engines, requiring throttle linkage or governor adjustments
  
• Bellhousing: May differ between automatic and manual transmissions, but the original bellhousing from the failed engine can usually be reused
  
• Horsepower rating: Typically set at 230–237 hp, but can be increased with pump tuning for construction or RV use
  

• Government surplus auction platforms
  
• Local military surplus dealers
  
• School district fleet auctions
  
• Heavy truck salvage yards
  

• Ask for engine serial number and CPL (Control Parts List)
  
• Request maintenance records if available
  
• Verify compression and oil pressure before purchase
  
• Inspect for signs of coolant intrusion or turbo wear
  

Overview of Bobcat T450
The Bobcat T450 is a compact track loader introduced in the late 2000s as part of Bobcat’s T4 series. Designed for tight spaces, landscaping, and light-to-medium construction work, it features a vertical-lift boom, a 49-horsepower diesel engine, and rubber tracks that minimize ground disturbance. Bobcat, founded in 1947 in North Dakota, has sold hundreds of thousands of compact loaders worldwide, with the T450 becoming particularly popular in North America due to its combination of size, power, and maneuverability.
Common Wiring Problems
Owners of the T450 frequently encounter electrical issues affecting the loader’s functionality. Key problems include:

• Intermittent Power Loss: Sudden shutdowns or failure to start, often due to corroded or loose connectors.
  
• Auxiliary Circuit Malfunctions: Problems with attachments not receiving consistent power, typically linked to damaged wiring harnesses or worn insulation.
  
• Dashboard Indicator Errors: Fault codes appear or gauges read incorrectly due to voltage drops or sensor connection issues.
  
• Starter Solenoid Wiring: Loose or frayed wires near the starter solenoid can prevent engine cranking.
  

• Visually inspect all wiring harnesses for frays, cracks, or pinched wires.
  
• Test battery voltage and confirm proper grounding points; the T450 relies heavily on a stable 12-volt system.
  
• Use a multimeter to measure continuity across critical circuits, including the starter, ignition switch, and auxiliary outputs.
  
• Check fuses and relays for corrosion or signs of overheating.
  
• Confirm connectors are fully seated, especially in high-vibration areas near the engine and lift arms.
  

• Replace damaged wires with equal-gauge, high-temperature, automotive-grade wire.
  
• Use dielectric grease on connectors to prevent future corrosion.
  
• Secure harnesses away from sharp edges and moving parts with clamps or cable ties.
  
• Consider upgrading older fuse blocks with new units if corrosion is extensive.
  
• For persistent dashboard errors, inspect sensor wiring and replace any worn components.
  

• Conducting regular under-hood inspections every 100 operating hours.
  
• Cleaning connectors and terminals annually to remove dust and moisture.
  
• Avoiding excessive moisture exposure and washing equipment carefully, keeping electrical connections dry.
  
• Labeling harnesses during maintenance to simplify troubleshooting.
  

Komatsu D45 Dozer Background
The Komatsu D45 crawler dozer was part of Komatsu’s mid-size earthmoving lineup during the late 1970s and early 1980s. Known for its mechanical simplicity and rugged undercarriage, the D45 was widely used in forestry, grading, and small-scale mining. Komatsu, founded in 1921 in Japan, became a global leader in construction equipment by the 1980s, with the D-series dozers contributing to its reputation for reliability and durability.
The D45 typically featured a naturally aspirated or turbocharged diesel engine, mechanical transmission, and a robust track frame. While not as electronically advanced as modern machines, its mechanical systems were serviceable and resilient—making it a favorite among independent operators and rural contractors.
Incident Overview and Initial Symptoms
In this case, the D45 had recently undergone undercarriage refurbishment, including new rollers and rebuilt tracks. The engine was reported to start easily and run smoothly, with no oil consumption—until the turbocharger catastrophically failed. A fragment from the turbo’s compressor wheel entered the intake manifold before the engine could be shut down.
Following the incident:

• The engine began to bind when cranked
  
• Oil was found exiting an injector port
  
• A deep knocking sound was heard during turnover
  
• A mechanic suspected internal damage reaching the crankshaft
  

• Dent or puncture the piston crown
  
• Bend intake or exhaust valves
  
• Damage cylinder liners
  
• Cause hydraulic lock if oil is forced into the cylinder
  

• Visual inspection of piston crowns and valve faces
  
• Detection of bent rods or cracked liners
  
• Assessment of head surface integrity and valve seat damage
  

• Searching salvage yards specializing in Komatsu equipment
  
• Checking with overseas suppliers in regions where older Komatsu machines are still active
  
• Considering engine swaps with compatible models from the same era
  

• Remove the cylinder head and inspect all combustion chambers
  
• Check piston travel and rod alignment manually
  
• Drain and inspect engine oil for metal shavings
  
• Evaluate turbocharger remnants and intake tract for additional debris
  
• Consult with a machinist before attempting any weld repairs
  

What Are 4N Grouser Bars
4N Corporation is a well-known manufacturer of grouser bars, which are metal bars welded or bolted onto the track shoes (or "track links") of crawler‑type machines (dozers, excavators, etc.). These bars help restore or build up the “grousers”—the raised bars that dig into the ground, giving better traction and extending the life of worn track shoes.
Popular Sizes (Sections) Offered by 4N
4N produces multiple “sections” (sizes/shapes) of these bars, each suited for different machine sizes:

• Section 820: Smallest size — good for compact machines or very small track shoes. (~ 25.4 mm length, 15.9 mm wide)
  
• Section 840: Very common — widely used on smaller track dozers (e.g., Cat D5/D6). (~ 35.1 mm × 19.1 mm)
  
• Section 850: Taller bar, commonly used for mid-size dozers like D6 / D7.
  
• Section 870: Larger still — typically for big dozers like D8 / D9.
  
• Section 890: Very wide cross-section; available in both regular and heat-treated versions for extreme use or older, large machines.
  

• Cost Savings: According to 4N, welding grouser bars to worn shoes is often much cheaper than replacing entire track shoes.
  
• Extended Machine Life: By “re-grousering” worn shoes, you can significantly increase a machine’s undercarriage life, which is often one of the biggest maintenance costs.
  
• Reduced Downtime: Using replaceable bars means less time in the shop — instead of waiting for full track‑shoe replacements, you can restore grip relatively quickly.
  

• Some mechanics raise a concern: do not weld the bars taller than the original grouser height, because building it up too high can stress other undercarriage components.
  
• One user mentioned using an alternative brand ("Dura‑Tuff") on a D8H dozer because the economics worked better than full shoe replacement.
  
• Another mechanic noted he’s never personally seen a weld-on grouser solution on his machines, preferring other repair options.
  

• Heat-treated bars are harder and more wear-resistant, ideal for harsher environments.
  
• Standard bars are suitable for less aggressive use or when cost is a key concern.
  

• 4N Section 820 Grouser Bar: Smaller bar for compact or mini machines.
  
• 4N Section 840 Grouser Bar: One of the most widely used bar sizes for mid‑sized dozers.
  
• 4N Section 850 Grouser Bar (1B): Taller bar for larger track shoes.
  
• Caterpillar 20″ Shoe Grouser Bar 6Y6291: OEM-style grouser bar used on certain Cat machines.
  

• Match the section of the bar to your machine’s track shoe size and type.
  
• When welding on bars, follow 4N’s recommended welding specs (preheat, weld type, etc.) to avoid damaging the track shoes.
  
• Check after welding: confirm that the new grouser height is not excessively above the original.
  
• Grease or inspect the undercarriage regularly to ensure the added bars are not causing abnormal wear or stress.