Caterpillarwork toolgrapple-log loading

Caterpillar GLL55

Maintenance schedule, common problems & OEM parts breakdown

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The Cat GLL55 is a passive, 360-degree rotating log/forestry grapple work tool, not a self-propelled machine. It has no engine, undercarriage, transmission, or onboard electronics; every grab, rotate, and open/close function runs off the hydraulic circuit of the carrier it's bolted to. The bare tool weighs 1297 kg (2,860 lb), spans 561 mm (22.1 in) wide, and opens from 127 mm (5 in) up to 1397 mm (55 in) at the jaws, with roughly 1153 N·m (850 ft-lb) of continuous hydraulic rotation torque. It sits mid-size in the three-tool GLL family, between the smaller GLL52 and larger GLL60, sharing the same width and rotation spec across all three sizes. It mounts to excavator-based forest machines in the 320-330 class (322, 324, 325, and 330 FM as an optimal fit; 320 FM as an acceptable fit) and to purpose-built log-loading forest machines (548 and 558 LL as an optimal fit; 538 and 568 LL as acceptable), and it can pair with forestry-equipped material handlers when fitted with the correct front linkage. GLL52, GLL55, and GLL60 share a common serial-prefix production block, and a later GLL55B generation has since carried the line forward.

Across the GLL family, the core hardware carries over unchanged from size to size: the same rotator design, cylinder valving, interlocking-leg geometry, and bolt-on Hardox wear strips just scale up with jaw opening, so GLL52, GLL55, and GLL60 share most service parts and procedures. The GLL55B update refreshed the line under a later production block, but no independently confirmed spec differences from the original GLL55 are documented, so it reads as a running revision rather than a re-engineered tool. In the used and parts market, the GLL55 stays relevant because its host carriers, mid-size excavator-based forest machines and log loaders, remain common in second-life logging fleets, and because parts commonality across the GLL sizes keeps pins, bushings, wear strips, seals, and rotator components easier to source than for a one-off, single-size grapple. Condition of the rotator bearing and leg pivots, more than cosmetic wear, is what actually drives resale value.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.

Caterpillar GLL55 specifications

Engine

Power sourceNo onboard engine. Passive rotating grapple attachment; grab, close, and rotate functions run off the host carrier's hydraulic circuit.

Weights

Operating weight1297 kg (2860 lb)
Ground pressureNot applicable — attachment does not contact the ground

Dimensions

Width561 mm (22.09 in)
Maximum jaw opening1397 mm (55.00 in)
Minimum jaw opening (closed on small stem)127 mm (5.00 in)
Overall height, jaws open1885 mm (74.21 in)
Overall height, jaws closed1958 mm (77.09 in)

Performance

Rotation360 degrees, continuous
Rotation (rotator) torque1153 N·m (850 ft-lb)
Grip/closing forceNot published by the factory for this model — holding power comes from the cylinder valve and interlocking leg design rather than a rated tonnage figure. Confirm with your dealer if a numeric closing-force figure is needed.
Rotation speedNot published by the factory for this model — depends on the carrier's hydraulic circuit.
Recommended host carriers (optimal match)Optimal fit on the 548 and 558 forestry log-loader machines and matching mid-size FM-series forestry excavators; acceptable (not optimal) fit on the smaller and larger machines in that lineup. Log length affects payload and machine stability — confirm grapple-to-carrier matching for the intended application.

Service capacities (summary)

Fuel tankNot applicable — no engine on the attachment
Hydraulic systemNo dedicated reservoir; draws from the host carrier's hydraulic system
Engine oilNot applicable — no engine on the attachment
Cooling systemNot applicable — no engine on the attachment

Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.

GLL55 fluids & capacities

SystemCapacityRecommended fluid
Grease points (pivot pins, bushings, rotator bearing)Not specified in liters. The grapple has grease fittings at pin, bushing, and rotator bearing locations; apply grease until it purges at the joint, per the standard work-tool lubrication schedule.No GLL55-specific grease grade is published outside dealer documentation. Cat multipurpose chassis grease (NLGI 2, e.g. Cat Advanced 3Moly Grease) is the standard recommendation for pin/bushing/bearing points on this class of work tool, rated for roughly -20 to 40 deg C (-4 to 104 deg F) ambient; colder climates call for a lower-temperature grease grade. Verify exact grade and interval against the GLL55 operation and maintenance manual lubrication chart.

Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.

Caterpillar GLL55 maintenance schedule

Service intervalTasks
Every 50 h
  • Inspect grapple legs, jaws, and bolt-on Hardox wear strips daily for cracks, gouges, or wear before starting work.
  • Check hydraulic hoses, fittings, and cylinder rod seals daily for leaks, weeping, or chafing near the heel.
  • Confirm the rotator mount and mounting pins are secure and correctly seated against the carrier's boom linkage.
  • Grease all pin, bushing, and rotator bearing fittings weekly (every 50 hours) with Cat multipurpose chassis grease until it purges at the joint; grease more often in wet, muddy, or high-cycle sort-yard duty.
  • Clean bark, mud, and grit from pin bosses and grease fittings before greasing so contamination doesn't get pumped into the joint.
Every 250 h
  • Check pin and bushing clearance at every joint and note the wear trend leg by leg.
  • Inspect cylinder rods for scoring, pitting, or bending.
  • Check the rotator motor mounting fasteners and drive coupling for looseness.
  • Inspect the mounting frame and crosshead welds for cracking.
  • Measure Hardox wear-strip thickness and confirm the heel guard still shields hoses from crushing.
Every 500 h
  • Pull and check pins and bushings for wear beyond factory clearance; replace any joint that's out of spec.
  • Check the rotator bearing for radial play or backlash by rocking the head against the housing.
  • Inspect cylinders for rod-seal weeping or cushioning wear; reseal at the first sign of leakage rather than running it dry.
  • Inspect lip-type excluder seals at each pin joint for cuts or hardening that let grit reach the induction-hardened pins.
  • Inspect leg castings, crosshead, and cylinder trunnions for stress cracks or weld fatigue.
Every 1,000 h
  • Replace pins and bushings that reached wear limits at the prior inspection, swapping worn pairs as a matched set per joint.
  • Inspect the rotator bearing race and drive-gear teeth for pitting or scoring.
  • Pressure-test grapple cylinders and the rotator motor for internal leakage.
  • Check crosshead and leg-pivot bores for oversize wear; sleeve or line-bore back to spec before fitting new pins.
  • Inspect hose routing and the carrier-side hydraulic couplers for wear or chafing.
Every 2,000 h
  • Tear down and rebuild the rotator bearing and gear-drive assembly if backlash or rotation speed has degraded.
  • Replace pins, bushings, and wear strips across the grapple as a matched set to restore jaw geometry.
  • Resurface or replace mounting-frame wear plates and the crosshead bore.
  • Rebuild cylinders showing internal bypass with new seal kits.
  • Inspect the main frame and leg gussets for fatigue cracking.
Every 4,000 h
  • Run a full structural and crack-detection inspection on the grapple frame, legs, and heel casting.
  • Rebuild the crosshead, main pivot, and rotator assembly as a complete wear-parts set.
  • Replace all cylinder seals and wear bands regardless of visible condition.
  • Evaluate frame and casting wear to decide between a further rebuild and replacing the tool.

Servicing the GLL55 beyond the schedule

Predictive Maintenance & Fluid Analysis

The GLL55 has no engine oil or coolant to sample; predictive care means watching the carrier's hydraulic circuit and the grapple's own wear points instead. Track cleanliness of the carrier's forestry attachment circuit, since rotator or seal wear shows up first as contamination or flow loss feeding the grapple. Log pin and bushing clearance at each leg joint and trend it over time; a joint wearing faster than its neighbors flags a lubrication gap or a failed excluder seal before it turns into play in the jaws.

Corrective & Common Repairs

Most GLL55 repairs trace to bark grit working past worn lip-type seals into the pivot pins and bushings, and to cylinder rod seals weeping from the same abrasive intrusion. Replace pins and bushings in matched sets per joint, not one at a time, to keep leg alignment square. Reseal a cylinder at the first sign of rod weeping rather than letting it run dry and score. Swap bolt-on Hardox wear strips before bare leg steel shows through, and check hose routing near the heel for chafing.

Overhaul & Rebuild Points

A full GLL55 overhaul centers on the rotator bearing and gear drive that lets the grapple spin 360 degrees, the crosshead and leg-pivot bores carrying jaw-closing loads, and the mounting frame that ties the tool to the carrier's boom. Backlash or race pitting shows up as jerky or off-center rotation under load and calls for a bearing and seal-kit rebuild. An oversize crosshead or pin bore needs sleeving or line-boring back to tolerance before new pins go in, or they'll wear out again quickly.

Seasonal & Environment Servicing

Switch to a lower-temperature Cat grease grade at every pin and rotator fitting before cold weather sets in; stiff grease stops migrating into the joint and accelerates dry-pin wear on startup. Check cylinder and rotator seals for cold-cracking after hard freezes. In wet, sandy, or ash-heavy ground, shorten the grease interval and wipe grit from pin bosses before each shot, since abrasive fines packed into a fitting grind the induction-hardened pins like paste. Coastal or wet timber work calls for closer wear-strip and seal checks against corrosion.

GLL55 attachments & work tools

Carrier / host machines

GLL55 mounts to Cat purpose-built forest machines (528, 538, 548, 558, 568 in Log Loader and General Forestry builds) and to excavator-based forest machines (320D FM/320D2 FM, 325C FM/325D FM and equivalent D/E-series FM variants) fitted with forestry-spec hydraulics. It is not intended for a standard non-forestry excavator lacking the forestry attachment control circuit.

Grapple size class

GLL55 sits in the mid-size tier of the continuous-rotation log-loader grapple line: GLL52 opens to 1321 mm (52 in), GLL55 to 1397 mm (55 in), GLL60 to 1524 mm (60 in). Weight scales with size, roughly 1253-1388 kg (2762-3060 lb) across the three, matching heavier grapples to larger-boom carriers.

Mounting / rotator system

The grapple bolts to a factory rotator rather than an excavator-style quick coupler. The bearing surface is machined to match the rotator, which increases mounting strength and reduces side load on the mounting bolts. Fitment is normally a factory-integrated linkage on the forest machine's loader boom/stick rather than a field-retrofit quick-hitch.

Hydraulic / control-circuit requirement

GLL55 runs off the carrier's dedicated forestry attachment control circuit, which supplies separate high- and medium-pressure flow for grapple close/open and rotation functions. Exact flow and pressure targets vary by carrier model and series — confirm against the specific forest-machine hydraulic spec sheet rather than assuming one figure.

Rotation system

Continuous 360-degree hydraulic rotation is standard, driven by a dedicated rotator motor in the torque class of 1153 N·m (850 ft-lb). This lets the operator align, pick, and sort logs without repositioning the boom.

Jaw / tip and heel options

The standard tine set uses interlocking legs with a minimum opening of 127 mm (5 in) for single small stems, up to the 1397 mm (55 in) maximum for bunched loads. An optional heel attachment with a flat, serrated rack can be fitted for extra log engagement and stability, and it doubles as a travel lock that protects the rotator hoses.

Construction / guarding

Legs are high-strength alloy steel with sealed pin joints and heavy-duty lip-type excluder seals to keep debris out of the pivots. This is standard build rather than an option, aimed at high-cycle picking, bunching, and shovel-logging duty.

All GLL55 assemblies by section

Every catalogued assembly group for the Caterpillar GLL55. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Frame And Body
270-9021 Cover Gp-Access
24***04Plate1
24***15Plate As2
27***48Plate-Cover1
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Hydraulic System
270-9016 Cylinder & Lines Gp-Grapple
21***42Cylinder Group-Hydraulic; -Grapple2
27***16Cylinder & Lines Group-Grapple1
29***66Hose As4
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231-9472 Cylinder & Lines Gp-Grapple
15***14Hose As4
21***42Cylinder Group-Hydraulic; -Grapple2
23***72Cylinder & Lines Group-Grapple1
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216-4042 Cylinder Gp-Hydraulic -Grapple
11***89Valve-Check (Po)1
15***11Lockwasher12
16***80Kit-Service; (Counterbalance Valve)1
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305-8112 Manifold Gp-Rotator
27***07Kit-Seal; (Manifold)1
27***10Plate-Wear1
29***09Plate-Stop1
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230-7927 Rotator Gp-Hydraulic
09***73Bolt; (Socket Head) (M12x1.75x60mm)4
16***32Hose As1
18***00Hose As1
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270-7838 Rotator Gp-Hydraulic
22***82Gear & Bearing As1
22***96Gear-Pinion; (13-Teeth)1
26***51Valve As-Relief; (1500-Psi)1
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Service Equipment And Supplies
253-9953 Film Gp
15***35Film-Warning; (Crush Hazard, Stay Back)2
15***36Film-Warning; (Read Operation Manual)2
24***61Film; (Cat, Gll60)2
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253-9952 Film Gp
15***35Film-Warning; (Crush Hazard, Stay Back)2
15***36Film-Warning; (Read Operation Manual)2
24***60Film; (Cat, Gll55)2
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291-2639 Film Gp
15***35Film-Warning; (Crush Hazard, Stay Back)2
15***36Film-Warning; (Read Operation Manual)2
29***26Film; (Cat, Gll60b)2
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291-2637 Film Gp
15***35Film-Warning; (Crush Hazard, Stay Back)2
15***36Film-Warning; (Read Operation Manual)2
29***24Film; (Cat, Gll52b)2
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253-9951 Film Gp
15***35Film-Warning; (Crush Hazard, Stay Back)2
15***36Film-Warning; (Read Operation Manual)2
24***59Film; (Cat, Gll52)2
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291-2638 Film Gp
15***35Film-Warning; (Crush Hazard, Stay Back)2
15***36Film-Warning; (Read Operation Manual)2
29***25Film; (Cat, Gll55b)2
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Work Tool Arrangement
219-2366 Grapple Ar
13***34Plate-Identification; (Work Tool)1
21***09Plate2
21***53Tong As-Grapple; (Male)1
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271-1534 Grapple Ar
13***34Plate-Identification; (Work Tool)1
26***31Crosshead As1
26***47Tong As-Grapple; -Female1
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271-1535 Grapple Ar
13***34Plate-Identification; (Work Tool)1
26***31Crosshead As1
26***48Tong As-Grapple; -Female1
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219-2365 Grapple Ar
13***34Plate-Identification; (Work Tool)1
20***25Shell As; (Male)1
20***34Shell As; (Female)1
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271-1533 Grapple Ar
13***34Plate-Identification; (Work Tool)1
26***31Crosshead As1
26***46Tong As-Grapple; -Female1
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219-2364 Grapple Ar
13***34Plate-Identification; (Work Tool)0
20***25Tong As-Grapple; (Male)1
20***33Tong As-Grapple; (Female)1
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Work Tools
270-9070 Fastener Gp-Grapple
09***73Bolt; (Socket Head) (M12x1.75x60mm)4
15***19Lockwasher8
25***30Spacer; (16.27x25.4x10.7-mm Thk)1
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270-9069 Pin Gp-Grapple
12***02Pin2
23***64Plate4
23***66Pin As2
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231-9474 Pin Gp-Grapple
12***02Pin2
12***04Pin1
13***37Pin1
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GLL55 serial number reference

The ID plate for a GLL55 grapple is riveted or bolted to the grapple mainframe, usually near the top mount/rotator bracket rather than on a leg or tine. It carries the work-tool model designation and the serial number as a 3-letter prefix followed by a 5-digit sequence (e.g. A3D00001); the letters identify the specific build record for this grapple line, and the digits are the build sequence within that record. If the plate is missing or worn, the number is often restamped on the mainframe near the original plate location.

PrefixIdentifies
A3DGLL52 / GLL55 / GLL60 logging grapples (shared work-tool build, base line)

Frequently asked questions

What carrier machines does the Cat GLL55 mount to?

The GLL55 is a passive work tool that runs its rotate, open, and close functions entirely off the hydraulic circuit of the carrier it's mounted on, rather than an engine of its own. It's an optimal fit on the 322, 324, 325, and 330 FM excavator-based forest machines and the 548 and 558 LL purpose-built log loaders, and an acceptable fit on the 320 FM and the 538 and 568 LL, plus select forestry material handlers when fitted with the correct front linkage.

What is the operating weight of the Cat GLL55?

The bare grapple weighs 1297 kg (2,860 lb) at 561 mm (22.1 in) wide, before any heel attachment or carrier-side coupler is added. Heel weight varies by carrier and style, from around 725 kg (1,595 lb) on a compact heel up to roughly 1,340 kg (2,948 lb) on a heavier offset heel, so total installed weight depends on the carrier and heel combination in use.

What replaced the Cat GLL55?

A later GLL55B generation has carried the size class forward within the same GLL naming, but no independently confirmed spec changes from the original GLL55 are documented in available sources. Treat the B-suffix model as a running production update rather than a re-engineered tool, and confirm exact differences with a Cat dealer for a given serial range before assuming parts or specs carry over directly.

What GLL55 owners discuss

What's typically the first wear item on a GLL55 in day-to-day log handling?
The bolt-on Hardox wear strips on the grapple legs. They take the abrasion from bark and dirt before the leg structure itself does, and they're designed to be swapped in the field with hand tools. Check strip thickness at the same time you check leg straightness - a strip worn thin lets the underlying leg edge take direct contact, which turns a cheap fix into a slower, pricier one. Most operators catch this on a quick walk-around at the start of a shift.
How often should the pin joints and rotator really get greased on this grapple?
The published interval covers light-to-moderate use, but continuous sort-yard or high-cycle loading dries the joints out faster than an 8-hour schedule keeps up with. If the machine is cycling all shift, grease the leg pivots and rotator more often than the sticker says. Dry joints wear the induction-hardened pins and bushings quickly, and once there's play in a pin joint, greasing won't restore the fit. As a bushing wears, the low spot in the bore can end up out of line with the grease fitting, so cycling the leg partway through its stroke while greasing helps push grease past the worn area instead of just packing it against the tight side. The lip-type excluder seals on the pins help keep grit out, but only if grease is actually pushed through often enough to purge contamination.
The rotator feels sluggish or won't spin as fast as it used to - what's usually going on?
Two common causes. First, flow and pressure mismatch: the grapple's rotation torque is rated for a specific hydraulic circuit, and a carrier set up with less flow than the rotator wants gives slow, weak rotation even with everything mechanically sound. Second, internal wear in the rotator motor or drag in the bearing increases internal leakage over time, which shows up the same way. If the carrier's work-tool circuit checks out to spec for flow and pressure and rotation is still slow, the rotator itself needs a shop look.
Is some weeping around the rotator housing or cylinder rods normal after a season or two?
Light seepage after years of log-handling side loads isn't unusual. The lip-type excluder seals and cylinder rod seals take a beating from embedded bark and grit, and rotation works grit past a seal faster than straight-line cylinder travel does. A light film around a fitting is a watch item. Steady dripping, or measurable oil loss between services, means a seal has actually failed and the cylinder or rotator needs to come apart for reseal. This grapple is built with fully serviceable cylinders specifically so that's a field-level repair, not a factory return.
What wear pattern shows up on the jaws and legs themselves from normal use?
Two things to watch. The interlocking leg tips that let the grapple close down for single, small stems take concentrated wear right where the legs cross - that's expected, but uneven wear there throws off the grip on small-diameter stems. Separately, legs that repeatedly take off-center, one-sided loads (dragging a log by one end instead of centering it) can bend or twist slightly over time, showing up as an uneven bite side to side. The heel is there to absorb impact and swing while traveling with a load and to protect the hydraulic hoses; heel wear or damage is normal and far cheaper to deal with than letting that shock load transfer into the leg pivots.
Any known quirks hooking this grapple up to different carrier machines?
Same issues that show up with rotating grapples generally. Hydraulic lines can pressure-lock when the grapple sits disconnected and warms up in the sun, making the couplers tough to reconnect until pressure bleeds off. Mixing coupler styles between the carrier and the grapple's hoses doesn't work without an adapter. The carrier's auxiliary circuit also needs to be matched to the grapple's rated flow and pressure for the rotator to perform to spec - an undersized or mismatched circuit produces the same sluggish-rotation complaint as actual wear. One specific pattern worth knowing: if the rotator turns fine one way but stalls or crawls the other way, don't assume the rotator itself is bad. Swapped quick-disconnects will drive it backward into a valve setup that isn't tuned for that direction, and a speck of debris holding a relief valve cracked open produces the exact same one-direction-weak symptom. Reverse the couplers as a first check; if the fault follows the grapple rather than the hookup, look at the carrier's relief valve for that circuit before condemning the rotator.
What should I check before buying a used GLL55?
Walk every leg pivot and check for play - wobble means the induction-hardened pins or their bushings are worn past service life. Grab the head and try to rock it against the rotator housing to feel for bearing play. Cycle the rotator a full 360 degrees both directions under load and listen for grinding or a direction-dependent stall. Check remaining thickness on the Hardox wear strips and look for a bent or twisted leg from off-center loading. Inspect cylinder rods for scoring or pitting and look for staining that suggests a failed seal. Look closely for weld cracks or prior repairs around the mounting frame and crosshead. Confirm the hose ends and coupler style match your carrier's circuit and that rated flow and pressure line up. Because a failure at the mounting frame, crosshead, or rotator bearing can drop a suspended log, have your dealer verify structural and bearing condition before putting a used unit into service.

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

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