Caterpillar GLS66
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar GLS66 is a Grapple AR-Shovel, a passive hydraulic work tool built for log handling rather than a self-propelled machine. It carries no engine, transmission or ECM of its own; it mounts to a host excavator's heel-boom linkage and runs entirely off that machine's hydraulic circuit, though it does carry its own hydraulic rotator (gerotor-drive motor) to swing the grapple independently of the boom. Approved hosts are the Cat 320B, 322B/C, 325B/C and 330B/C excavators fitted with the heel-boom option. The GLS66 is the largest of four sizes in the GLS grapple-shovel logging line (GLS55, GLS60, GLS63, GLS66), sized to match the heavier 325B/330B-class carriers. It dates to the mid-to-late 1990s, in line with the production era of its B-series excavator hosts, and carries its own serial prefix (T2A1-UP) distinct from its smaller siblings.
Across the GLS family, the grapple scales with the host excavator. GLS55 is the smallest, built for 320B-class carriers and using a 114.3 mm (4.5 in) bore x 193.7 mm (7.6 in) stroke grapple cylinder. GLS60, GLS63 and GLS66 step up in size and jaw capacity while sharing a common 127 mm (5 in) bore x 209.55 mm (8.25 in) stroke cylinder, with GLS66 at the top of the range. All four sizes share one OEM parts book, which keeps parts identification straightforward despite the age of the line. In today's used and parts market, the GLS66 turns up on older forestry and logging-focused excavator fleets. Published documentation is thin, and no hour-based maintenance manual for the tool itself is publicly available, but the pin, cylinder and rotator groups are still tracked by serial-prefix in Cat's parts system, which keeps these legacy attachments serviceable well past their original production run.
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 GLS66 specifications
Weights
| Operating weight | Not published for this attachment size. Weight varies by grapple-shovel size (GLS55/60/63/66 share one parts book but differ in shell/jaw dimensions); confirm using serial prefix T2A1-UP with your Cat dealer or parts lookup. |
Dimensions
| Mounting | Mounts on the heel-boom option of a Cat 320B, 322B/C, 325B/C or 330B/C excavator. Grapple is carried on the boom-heel linkage via standard pin-and-lug attachment; no independent swing or rotate joint of its own. |
| Jaw/shell opening and overall envelope | Not documented in published form for this specific size. The GLS-family shares one parts book across four sizes (GLS55/60/63/66) with jaw geometry sized to the shell/cylinder set fitted; verify exact opening and envelope dimensions by serial prefix (T2A1-UP) with your Cat dealer. |
Performance
| Grapple jaw closing force | Not documented in published form for this attachment; depends on host excavator hydraulic supply and the fitted relief setting. Verify with your Cat dealer using serial prefix T2A1-UP. |
Service capacities (summary)
| Grapple hydraulic cylinder - bore x stroke | 127 mm (5 in) bore x 209.55 mm (8.25 in) stroke. This cylinder set is shared with the GLS60 and GLS63 grapple-shovel logging attachments; the smaller GLS55 uses a 114.3 mm (4.5 in) bore x 193.7 mm (7.6 in) stroke cylinder instead - do not interchange the figures. |
| Rotator / powered rotation | Fitted. The grapple carries its own hydraulic rotator, driven by a gerotor motor, allowing the jaws to be positioned independent of the excavator stick. It is not a continuous-rotation forestry-grapple design; rotation is limited to positioning the grapple on the heel-boom mount. |
| Relief valve pressure | The rotator's gerotor motor circuit is offered with a factory choice of relief-valve settings — about 100 bar (1500 psi), 138 bar (2000 psi), or 207 bar (3000 psi) — selected to suit the host excavator's hydraulic supply. Confirm the setting fitted to a given unit with your Cat dealer. |
| Grease points | Grapple pivot pins and cylinder pin bosses take Cat Multipurpose grease (Cat MPGM), applied per the host excavator's attachment lubrication interval. No distinct fluid or grease capacity is specified for this work tool. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
Caterpillar GLS66 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 4,000 h |
|
Servicing the GLS66 beyond the schedule
Predictive Maintenance & Fluid Analysis
The GLS66 has no engine or transmission to sample, so predictive checks center on the host excavator's hydraulic oil and the grapple's own wear trend. Pull hydraulic oil samples from the host machine at its normal interval, since the grapple circuit and rotator gerotor motor share that same tank. Track pin-to-bushing clearance at the heel-boom and grapple pivots over successive inspections; a widening trend flags bushing replacement before metal-to-metal contact damages the pin bore. Watch rotator rotation speed under load as an early sign of gerotor wear before it becomes a leak.
Corrective & Common Repairs
Most GLS66 downtime traces to worn heel-boom or grapple pivot pins and bushings from skipped grease intervals, and to grapple cylinder rod seal leakage from shock loads in log handling. Chafed or pinched hydraulic hoses at the rotator swivel are a recurring failure point on tight heel-boom mounts. Cracked or bent jaw and shell wear plates from rock contact in the log deck are common and are bolt-on replaceable. Check the rotator gerotor motor shaft seal whenever oil shows up around the rotator base.
Overhaul & Rebuild Points
A GLS66 rebuild centers on three items: the grapple cylinder (bore, rod, seals), the rotator gerotor motor (internal wear, backlash), and the full set of heel-boom and grapple pivot pins and bushings. Since this is a passive attachment with no ECM, there is no electronic diagnostic path; rebuild decisions rely on measured pin clearances, cylinder leak-down checks and gerotor rotation speed under load. A structural rebuild should also recheck the jaw-arm-to-frame welds and heel-boom mounting lugs for fatigue cracking before the tool goes back into service.
Seasonal & Environment Servicing
Logging duty exposes the GLS66 to mud, sap and cold-weather startup through the host excavator's hydraulic system. Before winter layup, cycle the rotator and grapple cylinder fully to work grease into the pivot pins and coat exposed rod surfaces against corrosion pitting. In wet, abrasive ground conditions, shorten the grease interval on heel-boom and grapple pins rather than stretching it. Clear packed debris from around the rotator bearing and jaw pivots regularly; trapped grit wears bushings faster than load alone.
GLS66 attachments & work tools
Host excavator compatibility
The GLS66 grapple ar-shovel is not a base machine — it mounts on a Cat 320B, 322B/C, 325B/C, or 330B/C hydraulic excavator fitted with the factory heel-boom option. It is the largest size in the GLS grapple-shovel logging family (GLS55, GLS60, GLS63, GLS66), which share this same host-machine list; each size carries its own serial-number prefix in Cat parts records, confirming they are distinct grapples on a common host range rather than one interchangeable unit.
Mounting and linkage system
The grapple pins to the excavator stick in place of a bucket, with a heel arm pinned back to the boom (heel-boom / shovel-logging linkage). The heel arm steadies the grapple against swing and impact while traveling and shields the hydraulic hoses running to the tool. Specific pin and bushing diameters for the GLS66 mounting are not published in accessible documentation — match against the host excavator's own stick/bucket linkage pin sizes and confirm with a Cat dealer or the parts manual before ordering pins and bushings.
Hydraulic rotator and relief valve
The GLS66 carries a hydraulic rotator (gerotor-motor driven) so the grapple jaws can be positioned independent of stick swing, supplied through the tool's own cylinder-and-lines circuit off the host excavator's auxiliary hydraulics. The rotator circuit is offered with a factory choice of relief-valve settings — about 100 bar (1500 psi), 138 bar (2000 psi), or 207 bar (3000 psi) — matched to the host excavator's hydraulic supply. Confirm the setting fitted to a given unit with a Cat dealer or the machine's operation and maintenance/testing-and-adjusting manual before service.
Factory options across the GLS size range
Sibling-size note, not a GLS66 spec: the GLS55/GLS60/GLS63/GLS66 range covers four grapple sizes built on the same heel-boom mounting concept and sharing common part-group architecture (pin group, cylinder-and-lines group) across the line. Size-specific jaw/shell capacity and guarding option differences between the four sizes are not documented in accessible sources — confirm size-specific factory options for the GLS66 with a Cat dealer.
All GLS66 assemblies by section
Every catalogued assembly group for the Caterpillar GLS66. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Frame And Body
249-5124 Cover Gp-Access
| 24***04 | Plate | 1 |
| 24***23 | Plate | 2 |
| 24***15 | Plate As | 2 |
249-1008 Cover Gp-Access
| 24***04 | Plate | 1 |
| 24***23 | Plate | 2 |
| 24***08 | Cover Group-Access | 1 |
Hydraulic System
249-5099 Cylinder & Lines Gp-Grapple
| 17***03 | Hose As | 4 |
| 24***99 | Cylinder & Lines Group-Grapple | 1 |
| 24***00 | Cylinder Group-Hydraulic; -Grapple | 2 |
249-1006 Cylinder & Lines Gp-Grapple
| 18***78 | Hose As | 4 |
| 24***97 | Cylinder Group-Hydraulic | 2 |
| 24***06 | Cylinder & Lines Group-Grapple | 1 |
249-0997 Cylinder Gp-Hydraulic
| 11***13 | Kit-Seal | 1 |
| 1B***67 | Bolt, Hex. Hd., 5/8"-11 N.C. X 3" | 8 |
| 24***97 | Cylinder Group-Hydraulic | 1 |
249-5100 Cylinder Gp-Hydraulic
| 11***13 | Bolt-Hex Head; (M16x2x70mm) | 6 |
| 16***84 | Kit-Seal | 1 |
| 18***92 | Valve As-Counterbalance | 1 |
261-4654 Motor Gp-Gerotor
| 26***51 | Valve As-Relief; (1500-Psi) | 1 |
| 26***52 | Valve As-Relief; (2000-Psi) | 1 |
| 26***53 | Valve As-Relief; (3000-Psi) | 1 |
249-0172 Rotator Gp-Hydraulic
| 22***82 | Gear & Bearing As | 1 |
| 22***96 | Gear-Pinion; (13-Teeth) | 1 |
| 23***11 | Kit-Seal; (Manifold) | 1 |
Service Equipment And Supplies
249-3154 Film Gp
| 15***35 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
| 15***36 | Film-Warning; (Read Operation Manual) | 2 |
| 24***12 | Film; (Cat, Gls66) | 2 |
249-3153 Film Gp
| 15***35 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
| 15***36 | Film-Warning; (Read Operation Manual) | 2 |
| 24***09 | Film; (Cat, Gls63) | 2 |
249-3152 Film Gp
| 15***35 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
| 15***36 | Film-Warning; (Read Operation Manual) | 2 |
| 24***08 | Film; (Cat, Gls60) | 2 |
249-3151 Film Gp
| 15***35 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
| 15***36 | Film-Warning; (Read Operation Manual) | 2 |
| 24***51 | Film Group | 1 |
Work Tool Arrangement
243-5483 Grapple Ar-Shovel -Gls63
| 24***83 | Grapple Ar-Shovel; -Gls63 | 1 |
| 24***45 | Grapple Ar-Shovel | 1 |
249-3145 Grapple Ar-Shovel
| 24***14 | Housing As | 1 |
| 24***94 | Crosshead As | 1 |
| 24***76 | Shell As | 1 |
249-3143 Grapple Ar-Shovel
| 24***14 | Housing As | 1 |
| 24***27 | Tube | 4 |
| 24***28 | Shell As | 1 |
243-5484 Grapple Ar-Shovel -Gls66
| 24***84 | Grapple Ar-Shovel; -Gls66 | 1 |
| 24***46 | Grapple Ar-Shovel | 1 |
243-5482 Grapple Ar-Shovel -Gls60
| 24***82 | Grapple Ar-Shovel; -Gls60 | 1 |
| 24***43 | Grapple Ar-Shovel | 1 |
243-5481 Grapple Ar-Shovel -Gls55
| 24***81 | Grapple Ar-Shovel; -Gls55 | 1 |
| 24***42 | Grapple Ar-Shovel; -Gls55 | 1 |
249-3146 Grapple Ar-Shovel
| 24***14 | Housing As | 1 |
| 24***27 | Tube | 4 |
| 24***94 | Crosshead As | 1 |
249-3142 Grapple Ar-Shovel
| 24***94 | Crosshead As | 1 |
| 24***72 | Rotator Group-Hydraulic | 1 |
| 24***38 | Shell Group-Grapple | 1 |
Work Tools
249-3155 Fastener Gp-Work Tool
| 09***73 | Bolt; (Socket Head) (M12x1.75x60mm) | 4 |
| 24***55 | Fastener Group-Work Tool | 1 |
| 2L***01 | Bolt; (5/8-18x1.5-In) | 2 |
249-5165 Fastener Gp-Work Tool
| 09***73 | Bolt; (Socket Head) (M12x1.75x60mm) | 4 |
| 24***65 | Fastener Group-Work Tool | 1 |
| 25***30 | Spacer; (16.27x25.4x10.7-mm Thk) | 2 |
249-5159 Pin Gp-Grapple
| 24***92 | Pin As | 2 |
| 24***94 | Plate | 1 |
| 24***07 | Plate | 4 |
249-2901 Pin Gp-Grapple
| 12***13 | Pin-Keeper | 1 |
| 24***92 | Pin As | 2 |
| 24***94 | Plate | 1 |
GLS66 serial number reference
The PIN is stamped on the grapple attachment's own nameplate (riveted to the shovel frame or grapple base), not on the host excavator's PIN plate. Read the first 3 characters as the prefix (identifies the specific attachment model/size), followed by the sequence number; a plate reading T2A1 or higher confirms this GLS66 size rather than a GLS55/60/63 sibling.
| Prefix | Identifies | Notes |
|---|---|---|
| T2A | GLS66 Grapple Ar-Shovel | Single documented production prefix for this attachment size, covering T2A1 and up. Fits as a heel-boom-mounted work tool on 320B, 322B/C, 325B/C, or 330B/C excavators. No later or earlier prefix block is documented for this size; treat as the complete range unless a dealer lookup shows otherwise. |
Frequently asked questions
What excavators does the Caterpillar GLS66 fit?
The GLS66 grapple mounts to Cat 320B, 322B/C, 325B/C and 330B/C excavators fitted with the heel-boom option. It is not a standalone machine; it attaches to the host excavator's heel-boom linkage and hydraulic circuit.
Does the GLS66 have its own engine?
No. The GLS66 is a passive hydraulic work tool with no engine, transmission or ECM of its own. It draws its hydraulic power from the host excavator, though it does carry its own hydraulic rotator (gerotor-drive) motor that rotates the grapple on the heel-boom mount.
What is the GLS66's grapple cylinder size?
The GLS66 uses a 127 mm (5 in) bore x 209.55 mm (8.25 in) stroke grapple cylinder, the same size shared with the GLS60 and GLS63. The smaller GLS55 uses a 114.3 mm (4.5 in) bore x 193.7 mm (7.6 in) stroke cylinder.
What GLS66 owners discuss
What do owners and mechanics say about the hydraulic cylinders on this class of grapple-shovel attachment?
What wear issues come up around the heel-boom linkage pins and bushings?
What do people say about hose routing and hose damage during logging work?
What is said about the grapple jaw/shell wear plates and tips?
What should a buyer check on a used GLS-series (or similar era) shovel-logging grapple?
What do mechanics say about matching this grapple to the host excavator's hydraulics?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
Need a specific GLS66 part?
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