Description

Clark-hurth 15D, 20D, 12D Service Manual – Don’t Rebuild Without It

You got a Clark-hurth electric lift truck that won’t move, or the hydraulic pump sounds like a rock tumbler. Without the factory book, you’re gambling on a customer’s downtime and your own flat rate. This Clark-hurth 15D, 20D, 12D Service Manual is the exact 348-page document Clark intended for their dealers – not a third-party reprint, not a scanned photocopy missing half the wiring diagrams. I’ve seen guys waste an afternoon because they guessed a brake bleed sequence on a 20D. That’s billable hours you can’t get back. This manual fixes that.

Preliminary Service: The Pre-Delivery Checklist You Can’t Skip

Page 2 of this manual spells out the arrival and pre-delivery checklist that validates your warranty. Clark sends a sheet with every machine – this book shows you exactly what to check: transmission oil level, hydraulic unit oil level, battery charge and connection. And that deadman brake pedal? Read the warning on page 1. If releasing the pedal doesn’t kill power to the drive motor and set the brakes, the machine does not get operated. Period. I’ve dealt with electric forklifts that creep because some tech skipped this step. Don’t be that guy. The manual also covers operator qualifications – who should be driving, training requirements, and general rules for traveling and loading. If you’re running a shop, use this section to train your guys. It keeps them alive.

7 Major Systems Covered – From Frame to Mast

Section breakdown: Frame (Section 05) with battery retainer, load wheel, and castor assembly procedures. Instruments and dash controls (Section 10) including the emergency disconnect, auxiliary control, hand lift and speed control, and the brake assembly with theory of operation, adjustment, and bleeding. Transmission (Section 15) – drive motor removal and installation, drive wheel, full disassembly and assembly, and a troubleshooting guide. The electrical system (Section 20) takes up serious pages: the SCR system, diode and contactor coil tests, battery selection, EV-1 panel contactors, and a whole sub-section on the QU-IC3645AZA1 circuit analyzer. Hydraulic system (Section 30) covers the theory of operation, auxiliary pump, power steering, lift pump removal and installation, Cessna and Dowty pump rebuilds with running tests. Then tires (Section 35), shielding (Section 40), jacking and hoisting (Section 41), mast (Section 45), and a specification table and charts section (Section 50). That’s where you’ll find the torque values, fluid capacities, and adjustment specs. Don’t trust aftermarket data for those.

Transmission Rebuild – Drive Motor Disassembly Sequence

Section 15-02 walks you through the transmission theory of operation first – because if you don’t understand how the drive motor couples to the wheels, you won’t diagnose a no-go condition. Then it gives you the drive motor removal and installation steps, with separate disassembly and assembly procedures. The drive wheel removal is in there too. The manual tells you to inspect every component during disassembly – gears, bearings, seals – and then reassembles to factory clearances. There’s a troubleshooting chart after assembly that lists common failures like “motor runs but no drive” or “excessive noise.” Each symptom ties back to a specific inspection point. No guesswork. If you’ve got a 15D that jerks on startup, you work through the chart instead of throwing parts at it. I’ve rebuilt a Clark 20D transmission using this same book; the critical spec is the drive wheel nut torque – it’s in Section 50, and you better use it or the wheel comes loose.

Electrical System: EV-1 SCR Troubleshooting Without Smoke

Section 20 contains 60-plus pages on the electrical system alone. Starts with understanding volts, watts, and amps – basic theory that a lot of DIY guys skip, then wonder why they smoked a contactor. The manual shows you how to test diodes and contactor coils, then dives into the GE EV-1 SCR system. There’s a full subsection on the EV-1 Circuit Analyzer (QU-IC3645AZA1) including how to prepare the truck for troubleshooting, a preliminary checklist, and a quick check procedure. Failures are categorized: reduced or no motor torque, full motor torque with SCR control, misoperation of other features. Each failure type has a diagnostic tree. The Prestolite motor service instruction includes visual inspection, armature testing, field coil installation, and motor troubleshooting. And if you’re dealing with a master control switch that doesn’t give you direction, there’s disassembly and assembly steps plus a dedicated troubleshooting page. This is the kind of detail you need when you’re staring at a wiring diagram with 40 wires and no labels. For more heavy-duty transmission information, check out the Spicer Clark-hurth HR Service Manual – Factory Specs for Heavy-Duty Transmission. And if you need the smaller 55A series, look at Clark-hurth 55A SERIES II Service Manual – 136 Pages of Factory Specs. For the larger SM-715 platform, Clark-hurth SM-715, TMX12-25, EPX16-20s 2007 Service Manual – 502 Page OEM Facto covers it.

Source Validity: Why a Dealer-Only Manual Matters

Page 1 of this manual carries a clear warning: “Copyrighted Material Intended for CLARK dealers only – Do not sell or distribute.” That’s your guarantee this isn’t some aftermarket compilation that got the clearance specs wrong. Every procedure in this book was written by Clark engineers, reviewed by factory technicians, and used in dealer service bays. I’ve seen aftermarket manuals call out a torque of 150 ft-lb on a part that should be 180 because they transposed digits. With this OEM document, you’re working from the same source as a certified Clark dealership. The manual also references field modifications and updated pages – meaning Clark kept this alive as trucks changed. If you want to really understand how a manual transmission interacts with the drive motor, Manual Transmission has good background theory, but this book gives you the factory service procedure. The same applies for Manual Transmission basics – don’t confuse automotive transmission concepts with industrial electric forklift drives. They’re different beasts.

FAQ

Does this manual cover the Prestolite motor disassembly?

Yes. Section 20-04 includes the full Prestolite motor service instruction with visual inspection, testing, armature repair, field coil installation, and assembly testing.

What torque values are listed in the specification charts?

Section 50 has the specification table and charts. The exact numbers for your 12D or 20D drivetrain are there – wheel nuts, transmission bolts, hydraulic fittings. I don’t have the values memorized, but they’re in the manual.

Is this manual suitable for a beginner home garage mechanic?

If you can read a wiring diagram and turn a wrench, yes. The manual assumes you’re a qualified mechanic, but the step-by-step disassembly and assembly sequences are clear enough for a serious DIYer. Just don’t skip the safety warnings on page 1.

Can I use this manual for a 15D with a different pump than the Cessna or Dowty?

The hydraulic system section covers the Cessna D-40503 and Dowty D-40459-7 pumps specifically. If your 15D has an alternate pump, you won’t find it here. Check the serial number against the manual’s applicability – it’s for NP 15-20-12D series trucks.

This manual gives you the same documentation Clark dealers used to keep these electric forklifts running. Whether you’re replacing a contactor on a 12D, rebuilding the transmission on a 20D, or tracking down a SCR fault on a 15D, the factory procedures are in these 348 pages. Don’t trust your billable hours or your safety to aftermarket guesses. Access the Factory Manual and start working from the real specs.