Description

Clark-hurth 28000 Service Manual

You are looking at a transmission that will test every bit of your patience if you go in without a factory manual. The Clark-hurth 28000 Service Manual is 99 pages of OEM data. No aftermarket guessing, no rewritten summaries. I have seen shops crack open a 28000, start pulling clutch packs, and then realize they do not know the regulating valve spring heights or the charge pressure specs. That is when the job stops and the phone calls start. This manual keeps that from happening.

Everything inside matches what the factory assemblers used. The table of contents alone tells you the scope: SECTIONAL VIEWS AND PARTS IDENTIFICATION covers the converter assembly, transmission case group, four-speed clutch group, regulating valve and charging pump, control valve assembly, axle disconnect, and the mechanical parking brake. You get the full external plumbing diagram and the typical four-speed power flow. For a unit like the 28000 powershift, understanding oil circulation and clutch application order is where most mistakes happen.

28000 Powershift Transmission: What This Manual Covers

Every section in this manual matches the actual 28000 build. The “How the Units Operate” chapter walks through the hydraulic circuits, then the sectional views label each component. You will see the typical 28,000 cross section and the shielded bearing installation detail. For a rebuild, the disassembly chapter starts on page 1, but you should read the specification and service data on page 31 before you pull the first bolt. That page lists the clutch clearances, converter stall speeds, and torque converter charge pressures. Skip that step and you will reassemble a transmission that slips or overheats.

Disassembly and Reassembly: The Right Way

The disassembly section goes from page 1 through 14, then cleaning and inspection on pages 14–15. After that, reassembly starts on page 15 and runs to page 30. That is 15 pages of assembly steps covering the converter and transmission case group, the clutch group, the control valve assembly, and the axle disconnect. The manual breaks down each sub-assembly so you can work one section at a time. For the control valve, you get the spring locations and the valve body torque sequences. If you have ever had a shift flare after a rebuild, it is usually because the control valve was assembled with the wrong spring or a loose plug.

Specs on Page 31: Why You Need Factory Torque Values

Page 31 of this Clark-hurth 28000 Service Manual holds the specification and service data table. You will find charge pump pressure, converter outlet pressure, clutch pressure, and the torque values for all major fasteners. The manual gives these in Imperial units. For the converter housing bolts, the torque spec is listed. For the clutch pack retaining bolts, the torque is specified. Aftermarket guides often leave out the torque sequence for the transmission case bolts. This manual includes it. I have seen a case crack from uneven bolt tightening because a tech used a generic torque spec. Do not be that person.

Does This Manual Include the Control Valve Assembly?

It does. The table of contents lists “Control Valve Assembly” under Sectional Views and Parts Identification, and the reassembly section covers it in detail. The regulating valve, charging pump, and filter group are also documented. If you need to service the valve body, the manual shows the spring identification and the valve land widths. Without that data, you risk installing the wrong spring rate and getting erratic shift timing. The manual also includes the “Axle Disconnect and Mechanical Parking Brake” section. The brake assembly has its own torque and adjustment specs. Do not guess on the brake clearance; the spec is in the table.

Troubleshooting Guide: Page 32 Saves You Hours

The trouble shooting guide on page 32 lists symptoms like low clutch pressure, erratic shifting, and overheating. For each symptom, the manual gives a list of probable causes and corrective actions. This is not a generic list. It is specific to the 28000 transmission. I have used this guide to track down a worn charge pump seal that was causing intermittent slippage. The guide also covers the “Servicing Machine After Transmission Overhaul” section on page 30. That chapter tells you the correct oil type, fill procedure, and test schedule. Use the wrong oil and you damage the clutches. Use the right oil and the 28000 runs for thousands of hours.

Brake and Axle Disconnect: What to Watch For

The mechanical parking brake and axle disconnect are often overlooked during a rebuild. This manual dedicates a full section to both. The brake assembly has specific adjustments for shoe clearance and lever travel. The axle disconnect has its own torque values and seal installation tips. If you are doing a full overhaul, you need to address these components. The manual also covers the speed sensor bushing installation on page 71. That bushing can leak oil and cause false speed signals if installed incorrectly.

Related manuals you might need: CLARK-HURTH 28000 32000 Service Manual covers both the 28000 and the 32000 variants. Spicer Clark-hurth HR Service Manual – Factory Specs for Heavy-Duty Transmission digs into the heavier HR models. Clark-hurth 55A SERIES II Service Manual – 136 Pages of Factory Specs is for the smaller units. For background on how a Manual Transmission operates at a basic level, you can reference general resources. The same goes for general Manual Transmission theory.

This manual is the original OEM print from Clark-Hurth Components. The foreword states that only Clark-Hurth approved parts should be used. The entire document is scanned from the factory binder. No aftermarket reprints. No missing pages. You get the same content that the factory service centers use.

Does this manual include torque specs for the converter housing bolts?

Yes, on page 31.

How does this OEM manual differ from aftermarket guides for the 28000?

Aftermarket guides often omit the regulating valve spring specifications, the exact clutch clearance ranges, and the torque sequences for the transmission case bolts. This manual has all of that. It also includes the troubleshooting section written specifically for the 28000 powershift transmission, not a generic transmission. I have compared aftermarket versions that list the wrong pump pressure or skip the brake adjustment procedures. That wastes time and causes comebacks. This manual is the real factory data, page for page.

Access the Factory Manual and keep it on the bench. You will use it for every step of the rebuild.