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Selectamatic Hydraulic System

A schematic overview of the David Brown Selectamatic Hydraulic System

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This section features a detailed schematic of the David Brown Selectamatic hydraulic system, along with a repair guide and a selection of helpful maintenance tips.

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The David Brown Tractor Club gratefully acknowledges the contributions of Mr Alan Kellett, former Product Training Instructor at the Meltham Hall Training School, and Mr Karl-Olof Kulberg ("Ollek"), who served as Service Manager for David Brown and Case/IH in Finland from 1972 to 1999. Their expertise—alongside the encouragement and support of Mr Peter Murray—has made it possible to compile this valuable diagram and the accompanying documentation on the Selectamatic system.

Diagnosing Failure to Drop in the David Brown Hydraulic System
By Alan Kellett

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In this continuation of his series on the operation of David Brown’s hydraulic systems, Alan Kellett outlines a step-by-step diagnostic process for identifying the cause of failure in the three-point linkage or external service to lower.

This guide is intended for users without access to specialist tools or in-depth technical knowledge and should be used alongside previous magazine articles for reference. A failure to drop may stem from either a mechanical or hydraulic fault.

Initial Check

Start by loosening the bleed screw located at the front of the lift cylinder housing by one full turn—stand well clear of the linkage during this.

  • If the linkage drops: the issue is hydraulic – proceed to the Hydraulics section below.

  • If the linkage does not drop: the fault is mechanical – skip to the Mechanical section.

HYDRAULICS

  1. Check valve and lever positions
    Ensure the three-way valve is set to position L/1, fully to the right (offside). Move the selector through Height, then External/TCU settings, and finally set the quadrant lever to the drop position.

    • If the linkage now drops: issue resolved.

    • If not: continue to Step 2.

  2. Inspect the dump valve anchor-plate
    Remove the two ½-inch cap screws securing the dump valve anchor-plate. Rotate the plate anticlockwise until it contacts the bridge-piece (sometimes called the "camel’s hump").
    Now locate and observe the top of the spool valve. Cycle the quadrant lever and check for spool valve movement.

    • If the spool moves: proceed to Step 3.

    • If the spool does not move: skip to Step 5.

  3. Readjust the Group 3 linkages
    Refer to the Selectamatic Hydraulics section on the DBTC website for details. After adjustment, cycle the quadrant lever.

    • If the linkage drops: fault resolved.

    • If not: proceed to Step 4.

  4. Check latching valve and sleeve alignment
    The issue may lie with a sticking latching valve or a misaligned sleeve. Remove the valve chest from the tractor. Inspect, repair, or replace as needed.

  5. Free and reset the spool valve
    Recheck and readjust Group 3 linkages as in Step 3.

    • If there's still no drop: the spool valve may be sticking or out of adjustment.
      Remove the valve chest, undo the two 7/16" spool locknuts, tap out the spool if seized, lubricate it, and reset according to the etched markings on the spool base. Refit the valve chest.

 

MECHANICAL

  1. Verify lift latch disengagement
    Make sure the lift latch is fully disengaged.

    • If not: disengage to resolve the issue.

    • If already disengaged

  2. Check for mechanical obstructions
    Remove any attached implement. Then, undo the six cap screws securing the latch housing to the ramshaft assembly.
    Inspect the ram lever for fractures or signs of jamming. Also, check that the shaft bushes rotate freely.

    • If the lever is broken or bushes are seized: repair or replace components to resolve the issue.

    • If both are fine: continue to Step 3.

  3. Test the ramshaft for free rotation
    With the latch housing still removed, rotate the ramshaft by hand.

    • If it is seized: free it off—problem solved.

    • If the shaft rotates freely: return to Step 1 for further inspection.

 
This hands-on diagnostic method is designed to help you identify and resolve common issues in the David Brown hydraulic system using basic tools and systematic logic.

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