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The David Brown Selectamatic Hydraulic System

A schematic diagram of the David Brown Selectamatic Hydraulic System. Also a guide to repairs and some other useful tips.

The DBTC are indebted to Mr. Alan Kellett who was a Product Training Instructor at the Meltham Hall Training School and Mr. Karl-Olof Kulberg (Ollek) who was Service Manager for DB, Case/IH from 1972-1999 in Finland who between them and with encouragement from Mr. Peter Murray have supplied this schematic diagram and the other documents dealing with the Selectamatic hydraulic system.

In his continuing series on the operation of David Brown’s hydraulic system, Alan Kellett explains how to diagnose failure to drop. 

The procedures described in this article are designed for those without access to diagnostic tools or special knowledge, and should be used in conjunction with previous magazine articles. Failure of the three-point linkage or an external service to drop can be either mechanically or hydraulically based.

Initiate the diagnosis by slackening the bleed screw in front of the lift cylinder housing one complete turn while standing well clear of the linkage. If the linkage then drops, the problem is hydraulic, and thus you need to go to the procedure described below beginning at Hydraulics (1). If the linkage does not drop, the problem is mechanical, and so you need to begin at the Mechanical section further down the page, again beginning at (1).

Hydraulics

1. Ensure three-way valve is in position L/1 and fully to the right (offside). Move selector to ‘Height’ then ‘External/TCU positions respectively, then move quadrant lever to drop position. If linkage then drops, problem solved; if not go to 2.

2. Remove the two half-inch cap-screws retaining the dump valve anchor-plate and rotate the plate anticlockwise until it abuts the bridge-piece (camel’s hump to some).The top of the spool valve can then be felt and/or viewed. Then cycle the quadrant lever and check for corresponding spool valve movement. If the spool moves, go to 3; if not, go to 5.

3. Check and readjust group 3 linkage adjustments (as covered in the Selectamatic Hydraulic section on the DBTC website), then cycle quadrant lever. If linkage drops, problem solved; if not go to 4.

4. Problem is sticking latching valve or misaligned sleeve. Remove valve chest from tractor and rectify or replace chest.

5. Check and readjust group 3 linkage adjustments as in 3. If still no drop, problem is sticking or maladjusted spool valve. Remove valve chest from tractor, remove the two seven-sixteenth spool locknuts, tap out seized spool, lubricate and reset as per etched figure on spool base. Refit to tractor.

          Mechanical

1. Ensure lift latch is fully disengaged. If not, problem solved; if it is, go to 2.

2. Remove any implement on linkage, then remove the six cap-screws retaining the latch housing to the ramshaft assembly. Check the ram lever has not fractured and jammed on the housing. Then check the bushes are free on the shaft. If lever is fractured or bushes seized, remove and replace. Problem then solved. If lever and bushes are good, go to 3.

3. With latch housing still removed, check ramshaft for free rotation. If seized, remove and free off. Problem solved; if not return to 1