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• Blue Circle Cement operates a fleet of 310 tractive

18th July 1991, Page 31
18th July 1991
Page 31
Page 31, 18th July 1991 — • Blue Circle Cement operates a fleet of 310 tractive
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units and 400 trailers. Most of its artics are 3+2 Combinations, with Leyland Daf 6x2 tractors hauling Metalair tandemaxle trailers on RO-R running gear; the trailer brakes have anti-lock but no load sensing.

Typical annual distance covered is 80,000km and the combinations either run at 38 tonnes or unladen.

Fleet engineer Ted Wraight explains that the company was experiencing excessive trailer brake wear and, depending on terrain, lining life ranged from 15,000km down to as little as 6,000km.

The drivers had also noted very high brake temperatures.

As the trucks were on a repair and maintenance contract it was not immediately apparent how their brakes were performing, but checks revealed that the drive-axle linings were lasting up to 200,000km!

Following an extensive series of checks Wraight says: "We were convinced that the problems lay under check braking, but this is very difficult to prove." At this point he went to Leyland Daf for assistance.

Tests by the manufacturer revealed that it was indeed under check braking that the difficulties arose, specifically in the region of 0.2-0.4bar. At these low pressures the threshold of a relay valve on the unit was preventing the drive axle brakes from operating, leaving the two trailer axles doing the bulk of the work.

Leyland Daf changed the relay valve and with the predominance set at 1:1, the problem seems to have been eradicated. Wraight reports that although the six vehicles that have been modified have not yet done enough work to be certain, early indications are that trailer linings will last around 70,000km — a seven-fold improvement.

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