Dito this... however the back brakes are marginal at best on these asumming your taking about a leyland daf 45... in the end most people end up fitting new cables, drums and shoes!! but if your mecanic was doing his job properly he would have removed the drums and given everything a good clean and would be able to see the ajusters and how they work!!!!!as the most basic starting point........
Personally I would want to know that my brakes were as effective as they can be and passing on a "Lock" with a partialy loaded lorry is not exactly my idea of good policy. In 35 years of servicing lorrys I have never come across a "different" brake adjustment for horse boxes.Scraping through a test with marginal braking efficiency is not my idea of good maintenance. The biggest problem with drum brakes is that a freshly adjusted brake (especialy if it hasnt been regularly adjusted)will have a lower braking efficiency than an unadjusted one until it beds in.I may be being stupid but how would having "enough weight in the back" mean that your brakes are ok? I would want the least weight possible for a plating :/
I have a Leyland Daf 45 150 and have never weighed it down to get it through its test???
It has however failed on the handbrake - it's aparently a "known" thing for Dafs. The brakes adjustment for a horse lorry is slightly different for a normal truck - you don't want to stamp on the brakes and have the horse come through into the living (obviously they're still sharp enough to stop quickly)
The last time it failed on the hand brake, the measurement was 13% and my lorry mechanic just adjusted it and put it back through the test. This was however before a re-test cost the same amount as a full test (£95) - now it goes for a full workup before it's tested - flew through last week with no comments at all