i know what service and parking brakes are, but what are secondary brakes?
newdriver1234:
i know what service and parking brakes are, but what are secondary brakes?
Exactly what it says, they are a secondary braking system fitted to large vehicles normally operated by the parking brake valve. On modern systems the valve has a sprung secondary position, the bit between them being “off” and when the parking brake lever is locked with the lifting ring or button.
When your Grandad was driving, this was operated by steel cable by a cabin boy or trailer boy. 
Later on they dispensed with him, gave him his own lorry and fitted a three line air brake system to the fleet;
Red - Emergency. Blue - Secondary, & Yellow - Service. To confuse things further these hoses were normally coloured Black 
They couldn’t be mixed up though because the fittings were called C Type couplings and CA couplings. The C Types are still used today and are of separate genders. The larger Blue line was also dispensed with but due to European Legislation still had to have a secondary system so they included it within the parking brake.
The Blue line was a favourite tool of owner drivers as it had a separate hand valve and only operated the trailer brakes. This ■■■■■■ the ferry trailer operators right off as the drivers would save their own unit brakes and wear out the trailer brakes instead.
By the time you come to explain this to your grandchildren the brakes will be either nuclear fission or operated by a single air feed and fly by wire technology, we are not that far away now with ABS, EBS ETC
Next Week!
Why drivers had 3 logbooks 
newdriver1234:
i know what service and parking brakes are, but what are secondary brakes?
they are for the ooooooooooohhhhhhhhhh ssssssssshhhhhhhiiiiiiiiiiiitttttttttttt moments 
I have known mechnaics use the secondary function to warm up trailer brakes before MOT. They just drive round holding the park brake lever partially on
Doesn’t work with all tractor units (apparently) but basically as already mentioned the park brake control has a mid-way position that will apply the brakes - usually just the trailer but not always so.
Designed to allow partial braking on down hills etc I think.
Also a useful tool for annoying the cops manning a speed check (er - allegedly) 
I’m not suprised at this question, not many drivers actually know their vehicle has a secondary brake system (especially rigids) and think the handbrake lever is just that. It will operate the tractor rear and trailer brakes or rear brakes on a rigid, known as the Deadman (Blue line on three line system) when the system used a separate handle usually fitted to the left of the steering wheel and as the name implies a second system of braking if there is a problem with the service brakes (foot). Also called the Auxiliary brakes it wouldn’t operate the fronts as the front chambers only had the supply from the service brake. Wonder if those fitters realise they are holding the tractor rear brakes on the same time as the trailer when ‘warming up’ the trailer brakes, which in itself is an outdated practise that does nothing for brake performance that a good service of the brake system will do better when in the workshop for pre MOT, but that’s another subject. Franky.
Wheel Nut:
Next Week!
Why drivers had 3 logbooks
I’m going to keep you to that one lol