Brilliant! I was trying to draw a diagram better to understand the brake system but got rather stuck not knowing what was inside those valves.

Under the dashboard there is a valve and a small lever called "Emergency brake release" which I have never known its purpose! It is not the handbrake. When operated, the air from this control is sent to the lowest of the connections in the photo.

It depends on whether you have hydraulic or air brakes in the wheels and whether you have a spring-brake parking brake.

I would assume (!) that your emergency brake release supplies air to a spring-brake chamber somewhere on the vehicle.

Some vehicles had a spring-brake chamber that operated pull-rods that applied the rear wheel-brakes by mechanical levers whilst some vehicles had a transmission brake (drum or disk) on the rear of the gearbox or front of the rear axle.

This might help:- http://www.truckandbusforum.com/showthread.php?p=13927

http://www.greenmachinesurplus.com/b...1087-239-p.asp - or cheaper secondhand on eBay (carriage could be expensive, though).

It has hydraulic wheel cylinders and a spring brake parking mounted on the diff and operating pull rods to the rear hubs.

I'm guessing that the emergency brake release can supply air to the spring brake EVEN after a main brake system failure has caused the spring brake to apply?

It depends on where the air supply for this lever/switch comes from and how close to the spring brake chamber the pipe goes, but yes, the intention is that when all else has failed and the vehicle needs to be dragged off the highway, then the emergency brake release can avoid having to get down and dirty with the wind-off spanner.

Of course, if the spring brake chamber seal is knackered you will still need to wind it off mechanically!

The compressor feeds a small tank mounted below the passenger's feet. This tank feeds three more mounted amidships. The largest of the three feeds ONLY the emergency brake release (I think!). I assume that each tank is fed through a non-return valve to keep the systems separate.

The purpose of the small tank is to condense the moisture after the air has been compressed (and heated) then (for your age of vehicle) the air is passed through non-return valves to the reservoirs. The valve on the bottom of the small tank is an automatic drain valve which should drain off any condensed moisture from time to time (as the pressure fluctuates). You can 'drain' the moisture by gently pushing up the pin in the centre of the exhaust port (on the bottom of the drain-valve).

The non-return valves (on each reservoir) prevent back-feeding of air in the reservoir but offer no protection to the other circuit, so a major air-leak can deplete the air stored.

Later models have 'protection' valves that limit the leakage of air from a damaged system so that the air from the compressor (condensing tank) can be fed to other non-leaking systems and keep them operating (albeit at reduced pressure).

Ah, so that is why the little tank is down in the cool air flow at the front: that explains a lot. The valve on this small tank is also the one you hear blow off when the system is fully charged?

Not entirely, there is an unloader valve in the compressor which is controlled by a pressure regulating valve that will have small-bore plastic tubing connecting it to the condensing tank and also to the compressor, so you might be hearing the compressor 'unloading' - though the drain valve will emit a short 'Pffft' as it expels the condensate. You can check which one you are hearing by squatting next to the condensing reservoir as the compressor reaches cut-out pressure.

The pressure regulating valve looks vaguely like this:- http://thumbs3.ebaystatic.com/d/l225...VXCIHzEf0A.jpg

or this:- http://ace.imageg.net/graphics/produ...8622enh-z7.jpg

(both of these are more recent versions, but there will be a 'dome' with a screw and nut (for adjustment) on the top).
This valve signals the unloader (exhaust) valve in the compressor cylinder head.

I found the pressure regulator valve and the small bore hose to the compressor just as you described.

Here is the jack bracket gone!

One for G-C, am I correct in thinking that some TKs also had a starting handle clipped up under the cab. I don't think it could actually be used to start the engine but was used to turn the engine over if needed during servicing or repair, for example when adjusting valve clearances ?