TK mystery part
 

Does anyone know what this metal bracket/shelf and thread stud are for?

This is looking forward at the rear of the cab behind the driver's seat.

It is where the hydraulic jack is/was stowed.

I knew you would come up with the answer Tango November! I wondered whether it was the washer bottle but that is mounted elsewhere. I might just cut that bracket out and use that area to remount the power steering reservoir.
Are the other brackets for a wheel brace or a jack handle or something (semi-circular brackets across the back of the cab)?

Many years ago I was following behind a TK when the jack fell out from it's bracket, it hit the road then bounced back up and knocked a hole in the diesel tank. The driver was unaware on this and carried driving along the road leaving a trail of fuel for some distance until he noticed me flashing my lights and sounding the horn.

Indeed they are.

Here is the power steering reservoir just below the alternator regulator on the old cab. Is this original? It appears to have been added.

Power steering wasn't fitted to KG models when built (nor was the 466 diesel engine!) so it seems that yours has been updated with parts from a KM.

Here is a KM reservoir:-
http://www.ebay.co.uk/itm/Bedford-KM...81235802481%26

Though local sourcing might look different.

I don't remember where it was fitted - sorry.

Not quite the same as that KM one but I guess it really doesn't matter. I've cut the jack bracket off now and the reservoir can go just below where it used to be. It will be very easy to get at there.

Do you know what this valve is called and what it does?

It is an assembly of two changeover valves.

A changeover valve contains a free-moving piston which moves according to the higher incoming pressure and delivers air to the central (outlet) port - which can become the inlet to a second COV (change-over valve).

They are arranged to operate so that a system takes air from whichever circuit is pressurised and can alternate footbrake and handbrake air - selecting the higher pressure without mixing the inlets or can use supply air from tanks or compressor to feed downstream circuits.

These COVs can incorporate pressure switches (see the flange on the upper COV) such as stoplamp illumination or low-pressure warning (yours don't).

Tracing the airflow of your illustration, air pressure would flow from either of the top pipes (straight or elbow) - depending on which is the higher pressure - to the lower COV.
The outlet of the lower COV (the middle horizontal straight pipe) would receive the higher pressure between the upper COV outlet and the bottom horizontal pipe with the elbow inlet.

Seemples . . . :D

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 ?

Indeed you are correct on all counts.

The small (214 cu in petrol) was really just a car engine.

There was a 'keyhole' in the front bumper - click on the following then click on the image to enlarge it then look above the first 7 on the front number plate:-
http://upload.wikimedia.org/wikipedi...xtra_shine.jpg

The hydraulic jack supplied as standard (unless there was a delete code added) was a quality product (it had to be to lift a possibly laden truck for a wheel-change).

Can you explain a bit about how the air brake foot valve works? It has two air supplies from two independent tanks and two pipes to the servo on the master cylinder. I'll grab a picture if you need it.

A dual-air footbrake system provides a safety feature (the system will work if either of the circuits fail). Likewise, the hydraulic master cylinder is split so that failure of either circuit will provide at least 'residual braking' for the vehicle.

A diagram:- http://lh6.ggpht.com/_Ii1ukGkfijY/Sq...jpg?imgmax=800

From:- http://what-when-how.com/automobile/...em-automobile/

Does that answer your question - or would you like a more detailed explanation?

More detailed if possible please, particularly the TWO air lines to the servo. Does it use air pressure in both directions, like a double acting ram for applying AND releasing the brakes. The two ports on the servo are in quite different places, one in the end of the cylinder shape and the other about half way along on the circumference.

See above - come back if you still have questions.

Here's a rather crappy picture but it shows the two airlines going into the servo.

One airline feeds the 'front' piston and therefore has to be positioned halfway along the servo body whilst the other airline feeds into the end of the servo body and feeds the rear piston.
Because of the design of the pistons within the servo, each of the air supplies can operate the master cylinder.

Brilliant! I understand now. There is a further question I have about the hand brake circuit and those COVs but I'm not sure what it is yet! Thanks for your help, it is much appreciated.

I lifted the engine and box out on Saturday, BLIMEY that's a heavy lump, my front end loader would only just lift it.

Change-Over Valves are 'either or' - that is they pass air from either of two circuits to whatever is downstream. The valve prevents back-feeding into the 'other' supply circuit.

Think of it as a shuttle-valve.

Are you, perhaps, confusing a Quick-Release Valve? This is normally in a circuit where 'quick-release' is desirable (such as a spring-brake parking supply - or rear airbrakes). When pressure is applied a diaphragm is held over the exhaust port so that the air supply can be passed downstream to the actuator - when the input pressure disappears the spring lifts the diaphragm off the exhaust port allowing the residual air to escape directly rather than having to return 'upstream' to the application valve exhaust port.

A section through the brake servo:- http://s24.photobucket.com/user/Grou...P8509.jpg.html

I don't think there is a quick release valve on this truck, I think the parking brake exhaust is through the handbrake valve.

Here is the picture of the dual COV arrangement but I've labelled it this time.

The spring brake is on port B

Port A is a feed from the emergency brake release in the cab, so under normal operation COV2 always takes its air from port C

Port D is from the handbrake valve, port E is directly from one of the air reservoirs (one of the two footbrake reservoirs)

I don't see how the handbrake can be applied, since there seems to be always pressure in COV1. I've obviously missed something

Looking at your photograph, COV 1 takes pressure from port D and port E (alternatively) and then COV 2 takes pressure from port C and port A (alternatively) and delivers its output to port B.

The bit I don't get is this:

Driving along COV1 has pressure on both its inputs. Port D has pressure via the handbrake valve and port E has pressure from the foot brake circuit.

When the driver applies the handbrake port D is vented causing COV1 to take its input from port E and the brake stays OFF, still pressurised. I know this is not what really happens but I don't see it works. Port B has to be vented for the spring brake to apply.

Aha! there was a mistake in my notes, port E is fed from one of the lines to the brake servo so it only sees pressure when the foot brake is operated. Still not sure what this line does but I do understand how the rest works.

In theory, with the hand brake applied, pushing and holding the footbrake should release the handbrake; I'm not sure why you would want this but I'll have to give it a try one day when it's all back in one piece...

It is usual to have 'anti-compounding' so that brakes are not applied by two sources which could overload the mechanicals.

Oh I get it (I think) without this line it would be possible to apply the rear brakes with air pressure and the spring brake both at once, possibly damaging the parts.

As with most vehicles (although some folk don't realise) the handbrake serves as an emergency brake in the event of total failure of the service brake (usually split into service and secondary systems).

In the days before dual circuit systems, the handbrake (usually mechanical) was the 'last resort'. Although parking brakes are now typically spring operated, the control valve has to be 'progressive' such that the mechanicals don't break if applied when the vehicle is in motion.

I notice that the compressor pipe to the condenser tank takes a very long route. It goes right round the engine and back to a point on the chassis only about 2' from where its started although the pipe is probably 10' long. Do you think that is intentional for cooling?

Yes, the air is very hot when it leaves the compressor, and would rot the rubber hose needed to absorb the engine movement, also it helps to cool the air so that any moisture condenses rather than staying in suspension.