I thought this might be very difficult to do in comparison to earlier Disco's/Defenders/Rangys - mainly because you can't really see the PAS box from under the bonnet, and not a great deal of it from underneath either.
Once plastic panels/pipes are removed or moved, then it's much the same as any other PAS box, although there are a few difficulties to overcome.
Few special tools needed - torx sockets and drivers, breaker bar (or a length of pipe on a ratchet/T-bar), and a 40mm socket.
Also 6,8,10,13,18,24, and 27mm sockets, assorted extension bars, 11mm,24mm spanners, axle stand, jack, hammer, old screwdriver/chisel, philips screwdriver, Zip ties (cable ties), some 4-6mm I/D pipe, a container for the old fluid, and some ATF.
Anyway - on with it.
Vehicle is an 04 plate auto Disco TD5 with 59k miles on the clock'
PAS leak fixes have failed, and fluid is still leaking from the shaft lower seal.
Set the steering in the straight ahead position and remove the ignition key so that it locks in place.
Open the bonnet, remove the battery cover - turn the catch at the front 90-deg, lift the front a small amount, then release the two catches at the rear and remove the cover.
Disconnect both battery terminals, move the cables out of the way, then undo and remove the 10mm nuts that hold the battery clamp top plate. The battery will then lift out. Remove the bottle jack.
Remove the 4 x 13mm bolts in the bottom of the battery box.
Undo the 10mm nut that retains the centre of the main earth cable - replace the nut, leaving the other wire in place.
Remove the single philips screw that hold the ECU to the side of the battery casing.
The ECU will then lift out of the housing with all wires still connected. Lift it and turn it over and it will then rest back as shown. Do not apply any force to the ECU or wiring. It will move out of the way quite easily - if it doesn't, then you are doing something wrong.
Two more 13mm bolts holding the battery box in place - remove them, unclip the two coolant bypass hoses on the outer edge, then lift the battery box out. It won't come out cleanly - it catches on the wing channel and the radiator bracket, but it's flexible and will come out.
You can now see most of the PAS box.
Engine top cover next - one 13mm bolt on the drivers side, and two on the opposite side. Remove them, lift the front a small amount to clear the radiatop cover, then forwards and up.
Remove the intercooler hose (2 x 6mm jubilee clips)
Using zip ties, tie the various pipes out of the way of the PAS box. The battery positive cable will tuck away by the header tank.
Now to get underneath.
Apply the handbrake, slacken the wheel nuts on the drivers side wheel (27mm).
Raise the vehicle up as far as you can get it (put the jack under the lowest part of the hockey stick)
Place an axle stand under the chassis rail - just forward of the radius arm bracket is good. Remove the road wheel and keep it nearby - you can stand on it to make it easier to reach inside the engine bay.
You will now see the 4 x 15mm bolts that hold the PAS box the inside of the chassis rail.
Lower the jack until the vehicle rests on the axle stand, then keep lowering until the suspension is almost at it's extended limit. The anti roll bar will move downwards as the axle drops - this will give you more room to get at the PAS box from underneath, and access to the splash panel inside the wheel arch.
The splash panel is held in place by 3 x 8mm self-tappers - remove them and lift the panel away.
The splash panel rear mounting is held to the spring bracket by 2 x 10mm bolts, remove both and lift the bracket away - note that there's an earth cable under the top bolt.
Tuck the earth wire on the outside of the spring mount.
The two PAS pipes are held in place by a single 10mm bolt. Remove the bolt, place a sutable container inside the wheel arch and place both pipe ends in it and allow the system to drain down.
Note that one pipe has a flexible part, so can be easily moved. The other is rigid, so take care not to bend it.
Note that each pipe end has 2 small O-rings - if they get damaged or are otherwise suspect, then replace them.
While the system is draining - remove the 3 x bolts that are on the column link.
E10 torx socket either end, and T40 close to the PAS box. There's also a 4th bolt, but it's a security bolt and can't/mustn't be removed.
When the bolts are out - lever the steering rod away from the PAS box until it clears the splined shaft.
Once the system is empty (it'll drip forever, so find a way to block the ends), the rigid pipe will just tuck under the inner wing lower lip and it's tension will keep it there.
The second pipe can be zip tied to the radiator bracket.
The rearmost engine undertray has to be removed. There are 3 x 8mm self tappers and two press clips holding it in place. Lever the cap centres up and the whole thing will come away. Remove the screws and the tray will come off.
Steering link next - undo the 18mm nut, belt the drop arm with a hammer as shown (it'll seperate after a few whacks), then pull the rod down out of the way.
Panhard rod now - 24mm socket and spanner needed to remove the bolt. Note that as the bolt is pulled out, the axle will drift to the drivers side about an inch.
The drop arm nut has a tab washer on it - use an old screwdriver or chisel to bend the washer back, put a 40mm socket on the nut and undo it. It'll be very tight, so you will need increased leverage, such as a breaker bar or a length of pipe on the ratchet. Undo the nut until it's at the end of the thread.
All that's now holding the PAS in place are the 4 x 15mm bolts through the chassis rail - undo all 4 and remove them. The box will come loose, but pipework close by will prevent it from coming off.
One of the bolts is tight to the Anti roll bar link rod and may not come all the way out, but it will clear the thread in the PAS box, so it doesn't matter.
There's a steel coolant pipe that's held to the rear face of the front crossmember, undo and remove both 8mm bolts.
The pipework can now be moved away from the PAS box, but not much. You need to lever them out of the way (carefully), and the PAS box will just about come off. Be careful - it's very heavy.
The replacement - National Power Steering re-con item.
Note that when in the straight-ahead poition - the slot in the drop arm is in dead alignment with a threaded hole in the casing. There are 4 x master splines, so the arm can be fitted multiples of 90-degrees out.
To remove the drop arm - place the PAS on it's side, place a blunt chisel as shown and belt it really hard a couple of times. Turn the box over onto the other side and do the same thing again. After doing this a few times the arm will break free of the shaft - prevented from going any further by the nut. Remove the nut, washer, and arm.
Place the drop arm on the new unit (make sure it's on the right way up and the slot is inline with the threaded hole). Tap (don't belt), the arm onto the shaft and replace the washer (making sure it sits in the slot), then the nut and loosely tighten it.
The reason for the leak - looks like rust travelled through the seal - allowing oil to come out. Poor design really, and the most common reason for PAS failure.
Put the new PAS box on the chassis rail - levering the pipes out of the way while taking the weight of it is very difficult. Do not put the bolts back through the chassis rail just yet, but re-attach the pipes with the 2 x 8mm bolts. The PAS box won't come off, but will move along the rail - making it easier to reattach the steering column rod. Replace the three bolts (apply torque seal/threadlock to them), then bolt the PAS box to the chassis.
Make sure the O-rings are in place on the pipes, apply a thin layer of grease to them, fit the pipe with the reataining plate first, then the rigid pipe. Replace and tighten the 10mm centre bolt after applying threadlock to it.
Put a 40mm socket on a breaker bar and tighten the drop arm nut - it has to be very tight, so veins sticking out of the forehead really. The nut will seem to take ages to fully tighten, but this is just because the arm is being forced onto the shaft. Once tight - bend the tab washer over one of the nut flats.
Put the panhard rod back in the bracket - it will not lign up due to the axle moving, so lever it into position and re-fit the 24mm nut & bolt.
The battery clamp front bar has a habit of falling out, so before you put the battery box back in, tape it in place.
Replace the intercooler pipe, cut the zip ties and relocate the various pipes and battery positive cable, then replace the battery box, carefully re-fit the ECU (don't forget to twist it as it goes back), replace the earth centre fixing, the jack, and finally the battery. Do not connect the battery at this point, but clamp it in place.
From inside the wheel arch - replace the splash guard bracket - making sure the earth wire is located properly.
Reconnect the battery main terminals.
Fill the reservoir with fresh PAS fluid. From inside the wheel arch, attach a pipe to the PAS box bleed nipple and undo it a turn or more. Fluid will slowly syphon into the mainly empty system. This takes a long time unless you can force it through a bit quicker with some small pressure. The reservoir will need topping up a few times as the system fills.
Close the bleed nipple until it's only a half turn open, then start the engine. Turn the steering on full lock, hold it there for a few seconds, then turn to opposite lock and hold it there again for a few seconds. Do this 3 or 4 times until clear fluid is coming out of the pipe, then top up the reservoir as necessary.
Close the bleed nipple, remove the pipe and replace the splash guard. Replace the road wheel and lower the vehicle to the ground. Go for a test drive and feel for smooth and light operation of the steering. Once the engine (and therefore the PAS system), is hot, then check for any leaks.
Disco TD5 PAS Box Replacement
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