My Defender was starting to suffer from starter solenoid contact failure - a single click from the engine bay when trying to start. Turning the key back to off, then trying, again and again, several times, each with nothing more than a click, eventually, she fires into life as if nothing was wrong. Each day was getting progressively worse, and sometimes taking up to 10 attempts.
I ordered a new set of contacts and a new plunger from RepairKitsUK as recommended on the Land Rover forums, for Â£12 delivered. Despatch and delivery were quick and prompt.
The forums contain many threads with people saying that the TD5 starter motor is difficult to remove, and that the top nut is "from hell", and that the only way to do it is by removing the belly pan and going in from underneath, but I was able to do this relatively easily, from the top of the engine bay with a 15mm 3/8" socket, extensions and ratchet. This is my most major task that I have done my myself on a vehicle.
Firstly, disconnect the battery. We are potentially dealing with live 12 volts and lots of amps. Best not take any risks.
I found it easier to remove the engine cover and the flexible air intake pipe from the airbox to the solid intake pipe as that gave me more room for access. After disconnecting the live and earth wires, attach the 15mm socket to the extension and slide it in parallel and over the top of the starter. You can then put the socket on the nut. Next, slide in the ratchet and connect the two. Space is limited here, but you should be able to get some leverage and crack the nut loose. After this, it is easier to undo by hand, approaching from behind under the wiring loom. The other two bolts are 13mm and easy to reach from on top.
The starter motor is now free and can be pulled out past the wiring loom towards the suspension strut.
To replace the solenoid contacts, remove the three bolts holding the cover in place. Be sure not to lose the rubber gasket underneath as you will need it to reassemble.
When the cover is removed, you can pull out the old plunger, it is not held in with anything. Be careful not to lose the long spring that is on the shaft of the plunger. You need to put this on the new plunger. You can now start to replace the contacts, one at a time so you know which one is which. Undo the nut (14mm) on the outside, then pull it through from the inside. The live side of the solenoid has a connector to the motor, so undo the first nut (12mm), remove the connector, then undo the next nut (14mm).
Remember the order that you remove the nut (14mm), washer, plastic thingy and o-ring, as you should reassemble in the reverse order. On the connector side, its nut (12mm), connector, nut (14mm), washer, plastic thingy, o-ring.
Once these have both been tightened so that there are no gaps, you can replace the cover and start reassembly. Once you feed the starter motor back in place, slide the small back earthing cable back onto the connector. It's easier to do now than wait until it's bolted back on.
I found it easier to get the middle bolt on tight first, then the bottom one. To put the nut back on the top, attach the nut to a 1/4" extension with a little blue tack, then using the same process as getting the extension onto the nut, place the nut on the bolt. You can reach in and hold the nut steady while you turn the extension. Once the nut has taken the thread, you can hand tighten the nut, and once tight you should be able to get the socket back on to fully tighten.
Connect up the live power cable. Remove all tools and check for any disruptions in the engine bay, connect up the battery and try and start. Fingers crossed yours will start first time, just like mine!