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Replacing an LT77 gearbox in a Disco

Les Henson

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This thread is the replacement of the LT77 gearbox in a 200TDi Disco with a remanufactured item supplied by Ashcroft Transmissions.

The following instructions are for one person doing the work, so are understandably detailed and complex - the weight of the transmission assembly is beyond most peoples abilities to lift into position without specialist lifting equipment, so the transfer case and gearbox are removed as seperate units. Taking the weight of each seperately is also quite dangerous as you need to be lying directly under each one in order to remove/fit them, and there's a risk of either one falling on your face/chest if things go wrong. It's a lot easier to have at least a second pair of hands to do this work or at least a friend to help with the heavier side of things.

There are a few pictures missing at the start - the customer decided to have a go himself, but got scared pretty quickly :D , so the gear knobs have been unscrewed, the mat removed, the switch panel popped out, and the centre console screws are out already.

Two screws in front of the gear lever, 4 at the back under the tray mat, and the switch panel hanging out.




Remove the 12mm pinch bolt and remove the gearstick shaft.


Pull the handbrake on and remove the pin clip, release the handbrake and remove the pin that holds the cable to the lever.



Pull the handbrake lever up this far (if you go beyond the ratchet teeth, the pawl will flip over and prevent you from reconnecting the cable when the job is finished without pushing it back with a screwdriver.


If you want to you can twist/pull the hand brake shroud off and put it out of the way, but it doesn't tend to be in the way.

Remove the foam insulating pad.


Remove the metal plates around both the gear and transfer levers.



There is a thin steel retainer that holds the rubber seal in place with pop rivets. Drill them out with a 4.5mm bit.


With it out of the way, the top of the gearbox can be seen.


The transfer lever housing doesn't come with the new gearbox, so it has to be removed. It's held to the top of the gearbox by 4x13mm bolts - they are different lengths, so make a note of their position when you remove them.


There are two link rods that have to be disconnected - remove the clip and pin shown here -



The pivot point has the same arrangement.



Mark the second rod as shown and also the shaft so that it can be fitted in the same position.


Slacken the 10mm pinch bolt and the the second rod can then be removed.


Remove the 4x13mm bolts and the transfer lever assembly can be removed.


Unplug the two wires from the reverse switch - it doesn't matter which way the wires are connected.


Undo the gearbox breather (15mm) make sure you retrieve the copper sealing washers.


Exactly the same with the transfer box breather.


Unplug the diff lock switch - again it doesn't matter which connections the two wires go on.


Both breather banjo bolts are identical to each other, so no need to keep them seperate.


The pivot point has to be removed - it retains the breather pipes. There's an adjusting/lock nut on it, try not to move it on the thread.



Lift the breather pipes and wiring out of the transmission tunnel hole and tie them out of the way.


Remove the transfer case drain plug and drian the oil.


Same with the gearbox.


The gearbox drains quite slowly, so while it's doing that, disconnect the handbrake cable. Remove the split pin and pin.



Undo the cable locknuts with 2 x 19mm spanners.



You need plenty of room under the truck, so rather than disconnecting the prop at just the brake drum - remove it entirely.

4x14mm nuts on the handbrake drum and 4x14mm nuts and bolts at the diff.



The front prop can just be disconnected from the transfer case end and tied out of the way.


Gearbox mounts now - remove the following bolts/nuts






Speedo cable next. 10mm socket on an extension bar and retrieve the fork which will come loose.


exhaust clamp next - should be 2x13mm nuts. tap the join with a hammer to break the seal if necessary. Also undo the exhaust mount, just a 13mm bolt. The exhaust will now hang down and access to the transmission will be improved.



Raise the gearbox far enough to remove the mount assembly.





Remove the 5 nuts/bolts either side that holds the gearbox crossmember to the chassis rails.



There are now just 5 x 17mm bolts and 1 x 17mm nut holding the transfer case in place on the gearbox. Remove all the bolts first.






Undo the reamining nut - making sure that the stud doesn't come out with it. Once the nut is removed there is nothing holding the transfer box in place apart from the gearbox input shaft.


Lie under the transfer case, take the weight of it and carefully slide it towards the rear of the vehicle. There's bareley enough clearance for it to clear the input shaft and the balance of the case is very awkward. Lower it to the ground and remove it from under the vehicle.


Gearbox now. Remove the jack, remove the two 13mm bolts that secure the clutch slave cylinder and tuck it up on top of the chassis rail with the pipe still connected.


Bell housing nuts now - all are 17mm and then 4x15mm bolts at the bottom. Slacken one of the nuts on the side, but leave it loose on the thread. Using extension bars to get at the awkward ones - remove the rest.


Lay on your back, support the gearbox with your knees and remove the final nut. Slide the gearbox backwards a few inches to clear the clutch and lower it to the ground.


Various parts of the old gearbox have to be transferred onto the new one - bellhousing, transfer lever rod pivot point, and a stud. The clutch is quite new, so I'll be reusing it after checking it's still ok.


The old clutch fork has got the usual signs of excessive wear, so it'll be replaced with a reinforced item.


The new box - straight out of the crate.


The stud you have to swap over. Lock two bell housing nuts against each other on the thread and then unscrew it from the old gearbox. Use the same method to fit it to the new one.





The bell housing is held to the gearbox by 6x19mm bolts. There are two different lengths, so make sure you make a note of their position.



There are two locating dowels. there two new ones on the new gearbox, but make sure they aren't stuck in the bellhousing instead.



The dowels in place on the new gearbox - the longer two bolts go through these.


The new gearbox assembled.


Remove the two slipper pads off the old clutch fork and clean them.


Detach the operating rod from the clip.


The new reinforced clutch fork.


Put a blob of coppaslip or similar grease on the pivot point.


Also where the slipper pads go.


Dip the ball end of the pushrod in the same grease, attach a new clip, plus a cable tie to make sure the rod never comes off.


Don't forget the little clip that holds the fork to the thrust bearing.


A small amount on the pivot point inside the bellhousing as well.


The thrust bearing guide too.


Attach the thrust bearing with the small clip.


Clutch inspection next. It's held to the flywheel by 6x13mm bolts - slacken them progressively if you may be using the clutch again.




With the clutch off, carefully inspect the flywheel for damage, such as high spots (blue patches), or micro cracking - usually caused by clutch imbalance.


Same with the plate and cover.


The spigot bearing should also be checked. This one was loose and a new one is only about a quid, so this is how you replace it.


Press the new one in with your hand, making sure it's nice and square, then carefully knock it in with a soft metal bar, such as alloy, or some hard wood.




Make sure the clutch plate is this way round.


Put the clutch assembly back on the flywheel - making sure the locating pins are through the holes in the clutch cover, then put the bolts in just a few turns.


A centering tool makes things easy. I use a cut off input shaft to do it.


Use the centering tool to keep it all in line and then tighten the bolts progressively and in a diagonal sequence.

Once the bolts are tight, pull the tool out and slide it in again to make sure all is ok.


Put the gearbox crossmember back on with just a couple of loose bolts either side. The engine will have levelled out when the transmission was removed, so jack up under the crank pulley to tip it again.


Slide the gearbox under the truck, lay it on it's side and lift the back end up onto the crossmember.


Slide it up until it's balanced on the crossmember, then turn it upright, support the back of it and slide it towards the engine nice and level.


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By LES Henson:


If you are in the right position you will be able to see and carefully guide the input shaft through the splines and into the clutch. If it stops dead a couple of inches away from the engine, then turn the gearbox shaft to align the splines and the gearbox should then slide all the way on.


Put a few nuts on the thread to keep the gearbox in place and then tighten them. Replace the slave cylider - making sure the rod goes through the hole in the dust cover.


You can test the clutch by pressing the pedal. Replace and tighten all the bell housing bolts, remove the jack and put it under the gearbox and raise it a small amount.


The transfer case has a seal that fits over a land on the gearbox shaft, so grease the land.


There's a possibility that the transfer case seal could have been damaged when removing it from the gearbox or just as a precaution - replace it.

The old seal easily levers out - be careful not to damage the alloy housing.


The end of a hub nut box spanner is exactly the right size to press the new seal in.


Just slightly lower than the surrounding metal.


Remove the gearbox crossmember.

The transfer case is a very awkward shape and getting the balance right is very difficult. Try to position yourself so that you can make sure that you don't damage the new seal as you slide it onto the gearbox. Once again if it comes to a dead stop - you will have to turn one of the prop flanges to align the splines of the input gear and shaft. The transfer case should then slide all the way on. Replace the 5 bolts and but and tighten them. Jack the gearbox up as high as it will go, and replace the mounting.



Replace the crossmember and tighten all the bolts/nuts (13mm or 17mm). Don't forget that the speedo cable clip goes on one of them.


Reattach the speedo cable - making sure it's fully home before tightening the nut. Then the handbrake cable.



A smear of gun gum or similar on the exhaust joint. Tighten the nuts evenly to ensure a good seal, and then bolt up the exhaust mounting.



Lower the transmission down - making sure the holes all line up - replace the 17mm nuts/bolts.


The filler plug is on the drivers side of the gearbox - a 13mm spanner is the right size to undo it. This is also a level indicator, so fill with Dextron 3 or equivalent, until it starts to dribble out of the hole.



The transfer case has the same filler/level arrangement. The square key plug can be undone with a 1/2" drive ratchet.



Use EP80/90 oil in the transfer case.

Attach both breather pipes - making sure there's a copper washer either side of the banjo fitting, attch the wires to the diff lock switch, reverse switch, and the pivot point for the transfer lever rod (there are two thin plastic washers that go either side of the eye - if they are loose, apply a small amount of grease to keep them in place).





Grease the mechanism of the transfer lever inside it's housing and then bolt it back down, and attach the two link rods - making sure the previously made marks line up.


Reassemble the tunnel cover rubber and attach it with pop rivets.


Attach the hand brake cable, put the foam insulation back on and then the tunnel cover.

That's it. Take the vehicle for a test drive - the gearbox may be a little stiff initially, but will soon settle in. The gearchange is very accurate, so expect a few mistakes until you get used to it.

A few things to remember -

If you need to stop for a break, don't do it with the transfer box or gearbox not bolted on properly. They could fall off and be damaged. Try to make the time the gearbox and end engine are only supported by the engine mounts - they could get split if you don't get on with it. It takes a lot of physical effort to remove the transmission, so take a break after removing/replacing them. Use the recommended oils - the wrong type will damage the transmission and may cause it to fail prematurely and require replacement. If you can get anyone to help you with at least the heavy lifting, then do so. If you slip or something goes wrong, you can be seriously injured.

I had to do it on my own - I have no mates :D

Les. :)

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Having just done the transfer box on my 200 tdi disco on my own, I will testify to just how physically demanding it is. :o

The other thing to note when doing the transfer bos is just how little room you have to slide it off the ouput shaft from the gearbox. If you need a bit od extra clearence (and I did, having not removed the gearbox mounts or crossmember) taking the 6 bolts and the coverplate off the back of the transferbox helps immensely.

Also, when lowering or raising the boxes unelss you have a specialist transmission jack, there is some potential for the box to move on the trolley jack. I found having a couple of big bits of wood strategically placed such that if the box does fall it falls on them, and not me, was very usefull.



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Impressive Les, one question though, how do you get the box out from under the car, I've found the disco to be very low after working on the 90, is it worth putting it up on wheel ramps or do you just jack the bugger out of it to make space to slide the boxes out after freeing them?

The only other suggestion is that on the disco box you have there, with the central mount, making an aligning doofer like I did (over on disco area) can possibly make the job a lot easier as it will level the transfer box as you jack it up. Possibly less an issue if you are splitting them as you do here.

Oh and putting all the rivets back in the interior is a fore arm building job :)

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You're right Steve. In fact I did raise the drivers side front and rear wheels in order to gain more room/rotate the props to undo the bolts/get the gearbox out from underneath. It took me 10-hrs to upload the pictures (126 of them), and then work out the text, and I made a few mistakes. I have yet to correct some spelling mistakes and a few other things.

It'll be better tomorrow :D


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