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Replacing a 90/110 gearbox

Les Henson

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Those of you that have the LT77 gearbox as fitted into 90/110/Disco will probably be familiar with the mainshaft wear that these gearboxes suffer from. You either rebuild the gearbox or replace it, along with the associated gear. The eventual outcome if you ignore the loud clunk whenever you let the clutch out is that you will lose all drive between the gearbox and transfer case. The replacement gearbox is a re-con unit supplied by Bearmach (£420), some of their stuff is excellent and some isn't - considering the amount of work involved in the job, lets hope it's going to be ok. While the gearbox is off - the clutch is replaced with a Borg & Beck kit, also the crankshaft rear oil seal and the reinforced clutch operating fork.

You can seperate the geabox and Transfer case and remove them as seperate units from the vehicle. I prefer this method, but the whole thing can be removed and then done on the deck.

Biggest headache was siezed nuts/bolts - both on the bodywork and also the gearbox itself.

The floor plates, transmission tunnel cover, and seatbox have to come out. It took about three hours just to do this - the 4-bolts that pass through the 'b' pillar just turned along with those ridiculous nut retainers, so all 4 had to be drilled out, plus the usual floor screws breaking off or shearing. No pictures of the floor being taken out, as there seemed little point, so this thread starts with the floor, transmission cover, seatbox, and both props removed.

Drain the oil from both the gearbox and transfer case.


First - disconnect reverse light switch wires from the rear of the gearbox - feed the two wires out of the way and put in the drivers footwell (wrap around a pedal to keep them out of the way. Also the single wire that goes to the diff lock switch near the fuel tank - again tuck out of the way.

The layout of the transfer and gearbox breathers, and associated linkages is very tight and you have to be careful to put it all back together the exact same way it came apart or pipes will rub which will allow water to get in. One of the transfer linkages is on a spline, so you will have to mark it to make sure it goes back in the same position.

The first arm is just two pins and clips - remove these and leave the arm connected to the transfer case


Mark the inner and outer rings by scratching with a screwdriver


Then undo the 10mm pinch bolt (no need to completely remove it). Slide the outer ring off and again leave it attached to the transfer case.

Breather pipes next - each one has two copper sealing washers, so clean around the banjo bolts, remove the pipes and then screw the bolts back in their holes

Gearbox breather:-


And transfer:-


The pipes are clamped to the side of the gearbox in two places - the pivot point for the transfer link rod, and one bolt by the gearchange housing. The pivot point is adjustable, so slacken the locknut, then turn the whole thing to release the two pipes. Teporarily screw the pivot point and bolt back in once the pipes are free. No need to completely remove the pipes - just tuck them out of the way.


You now need to remove the gearstick and transfer lever housings - very simple - just 4 x M8 x 13mm bolts each. Undo and lift off each housing and put the bolts back in their holes for the time being. Gearstick bolts are the same length, but not the ones for the transfer.



Speedo cable next - just a 10mm socket needed and the fork, washer, and spring clip put to one side - again just tuck the speedo cable out of the way (drivers footwell)


Now from under the vehicle:-

The exhaust intermediate pipe has to come off, it has 3-bolts either end and a mounting point on a bracket that's held in place by the gearbox mounting bolts.

Front, where it joins the downpipe.


At the rear where it joins the mid silencer and the mounting bracket (13mm long reach socket and spanner to undo)


Now for the gearbox/transfer case mountings.

On the passenger side bend back the lockwasher tabs and undo the 4 x 12mm bolts (19mm spanner)


Drivers side just the central 17mm nut


Place a jack under the gearbox and raise it until the two mountings clear the chassis mounts.:-



The mainshaft gear next. This is what clunks when you let out the clutch. Once the circular cover and bearind track retainer are removed it can be teased out of the transfer case.

6 x 17mm bolts in order to remove the outer cover


Then 2 countersunk M8 screws to remove the bearing track retainer this is a tight fit and is also made of alloy - take care not to damage it.


The new gear is cross-drilled - and the drilling can be plainly seen in this picture:-


Bearings fitted:-


There are 6x17mmbolts, and one 17mm nut that hold the transfer case to the gearbox. some will be buried under mud, so you need to dig them out. Passenger side 3 are easy to spot:-


Two others are buried between the transfer case extension and inner face of the gearbox.

There's one in there somewhere!


There you go!


In here too.


And the single nut on a long stud at the top.


The transfer case is very heavy and awkward, best to have a bit of help here. With the bolts and nut undone - it'll just slide off the stud and one dowel. No further work needs to be done on it - so put it to one side.

Should look something like this now wear to the mainshaft spines is clearly evident:-


Now to remove the gearbox

Undo the two 13mm bolts that hold the clutch slave to the flywheel housing - then tuck the slave up on the chassis rail out of the way. Make sure the dust cover is on it or the piston could slowly creep out.


Move the jack to the rear of the engine, close to the flywheel housing and raise the jack slightly so that the gearbox mount on the passenger side is clear of the chassis mount. Make sure also that you do not go so far as to prevent access to the upper bell housing bolts:-


The gearbox itself isn't very heavy in comparison to the transfer case, so undo all 17mm nuts and lift off the gearbox. They quite often stick in place, so a bit of careful leverage might be needed.

If you only intend replacing the gearbox, then that's it as far as the engine is concerned. However the clutch and crank rear seal are going to be replaced too.

Gearbox off, and rusty clutch can be seen.


Jam the flywheel with an old screwdriver:-


Undo the 6x13mm bolts that hold the clutch to the flywheel and it'll come away from the three locating pegs.


The crank rear seal is going to be replaced as well, so the flywheel has to come off. The bolts are 22mm, and are very tight. Jam the flywheel with a screwdriver, and using a breaker bar or similar - undo all 8.

With a bit of careful leverage - the flywheel will lift off it's locating peg.

The crank rear seal - this one looks as though it is just starting to weep a small amount, so it was a good idea to do it now.


Method of removal is as follows - drill a small hole in the outer edge of the seal, screw a self tapper in the hole, then lever out with claw hammer.




Clean around the hole, grease the lip of the seal and the edge of the crank where the seal runs. I also use sealant around the outside edge of the seal to keep it in place.


Clean the threads of the flywheel bolts, apply thread locking compound to them and then re-fit the flywheel. Lock it as before, and do up the bolts in a diagonal sequence and to the recommended torque.

Fit a new clutch and ensure it's centred correctly. I use an old input shaft, but clutch aligning tools or a carefully sanded piece of wood will do.


That's the engine all ready for the gearbox to go back on.

The new gearbox comes minus the bell housing and some fittings, so you need to remove the relevant parts from the old one. The 6-bolts that hold the bell housing were heavily corroded due to lack of use of a wading plug. The clutch fork pivot point has to be removed, and the two 13mm bolts that secure it had to be drilled out. Forunately the remaining thread came undone easily.



Bolt the bellhousing to the new gearbox, plus one stud and the pivot point for the transfer link.



I welded a 3mm thick plate on it to prolong it's life.


Plenty of copperslip grease on the pivot point and grease the thrust bearing slide too. A small amount on the spigot bush, and all is ready to start putting it back together.

Be extremely careful when putting the transfer case back on, as it's very easy to damage the shaft oil seal.

A bead of RTV sealant is a good idea as well.

The new mainsgaft gear will slide easily onto the new shaft, and the bearing track housing and outer cover will aslo need sealant as they are prone to leaking.

Use new oil in the gearbox (ATF), and transfer case (EP80/90)

Reassemble in much the same way - taking care with regards to the breather pipes and transfer linkages.

The whole job was done in a day, but took almost 13 hours to do due to the bolts that needed to be drilled out. If they had come undone ok it would have been at least 4-hours less.

Vehicle is owned by Mark Jenkins of this forum, who (apart from handing over a bucket of beer tokens), also helped and occasionally hindered :D

Fit a bluddy wading plug!! :rtfm:

Les. :)

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Guest diesel_jim

Good write up there Les!

on a side note... in one of the pictures of the cross drilled gear, there is a red series door bottom in the background..... :D

do you have the pair?

are they for sale?

if so, how much?

are they in good condition?

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Good post Les. Amazes me how you can do the job and take enough pics etc to do the write-up - I generally find that I end up covered in oil/grease/waxoyl/all of the above, and wouldn't go anywhere near something like a digital camera.... ;)

Do you find it easier to strip the vehicle out as far as you have? The reason I ask is that the last time I changed a main box in a defender, I left the seatbox in place and lowered the 'box out under the car - still plenty of room to manouvre and less to strip out?



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An engine crane and drop it on the deck is another option, and you can hire a hoist for not a lot of money. I don't have a hoist at present, so the method I used was my only option really as the job was done at the side of the road. As it turned out it would have been quicker to drop the whole lot down and then strip - but a matter of choice I suppose. Next one I do I'll do it with the seatbox in as a comparison. Transfer box seals and bearing is next later in the week - with it in the vehicle, then 300TDi cam belt change this weekend if anyone is interested and about to do one or the other.

Les. :)

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Guest diesel_jim

Les, if you need any close up pics of a 300 stripped down, i'm currently rebuilding one in my garage. all clean and shiney if you wany andy nice artistic shots!!

PS. i've got a 2 ton engine crane if you ever need to borrow one.

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My 110s reversing noise is getting decidedly worse as well so I think I will be next to do a gearbox swap :(

Probably engine out route for me as I need to weld the exhaust bracket back, sort the starter, sort to tiny bit of rot thats started on the bulkhead and rewaxoyl the front end. Oh joy I can't wait.

It will be interesting to see how my clutch fork has beared up since it was replaced...

Excellent write up Les, just wish i hadn't looked at it and reminded me of whats to come :(

Will B)

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