Technical Library

FAQs

What oil should I use in my LT77 gearbox?

We recommend ATF Dextron 3. We find this very good : ATF

My gearbox rattles on idle, in neutral, with the clutch up

This is very common on Diesel engined vehicles. The clutch friction plate has a ring of springs, which are there to soften the knock of the diesel engine to stop it being transmitted to the driveline. Often especially with a new clutch these springs are quite tight and a lot of the engine knock goes through to the gearbox and makes the gears "chatter" together when the box is in neutral and the clutch up, it goes when the clutch is depressed. This can sound quite bad and does vary from car to car but is not detrimental to the life of the gearbox and we view it as an undesirable characteristic of the LT 77 and R 380 as opposed to a fault with either the gearbox or the clutch.

The LT77 in my Defender does not engage 1st / 2nd nicely, the gate is tight and hard to find. Why ?

When you move the gearstick to the left it stops when it hits the spring loaded reverse plunger, it should then move up to 1st and down to 2nd, sometimes the position of the plunger needs adjusting to allow either the stick to go further to the left or sometimes not as far over so it lines up better with the 1/2 gear positions. The is done by adding or removing shims behind the reverse plunger body which is held on with 2 M8 bolts to the right of the shifter turret in the top housing.

I've just fitted a rebuilt gearbox to my defender, the third and fourth shifts are not very good. Why?

Most rebuilt gearboxes, including ours, come without the "turret". This the part that the gearstick bolts to. If you pull back the rubber boot on the turret you will reveal two large springs and two adjuster screws and locknuts. The role of these springs and screws is to set the rest position of the gearstick when you let go of it and is referred to as the 3/4 bias setting. When you fit a new gearbox this can sometimes need adjusting to agree with the selector shafts to ensure a clean gearshift. Firstly you need to work out which way to adjust it, to do this drive the vehicle but when shifting into 3 and 4 in stead of letting the gearstick go where it wants to go try holding it a little to the left then a little to the right, one way or the other it will drop in nicer. When you have worked this out you can adjust the screws the springs are resting on to lean the stick left or right until it shifts better.

My 200 tdi Discovery is very difficult to change gear from 1st to 2nd or 3rd to 2nd. Why?

A common fault with these boxes is a thrust washer in the 1 - 2 synchro assembly splitting in half and blocking movement. Rebuild the gearbox and replace both thrust washers in the 1 - 2 assembly.

I've just fitted a rebuilt gearbox to my Disco, the third and fourth shifts are not very good. Why?

When you let go of the gearstick on either the LT77 or the R 380 Discovery boxes the stick will spring to the 3 / 4th gate. This gate position is set by the position of the bias plate. This gate position must be adjusted correctly to agree with the selectors in the gearbox to ensure a good gearshift. When we rebuild the boxes we set this position but sometimes it needs fine tuning when in the car.If the shifts to 3rd and 4th are not clean you may want to adjust this plate, to do this first you must drive the vehicle but when shifting into 3 and 4 instead of letting the gearstick go where it wants to go try holding it a little to the left then a little to the right, one way or the other it will drop in nicer. When you have worked this out you can slacken the 4 screws holding the plate and move the plate left or right accordingly to improve the shifts, the holes are elongated to allow some movement.

I am familiar with the much talked about mainshaft wear problem on my Defender/Discovery but I don't know how bad mine is, or if I need to look at replacing my gearbox?

The best way of ascertaining the degree of wear is to chock the two front wheels, handbrake off, mainbox in first and jack up a rear wheel. Remove the PTO cover to the left of the handbrake and you will be able to see the gearbox mainshaft in the centre and the transfer case input gear around it. By rocking the handbrake drum you will be able to rock the gear around the shaft thus getting some idea of wear / backlash between the two.

When driving my 200 Tdi Discovery / Range Rover the gearstick has suddenly become very vague and the stick is fallen to the 1/2 plane not the usual 3/4 plane. Why?

Inside the aluminium top cover of the gearbox, which is secured by two large Phillips head screws, you will find two large springs which rest on a L shape steel plate which give your 3rd/4th bias gate position. This L shaped plate is very prone to cracking off where it is bent which will result in you losing the 3rd/4th rest position when in neutral and thus the shifts will become vague. This plate is inexpensive and can be changed with gearbox in situ.The part number of this Bias plate is FRC9340.

I have just fitted a rebuilt LT77 in my disco and the 1st and 2nd gear positions are very tight,

When you lean the gearstick to the left to select 1st or 2nd the lever will stop when it hits the spring loaded reverse plunger, this is termed the 1/2 bias position, then you go up for 1st and down for second, sometimes the plunger needs adjusting to move this 1/2 bias position a little to the left or right so that it agrees with the internal selector forks. This position is adjusted by adding and removing shims that are located behind the reverse plunger which you will find inside the top shifter housing.

After a long run in my Discovery, when the gearbox gets hot, the gear lever becomes stiff when moving from side to side. Why?

The nylon cage at the end of the selector rail can swell when hot, and cause friction. To rectify this, the parts needs replacing. You can find this part here

I have a Range Rover classic and want to remove the V8 and fit a 200 TDi, will the 200 fit the LT77 gearbox ?

There are 2 ways to do this :

1. use the gearbox as it is and fit the 200 TDi disco LT77 bellhousing together with a special spigot bush (STC1166) and clutch friction plate (STC1169), these 2 parts are different as the V8 input shaft spline is different to the 200 TDi one.
2. the other option is to use the same 200 TDi disco bellhousing and use the stock TDi clutch but you will have to strip the gearbox and change the input shaft for the correct 200 TDi one (FTC1426).

Can you rebuild my 2 wheel drive LT77 ?

We often get asked this and the answer is 'maybe' the problem is not all parts are available, so it really depends what required,The bearings and syncro rings are no problem but if the pinion or layshaft have failed then some of these are no longer available,You can send your unit in and we can strip and advise, we will certainly rebuild and return if we can, its in our interest to do so,

Can I remove the LT77 in my 200 TDi Defender and make it auto ?

Yes and no, it can be done but because the ZF auto is about 100mm longer than the LT77 in the 200 TDI Defender you will have to move the engine forward to the 300 TDI position. You will also need the 200 TDI auto adapter plate, the rest is the same as the 300 TDi auto kit.

Are you able to supply rebuilt 2 wheel drive LT77's ?

We are not able to supply these from stock, we can rebuild and return your unit if you send it in to us subject to parts availability, we stock all the bearings and syncro rings but some of the internals are no longer available so if your unit is too far gone we may not be able to rebuild it. We will always try our best to complete it for you but there is no point in us doing it if the parts are bad and new are not available.

I cant get reverse gear on my Defender LT77, the stick wont go across to the left far enough.

There is a spring loaded plunger located on the right of the top housing, sometimes this can jam or be sticky and may either need to be stripped and oiled or if you have the type with the slotted screw head and locknut at 90 degrees to the plunger, you can back out the screw one turn at a time to relieve the spring tension which will allow the stick to move to the left so reverse can be selected easier.

Technical

LT77 Development

The LT77 was introduced to the Landrover range in approx 1983 with the suffix 'D' box and was developed over the years to the suffix 'H' which was last used in 1994.

The 'D' and 'E' are very similar the only difference being the reverse gear was a little fatter in the E,

When they went from 'E' to 'F' larger layshaft bearings were used.

The 'G' was further improved by all the gear teeth including the pinion getting approx 20% thicker. Also a much wider pump was used to increase the lubrication and cope with the fact that some of the LT77's were now being supplied oil cooled, ie V8 NAS 90, 3.9 RR Classic and the 3.5 EFI Discos.

The 'H' (termed the LT 77S) was the same as the 'G' in terms of strength but used a different synchro set up called the'Double Synchro', In reality it didn't work much better.

Upgrades to the R 380

Should the LT77 fail on your vehicle you will usually have the opportunity to replace it with a later R 380, unfortunately surcharges will apply but if you are either planning to keep the vehicle, working it hard for a living or going on an overland trip where both reliability and the facility to add an oil cooler are important then this additional expenditure may well be worthwhile.