gearbox question

i got an lt77 box that all selects fine but wont go down from fourth to third. as i say no funny noises, just wont select that sequence, any good ideas or suggestions what it could be, if not i'll live with it till i win the lottery
cheers, tom

Does this happen only when driving, or does it happen when stationary with the engine stopped too?

Can you change from 2nd to 3rd when driving?

If it does it with loads of gnashing of teeth I'd suspect the synchro rings if it just locks solid I'd suspect the slipper pads in the synchro hubs. Either way it's as easy to do both at the same time. Before you take the gearbox out try adjusting the gearlever and if the springs worn replace it. Mine was a pain to get into third till I moved the lever round a notch on its splines!!

There is a slim possibility of the interlock plungers being dirty and sticking.
I think these can be attacked from the top of the gearbox.

But we need more answers if we are to give a better diagnosis.

right then, all gearbox operations are as normal except that when changing down gears between 4th to 3rd it simply wont go in. no grinding no crunching, its like the gear simply isn't there, like if you try and jam the the gearlever into the space between gears. interestingly i have just managed to get it in 3rd while down shifting from 4th but only after nearly coming to a halt and lots of jaming the lever about. again no funny noises or crunching, once it was "ready" to be down shifted it slipped strait in and drove as normal.

Dunno what Charlsey means by interlock plungers.

Gearlever waggles a rod back and forth and round. Rod waggles a selector yoke which waggles another rod this has a detent ball which drops into a groove, I doubt if it's this cos then all the gears would be difficult to get, any old how this shaft pushes a couple of selector forks about, selector forks push the gears about. The synchro hubs you've got three, one on first and second gear one on third and forth and one on fifth, Any how they have three slipper pads inside with a spring pushing them out these hold the outer hub bit central on the inner hub bit and helps hold an pull the gears into place anyhow these can wear and stick, and stop or make it difficult to engage gears. On mine it was second into third that was difficult, If I went from second to fourth then into third without releasing the clutch it went in a dream. Any old how it was the slipper pads that were worn, I'll bung a pic in my gallery of em if I get round to it. It's still worth setting the gear lever up to the haynes instructions fost though and having a look at the spring on the lever. And as I said before just moving the lever round a notch made selecting gears easier I was forever crunching First to second till I did mine.

On top of the gearbox lid are four selector rods
From right to left they are for

Fifth..... 3rd and 4th ......1st and 2nd .... Reverse (i.e. opposite to the top of the gearlever)

If any TWO of these went into gear at the same time while on the move the gearbox would be instantly destroyed, so there are a series of little balls and plungers in the lid cunningly arranged so that (1) from neutral you can select and engage any one gear by moving its rod by the gearlever, and (2) when it is in any gear all the other rods are locked in neutral. To get from any gear to any other gear you MUST pass through neutral, and from there you can only select one gear.

I happen to know this. My neighbour has a series up the road with EXACTLY this same problem, and we reckon it's the detent interlocks needing cleaned and freed off and lubed.

ALL manual gearboxes have interlocking plungers on their selector rods, without exception.

CharlesY

On top of the gearbox lid are four selector rods
From right to left they are for

Click to expand...

Not on my Lt77 there int.

GRUNT said:

Not on my Lt77 there int.

Click to expand...

Near enough ... there are four selectors controlled by interlocks.

It isn't quite as simple and obvious as a real car, but that's because it isn't - it's a LandRover.

The standard way to jam a gearbox solid to undo big nuts is to engage two gears at the same time. It's a total disaster at any other time.

CharlesY

Not in here there int.

http://www.landyzone.co.uk/photopost/showgallery.php?cat=634

ere charlsey, your on about a series box and i know what you mean about them rods but on a lt77 box its only got 1 rod tat goes into the box and then selects the gear wheras s3 box the lever selecs which rod to push/pull and each rod selects a gear

Ahh that'll be it then.

You're right of course, but the principle is the same, and the stuck gear MAY be caused by a failure in the interlocks.

It might also be something else though .... those are dodgy gearboxes.

CharlesY

try double de-clutching when u downshift [selecet neutral, clutch out, rev, clutch in, gear down] I have a habit of doing this on any manual box, a habit i picked up from years of driving a '49 Morris Minor. Good habit to have as your synchros never get worked hard.