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SIII gearbox overhaul

peaklander

peaklander

Accelerating Away
Hi all,
I know the answer is somewhere on the forum but only got time for a quick look and can't find it - so sorry if I am repeating something already posted...

I am preparing to delve into my '75 SIII gearbox (mainbox) to see what damage there is inside (found a small piece of tooth and some flat blue coloured metal strip in the oil when I drained it! :( ). I have only driven this landy about 1/2 mile so don't know the symptoms.

I have seen somewhere that I will probably need a 32mm? modifed socket to undo the mainshaft nut. Could someone tell me exactly what I will need - I don't have one but can get one if it is better than a drift. If so should I get 6pt or 12pt and will I need a long extender - in other words - what is the mod. needed?

Thanks in advance
 
The socket just needs to be strong - it doesn't matter if it's hex or double-hex, as what you'll be going is grinding the end down to leave protruding teeth, like a rook in chess. Halford's Profesional range would probably be a good brand for this - they're relatively cheap and seem very strong. Don't be tempted to buy a very cheap socket - remember that you'll be applying a lot of torque through these small gorund teeth, and you don't want them to shear off.

The damaged parts sound like they're from the 3rd/4th gear synchro hub, which is not an uncommon failure.
 
Thanks for the feedback Snagger. I have had a little look around and found this-

https://www.lrukforums.com/forum/showthread.php?t=13817

Your advice is great and I will be ready with the socket altho' probably won't have chance to do the work for a few weeks. Meanwhile I continue to put the whole thing back together during an odd hour here and there- it now starts with a key in the ignition! Hooray.:)
 
The tooth looking piece will most likely be one of the bits that always seem to break from the hub of the 1st/2nd syncro. The blue flat bit is/will be a 3rd/top syncro hub plate spring, again common failure on all series boxes(STG1 V8 excepted).
 
Thanks for the feedback/advice. I guess I can have an initial look from the top by removing the selectors? Are these parts available and if so where do you recommend - I have seen some threads suggesting that the copy parts are not good enough.
Never done any work on a gearbox so it will be a challenge...
 
The flat springs are about 39 p each and you'll need 3 - part no RTC 1956. However it sounds as though something else has broken off as well and you'll need to strip the box to find it. Most parts are available without problems including gasket sets. While you've got the thing out and apart at the very least you should do the external seals (handbrake and transfer box front) as well as the seal between the main and transfer box. - as well as examine the clutch with a view to replacement.
 
Yes, good advice i'm sure, about doing the otherstuff whilst there's chance. The box is on the workbench and I have now got the socket (was driving past a Halfords in Ashbourne - took your advice on the source) - may get chance to start soon. It's good to hear the parts will be available. Wonder how many more bits i will find in the bottom of the case?
Thanks for a great forum
 
Made a start and separated the transfer box from main, got the intermediate gear cluster and removed the selectors. However at the front-end I can't shift the bolt on the end of the lay shaft - just how hard do I need to try??! My socket is 3/8 drive (only), the box is on the bench of course so wants to move around a bit - but do I need a big pipe or is it more to do with a shock of a hammer on a bar.

Any help would be much appreciated.:)
 
Remove the top cover and the selectors, then slip the box into 2 gears at the same time to lock the gears, then with somebody holding the box the bolt should come undone, IIRC it is tightened to 75Lbs/ft.
 
Finally got my bit of spare time and have started to open-up my gearbox.
The most obvious problems are a fairly noisy bearing at the bellhousing on the input shaft, a single half-tooth missing on the pinion gear (see pic), and a complete absence of any springs on the 3/4th synchro (see pic).

What advice can anyone give me about the primary shaft -replace or not? I will have to change the bearing but I don't want to spend if not necessary...it might be a bit penny pinching though...

Also, could someone show a pic of a 'good' 3/4th synchro? I have no idea how the springs fit - or even how to tell if there is some wear in mine.

Finally, although I have the LR workshop manual I don't have a parts explosion - could anyone direct me to a copy of the relevant sheets that I could look at..

Thanks in advance...
 

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Definitely replace the pinion - the rest of the failed tooth will have fatigue cracks, and other teeth may have cracks too.
 
Just refitted my rebuilt SIII box and can recomend the following.

New Bearings and Gasket Seal Set (incl 3/4 Syncro springs) from LEGS
http://www.legs.co.uk/14-series-main-box-kit.html
If you order over the phone before one you'll get next day delivery if not they say 5 days !

I replaced my 3/4 Synro (Part No :- FRC1758) as all the spings were missing too http://www.lrseries.com/shop/produc...html?page=2&search=synchromesh 3rd 4th&page=2

However, when I tried to fit the replacement springs from LEGS in the old syncro, they were a poor fit. Best check.

Best of luck
 
I've had chance to have a look at the 'bits' from the gearbox.
Input shaft - missing 1/2 tooth as I said - I'll take your advice Snagger, and replace (don't know from where though yet)

Layshaft (stamped 'C')- Ok except for pitting on one side of all teeth on the second gear from the end with the bearing (reverse I think). I don't know which way it spins so can't say if it is on the drive side or not. (see pic). The reverse idler gear looks ok (in case still) and I'm not planning to remove it.

The dog teeth in 1/2nd synchro were full of paste from the missing 3/4th detent springs I suppose. The sliding blocks, balls and springs in the 1/2nd synchro seem fine.

The thing I can't decide is whether the synchro rings are worn as I have nothing to compare them with. If I get the LEGS kit I think I get new ones for 1/2nd, but for 3/4th, LR show two replacement parts, one being genuine and twice the price. Is the difference worth the cost and do I need one anyway? Having never driven this vehicle I've no history.

Looking at my 3/4th synchro, there must be about 1/2mm of 'slot' depth left and the ribs or milling around the ring (if that's the correct term) are almost invisible on the outer part and resonably defined on the inner.

As for possible dog teeth wear, again I've nothing to compare with but there's none missing and they all 'look' ok!!

The bushes under 1/2 and under 3/4 seem fine.
Any comments/advice gratefully received - thanks.
 

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