Gearbox failure

Hi guys

We are currently having some gearbox issues, if you could shed any light and help that would be amazing.

Ok to set the scene

We have a 77 series III. It had a 2.5 diesel freight rover engine with the series III gearbox and a fairy overdrive.

We had no previous gearbox issues. And the oil was changed 6000 miles ago

We were travelling on a flat road, not accelerating, not under load , in Third gear. All of a suggen we came to a very quick halt with the sound of grinding and crunching. Like when you miss a gear but way worse. We lost all forward drive.

When the gearbox was removed it was found that the gear directly below the top cover (where the selector forks are) was completely shredded along with another further inside. Any ideas why this happened? We had no previous issues and it had been running fine.

We were in Guatemala and had to replace the entire gearbox. We got hold of a 1979 gear box from a series III 88 Santana.

The gearbox is now in our series III 109 and apart from the slightly slower gearing it appears to be working.

However
When engaging second gear, every time without fail we get a grinding noise like when you don't get a gear properly. It falls out of first and second really easily on smooth and rough terrain.

When any gear is selected and you accelerate it sounds as if something is rattling around. We used to only et this when low range was selected and drive was taken up initially. Kind of sounds like the drive shafts may be loose but I have checked these.

Also when revs are low, say if you should be in second but you are in third the gearbox sounds horrendous. Like everything is loose inside

Any solutions would be amazing. We don't want to be stranded somewhere else again.

Thanks in advance

Private message jamesmartin, he's our gearbox (and many other things expert) but a few things occur.

Popping out of gear could be loose mainshaft nut at the rear (the big one just in front of the overdrive (if you still have that fitted).

Crunching into 2nd sounds like synchro gone (don't know if the Santana box is full synchro or not?) but double de-clutching should overcome this if that is what it is. Sorry if I'm teaching you to suck eggs but did you check the prop U/Js with the wheels chocked, handbrake off and transferbox in nuetral to check for any play other than rotational?

The second gear thing.

Second will engage very stiff, then you can pass where second should stop and hit the crunch. Santa box is full synchro. The box was full refurbished before being put in. Is it possible to reach the main shaft nut without removing the gearbox?

I would have to remove the overdrive and the bearing which sits on the shaft. Where is the nut?

Thanks

Yes you can reach the mainshaft nut with the box in place. Remove the overdrive from underneath and through the seat box and then remove the cover plate on the top just in front of the O/D. You see the crown nut which is held by a tab washer. There's a special tool to do it up but you can do it from the top by tapping it round with a punch.

If you remove the gearbox tunnel so you can see the top of the gearbox you'll see 3 selector shafts. 1st/2nd is the middle one and it's held in position when in gear by ball bearings and springs in indents in the shafts. #7



The actual gears are selected by the fork #13 (moves forwards to select 2nd) which is clamped to the selector shaft. I think it's all accessable under the cover plate at the front of the box but you need to remove the indent springs and balls before taking it off else they drop into the box. The fork can slide out of position on the shaft (had it happen on my overdrive which is a similar set-up).

The stiffness and over shooting the gear could be a problem with the indents and/or the fork position but I'd talk to jamesmartin before doing anything other than checking the mainshaft nut

Sounds like a synchro has lost all its springs and is rattling around loose.
IMHO that will explain most of the symptoms.

If I leave the loose synchro, will it cause any further damage or just annoy me ?

Main shaft nut tool here if needed, I have just made four. Post is about £6
I would like a deposit to make sure of getting it back, refundable on return.

What is this tool for?
i have a gear box in little pieces , and i cannot remember how to re assemble it........

ciderman said:

What is this tool for?
i have a gear box in little pieces , and i cannot remember how to re assemble it........

Click to expand...

The tool is for the castellated nut at the rear of the mainshaft. You dont really need it as you can get away with useing a punch and hammer to tighten and loosen it

Gwynswift said:

If I leave the loose synchro, will it cause any further damage or just annoy me ?

Click to expand...

If the synchro springs have fallen out, you will have small spring steel strips loose in the gearbox. While I have heard of people ignoring this for a while, it's not a good thing, as they could end up in the gears.
The synchro body is hardened steel and brass. If you get at it soon enough, it can be re-used with new springs.
To be honest, I'd be thinking about getting the gearbox out as soon as possible, just in case it causes more damage.
With the box in situ you just take the gear lever/selector unit off, you should be able to shine a light into the box and see if anything looks amiss. You can also get a magnet on a piece of wire down to the bottom of the box to pickup the springs - assuming that's what it is, of course.