gearbox help please

[rdm5555]

My gearbox jumps out of 2nd or won't engage 2nd when going down hill, it's fine for the rest of the time, any ideas? Many thanks.

[bmcecosse]

It' s worn out! There's no other way to tell it. It will need at least a new second gear and matching syncro cone - but it may also need a new first/second selector hub - depending on the wear. Once they start jumping out of gear -the end is near........ Can only suggest minimising use of second - go down hills in third! It should still be ok going up the box - just avoid going down the box. And start looking for another box to swap into the car. You are looking for a rib-case box to suit the 1098 engine.
Here's one - be quick! http://cgi.ebay.co.uk/Morris-1000-gearb ... 45f8bfef85
And another - but may not be as good....... http://cgi.ebay.co.uk/MORRIS-MINOR-1000 ... 43a52e3bea
And yet another.... http://cgi.ebay.co.uk/MORRIS-GEARBOX-/1 ... 19c35b033c
And here's one that is STUPIDLY expensive.... http://cgi.ebay.co.uk/Gearbox-Morris-Mi ... 3f01aa8786

[rdm5555]

It' s worn out! There's no other way to tell it. It will need at least a new second gear and matching syncro cone - but it may also need a new first/second selector hub - depending on the wear. Once they start jumping out of gear -the end is near........ Can only suggest minimising use of second - go down hills in third! It should still be ok going up the box - just avoid going down the box. And start looking for another box to swap into the car. You are looking for a rib-case box to suit the 1098 engine.
Here's one - be quick! http://cgi.ebay.co.uk/Morris-1000-gearb ... 45f8bfef85
And another - but may not be as good....... http://cgi.ebay.co.uk/MORRIS-MINOR-1000 ... 43a52e3bea
And yet another.... http://cgi.ebay.co.uk/MORRIS-GEARBOX-/1 ... 19c35b033c
And here's one that is STUPIDLY expensive.... http://cgi.ebay.co.uk/Gearbox-Morris-Mi ... 3f01aa8786

Many thanks, I've bought 1 to replace it but wanted to know what was wrong as I plan to rebuild it. Regards ross

[rayofleamington]

what actually needs replacing is not easy to tell without a CMM and a load of drawings to work with...

Not sure what you know about gearboxes. Synchro hub operation is difficult to describe without some nice pictures (I used to have some excellent ones but I don't work there anymore).
In most car gearboxes, the gears mesh all the time - shifting gears doesn't actually move the gear teeth. One of the gears is free to spin on its shaft - shifting into a gear locks the gear to the shaft and makes that gear work. Obviously you only want 1 gear engaged at a time in a manual box, and that is taken care of in the selector mechanism.

The bit that locks the gear to the sdhaft is in 'the hub'. Thats the bit with a big grooved ring/sleeve around it. The selector fork sits in the groove on the sleeve. Moving the gear lever results in a movement of the selector fork / hub sleeve.

To engage the gear, basically the hub travels past the V's on the gear and onto a 'flat' area beyond. The flats actually have a small reverse angle so that any torque (+ve or -ve) holds the hub in gear. When there is no torque the hub should be held in place by the hub detent/s.
When you go from +ve to -ve torque the load is racted on a different face of the dog and for a short period in between the hub is held by the detent.

Put simply, If a gear jumps out, then the hub isn't positioned far enough past the V to lock onto the flat area. When it is on the V part, any torque through the gearbox will force the hub backwards and out of gear.

So why does it only show a problem in one direction?? (e.g. engine braking, but not when accellerating)
The answer is very simple - the gears are helical* (at a slight angle) and therefore under load they create torque,

and

an axial load. The axial load moves the gear and the shaft across a bit, thus the flat area is in a slightly different position (i.e. further away from the hub position in one direction and nearer in the other)

* 1st and reverse are straight cut not helical - hence they make a different gear load noise. On more modern boxes only reverse is straight cut so this axial movement problem can happen in 1st gear also.

so what is needed to shift the hub far enough? It may be wear in the hub, the shaft, the gear, the fork or the selector mechanim that causes the problem. It's best to fix the actual cause (which is likely to be a combination of many worn parts) rather than to attempt to fix the symptom.
To 'work-around' a solution by modifying parts is rarely a great idea as most of the tolerances and positions are a sum of the other functions - if you shim a gear shaft axially in one direction you may assist 2nd gear but create a problem in 3rd etc.. If you modify the parts that create the hub travel stop it may work intermittently as the detent position may still be wrong (so it may work under load but not if you come off and reapply the load) etc...


As for how much longer the gearbox will last - I had a box that jumped out of 2nd on engine braking. We drove that to Gambia including a severe thrashing in the desert. To get it to stay in gear whilst the car bobbed around in soft sand etc.. the passenger needed to hold it in gear as the driver needed both hands to try and keep going the right way. On roads the driver just held it in 2nd.

[bmcecosse]

Holding in gear - wears the selector fork down very quickly. Not recommended unless you plan to just throw the box away.

[rayofleamington]

"very quickly" is subjective - most peopel don't drive thousands of miles in 2nd gear, so although it increases the wear rate don't be surprised if the box lasts many more years.

[newagetraveller]

If the selector fork is worn then why not just replace the selector fork?

[rayofleamington]

certainly if only one component has significant wear, it should be an easy repair. However in a ~40 year old gearbox, it's unlikely to be just 1 worn component.
Without stripping, you will never know, but measuring these kind of components is far from simple

[bmcecosse]

It's not the selector fork that's worn at the moment - it normally plays no part in securing the gear once selected. But forcing the gear to stay IN by holding it there by force with the selector will wear it away - and so it will then need replacing along with at least a new 2nd gear and syncro ring, and possibly a 1st/2nd hub. Very often the laygear needs replacing (the 1st gear section takes a beating) and the layshaft wears rapidly and the needle bearings too..... And the main shaft bearings are likely to be past their best ....... It's rarely worth rebuilding these boxes when cheap 2nd hand boxes are still readily available. I'm not sure about the supply of spare parts anyway!

[rdm5555]

Thanks guys for all the advice, I have 2 Minors 1 has done 65k ( the one with the gearbox problem) and the other 128k on it's second box, so when I get the faulty one out I'm going to try and rebuild it, Bullmotif have a rebuild kit. I'll let you know how I get on. Ross

[bmcecosse]

If the 'rebuild kit' is just gaskets and main bearings - it will be a waste of time and money..........
I don't see them listing a kit - and they don't seem to have new 2nd gears either...... 1st/3rd/rev/laygear yes - but no 2nd gear - and that's the one that takes the biggest hammering