Diagnosing a gearbox

[1000wannabe]

Hi Guys,

I just finished fitting a rib case gearbox into my Morris. It was a bit of a punt as the history of the box was unknown. On the surface of it things looked pretty good.
It is a nice quiet box, changes nicely and feels to have good synchros but it jumps out of top (4th) gear on acceleration.
These boxes are very hard to come by here in Australia, so just swapping it out isn't possible.

Can anyone suggest an order of things to inspect, before having to remove it and then, if removal is necessary, what to be checking in what order?
I've read that it can be a worn selector, detent springs etc. I'm comfortable that it is not a totally worn out box. It appeared to have had some work done..
Which detent springs/balls are for the 3rd/4th shift?
I'm not eager to have to pull it all apart again having just gone through all the rigmarole of converting a Series 2 to a rib case. If I can avoid it initially in situ it would be good.
Constructive thoughts would be appreciated...
Cheers, Chris

[rocco]

Not exactly a suggestion but this video looks fairly comprehensive and something I'd watch if I was going to do any gearbox work/investigations. There are some other videos on the same topic there too.

https://www.youtube.com/watch?v=H6_r0RQiaO4

There also another thread on the topic here too, from another Aussie member.

viewtopic.php?t=70060

[mowogg]

Have you got the correct gear handle? I l am pretty sure the 1098 was different to the 948 and to they are not interchangable. It's possible it might need to be swapped for a 1098 handle.

I am sure someone will correct me if this is incorrect

[don58van]

I am sure someone will correct me if this is incorrect

It is correct. The protrusion below the 'ball' is a little longer on the 1098 lever. The difference is enough to cause problems with selection of gears if a smoohcase lever is used with a ribcase gearbox. I haven't heard of it causing the box to jump out of gear--but it is possible if the if the lever does not push the selector fully into the detented position.
Don

[1000wannabe]

Thanks for all the comments.
The shifter I believe to be correct it also came with the box.
If it was incorrect, I would expect it to cause problems in all gears, not just top.

I spoke to someone with 50 years experience in A series engines and all derivatives of the gearboxes today.
I mentioned the usual suspects (detent springs, balls and shift forks) and he dismissed all of them almost immediately.
Apparently the most common cause of this particular problem is wear in the 3/4 synchronizer and it's dog teeth. Specifically where they mate into the input shaft. The more times it is allowed to jump out of gear, the greater taper they wear. It is the fact that it happens on acceleration and not deceleration that the common causes are ruled out.
The necessary parts are painfully expensive here, also made worse if it is in fact, an early or mid Minor specific rib case and not the last box made or a sprite box as the Minor parts aren't available.

I have no option but to remove the box and disassemble, establish what it is, then most likely search for good used parts.

The most annoying part of all of this is when I bought the car it had a 1098 in it with a smooth case box. We discovered fairly soon after that the 1098 needed a rebuild and I had the choice to either do the 1098 or a spare 950 I had. I was persuaded to do the 1098.. If I had gone with my gut, I wouldn't have had the 1098 done and fail, then redone and then have to go down the gearbox upgrade/ change rabbit hole...
At least I've learnt a lot, even if I have one of the most expensive series 2 minors around now...

[mowogg]

On my earlier point, I would suggest you check the levers first. It may still need a rebuild but it's. A quick check. I knew someone who fitted 2 gearboxes and both jumped out of top. I think the handle was the issue in both cases.

Assuming you have not started the removal, can you remove the lever and post the dimensions.?

[1000wannabe]

I haven't started removal.. checking the shifter dimensions is easy enough. What length/dimensions should I be looking for?

[don58van]

What length/dimensions should I be looking for?

I mentioned earlier the difference between the two levers is the length from the 'ball' (ie the pivot for the lever) to the tip of the selector (that engages with the selector rods). I suggest that you measure from the base of the pivot ball to the tip of the selector. Have a look at the photo in this link: viewtopic.php?p=689181&hilit=gear+stick#p689181

Don

[MM1949]

The attached should help. Smooth case on the top in the photo.

[1000wannabe]

That's great. Thanks for that. I'll have a look in the morning..

[1000wannabe]

Ok, so it turns out I have the wrong shifter...
According to those measurements I have the smooth case box shifter

PXL_20250213_022143576.jpg (2.3 MiB) Viewed 4814 times

[don58van]

Let's hope that it is problem solved!

You will probably have to source a ribcase one from the UK.

Don

[1000wannabe]

Yes I think so, but I've asked the person who sold it to check what they have. I also note that it's just the stick going into a metal ball socket, no plastic parts or springs so I need to check parts diagrams to see what should be there ..

[mowogg]

Do you have a smooth case box? You could swap over the remote mechanism if so which I believe will work with your gear stick

[MM1949]

Yes you have a smooth case gear stick, you need to source a rib case gear stick.

I don't think the gear shifter is a straight swap from the smooth case to the rib case, I understand the gear shifter and gear selecting rods on the smooth case is shorter than the rib case so the gear shifting rods won't select the gears.

There is a lot of info on the differences on the MG Sprite sites, they used similar gearboxes.

[1000wannabe]

An update:

I sourced the correct gear stick and it did improve the situation somewhat, but unfortunately didn't cure it.
Continual loading of the box under acceleration still results in it jumping out of 4th it just takes a little bit longer to happen (almost instantly before)
It seems a strip down is needed, it will however have to wait until I move house and get resettled..
At least I'll be able to drive it up onto the trailer...🫣