The driveshaft is a custom made one with what I was told was a yoke off a 120y on the gearbox end.
Do these two parts not go together? If so then that would totally explain the problem.
I have a vague recollection that my original gearbox didn't have the copper coloured bit on the back of the gearbox (dust cover? or seal?) which would have let the yoke go in another ~20mm.
What is it meant to look like on an original 1200 or 120y?
I guess this is the problem with putting together a bunch of parts that weren't designed to go together.

That gap is way too big, nothing can spin concentric with that much gap.

The issue is that that peripheral flange on the adjoining face of the union is stopping the drive-shaft from going any further into the gearbox.

What is the tailshaft from?

Thanks for you reply. I have had the wheels balanced several times, so I don't think that's the problem.
I have only had one driveshaft place balance the shaft so it could well be that. I guess it's worth looking into.
I didn't notice the vibration while driving before, but now I do. It's not really in the steering bit it's really noticable in the gear lever so seems to be directly related to the drive train.

I have attached a couple of pics to show how it currently looks. I tried to include a tape measure for scale, but it didn't really work. The gap is around 10mm.

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  IMGP0002_s.JPG (110.38 KB)

this assumes a morris minor has a solid rear axle

the yoke (yolk) should go in half the length of the shaft on it, when the car is at ride height (or the car is held up by stands under the diff). this way it has room to slide in and out as the diff travels up and down

you probably have a balance issue with the new shaft, a good tail shaft guy can be hard to find. i have heard of many people having re-occurring issues using the same tail shaft guy, then taking it else where and getting a much better job

can you feel the vibration driving the car? if so it's either out of balance wheels, out of balance tail shaft, broken engine mount or gearbox/ engine jammed to or hard mounted to car

an obvious thing is if the steering wheel shakes when it vibrates, if so front wheels are out of balance if not then its one of the other things

Hi Guys,
I have a Morris Minor with an A12 (B310 I think) motor and 56a 4 speed gearbox which is giving me some trouble.
The original gearbox I had in it gave me no problems for 5 years before falling apart. I got a replacement really cheap which I had reconditioned.
Since putting the new gearbox in I have had no end of problems with vibration and wearing out the bush at the back of the gearbox. I have had my driveshaft length modified too, so that there is what I thought was the correct amount of clearance at the back of the gearbox. Also new yoke/universal joint attached.

The problem is that once again I tried to take the car on a roadtrip and after an hour at 100km/h the back of the gearbox had gotten really hot and started vibrating more again.
What I'm wondering is what the yoke / gearbox join should look like when set up correctly? How much clearance should there be? If anyone has any photos it would be really helpful (I will put some photos of mine up soon). I have had trouble with this for so long now that I can't remember what it all looked like before the first gearbox died.

Any help or advice would be much appreciated.