Gearbox issue - not possible to select 3rd and 4th

[csb123]

Hello,

I wonder if anyone can help with advice with a gearbox probIem I have please.

My camper van is a 1988 1.9 petrol water-cooled T25.  88k miles. 
It has a 4 speed manual gearbox (4 forward gears) which has an ABD code stamped on it.

Without any prior gear change problems, it got stuck in 3rd gear after a reasonable hill descent in Dorset.  I managed to get it out of 3rd, but can now only select 1st, 2nd and reverse.  Not possible to select 3rd or 4th anymore.

I then disconnected the forward linkage to the nylon ball and tried to change gear using just the lever on the side of the gearbox only.  Problem still there, so decided to remove gearbox.

The oil is in good condition and there are no signs of metallic flakes or any other debris.

I removed the most forward cap, where reverse is located, but couldn't get to 3rd or 4th from there.

Is this a common problem and is there an easy fix?

I have watched a few video's and it looks like you have to remove the differential/bevel pinion to get to the 1st to 4th gears - is that correct?

If it does need a rebuild, are there any suggestions who to use.  I have seen vantopia and the engine shop.

Regards
Chris

 

[DoubleOSeven]

Aidan told me to disconnect the adapter plate near the nylon ball, well, loosen it. Then set up the gear selection. It worked for me.