My gear stick was getting stuck when changing gears and the mechanic thought there was a problem with the gearbox, so he took it out and replaced it with a 1.4 gearbox (my car is 1.2). I got the car back last night and I've driven a few times since, but the clutch is vibrating/ shuddering when I change gears. I've never had a problem with the clutch before this. I'm just wondering if this is normal? Do I need to just give the car a couple of days to "settle" or has the mechanic created a new problem that I need to fix? MOT is due soon - I'm guessing this won't pass. Thank you for any responses.
No, that is NOT normal. Something is now wrong with the clutch as it should work fine from the start after a repair. I suspect that the clutch may have become contaminated with oil or grease during the transmission swap out or possibly re-installed improperly.
Either way, you should return to the shop that did the work and have them fix the problem. If the clutch was fine before the transmission change, it should still be fine. If there was a problem with the clutch or is was worn when they had it apart, they should have advised you of the problem and let you decide to fix it at that time. The incremental cost to replace a clutch when the transmission is out if minimal since most of the work in a clutch replacement is removing the transmission to get at the clutch.
There are a good few things to take into account when something like a gearbox is swapped, especially for a different version. The other techs cover some of these. As mentioned clutch contamination or damage are possible causes for the vibration. Unless the clutch has been recently replaced it would have been a good plan to have it replaced during the Gbox swap, as this prevents any unnecessary future work in the same area for a good while. There could also be an issue, wear or differences between the pilot bearing and spigot shaft diameters, an issue here will cause clutch vibration. The pilot bearing should be checked/replaced during such work to prevent chances of clutch vibration on reassembly.
Return the vehicle to the garage that did the work for you and explain that this is a new fault that has only occured since the repair.