I have a 1989 Nissan Skyline R31 and when I put it into reverse, it will refuse to come back out of gear. The clutch was changed a few thousand km's ago and has had this problem recently. The only possible way to get the car into neutral from reverse is to release the brakes and let the car roll while forcing it out of reverse. The problem is the same whether the car is running or not. Any help greatly appreciated.
This sounds like a problem with the shifter linkage; Had a problem similar on a Nissan that came through the garage, though not a swanky skyline. It just needed unbolting and then pushing through the little shifter apeture until it stopped moving, as the previous mechanic (Apprentice who did a gearbox gasket replacement and throw-out bearing replacement) hadn't pushed it all the way through. It has little flat spots to stop it sliding all the way out again. Look for a repair manual and try following that; It'll hopefully have in-depth information.
I'd also say, however, this 'could' (I say 'could' because it's not very likely, however still possible) that the syncronisers have worn out. I also can't find out about any TSBs seeing as it's such an old vehicle, but there's all the chance that the reverse gears could have a common problem.
There is a check you can do: If you push the clutch down and you get free movement in neutral and the gears other than reverse, it's almost certainly the clutch or a serious transmission problem, or perhaps the syncros have worn to the point of being completely useless. If there's trouble getting it into a couple of gears or all with or without the clutch pressed down, it's pretty likely to be a bad shifter linkage not being fully 'engaged' or 'seated' in it's receiver. (Calling it that because I can't think of the correct terminology off the top of my head)
Things to do quickly: 1: Pump The Clutch. - Even if it's not a hydraulic clutch (I don't know much about the older cars) pump the clutch, as cable-actuated components may get pinched and may free up again after being pumped repetitively and all the way down a load of times. 2:Check out For Leaks! - Quite easy to overlook, a low fluid level can actually inhibit certain gears as I found on my old Peugot 405 and Vauxhall Corsa B. 3: Check any modifications. - Short-Throw Shifter? Different gearbox mount? Some sports-type clutch that could be too thick for the transmission? Any of these modifications could potentially cause problems with shifting, not to mention having a short throw shifter that isn't limited; If it's not a limit-able type for the selector throw, it'll chew up the selectors.