My gearbox wont select 5th gear - 1994 Nissan Sentra 4-Door

I am sorry to tell that the gearbox need to have some major repair. It is also not advisable to continue driving as the gearbox can breakdown completely leaving you stranded. At least one the cluster drive gears in the gearbox is damaged (gear tooth stripped off) that will result in that only some of the gears being able to be selected. The broken off tooth are still in the gearbox and due to the oil movement in the gearbox it can be "washed up " in between to engaged gears destroying those as well. This will happen up to the point where there are no gear selection at all.

If selects all other gears normaly.PROBLEM can only be gear control cables or linkage, possible 5th gear dammage in gearbox

first pull the fill plug and check the oil level if low add some if not then it's a bigger problem and you need to take it in.

Would need a good look myself to determine the problem but without a good look i would advise checking the linkage first .Now 5th and reverse on most cars have a mechanism to move the selector on top of the gearbox now if of this type and reverse is ok then it could be the operating lever inside the gearbox as the 5th gear sits on the outside of the gearbox behind a metal cover and its possible that this operating fork inside has broken or the retaining dowel pin has broke or just fallen out .But as stated i would need a on the job inspection so i would advise you to check the obvious then ask a dealer to have a look ?remember you do not need to drop the gearbox to fix the 5th gear in case they try it on.

i would say more like a recon gearbox ,or rip it out and fit a manual gearbox ,No parts are available for this gearbox well in europe anyway so its a complete exchange gearbox from dealer cost in excess of 2500 euros so it could be time to trade it in quick for a newer model

driving along in 5th gear but then after about 30 seconds it pops out of gear and i have to put it back into 4th coz it wont go back into 5th.

No good news on this one I think
Your whining sound problem is the Layshaft bearings in the gearbox are badly worn. It also seems that the baulk rings are damaged on 5th gear.
John

when it pops out of gear and wont stay its possible that teeth on the gear are worn frm grindin or might be broken which cause it to pop out

wont stay in 5th gear 1997