I have a 1995 nissan pickup the transmission have a metal to metal. 5 sp manual 4th gear is but all other are ruff,with u let out on the clutch.

Transmission

check the fluid in the clutch system (if hydraulic) (replace cable if manual). Bleed air out of system replace the clutch master cylinder.

Hi TIM,I got a 85 nissan 720,and check your clutch fluid in reservoir,may be empty,which means your clutch slave cylinder is bad and not holding pressure,here's a link to it,very easy to replace. here's the part.Your clutch master cylinder uses brake fluid,dot 3.

Sounds like the friction surface of the clutch disc is slipping. You would have to install a new clutch (clutch disc, pressure plate, and clutch release bearing), and have the flywheel surface cut and polished back to perfect smooth by a shop.
Manual transmission gears don't slip like automatics. And lack of fluid in the transaxle or the hydraulic clutch system won't cause this either.

INTERNAL TRANS SYNCROS, SLAVE CYLINDER,SHIFTER ADJUSTMENT......CHECK ALL

Could be your clutch slave cylinder is bad,check your clutch fluid,if real low or empty then it is bad,it's located on the side of the transmission with a hydraulic hose connected to it,I have a 85 Nissan 720 4x4 5- speed,had to replace mine a few times.Here's a link on how to do. Repair Guides Clutch Clutch Release Cylinder AutoZone com Here's another link. Repair Guides Clutch Clutch Master Cylinder AutoZone com Here's the new part. Duralast Clutch Slave Cylinder 12425 Read Reviews on Duralast 12425 Your master cylinder probably is good,I just had to change the slave cylinder on mine,unless your's is leaking.If you are in a bind you can add brake fluid,yes it uses brake fluid.Then bleed it then it will get you home,you can get a one man bleeder kit,I have one,here it is. OEM One man brake bleeder kit 25036 Read 17 Reviews on OEM 25036

No, By pushing in the clutch to stop the hum all you are stopping from turning is the transmission and ( transfur case if 4 wheel drive ) the engine is still running ..and some parts in the rear differential . I have had 4 nissan pickups and currently drive a 1995 pickup, without actually hearing the noise I would look toward the transmission, these Manual transmissions are very prone to bearing failure. This has happened to 2 of the one's I have had including the one I have now. You can also see as time goes by if the noise is quieter in fourth gear than others because this is direct drive and not as many trans bearings are involved Good Luck

your luck as with mine is not good. thought I had a bad bearing, after droping the tranny and seperating the housing, I have a broken counter shaft. after looking for another with no luck, the tranny shop informed me that was common for these transmissions. parts are expensive, to rebuild would cost aprox.$800.00 or more. the main cause is the front bearing is supported in alum. causing shaft to move which first takes out the bearing, then the strain snaps the shaft. taking out all gears except 4th and only moves while in 4 wheel drive.

i had a nissan pickup that would whine in all gears except 4th...it started out with 1st then reverse then went to the rest...solution was new transmission...or rebuild cause the syncronizers or the gears them selves are being chewed up...the new transmission was cheaper then a rebuild. or take it to somewhere that will do free diag on the transmission.

THE WATER HAS DESTOYED THE CLUTCHS THE TRANS IS GOING TO BE REBUILD TO WORK RIGHT