The 1986 Nissan Pickup clutch allows the engine to be engaged and disengaged from the manual transmission and the rest of the drivetrain. It includes a clutch disc, pressure plate, flywheel and release bearing and is actuated through a hydraulic system attached to the clutch pedal. The clutch is located in between the engine and transmission and cannot be inspected or repaired without removing either the engine or transmission. Removing the transmission is the simpler choice of the two.
Put the transmission in "Reverse" with the engine running. If it doesn't go into "Reverse" at all or not without grinding or pushing hard on the shifter, remove the transmission. There may be internal problems in the clutch or with the hydraulics. Something is keeping the clutch engaged if it won't go in reverse. Usually, either the clutch plates are frozen together or the hydraulic system is not able to push the two sides apart.
Inspect the clutch hydraulic system for problems. Check the fluid reservoir on the driver's side firewall in case the level has dropped. Fill to the line with brake fluid, pump the clutch a few times, and check again to see if the level has dropped again. This could indicate either a leak in the hydaulic lines or air in the lines that needs to be fixed.
Follow the hydraulic lines to the bell housing where they are attached to the slave cylinder. Look for signs of leakage. Use a wrench to remove and replace any section of broken line. Bleed the system by connecting a tube to the bleeder screw on the slave cylinder and dipping the end of the tube in a jar of clean brake fluid. Have someone depress the clutch all the way very quickly. Watch for bubbles in the jar. Keep the reservoir full and repeat the procedure until no air bubbles are visible in the jar. Close the bleeder screw, and remove the tube. If bleeding the hydraulic system and fixing breaks or loose connections does not help, it may be that the piston seal in the master cylinder is damaged and not sealing properly
Remove the transmission and inspect the clutch plates. They may be contaminated with oil and require replacement or cleaning with brake cleaning solution. Replace the clutch plates if they appear warped or damaged. Check the diaphragm spring for fatigue, and look for leaks in the hydraulic system inside the clutch assembly.
Inspect the clutch plates for wear and contamination from brake fluid or oil. Replace any worn or contaminated clutch plates
Inspect the diaphragm spring, as it may be weak or damaged and need to be replaced. Other causes of slippage include a warped flywheel and debris that keeps the hydraulic piston from going back to its normal position.
Give your clutch a week or so to get broken in if you have just had new clutch plates installed. It takes between 30 and 40 starts with the clutch before the plates match perfectly.
Inspect the clutch plates for oil or hydraulic fluid, and replace them if they have been contaminated.
Inspect the engine mounts. If they are worn or loose, they will cause the engine and drive train to rattle and shake as the clutch is engaged. Tighten or replace the mounts, if necessary.
Inspect the splines on the driveshaft just behind the transmission. If the splines are worn they will cause a clanking noise at startup and gear changes. Replace them if they are worn.
