The reverse wouldn't engage on my friends 2002 vw jetta 2.0 someone else replaced the master and slave. when you first turn on the car it whistles and when trying to shift it grinds. I took the slave

This should get you going.

http://forums.vwvortex.com/showthread.php?786590-just-posting-for-the-diy-post

first thing would be to replace the lockout solenoid inside the transmission.

Start by checking the switch above the clutch pedal ... I have seen where they come loose, brake or move and when you push in the clutch it doesn't engage the safety switch all the way.

you most likely have a hydraulic clutch, which the clutch master cylinder is located on the firewall on the driverside close to your drivers side windsheild.it takes brake fluid to fill dot brake fluid will fill it properly. however if your slave cylinder on the transmission is leaking,this will require a replacement of the clutch slave cylinder. look for leakage under passenger side,,just under or below passenger side seat onto ground. recommend if you replace the clutch slave cylinder,you also replace clutch master cylinder located on the drivers side firewall at wind sheild.look under the car while someone pumps the clutch in and out,if you see brake fluid leaking under car onto ground or inside onto carpet at brake pedal,you have a bad clutch master cylinder. recommend you replace both slave cylinder and clutch master cylinder. this will save you lots of time and headaches. thank you for choosing fixya.com

Follow the given link, maybe you get something useful. volkswagen

This is tell you that your gear box is start to deteorirated. Please get it repaired soon, before it spread to other gears.

Regards,

Replace the Engine Coolant Temperature (ECT) sensor. ECT sensor is placed in the right back side of the cylinder head on 2002 VW Jetta 1.9 TDI. See picture below:



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hydrolic failure, you need a clutch master or slave, or both.

jump the starter or hit it with hammer if it starts starter is bad replace starter

There is small chance you problem is with the slave cylinder, or the clutch master cylinder.
Check the brake fluid under the hood in the clutch master cylinder. If it is gone, or low, you may be leaking brake fluid either from the slave cylinder on the transmission, or the fluid could be bypassing the rubber seals inside the master cylinder.
I hope this is what is wrong, as it is much less expensive than having the transmission repaired.
God bless your efforts.