My son has a 2000 elantra with manual transmission, there was no pressure on the clutch pedal, when I checked the hyd oil it was empty, filled it and bled it off, but now the transmission acts like it's stuck in an upper gear? You can move the shifting lever and can even get the back up switch to actiivate, but it stays in this forward upper gear? could it still be the master clutch cylinder not fully engaging? or what??

Friend, you have a hydraulic clutch. Nothing to do with transmission oil. Use brake fluid and fill the empty container by removing the cap from the empty container. Fill the container and start pumping the clutch pedal, or go to the clutch slave cylinder on the transmission and open the bleeder at the slave cylinder top while someone pushes the clutch pedal down, close the bleeder then let off the clutch. Do this a few times and the clutch will begin to work. At times it will take a while before the clutch comes all the way back up, but eventually it will. Now, there has to be a reason the clutch master cylinder was empty. A possible leak. Check to see if any fluid loss while in use. You may need to replace the slave cylinder. I've been through this and it's fairly easy to do.

Stuck? Do you mean the clutch pedal is sitting on the floor and won't come up?If so, pull the pedal up with your hand and check the fluid level in the clutch master cylinder as it may be low/empty and fill as required with brake fluid. You may have to bleed the system in order to get the clutch working properly again

Check the fluid level

when you put it in reverse,first thing you feel a spring.after tthat you lift,
a security plate,this plate prevent you from going reverse into 1 gear.
cause the axel turn a little further when you allreddy has stop the car.
this takes two sec.thats why when putting it in reverse after you feel the spring you wait two seconds,then puch al the way in reverse.

Check your clutch linkage from the pedal to the bell housing. if you have a hydraulic clutch check the hyd. line and the slave cylinder---anything that moves when you work the clutch.
Check for loose wires hanging down or making contact with the clutch assy.---sounds like you have a rub somewhere that is grounding out or pinching a wire to the oil sending unit when the clutch is depressed. This will trigger the oil light. Hope this helps.

check the slave cylinder for leaks

10W-30 grade oil is recommended for your car

• The manual transmission in your Hyundai Elantra uses a clutch to engage and disengage the power from the engine to the transmission.
• The clutch disc is sandwiched between the engine flywheel and the transmission pressure plate.
• When you switch gears and let off the clutch pedal, there is a short period during which the clutch is slipping to transmit the power in a controlled way. This causes wear on the clutch; over time it will require replacement.

The procedure to replace the clutch is as follows:--- 1) Jack up the Hyundai Elantra and place on jack stands. 2)Drain the transmission gear oil into a catch pan. To drain the gear oil, loosen the drain bolt with a ratchet. 3)Disconnect both drive axles (half shafts) from the transmission. Use a ratchet to remove the two bolts that hold the steering knuckle to the strut. Once those are out, you can easily pull the axles out of the transmission. The steering knuckle is the component that the wheel and strut attach to. 4)You can locate the two bolts to remove by following the strut down from where it's bolted into the engine bay Removing these two bolts allows you to pull the steering knuckle outward so you can pull the drive axle out of the transmission. 5)Remove the exhaust downpipe from the rest of the exhaust. It will be held on with two bolts at both ends and can be removed with a ratchet. Removing this piece is necessary to gain access to the transmission. 6)Disconnect the shifter cables connected to the transmission. Use a ratchet to remove each shifter cable and its housing.Remove the bolts holding the transmission to the engine block (there will be about seven or eight bolts). Place a transmission lift underneath the transmission to hold it and lower it down. If you don't have a transmission lift, you can use a transmission attachment for your jack.Shift the transmission back and forth until it drops onto the jack. Pull the transmission straight back, ensuring that no pressure is put on the input shaft, then lower the transmission to the ground. 7)Remove the pressure plate and clutch disc from the flywheel with a ratchet tool. Then remove the flywheel with a ratchet tool and replace it with a new flywheel. Alternatively, have your flywheel professionally machined at a machine shop then replace it in your car. Torque the flywheel down to the manufacturer's specifications. 8)Place the clutch disc on the clutch disc alignment tool and insert the tool into the flywheel input shaft hole. Connect the new pressure plate to the flywheel and torque the bolts. Once the pressure plate is torqued down, remove the clutch alignment tool. 9)Grease the new throw-out bearing and place it on the input shaft of the transmission. Once the transmission is installed, it will push against the pressure plate. 10) Reconnect all the parts which you removed while replacing the clutch. Thanks. you can rate this solution and show your appreciation.

The transmission doesn't have anything wrong, is simple the pressure plate, one of the 3 parts that conform a clutch. Just take the car to a honest mechanic and tell them that you can to replace the clutch. The advantage of a manual transmission is the fact that they are practically for ever, unless you leave them for months without the high viscosity (w-90) oil that they use.

While the suggested resistance check of the clutch safety switch should catch a bad switch. However it may still be bad. I had the experience on my 2001 Elantra with the same problem happening intermittently. I checked and I had the delay check the switch and it looked okay. After three more trips and having them test other things including replacing the Starter motor under warranty they just replaced the switch. No more problem until 3 years later same thing started happening. I asked them to specifically check this and they just adjusted how far the switch button stuck out for teh clutch pedal to engage it under the dash. 4 days later it happened again. I said f it or something like that and went and bought the 15 dollar switch and put it in myself. I've not had a problem since then. But then I'm just coming up to the 3 yr anniversary of that switch.
You can also just bypass the switch and remember not to crank your starter without the clutch engaged unless you want to experience what whiplash is like firsthand.
Just change the switch.