How do i add transmission fluid? Why won't it stay in reverse gear?

No forward gears or reverse, I would check the fluid level first. Otherwise your torque converter or transmission oil pump may have went out.

Reverse is not "synchronized" forward gears are, so it does make some noise, try shifting to 2nd before engaging reverse to slow gear rotation and limit gear clash or grind.

If it is an automatic transmission, first check the fluid level. If it is low, fill it up and try it again. If the level is fine, then there is a bigger issue and you should seek a professional's help.

Based on Info...
Possible Sun Gear Failure, or Other Internal.
Check Fluid Level. Although it Seems Damage is Done.
Remove and Replace.

suggest that you check your transmission fluid post haste please. you may only need to add transmission fluid to your car. also,if you have to add the fluid,where did your fluid leak? check for leaks under your car when parked. you may need transmission fluid and filter change,suggest that you do this with new filter and add lucas transmission treatment to the fluid change also. you'll need to purchase this yourself,unless you have a mechanic in the family that can do it for you.if not i suggest you find a mechanic you trust,then tell him,or,her to add this to your tranny fluid change. also suggest while the mechanics there at the transmission to check the modulator valve on the transmission,and the vacum line that operates it. just a hint. thanks for choosing fixya.com

TRANSMISSION FLUIDS CAN BE CAUSED BY ONLY A COUPLE OF THINGS. MOST COMMON BEING A WORN OR BROKEN SEAL. THE TRANSMISSION SEALS ON MOST CARS ARE MADE FROM RUBBER OR METAL. BEING IN ALL KIND OF EXTREME TEMPS FOR YEARS ON END NOT TO MENTION THE PARTS MOVING AROUND THEM WILL EVENTUALLY CAUSE LEAKS. ALSO FAULTY INSTALLATION (OF A SEAL) CAN ALSO CAUSE A LEAK TO HAPPEN. THE ONLY OTHER THING THAT CAN CAUSE A LEAK TO MY KNOWLEGE WOULD BE IF YOU BOTTOMED OUT A CAR LOW ENOUGH THAT IT CAUSES DAMAGE TO THE TRANS CASE OR PAN. One cause of grinding when shifting into reverse is improper adjustment of the clutch linkage. If the adjustment is correct when the clutch is depressed the gears should stop turning and eliminate the grinding. Make sure there is some free play in the linkage when the clutch is not depressed. Most manual transmissions do not have a sychronized reverse gear. When you try to go into reverse from neutral, the transmission countershaft (which is linked to the pilot shaft) is still turning. The main shaft (which is linked to the tailshaft) is not turning. Therefore, since there is no sychronizer (or clutch brake like on a heavy truck tranny) the sliding cluctch gear (splined to the main shaft) grinds against the main shaft gear (floating over the main shaft but meshing its respecive countershaft gear through the reverse idler). The slider's function is to lock the main shaft gear to the main shaft thereby transmitting power to the rear wheels in the desired gear ratio (depending on which main shaft gear is locked to the main shaft). The way to cure this is to select a forward gear to stop the transmission and then go to reverse, all the while holding the clutch down. If it still won't go into gear you can either slip the clutch ever so slightly to "bump" the gears while gently pushing the stick into reverse (not too hard!! you can bend or break forks!! OUCH!!) or go into neutral, let the clutch all the way out, go into a forward gear and then reverse.

Start the engine and allow it to get to operating temperature.

Place the gear selector in Reverse, then slowly through all the forward gears, while holding the brake.

Replace the selector in Park, but leave the engine running.

Check the transmission fluid level.

If low, add fluid until level is correct, then repeat above procedure and check fluid level again to ensure that transmission is filled to proper level.

If level is correct, perform fluid/filter exchange. If problem persists, see qualified service technician for further diagnosis. Transmission damage will require overhaul to repair.

if this is a 5 speed manual transmission...all you need to do before putting your jeep into reverese is puting it into first gear and then shifting it to reverse to avoid any grinding or problems shifting into reverse...this isn't a problem just a poor jeep design by not installing an extra gear to eliminate this grinding or shifting problem

Have them flush the fluid out under warranty and put in new fluid, and have them bleed the clutch lines in case air is getting in there. Audi and VW claim lifetime transmission fluid but it's BS - I've changed relatively low mile fluid from these cars and it was horrendous. It's possible that the fluid itself is causing trouble, but it's more likely that it is a synchro problem. If it was a clutch issue, you should have problems with more than just reverse gear - a clutch simply engages and disengages the engine and transmission, regardless of which gear it is. The problem (if not fixed by fluid) is in the transmission, and being under warranty, don't accept another "suggestion" like they're giving you. Changing your clutch isn't gonna do it.

Make sure you have enough fluid, and honestly, regardless of the fluid level, change it and put in new transmission fluid. If it's an automatic, change the transmission filter too. You can try adding some Lucas stabilizer as well. If that doesn't do it, you may be looking at a rebuild or replacement.