Won't go into gear when running, clutch rattle sound.

Sounds like a release bearing is going bad.

An automatic transmission with 300,000 miles on it should be in some kind of record book it's unheard of !!! It seems counterintuitive but changing the fluid on a tranny with this many miles can be the death knell. I have seen it many times but if you got that many miles out of it was on deaths door anyway. If you are really attached to it don't even think about a junk yard tranny, they will be just a little less worn out that the original in you car now. FYI it's going to be at least 2G's to have it rebuilt.

Check your input or output sensors on top of tranny. Check engine light?

Sounds like the clutch slave & throw out went
or is leaking & the clutch won't release

Sound like a worn bushing or a synchronizer, How does the clutch pedal feel like, does it feel spongy? Try this with the vehicle off not steping on the clutch can you run it in gears? is it smooth? Now with the engine running step on the clutch do you have to push effort so much?For first the car must be in a complete stop. the sychronizer wont allow you in gear.2nd gear is a differnt story it will allow you in gear easily wheather rolling slowly foward or a complete stop. Take a look at you clutch hydraulic fluid level before you drive off pump the clutch and see if that eases the problem if it does then you are looking at a clutch hydraulic problem.If no change is felt a new clutch assemble with a hydraulic slave cyclinder will be in the work for the Rav4 (why I say this the pilot bearing tend to binds)

I would be checking the throwout bearing. But, if the clutch isn't slipping, maybe leave it for now?

If you put it in 5th gear, let out the clutch with handbrake applied and it stalls--the clutch isn't slipping for sure.

Sounds like a bearing issue too me. Have your transmission shop take a listen.

Release bearing problem.Change the clutch Assembly

hi is this manuall if so does the noise dissapear when the clutch is pressed if so your first motion shaft bearings gone in your box is there any play in the gear shift as as it could also be the selectors have play in them as they use the same fork and gearhub if this is the case if it was mine i would overhall the box as it would be another hours labour +parts replaced yates210456