What the problem of my tranny its ah manual when im going to down shift in 3rd or 4th gear have ah grinding sound what the problem of my tranny pls help me thank you.

Sounds like the syncro may b damaged. Typically a clutch problem would be noticeable in all gears, especially shifting into reverse when vehicle is running but not moving. Try giving a 2 count for engine RPMs to drop before going into third to see if that helps. Won't fix anything but might cut the grinding sound. Till you can get the tranny fixed or replaced.

4th gear is not a gear as such but a coulping of the input and out put shafts to make a complete shaft
If there is a problem moving this coupling it indicates a syncro ring problem or spigot bearing failure in the end of the input shaft
either way it amounts to a gear box removal and pull down for repairs.

Sounds like you have a manual transmission. The problem as described is more than likely a worn detent on the shift rail. This is a job for a gearbox specialist.

Does that transmission have external shift linkage? Sounds like a linkage broke or the neutral gate is way off.

The car is a manual tranny car, your synchromesh gear is not engaging properly, take to a tranny shop to check it as a bearing may be out in 3rd gear.
Hope it resove your query.

sounds like the syncros in your tranny are toast. they are what let your car go into gear and have little teeth on them. You know they are going bad when they start grinding. Id look in a salvage yard for a new tranny or have yours rebuild. Which can be pricey. Rate my answer man!

Sounds like you have a scrinco stuck or worn out and the way you will get away with out grinding till you can get it done is to drive it like the old cars and trucks and that is to double de clutch between 3rd and 4th
all you do is to clutch in pull into nutural clutch out and in again fast and in to 4th gear (simple).

if its a manual then you have moved the splined shaft under the car ,just re adjust it ,slacken pinch bolt and look for original marks in the grime to re set it

There are to many things that can cause this problem, best thing to is go get the ECM scanned for DTC codes at a transmission shop or Auto zone or Parts Source since they scan for free.
The ECM should have DTC code in it's memory on how the transmission is Performing and have the Transmission line tested for Fluid pressure.
Good luck and hope this helps. Oh and also ways check with more then on transmission shop if there tell you that you need a new Transmission,
It could be a simple as the transmission filter falling off causing the lost of transmission fluid pressure. Check the transmission fluid too.

if you are going to fast and down shift of course its a grind maybe your suppose to be on 4th gear not third gear so that means you need to shift to 3rd.