most likely the U joint
sounds like transmission problems( not moving in drive) and u-joint problems(pop or clunk
You may have U-Joint problems
Possibly weak u-joints or transmission mounts
You need to use the clutch and the shifter smoothly together!
Are you sure it is the transmission that is clunking? It could be the u-joints on the drive shaft that are making the noise. When the u-joints on the drive shaft are bad, there is an audble clunk when you accelerate and when slowing down (basically the same motions you go through when shifting gears).
The Transmission needs SERVICED A.S.A.P Hope This Helps.
Just out of curiousity, how is the transmission in this vehicle. Could the transmission be out of sync with the engine? This has happened to me when i had the transmission replaced in a dodge caravan, Good Luck
A very likely possibility other than problems within the transmission itself would be the transmission mount. This is a rubber bushing in a metal bracket that supports the transmission by connecting it to the frame. When the bushing becomes worn it allows the transmission to move and it is very noticeable because the hard shifting of an automatic transmission is masked or absorbed by this bushing. Hope that helps, good luck!
It could be that the transmission fluid is low, or it could be that mechanical parts have worn down. If so, it may be time for a replacement.
Check the transmission fluid level, be sure it is at the full line. A worn out universal joint could be the source of the clunking noise when the transmission is shifting.
Worn U joints, flex disks, or CV joints.
sounds like a motor or transmission mount is your likely problem