Could be a number of things. I would check the U joins first then the motor mounts. Could also be the clutch plate (might have faulty springs that help to make it engage smoothly and absorb shock from releasing the pedal to quickly). Could be too much slop in the gears. Excessive wear in the gears and universal joints causes them to be loose and can make a clunk when they slap against eachother. Is the lever going into the transmission striking against something in the engine compartment? Maybe something has come loose and is being struck. Don't want to break a critical component. A broken motor mount will let the engine raise up and then slam down as the load on the engine is changed. (I had this happen in a '66 Caprice... or was it my '73 Fury?) All good answers,I'd check front u-joint first..my 2 cents answer all good answers, but before you dive into clutch or gearbox, check for slop on pinion shaft in differential also try letting clutch out slower
You need to use the clutch and the shifter smoothly together!
Possibly weak u-joints or transmission mounts
most likely the U joint
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 throwout bearing in your clutch is the likely culprit here. Your clutch may be shot in addition, but you are probably looking at a costly fix here.
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
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.
sounds like a motor or transmission mount is your likely problem
Worn U joints, flex disks, or CV joints.
broken transmission mount there is a front left, rear left and a center mount