Transmission clunk

[txhawg]

I have been noticing something that bothers me, and wondering if it is normal for these trucks. I have the 600 and 48RE transmission and about 23K miles on it now. It seems like when I accellerate lightly from a stop, then let off the gas, I hear a clunk. I can't tell where it's coming from, except that it's under the truck. I think it's been there since it was new (wife says so), but being a little hard of hearing, I couldn't say for sure. It seems to do it most often when the engine is cold. Do I have a problem? Thanks in advance for your help

 

[MMead]

Whenever my truck is under 20mph the transmission is constantly shifting up and down. Like your truck, when I let my foot off the gas it will clunk into the next gear, but the second I touch the gas again it shifts back down and a second later back up. Of course the five star dealer says it's normal.



Between my random shifting transmission and the 70mph drone, I'm almost embarrased to have passengers in my truck.

 

[DArndal]

My 04 has done the same thing since new. I talked it over with a Dodge diesel mechanic at Tempe Dodge in Arizona, and he said it is very common. If you just turnup the stereo that clunk will go away, or just don't accellerate lightly.

 

[Tony T.]

Try the Learn Run Procedure.

I'm not 100% sure if this is related to what your hearing or feeling, but I did a "Learn Run" on my 03 truck several months back an lost the clunk sound I believe your describing or maybe I just changed my driving habits getting more use to the truck. There again the procedure I did might or might not fix it. It sure won't hurt, I disconnected both negative battery cables from post for a little while. Then reconnected them, turn key to run position, don't start truck, slowly push accelarator pedal all the way to floor an then return back slowly to idle position. Took it out an tried it out an truck really seemed to shift better to me. There is a thread on this "Learn Run" procedure check out search forums. I know Steve M posted it once.



For myself if I'm running around town say 35 to 40 mph I always turn off OD button. Some do this an some don't. I just feel that running a little higher RPM is better on the engine an transmisson at the slower speeds. It really has not effected my mileage either, might even help.



Tony

 

[agkrueger]

Mine has done the same thing since new. I only have 7k on her but it hasnt gotten better or worse. I am concerned that it is play in the rear end and the sound is coming through the driveline. Mine will be going in for other warranty issues and I will see what the dealer says and post the results.

 

[Kirwin]

Drive line "play"

This has been hashed out here before. The drive line has enough "play" in it that this clunk shows up. Its worse on manuals but do to the different method of shifting its not nearly as noticable. The automatics make this more pronounced when performing lifted foot upshifts. Since there is at least some torque transmitted during normal throttle applied upshifts, it keeps the "play" all in the same direction if shifted under load. When a lifted foot shift occurs the play causes torque reversal as the transmission upshifts. Think of it this way the engine is driving the transmission with no load. You take your foot of the accelerator and the transmission becomes a load on the engine and the transmission up shifts and the engine is now trying to turn the transmission again, thus the drive line play is taken up in one direction then the other. This is when the clunk occurs. Another way to see this in the extreme is to remove your hood, accelerate the truck up to 60 MPH, and floor it then let off and see how much things move around under the hood when applying 610 lb-ft of torque. Ken Irwin

 

[txhawg]

Ken, thanks for the info. I kind of figured that was what was happening. This doesn't seem like it is good for the transmission, or rear end. Any idea what part of the driveline typically does this in our trucks? The noise itself is not annoying to me. I am concerned that with every clunk there is some damage being done. Is it something I should go back to the dealer for?

 

[Kirwin]

Dealer Fixes

I guess it depends on how bad it is in your opinion. The most likely place for excessive paly are internally in the trasmission and the differential. This assumes you don't have a 4X4 and all your u-joints are good. There is a lot of play that is normal to heavy duty gear boxes and differentials. Every gear box has some clearence and add up all the gear boxes and the sum of the clearences can be a fairly large amount of motion. All IMHO. Ken Irwin

 

[agkrueger]

I confirmed that mine has nothing to do with up shifting. I can have it manually in any gear and just let off fast and clunk. My 83 GMC auto with 183,000 miles had less play than this truck. I have just learned to not let off fast unless its a emergency.