Transmission shift "thunk"

[donpiontek]

I'm new to the group. But I find this site enormously helpful. I've got an 01 3.5, 126M miles. Over a year ago, I was driving on a hot summer day when I noticed the tranny making some "premature"rather harsh shifts, accompanied by a second "thunk" after it shifted.

Pulled over into a gas station, checked the tranny fluid (good), and the oil (down a quart and a
half). Put some oil in (synthetic, which I use). Problem gone! I've routinely had the transmission flushed about every 45M miles. The 3.5 does burn some oil (not a lot), and it appears that when it's a bit low, the tranny acts up. This doesn't really make sense. I've read that the real problem could be a solenoid in the transmission. Any ideas?

[aurorabrain]

Here's my theory. You have possibly a bad solenoid, because when it's throwing a code your trans is going into default line pressure (max). Have it scanned for codes, i would think it has something to do with the pressure control solenoid. The harsh shift followed by a second thunk is a shift to 4th and then the torque converter locking up.

[centennialman]

To add to aurorabrain's post, I had an identical problem, and 'they' replaced one of the solenoids in the xmission - don't know which one, but likely the pressure control. It was covered under the xtended warranty, but the repair bill was large. Also, there is a TSB out concerning the routing of a pressure line - the mechanic moved it the second time this happened since it was too close to the engine in some way, and was overheating. The problem has not reoccured in 2 years.

[ahh00]

I had the same problem with my 2001 3.5L (minus the oil being low/burning) and it was the pressure control solenoid on the transmission. I suggest having that checked first.