My 4l60e has had some strange problem with downshifting for 3 years now and it's driving me insane trying to figure out what it is.

Pretty much it either doesn't downshift properly or when it does downshift it makes a physical thump or clunk and the other day it did something strange, it tried to downshift and actually made the engine lug and then came back around and did the downshift wtf?

Transmission has 130k genuine miles on it, never towed anything, never thrashed it, filter and fluid regularly changed since new, no burnt smell on dipstick, no metal in pan. Even threw parts at it and replaced both shift solenoids,3-2 downshift, pressure manifold switch,pwm solenoid all with 100% genuine ac delco parts. Next on list is epc solenoid. I even installed a transgo hd2 shift kit with new separator plate, not to fix it, just because I wanted too and still after all this it behaves exactly the same. So if anyone who knows these transmissions can tell me what would make a 4l60e not downshift, or thump on the downshift or even make the engine lug i'd greatly appreciate it. And another strange thing is that it can operate absolutely flawlessly and then goes back to this state. Also, when i am just coasting without my foot on the accelerator and then try to accelerate again as soon as i touch the accelerator the transmision THUMPS before speeding up.

 

I'm just going to take whole transmission out and replace the torque converter with a brand new one because this is the only thing it can be imo. Other people have told me it could be trans/engine mounts but i've replaced those and it still does it. Have also been told it could be u joints or drive shaft checked all that and it's in perfect condition. And if it was engine/trans mounts or driveshaft related then why would it make the engine lug? everything pointing towards torque converter. But first i'm going to drop the fluid and fill it back up with the same castrol trans fluid i used when i filled it up after installing the shift kit because it seemed to go better after I put the straight castrol dex 3 fluid in. Other fluid i used for previous service was a multi-vehicle dex 3 so maybe that's even causing it? so if i drop the fluid again and fill it back up with the castrol it should be around 85% castrol fluid.

 

Whoa, just a little. Wait a minute. Let's not throw parts at it just yet. Have you checked to see if your presently installed torque converter clutch is working? Engine lugging could be related to the torque converter staying engaged after you tap on the brake pedal.

In other words, this might be an electrical problem at the brake pedal switch wiring.

Rick