Clunk under Acceleration, now will not accelerate reasonably

Discussion in 'GM Powertrain' started by lifted_neutrino, Oct 28, 2012.

  1. lifted_neutrino

    lifted_neutrino New Member

    Vehicle Info: 2007 NNBS Chevrolet Silverado Z71 w/ 4.8L Automatic Transmission

    Hey guys, I have no knowledge of AT and their inner workings. With that being said, last night I was driving and was stuck behind a row of slowly moving people. I saw an opening and depressed the gas pedal enough to downshift and engage OD but when I did, I felt a pretty solid clunk. I immediately let off the accelerator and pulled to the side of the road to inspect and ensure I had not blown anything.

    Upon inspection, nothing appeared out of place. I got back in the truck, started it back up and went to drive off. To get the truck rolling, I had to raise the RPM to above 2,000, as if my clutch was not engaging properly or something. I used my Superchips to return the transmission tune to stock thinking it may have been a faulty transfer, but to no avail.

    With what is said above, does anyone have any clues on what might be wrong? I am hoping to get the truck running by this weekend as my girl and I are supposed to be going camping before the temperatures drop much more and I would hate to have to cancel.
  2. stratct

    stratct New Member

    Check the trans fluid if you haven't yet. If it's low you should add some (duh) lol. Make sure it's running and on a level surface and up to operating temp when you check it. Sounds like a ether a bad TQ converter or it's low on fluid not allowing the TC to engage right.
  3. lifted_neutrino

    lifted_neutrino New Member

    LOL. I checked it earlier today and it was at correct level, however... it was not up to temp. Does it have a need to be used to elevate the temperature?

    I was thinking that it was something with the TQ converter, because it's not engaging the gears correctly. The converter is essentially an AT clutch, correct?

    Neighbor kinda has me spooked. Said it sounds like I dropped first gear...
  4. stratct

    stratct New Member

    I doubt it. Id put money down that it's the converter. The temp thing isn't THAT necessary, but I'd warm it up to check. You could always drop the pan, change the filter and fluid, and clean the pan magnet(s), and see what happens after a little bit. If it doesn't improve, id do a new converter. Is your truck a little jumpy off the line now too? Just a thought. That's another sign of a bad TC. some people will say that changing the fluid with over 75k is a bad idea but I don't see (scientifically) how that would harm anything.
  5. stratct

    stratct New Member

    PM me if you need specific help too. I'm USUALY around Haha
  6. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    Does it behave the same in reverse?
  7. lifted_neutrino

    lifted_neutrino New Member

    Yes. It is slow to move in Reverse, but if I push down a little more on the accelerator it pops/jumps and starts moving.

    I had thought about replacing the fluid and screens and seeing what happened. Hoping that it's not a TC because I don't feel like doing something that in depth and it's going to require a lot more time... If it'll fix it though, I'm fine with it.


    Alright, here are some videos that I took today to aid in explaining what is actually happening. To me, it seems that something within the transmission is not fully engaging to turn the driveshaft, mostly affecting first gear (seemingly all gears because of precedence). Any comments, ideas or solutions would be GREATLY appreciated.

    WOT in Drive

    WOT in 1st, selected. Acceleration in 2nd, selected

    Exterior of 1st WOT

    Under Truck Exterior of 1st WOT

    Driveshaft Focus 1st WOT
  8. lifted_neutrino

    lifted_neutrino New Member

    Yes. It will drop in, but when I go to accelerate, it pops a little bit... feels like notchy grinding.

    Does anyone know the OEM stall/specifications for the 4L60E? I am looking to keep the truck similar to stock I suppose (since I know little about AT right now). It will be used for city/highway driving, off road through mud and towing.

    Would something like this work? I know this company is quite popular with performance transmissions.

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