Transmission or Torque converter?

[Twistedpinion]

I have an issue that just recently started with my 2005 z71 Silverado. It only happens given certain conditions but I'll explain what I do to replicate the problem.

When traveling about 50mph, light throttle to maintain speed the truck will begin to violently shake/shudder unless I:

Tap the brake
Hit the tow/haul mode
Hit the gas
Drop to neutral


If I'm traveling below 45 or above 70 it doesn't happen. If I'm accelerating through the range it doesn't happen. 50 seems to be the sweet spot but it does occasionally occur anywhere in that range.

I topped off the transmission fluid which did ever so slightly lessen the effect. Other than that I was going to start with a fluid change, and maybe replace the converter, but figured I'd float the question here first.

[Jimmiee]

It could be the torque converter but more likely it's an engine misfire. You don't feel it most of the time because the torque converter absorbs the misfire until it locks up. Once it locks up the fluid cushion is gone and you feel the miss. That's why when you step on the brake the problem disappears.
Now if on the other hand it's the torque converter chattering they usually chatter while locking up and then stop. What I would do if I were you is to first check all your tune up parts, plugs, wires, coils etc, and make sure they are in good shape. Add some injector cleaner or Chevron Techron gas. Next get the engine scanned and look for misfire codes. Lastly, pull the pan and inspect the filter. If the converter is coming apart you will usually see evidence inside the filter. You will have to break the filter open to see if there is any debris within the filter.

[Twistedpinion]

I had changed the spark plugs on Sunday, but after some digging found I set the gap wrong. I'll fix that tomorrow. I'll also check all the other maintenance items at that time.

No stored codes at the moment, and on Sunday I did drive around with the computer connected to see if I could catch it in the act but no such luck.

Tranny pan will come after that.

Thanks

[brianj]

You may also want to check the drive shaft carrier bearing.I have seen some odd and similar problems from this- the carrier is worn, or plain wiped out, and when the harmonics on the drive shaft get just right, it sounds like the truck is coming apart.

[sc99z71]

Mine used to do that and then it turned into the Torque Coverter locking in overdrive. When it does it see if you can take it to a transmission shop and see if they'll throw the scanner on it for you. If you get a P1870 code then TransGo makes a shift kit especially for that as well as makes your tranny stronger. I installed the shift kit on mine after the problem with th TC not locking up and now my truck runs better than ever. The shifts are strong and fast and never once has it "shuttered" between 45-55 and never has the TC slipped, when it locks it LOCKS.

[Twistedpinion]

Update:

Set the plugs to the proper gap, checked plugs, wires etc... took it out to run errands with the computer hooked up actively scanning. Shudder still occurred, no codes. On the way home I stopped and got some gumout transmission additive with the anti shudder formula. Within a few miles it had cleared up and was behaving normally. Not bad to an $8 diagnosis.

I guess this weekend I'll replace all the fluid and filter and go from there.

[Jimmiee]

Glad you got it fixed. Once it's working properly it is a good idea to change the fluid and filter.