Odd noise - tranny issue??

316hepster · October 5, 2016

I'm stumped. I have 14 Sierra 1500 Z71 w 7" RCX lift and 65k miles. A few months ago I started hearing a slight howl whenever I would quick accelerate. Just lasted about a second. I researched and assumed it was the exhaust flap problem. Two weeks ago I sold my 20" wheels w 35x12.50 mud tires and put 18" stockers back on w 265/65-18s. About 5 days later I start having what feels like a combination of engine miss and transmission trying to find an appropriate gear w normal driving conditions from 40mph and up. There's an occasional grind/vibration sound seemingly from the rear but I'm not certain. It feels like the truck is lugging and not smooth. It's really annoying bc it's difficult to describe. It just doesn't drive right. Took it to local dealership and they drove it and just noticed some vibration, but they wouldn't touch it further bc of the lift...

Anybody have any idea as to what's going on???

Brianibew · October 5, 2016

U joint going bad? Stress from the lift.

316hepster · October 5, 2016

Hmmm. Doesn't seem like it's the u joint, but maybe.

316hepster · October 5, 2016

The noise vibration seems to be happening when transmission is in 6th. If I do manual shifting I can drop it down to m5 when it starts vibrating and it stops. As soon as I put it back in m6 it starts vibrating and making noise again.

07Softail · October 6, 2016

AFM and that damn exhaust flapper valve!

RT

316hepster · October 7, 2016

Yeah... I investigated that. I think it's more than that. Thx though

HondaHawkGT · October 15, 2016

Yeah... I investigated that. I think it's more than that. Thx though

I would try to find someone with a diagnostic scan tool that can capture live data. He can plug it in to your truck and watch for signs of an issue as you drive. It might not find the direct cause of your issue but it can save a lot of time and money by pointing you in the right direction.

Modern powertrains have the engine control module and transmission control module so highly integrated that the problem could be something as simple as a misfire or faulty knock sensor, yet all the symptoms you sense seem to point towards the transmission being the problem. The opposite is true too, the transmission may be acting up and the ECU is pulling power to avoid damage.

I know I've had similar symptoms when I accidentally left my parking brake engaged just enough (one or two clicks) that it was dragging but the parking brake indicator light wasn't lit. It drove fine but the throttle response was sluggish, shifting was a bit off, it wouldn't let me set the cruise control. And once I got up to about 55 mph, a slight vibration started to come and go. It was sickening when I realized what was going on haha.