2013 Tahoe 4th gear 20-40mph shimmy

2013thoe · March 15, 2020

In 3 and mainly 4th gear from 20-40 mph the vehicle shakes and if under load like going up a hill it is really bad shaking! Had the tires rebalanced already and the driveshaft is good u joints are not loose. It is not the AFM it stays in v8 mode. Vehicle has 70k miles on it. Have note done a fluid and filter replacement yet but that is coming next. I can’t figure it out!! It is driving me crazy! Someone please help!!

SunShine01 · March 16, 2020

In 3 and mainly 4th gear from 20-40 mph the vehicle shakes and if under load like going up a hill it is really bad shaking! Had the tires rebalanced already and the driveshaft is good u joints are not loose. It is not the AFM it stays in v8 mode. Vehicle has 70k miles on it. Have note done a fluid and filter replacement yet but that is coming next. I can’t figure it out!! It is driving me crazy! Someone please help!!

I was thinking u joint but might be tranny ? Does it go away at high speed ?

Sent from my iPhone using Tapatalk

sefiroxx · March 16, 2020

Broken motor mount?

2013thoe · March 16, 2020

8 hours ago, SunShine01 said:

I was thinking u joint but might be tranny ? Does it go away at high speed ?

Sent from my iPhone using Tapatalk

It doesn’t do it under 20 or over 40 mph and if you are giving it more throttle so the rpms go higher and it stays out of 4th gear in the speed range it doesn’t do it. It only does it in 4th gear at those speeds. I tried to move the driveshaft to see if it was loose and the u joints were bad but it is as tight as it can be.

2013thoe · March 16, 2020

5 hours ago, sefiroxx said:

Broken motor mount?

If it was a motor mount wouldn’t it do it all the time? Idk just asking.

2013thoe · March 16, 2020

8 hours ago, SunShine01 said:

I was thinking u joint but might be tranny ? Does it go away at high speed ?

Sent from my iPhone using Tapatalk

I was thinking it was the 1-2 accumulator but it does it in 4th gear so that eliminates that idea

SunShine01 · March 17, 2020

Weird huh ?

Sent from my iPhone using Tapatalk

riverbanks · March 17, 2020

Your ujoint test is not the best,to be sure,I would remove the driveshaft,and hand rotate front and rear joint, checking for a stiff spot,but,what about the radiator,any leakage at tranny lines going into it, contamination of antifreeze into tranny,can cause the dreaded torque converter shutter

sefiroxx · March 19, 2020

If it was a motor mount wouldn’t it do it all the time? Idk just asking.

Rpm's combined with torque create harmonic vibrations, so the right harmonic only occurs at certain speeds/gears

2013thoe · March 19, 2020

So it ended up being the torque converter locking and unlocking when it wasn’t supposed to that caused the vibration! Chevrolet said they would just put a new transmission in be cause by the time you rebuilt it with cost of torque converter, pump that probably blew up etc. with labor it would be around the same price as a new one and you get a 3 year 100,000 mile warranty out of the new one. Downside is the transmission with labor and tax costs over $4,000 from Chevrolet! I found my local Aamco was willing to do it for $3,000 but with a year and a half warranty. Aamco sold me because they are also installing upgraded internal parts in weak areas that are known to fail in a 6L80 and an upgraded billet back torque converter!!!! Aamco also sold me because I went by there afternoon yesterday 18MAR2020 and I will be picking it up today 19MAR2020! Chevrolet would have taken a minimum of 3 days! Welp that’s it I will let everyone know how it goes!