Is my transmission talking to me?

[Marky Dissod]

You should DEFINITELY update, if not upgrade the ATF thermal bypass valve.
Don't know if using 8L90 ATF is necessary,
although I know a guy who's been using it in 4L60s for years with no issues whatsoever.
If you're gonna update / upgrade the ATF thermal bypass valve,
might as well change the ATF & filter.

 

[NickTransmissions]

Doing research on this transmission issue, stutter when accelerating. My Tahoe seems to run fine when the trans temp is reading low, that is below 130.
But as it heats up 180 and above, I notice the stutter is more pronounced. Max temp I have seen is 195, but it was probably much higher a few months ago
when I was towing a cargo trailer. At that time, I did not detect the stutter... I thought it was the usual slack of the trailer hitch noise.

So I am considering replacing the Trans temp bypass valve with an after market product. Currently looking at this...

PPE Transmission Fluid Thermal Bypass Valve(14-18 Tahoe w/ 6L80 Transmission)​

Also considering adding the magic sauce, Instant shudder fix additive to the existing fluid.

I could also replace the trans fluid with GM ACDelco 8L90 Transmission Service FILTER Kit Mobil 1 HP Fluid For Chevy GMC, although I think my tranny is
a 6L80 model. But since this is more complicated, I am favoring the first two options. Should the fluid change be required, I would also replace the filter
and gasket, and hope the pan can be removed without too much trouble.

Thoughts, Advice, Input.... all appreciated!

Run a Superior Tech delete kit. Take it for a test drive with a two-way scan tool plugged in with live trans and converter displayed. Look at TCC slip speed and duty cycle. Slip speed should be no more than 10 rpm at max duty cycle. Also look at engine data for anything unusual like misfires, etc...If the TCC is slipping when in lock up, it will need further diagnosis to determine why it's slipping. You may end up needing a new converter and perhaps an overhaul of the transmission...

 

[BlackBrud]

Doing research on this transmission issue, stutter when accelerating. My Tahoe seems to run fine when the trans temp is reading low, that is below 130.
But as it heats up 180 and above, I notice the stutter is more pronounced. Max temp I have seen is 195, but it was probably much higher a few months ago
when I was towing a cargo trailer. At that time, I did not detect the stutter... I thought it was the usual slack of the trailer hitch noise.

So I am considering replacing the Trans temp bypass valve with an after market product. Currently looking at this...

PPE Transmission Fluid Thermal Bypass Valve(14-18 Tahoe w/ 6L80 Transmission)​

Also considering adding the magic sauce, Instant shudder fix additive to the existing fluid.

I could also replace the trans fluid with GM ACDelco 8L90 Transmission Service FILTER Kit Mobil 1 HP Fluid For Chevy GMC, although I think my tranny is
a 6L80 model. But since this is more complicated, I am favoring the first two options. Should the fluid change be required, I would also replace the filter
and gasket, and hope the pan can be removed without too much trouble.

Thoughts, Advice, Input.... all appreciated!

I installed that same PE bypass in my 6L80, dropped the pan, replaced the filter, and did a few drain and fills with fresh atf.

That should get it running smoother. Mine rarely gets above 190 unless I’m driving hard in the mountains.

Will that fix the issue completely? Hopefully. If not, you’ll have crossed those off the list of causes.

 

[Hey you]

Thanks for all this info guys! I think the bypass kit is a good idea, this way the fluid is always going thru the cooler and should not get so hot.
What fluid do you guys recommend... is Amsoil better? Would Mobil 1 synthetic work? I have noticed the shudder does not seem to occur when the fluid temp is cooler.
Will I be able to remove the pan completely, or will it have to be cleaned while resting on the exhaust.
Also, I will be on the lookout for a deal on a scan tool.

 

[Marky Dissod]

I tend to recommend LubeGard ATF, but any 'certified' 6L80 /6L90 ATF will do.

 

[Hey you]

OK, after installing a thermal bypass valve, accomplishing a fluid flush and filter change, and also adding the special sauce... instant shudder fix additive... I still have the problem.
It seems to occur only in the 5th and 6th gears when under a load, and sometimes in lower gears when heavy acceleration.
I can see the tach jumping when the shudder occurs.
So now I think I will look into a rebuilt tranny, and hope it comes with a warranty.
If I am missing something, please advise.

 

[Marky Dissod]

Before you do that - just checking - did you look into replacing / upgrading the torque converter?

 

[Hey you]

Did not think of that! But certainly the cost of that alone would almost be the same as a rebuild, with removal and install!
Has anyone tried this before?
When my shudder occurs, I can control it by backing off the pedal, or shifting down a gear.

 

[89Suburban]

Did not think of that! But certainly the cost of that alone would almost be the same as a rebuild, with removal and install!
Has anyone tried this before?
When my shudder occurs, I can control it by backing off the pedal, or shifting down a gear.

You are on borrowed time.

 

[Marky Dissod]

Did not think of that!
But certainly the cost of that alone would almost be the same as a rebuild, with removal and install!
Has anyone tried this before?
When my shudder occurs, I can control it by backing off the pedal, or shifting down a gear.

You say, 'but certainly the cost of that alone would almost be the same as a rebuild, with removal and install!'
Someone who removes rebuilds and installs transmissions, also removes and installs torque converters.
They'll provide you with even more certainty.

If you can control the shudder by backing off the pedal or downshifting, it's very likely it's the torque converter.
My experience, that's a helluva lot less than a rebuild.

Don't know if replacing the torque converter will prevent or delay a rebuild, but it's your best bet.
Otherwise the torque converter clutch will eventually fail, and take out the transmission very soon after.

The other possibility is that your transmission is already on borrowed time.

@NickTransmissions is definitely qualified to correct me here.