Feels like something slips, but only at part throttle

[gooffeyguy]

2012 Denali AWD

So lately I've been noticing from a stop with medium throttle it feels like the tires are slipping/spinning for a fraction of a second then they grab and I go. It doesn't do this at light throttle or heavy throttle. I know the tires aren't really slipping/spinning, but it's that feeling. Almost like a clutch slipping then grabbing on a manual transmission.

I don't have any codes and all drivetrain fluids have been changed within the past year. I've checked the drive shafts/U-joints and they seem fine with very little play. I was thinking maybe something like a bad motor or differential mount, but the symptoms don't seem the same.

Other than this slight annoyance when leaving a stoplight, everything else is fine, quiet, and smooth. I wonder if it's something internally with the trans?

 

[wjburken]

2012 Denali AWD

So lately I've been noticing from a stop with medium throttle it feels like the tires are slipping/spinning for a fraction of a second then they grab and I go. It doesn't do this at light throttle or heavy throttle. I know the tires aren't really slipping/spinning, but it's that feeling. Almost like a clutch slipping then grabbing on a manual transmission.

I don't have any codes and all drivetrain fluids have been changed within the past year. I've checked the drive shafts/U-joints and they seem fine with very little play. I was thinking maybe something like a bad motor or differential mount, but the symptoms don't seem the same.

Other than this slight annoyance when leaving a stoplight, everything else is fine, quiet, and smooth. I wonder if it's something internally with the trans?

Had similar symptoms on our ‘07 Denali. Replacing the transfer case helped and a new front differential took care of the rest. Also had the pinion bearing/seal on the rear differential replaced in the process.

 

[gooffeyguy]

Had similar symptoms on our ‘07 Denali. Replacing the transfer case helped and a new front differential took care of the rest. Also had the pinion bearing/seal on the rear differential replaced in the process.

How many miles were on it at the time? I just hit 120k, and everything underneath looks great, no leaks, seepage, or gunk anywhere

 

[wjburken]

How many miles were on it at the time? I just hit 120k, and everything underneath looks great, no leaks, seepage, or gunk anywhere

I was a little further down the line than you are. This all started above 200K. 120K seems a little soon for that type of stuff.

Might double check your front diff mount bushings closely.

 

[donjetman]

Maybe a torque converter

 

[91RS]

Broken engine mount?

 

[Jimmyy]

Try shifting into 1st when stopped and manually shift up. You could have a lazy pressure solenoid.

 

[gooffeyguy]

I'll check the front differential mount next time I get under it.

Engine mount is easier to check, I'll try to do that this week.

I'll try manual shifting it into 1st when stopped next time I drive it.

It's not that noticeable, and it's weird that it only does it (or it's only noticeable) with only part throttle (probably 30-50%) take offs. Not with normal, slowly easing into it take offs or hard, 50%+ throttle take offs.

What would signs of a bad converter be?

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[Rocket Man]

Just drive WOT all the time, problem solved. Plus it’s fun as f.

 

[gooffeyguy]

I messed with manual mode a bit on my way home from work today.

I think it may have something to do with the hill start assist

Like maybe I'm only noticing it when I'm on a slight incline, up or down.

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[Jimmyy]

I messed with manual mode a bit on my way home from work today.

so did it shift correctly using manual mode?

 

[gooffeyguy]

so did it shift correctly using manual mode?

The 3 times I was at a stop light and shifted into 1st, yes it left from a stop fine, but I wasn't on any hills, so that got me thinking about the hill start assist. I need to do more testing.

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[Doubeleive]

my torque converter was going out, my symptoms were shuddering started out doing it occasionally at low speed maybe 25-35 mph just cruising, then it started to do it more often at higher speeds, then if I got on the pedal full throttle it started to slip on the 1-2 shift, if I drove it normal it worked fine you could not tell anything was wrong unless you felt the shuddering. Apparently the torque converters are a weak link on these 6l80's, the shop told me it's the most common problem. I knew mine was likely to go out before it did I had asked the shop how much to replace it like over a year ago and then never got around to it until now, had it upgraded with a billet torque converter and basically rebuilt with better parts, now it's back in the shop because the 3-4 shift wasn't working right but should have it back shortly. the 3-4 shift problem I was having sounds like what you are describing sort of, my rpm's would jump maybe 500-1000rpm when it slipped but otherwise drove fine.

 

[Rocket Man]

my torque converter was going out, my symptoms were shuddering started out doing it occasionally at low speed maybe 25-35 mph just cruising, then it started to do it more often at higher speeds, then if I got on the pedal full throttle it started to slip on the 1-2 shift, if I drove it normal it worked fine you could not tell anything was wrong unless you felt the shuddering. Apparently the torque converters are a weak link on these 6l80's, the shop told me it's the most common problem. I knew mine was likely to go out before it did I had asked the shop how much to replace it like over a year ago and then never got around to it until now, had it upgraded with a billet torque converter and basically rebuilt with better parts, now it's back in the shop because the 3-4 shift wasn't working right but should have it back shortly. the 3-4 shift problem I was having sounds like what you are describing sort of, my rpm's would jump maybe 500-1000rpm when it slipped but otherwise drove fine.

Still don’t have it back this go-round?

 

[gooffeyguy]

I wonder if there is a way to disable the hill start assist, either by pulling a fuse or with the Tech2. Then I'd be able to tell for sure if it's that system that I'm feeling when I'm not expecting to.

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[Doubeleive]

Still don’t have it back this go-round?

I just dropped it back off this morning, he said a couple days, they have to test the tecm to see if that is it, if not then they have to pull it and replace a piston in the drum
I had it for about 400 miles but didn't get on it because it was supposed to be relearning, seemed to be fine except the 3-4, it was hard to tell what was normal during the relearn and what wasn't.

 

[Doubeleive]

I wonder if there is a way to disable the hill start assist, either by pulling a fuse or with the Tech2. Then I'd be able to tell for sure if it's that system that I'm feeling when I'm not expecting to.

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what year is yours?

 

[gooffeyguy]

what year is yours?

2012

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[Doubeleive]

2012

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unless you are stopped then hill start assist has nothing to do with what you are describing
Hill Start Assist (HSA) Non‐hybrid vehicles with StabiliTrak have a Hill Start Assist (HSA) feature, which may be useful when the vehicle is stopped on a grade. This feature is designed to prevent the vehicle from rolling, either forward or rearward, during vehicle drive off. After the driver completely stops and holds the vehicle in a complete standstill on a grade, HSA will be automatically activated. During the transition period between when the driver releases the brake pedal and starts to accelerate to drive off on a grade, HSA holds the braking pressure for a maximum of two seconds to ensure that there is no rolling.The brakes will automatically release when the accelerator pedal is applied within the two‐second window. If the vehicle is equipped with the Integrated Trailer Brake Control (ITBC) system, HSA may also apply the trailer brakes. It will not activate if the vehicle is in a drive gear and facing downhill or if the vehicle is facing uphill and in R (Reverse). There may be situations on minor hills (less than 5% grade) with a loaded vehicle or while pulling a trailer where HSA will not activate.

 

[gooffeyguy]

unless you are stopped then hill start assist has nothing to do with what you are describing
Hill Start Assist (HSA) Non‐hybrid vehicles with StabiliTrak have a Hill Start Assist (HSA) feature, which may be useful when the vehicle is stopped on a grade. This feature is designed to prevent the vehicle from rolling, either forward or rearward, during vehicle drive off. After the driver completely stops and holds the vehicle in a complete standstill on a grade, HSA will be automatically activated. During the transition period between when the driver releases the brake pedal and starts to accelerate to drive off on a grade, HSA holds the braking pressure for a maximum of two seconds to ensure that there is no rolling.The brakes will automatically release when the accelerator pedal is applied within the two‐second window. If the vehicle is equipped with the Integrated Trailer Brake Control (ITBC) system, HSA may also apply the trailer brakes. It will not activate if the vehicle is in a drive gear and facing downhill or if the vehicle is facing uphill and in R (Reverse). There may be situations on minor hills (less than 5% grade) with a loaded vehicle or while pulling a trailer where HSA will not activate.

What I'm experiencing is when starting from a stop, not while already moving and shifting

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