RPM Fluctuation

[B-train]

When the torque converter went out on my 2015 3500HD with the 6.0L, it was doing similar things. I went on the test drive with my buddy at the GM dealer and watched while he drove and recorded slippage. Similar with my 2017 6.2L 8 speed trans with the shudder before the fluid was changed.

The speed and rpm you mention definitely seems like TCC to me.....you're right at the sweet spot of lugging it in OD.

 

[donjetman]

sounds like torque converter to me too

 

[RobbyD]

When the torque converter went out on my 2015 3500HD with the 6.0L, it was doing similar things. I went on the test drive with my buddy at the GM dealer and watched while he drove and recorded slippage. Similar with my 2017 6.2L 8 speed trans with the shudder before the fluid was changed.

The speed and rpm you mention definitely seems like TCC to me.....you're right at the sweet spot of lugging it in OD.

sounds like torque converter to me too

In your guys' experience/opinion, does this sound like something that can be suppressed/stopped from getting worse, or is this a torque converter replacement type deal?

 

[RobbyD]

What you describe is the easiest time for it to slip. And since it's oscillating gently, it might be sneaking past your seat-of-the-pants dyno..

I believe your scan tool should have TCC slip. If not, you might have to compare input shaft speed and engine rpms or something.

Might be good to dig up the tranmission rebuild receipt if you still have it. Have heard of aftermarket clutches not liking the factory programmed slip amount.
Possibly can get it tuned to help lockup, may want to check your trans fluid.

Once @NickTransmissions sees this, you'll be set! I'm out of my comfort zone, so I'll shut up now before I add confusion!

You've been very helpful. Thank you for the insight. Here I was thinking it was something stupid like an intake manifold gasket or something off with the TPS.

 

[Geotrash]

In your guys' experience/opinion, does this sound like something that can be suppressed/stopped from getting worse, or is this a torque converter replacement type deal?

Depends on how much wear it's caused on the lockup clutch (assuming that's the problem). My guess is that if it's slipping that badly, the clutch is probably shot. But the clutch may not be the root cause. The root cause may be insufficient pressure in the circuit to keep it locked, which would point to another problem such as a valve body problem or the pump itself being unable to generate sufficient pressure. Who rebuilt your trans, and do you have a list of what they did?

 

[Marky Dissod]

In your guys' experience/opinion, does this sound like something that can be suppressed/stopped from getting worse, or is this a torque converter replacement type deal?

(Geotrash, forgive me for riding along on the coattails of your post ...)
In other words, replacing the TCC alone may not solve your problem.

Who rebuilt your trans, and do you have a list of what they did?

Just as important: WHEN?

 

[RobbyD]

Depends on how much wear it's caused on the lockup clutch (assuming that's the problem). My guess is that if it's slipping that badly, the clutch is probably shot. But the clutch may not be the root cause. The root cause may be insufficient pressure in the circuit to keep it locked, which would point to another problem such as a valve body problem or the pump itself being unable to generate sufficient pressure. Who rebuilt your trans, and do you have a list of what they did?

It was an independent transmission shop here in North Jersey. They're reputable here in the area and I was referred to them by other mechanics/customers. I have to see if I can dig up the RO or maybe I can call them and they'll have one on file. M&O Transmission in Mine Hill, NJ if anyone cares to look them up.

(Geotrash, forgive me for riding along on the coattails of your post ...)
In other words, replacing the TCC alone may not solve your problem.

Just as important: WHEN?

Rebuild was done June 7, 2021 at just under 200,000 miles (198,000 or so if I remember). I'm now at 230,000 and change. I had asked him when I picked the truck up if I would need to do a trans flush after any certain amount of time and he said I would be good for normal factory intervals (i.e. no break-in period).

 

[Marky Dissod]

Rebuild was done June 7, 2021 at just under 200,000 miles (198,000 or so if I remember). I'm now at 230,000 and change.

I'd've ALREADY changed the ATF and ATF filter - I change ATF & coolant every two years.
I say go back to M&O and see what he says ...

 

[RobbyD]

I'd've ALREADY changed the ATF and ATF filter - I change ATF & coolant every two years.
I say go back to M&O and see what he says ...

I'm not really towing with her anymore, so I haven't been as strict with my changes as I once was. And I just hit the 30k mark which is the max I would usually go, but again just commuting now a day 70/30 highway/city.

I'll be giving them a call later today and see what insight they can provide.

 

[Dustin Jackson]

Before jumping to the torque converter being bad lets investigate things that would cause the TC to engage or disengage. Maybe the transmission is being commanded to exit/enter TC lockup?

This looks like a 07 4l60e