TRNW-2: Chevy Active Fuel Management Killing 6L80's?

[Dan Hogan]

456 clutch failures are not related to AFM in my opinion.  I agree with Steve as most 456 failures are the result of excessive metal debris related to converter issues resulting in restricted pressure and sticking valves / filters.  Customers who bring their vehicles on the front end of converter failures tend to have intact 456 clutches.  The ones who keep on getting it until the vehicle won't move or slipping badly on highway drives tend to arrive with a roasted 456 clutch.  Usually can hear the pump whining at this point as well.

How are you dealing with the converter clutch failure debris in the cooler system?  We still have local shops who don't flush or do anything besides a can of flush and install a unit or rebuild and wonder why they have repeat failures.  I don't do carry-out work anymore as I don't want to fight these folks. The amount of debris from these failures is significant.  Even hot flushes sometimes don't get all the debris out of the system.

I'd look over your methods to manage contamination as it's a big deal and I suspect the main cause of rework.

Now diagnosing AFM malfunctions vs TCC shudder can be difficult and most dealers don't have the personnel to do fine level diag work from what I see and hear now.  It's just swap until fixed and customer gets to pay.  I don't recommend any young folks get involved with dealers at all anymore.




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Dan Hogan

Buster's Transmission Service

https://busterstransmission.com

704.847.5321

________________________________
From: trnw2-bounces at trnw.net <trnw2-bounces at trnw.net> on behalf of Tony's Autoworks via trnw2 <trnw2 at trnw.net>
Sent: Tuesday, June 17, 2025 8:52 PM
To: Technical Discussion Forum <trnw2 at trnw.net>
Subject: TRNW-2: Chevy Active Fuel Management Killing 6L80's?

Hello group,

Wanted to get an opinion of what I have seen over the last 3 months. I
have rebuilt six 6L80/6L90 and have had a few other vehicles come in
the door with similar problems that I will explain in a moment. Of the
6 I rebuilt, all had 4-5-6 clutch stacks completely burnt and 3 of the
6 had pumps that were not reusable. Of the 6, 2 of them were towed in
with no movement. Just finished the 2nd of the two yesterday and
completed a test drive for the new techem to adapt. But noticed both
towed in units having some issues but could not determine the cause
until now. After a certain amount of time test driving I'm noticing
rpm fluctuations and an intermittent shudder noise on the most recent
unit. Checking scan tool data the TCC is applying and no TCC RPM slip
is occurring when the shudder happens. I noticed the same issues on
the last unit but NO shudder until today the customer told me he
experienced it and I just test drove to confirm.

I also have a customer with a 2015 Suburban that had a transmission
installed a few weeks prior from a different city and started
experiencing the shudder issue. He thought maybe he had a defective
torque converter. I noticed the shudder in the Suburban sounded
different from the shudder in the silverados so I thought maybe the
converter was defective. The suburban customer took the vehicle to the
dealership and they diagnosed the Active Fuel Management causing the
shudder when the system is activated and recommended a new engine or
complete replacement of all AFM components.

I took my recent rebuild on another test drive and with the traction
control off (a friend from the chevy dealer advised this test) and now
there are no RPM fluctuations and no shudder. Same with the other unit
with similar issues.

So now I have 2 units that have been rebuilt that looks like the
Cylinder displacement may have been the cause of failure? My friend at
the Chevy dealer says they are seeing a lot of these units come in and
if they catch them in time they can save the transmissions. And most
are replacing the engine rather than components.

My question is this: Unless there are engine codes to know that the
Cylinder displacement is an issue, how do we sell the build?
Especially if the vehicle can not be test driven. I have 2 customers
that have spent money on rebuilt units but now are looking at twice as
much to fix the engine issues.

I'm sure this topic has come up before and I guess I missed the memo.
Just curious of your opinion and what have you done to diagnose this
issue before selling a build.

Thanks for reading,
Tony
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TRNW Inc., 2825 Walnut Terrace, Modesto, CA 95355
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