2012 Yukon XL 6L80 lost 4/5/6

[WillL84]

So my wife's 2012 lost 4/5/6 the other day. 1-3 work perfectly. Truck only has 99 k on it, trans was serviced around 60k. Fluid is full and looks about as you'd expect. There's no CEL. No bucking or anything, just shifts into 4th and VROOOM.

Everything I've seen online says things from the 4/5/6 clutch burnt out due to a leaky pump gasket to a broken input shaft somewhere. Anyone have any insight on this failure and general cost to rebuild/replace? I've seen prices from $2k-$3k for a reman unit (plus labor).

Thanks in advance.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

I cannot personally help you with your question; however, other members on this Forum that are much more knowledgeable than me will chime in.

 

[Geotrash]

So my wife's 2012 lost 4/5/6 the other day. 1-3 work perfectly. Truck only has 99 k on it, trans was serviced around 60k. Fluid is full and looks about as you'd expect. There's no CEL. No bucking or anything, just shifts into 4th and VROOOM.

Everything I've seen online says things from the 4/5/6 clutch burnt out due to a leaky pump gasket to a broken input shaft somewhere. Anyone have any insight on this failure and general cost to rebuild/replace? I've seen prices from $2k-$3k for a reman unit (plus labor).

Thanks in advance.

Common issue. It's a failure of the 4-5-6 clutch assembly. The piston cracks and can no longer hold the clutch plates tight enough for forward motion, and yes, the pressure regulator in the pump can be a root cause. I doubt the shaft has failed though as I believe that 2012 units have the updated shaft design from GM.

Transmission will have to come out and be disassembled to repair. Make sure that the shop you use for the work will use the Sonnax kit for this particular issue because it includes a stronger piston (plate) for the 4-5-6 clutch assembly. Best guess is around $3500 for a quality job, including R&R labor. Find out what they will do for that money though. You also want new friction plates throughout, and the valve body rebuilt with updated check balls that don't shrink.