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Piston Slap: No Solace For a Stationary Silverado
Daniel writes:
I have a 2009 Chevrolet Silverado 2500 HD (6L90 transmission). The truck is my snow plow and I am too old and too poor to get a new one. The tranny however has pretty much stopped moving the truck around. It has a six-liter Vortec that runs good.
Can I adjust the bands to get it to move? I did it on my old Dodge truck, but I don’t know about GM trannies. The fluid is full and clean but it doesn’t move. Please help!
Sajeev answers:
Unfortunately the GM 6L90 transmission in your Silverado 2500 HD does not have easily adjustable bands like the Dodges of decades past. The six-speed GM gearbox is built much differently, and is known to have fail points that match your description of the problem. But before we proceed, perhaps let’s watch this quick video on adjusting bands in a Dodge to get a baseline understanding.
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Sadly, the 6L90 is a totally different beast. There are several items to check, however. What follows is only given for educational purposes, because performing these steps requires specialized knowledge, tools, and the ability to disassemble a transmission on a work bench.
And reassemble it, which is always my problem.
The basics of checking the transmission’s fluid level and condition, a scan for error codes, a visual inspection of it (and the driveshaft!), a pressure test, etc. should be performed first before tearing into any modern transmission.
If all that passes muster, the above video from Precision International explains where the 6L90 fails internally. The first is the parking rod actuator assembly, and the second is a stripped output shaft.
But, as we see here, there are other problems near the 6L90’s output shaft that can occur.
Daniel, I wish I had better news for you. Like most Piston Slap readers, you are good with servicing your transmission on a regular basis. And because of that I fear there is something wrong deep inside the transmission case, but “Internet troubleshooters” like yours truly cannot possibly narrow things down any certainty.
I encourage you to find a good transmission shop in your area, and see what kind of deal you can work with them. This job will either be pretty simple for a professional, or it will require a full teardown and reassembly.
And now the torch is handed off to you, dear readers of Hagerty Media. What do you think could be wrong with Daniel’s Silverado?
Have a question you’d like answered on Piston Slap? Send your queries to pistonslap@hagerty.com—give us as much detail as possible so we can help! Keep in mind this is a weekly column, so if you need an expedited answer, please tell me in your email.
I would first have to ask being that this your “snow plow” does this mean just for you or is it a side job? Honestly I’ve never met anyone who plows regularly during the winter that hasn’t talked about the beating it puts on the truck, regardless of manufacturer. Todays trannys are asked to do and do much better at doing certain things but at the sacrifice of simple old school reliability like your old Dodge had. That’s the simple answer that you don’t want to hear.
I’m not so sure that a professional shop teardown/rebuild is the best option – that can get pretty expensive (and like Sajeev hints at, most of us are not going to try and tackle that on our own). Might it be simpler to do a swap?
I would also add, check your transfer case. Check fluid level and condition to start. These take just as much of a beating as the transmission. I’ve seen plow trucks with damaged transfer cases cause a no engagement issue.