4L80E downshift then over rev

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4L80E downshift then over rev

Home > Discussion Forum > Mechanic's Corner - Transmissions

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All Messages in Thread	Author	Date
4L80E downshift then over rev	Steve	2-3-06
I have a 1997 K2500 4x4 Chevy Suburban that has a 4L80E transmission attached to a 454 7.4L engine. In recent months when going up a hill, passing while at speed or increasing throttle when already at 2000 RPM the transmission will, instead of downshifting from overdrive into high gear, will shift into no gear and the engine will quickly over rev. If I press the accelerator all the way down it will kick into gear and hold. I can also move the gear selector to 3rd and it will hold. I changed the trans fluid and filter but the problem remains. There was no debries in the pan and the fluid was not burnt. I took the truck to a tranny shop and they gave me a guesswork diagnosis about internals and a high rebuild estimate. I don't want to get charged for a whole expensive tranny rebuild if it's not necessary, especially when they can't specify the problem. Anyone have the same problem and a solution. I am also open to suggestions of possible corrections.
Re: 4L80E downshift then over rev	Steve	3-13-06
Thanks Patrick. Never used it for towing, some hauling. I admit to too much heavy foot passing, but that's about it. Mechanically, it seems fine. I can put it in any gear and it doesn't slip at all...any speed, any RPM. Just slips after downshifting when under load (automatically/electronically) and RPM is between 2100-2400...hills, leaving stoplights, freeway over 60MPH. Maybe the TCC solenoid or a speed sensor? Although, the speedometer works fine and everything's fine if I manually shift or force lockup by flooring it. I guess I'm going to have to break down and pay to put it on a Genisys or dealer scanner and see what kind of codes are setting.
Re: 4L80E downshift then over rev	Patrick	3-8-06
Sounds like you have a bad torque converter. These were designed to kick out of OD if slipping is detected (electronics) or the convertor may just be bad. Lot of pulling will do it in 60 70K miles. 300-500 repair.
Re: 4L80E downshift then over rev	lost pioneer	6-22-06
I had the same problem and a dealership found my O2 sensor wire was grounded out on the exhaust. The dealership made the repair and it fixed the problem.
Re: 4L80E downshift then over rev	lost pioneer	6-22-06
Sorry I didn't read your message right. My first answer is wrong. Try replacing your TCC switch, it's messy, but fairly easy.
Re: 4L80E downshift then over rev	matt	1-9-08
My chev 3500 truck is doing this same thing sure would like to know what the problem is... matt
Re: 4L80E downshift then over rev	matt	9-19-08
Late update: ended up changing the speed sensors and shift solenoids. problem gone. hope this helps. matt
Re: 4L80E downshift then over rev	Pat	12-27-07
Did you ever find out what the problem was for sure? Mines doing the samething. Where is the TCC switch at, and how hard is it to change? Thanks for any information. Pat
Re: 4L80E downshift then over rev	Rod Hays	4-25-07
I'd like to know the answer also,I have one doing the same thing too
Re: 4L80E downshift then over rev	Brock Roffey	12-3-06
What did you find to be the problem with your trans? I just bought a 95 6.5L diesel suburban that is doing the same thing. Thanks Brock