97 Tahoe Transmission

BBShark

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My Tahoe seems to "hunt" for a gear at certain speeds. About 40 and 60 mph with steady throttle and level ground. It's weird, like maybe the converter is trying to lock causing the truck to very slightly buck intermittently unless you speed up or slow down. 3 mph up or down and it goes away.

Any ideas?
 
The converter clutch is a pwm type and you do not normally feel it come on and off, does tach go up and down when this happens? If not could be an engine miss. Also watch speedo to make sure it is steady,if not could have a bad vehicle speed sensor. Any check engine light?Let me know.
 
The converter clutch is a pwm type and you do not normally feel it come on and off, does tach go up and down when this happens? If not could be an engine miss. Also watch speedo to make sure it is steady,if not could have a bad vehicle speed sensor. Any check engine light?Let me know.

PWM?? why?? what does that scheme bring to the table???

:huh:
 
The converter clutch is a pwm type and you do not normally feel it come on and off, does tach go up and down when this happens? If not could be an engine miss. Also watch speedo to make sure it is steady,if not could have a bad vehicle speed sensor. Any check engine light?Let me know.

Great, I drove it tonight and tried to get it to act up:hunter:. Not a hint of doing what I described. Also, no check engine light ever and I have had this truck for 4 years.

I can certainly live with this, it does not happen frequently and all I need to do is back off the throttle a little and it's fine. Thanks for the help.
 
The converter clutch is a pwm type and you do not normally feel it come on and off, does tach go up and down when this happens? If not could be an engine miss. Also watch speedo to make sure it is steady,if not could have a bad vehicle speed sensor. Any check engine light?Let me know.

PWM?? why?? what does that scheme bring to the table???

:huh:

That'd be smoother/softer engagement, with less chance of a shudder. That was one of GM's big complaints in the earlier days of lockup converters. It'd get the signal from the ECM to lockup maybe a touch early, and it'd shake like a possum passin' a peach seed.
 
That'd be smoother/softer engagement, with less chance of a shudder. That was one of GM's big complaints in the earlier days of lockup converters. It'd get the signal from the ECM to lockup maybe a touch early, and it'd shake like a possum passin' a peach seed.

Is the lockup done with a PWM controlled solenoid? Maybe that is what I'm feeling. Do these things act up intermittently?
 
Now you're making my head hurt. IIRC, line pressure and convertor are both PWM controlled. I was also thinking about your initial description too. There are 2 sensors involved here- input speed and output speed. I don't have any kind of a troubleshooting manual, but if the input/output ratio gets funky for some reason weird stuff happens. And all it takes is a flake of metal on one or both sensors..
 
My Tahoe seems to "hunt" for a gear at certain speeds. About 40 and 60 mph with steady throttle and level ground. It's weird, like maybe the converter is trying to lock causing the truck to very slightly buck intermittently unless you speed up or slow down. 3 mph up or down and it goes away.

Any ideas?

If it's a 4L60e transmission, it's a factory defect problem. Something to do with the bores in the valve body wearing out and not holding pressure.

You can buy a "fix it kit" on ebay for around $40 and requires pulling the valve body and tearing it down to re-drill the bores with oversize seals.

My 2000 S-10 done the exact thing your describing, I bought a used valve body off ebay from a transmission vendor that guarantees these to work. He cleans and checks them. It cost me less than $100 and 8 hours of my time to replace.....my car shifts and runs like it did the day I bought it.

Dealers charge upwards of $350 - 400 to do this repair..

Do a search for "code 1870" on google and you'll see what I'm talking about. Sometimes it will throw a check engine light...sometimes it won't.
 
Now that you mention that it seems to me that there was a special policy out on some of the S-10s with 4L60E trans that we were replacing the valve body for a similar complaint. I kind of forgot about that one, it was a couple years ago. But either way he said no check engine light.
 
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My Tahoe seems to "hunt" for a gear at certain speeds. About 40 and 60 mph with steady throttle and level ground. It's weird, like maybe the converter is trying to lock causing the truck to very slightly buck intermittently unless you speed up or slow down. 3 mph up or down and it goes away.

Any ideas?

If it's a 4L60e transmission, it's a factory defect problem. Something to do with the bores in the valve body wearing out and not holding pressure.

You can buy a "fix it kit" on ebay for around $40 and requires pulling the valve body and tearing it down to re-drill the bores with oversize seals.

My 2000 S-10 done the exact thing your describing, I bought a used valve body off ebay from a transmission vendor that guarantees these to work. He cleans and checks them. It cost me less than $100 and 8 hours of my time to replace.....my car shifts and runs like it did the day I bought it.

Dealers charge upwards of $350 - 400 to do this repair..

Do a search for "code 1870" on google and you'll see what I'm talking about. Sometimes it will throw a check engine light...sometimes it won't.

I'll have to check into that, thanks.
 
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