Downshifting problems

hamel01 · January 24, 2004

Guys,

Was on my way home today when i went to pass someone and my truck wouldn't downshift. Tired a few times and same thing. If i play with i can get it to pick upi speed but it will not down shift. It will unlock the torque converter but nothing after that. Looked in my haynes manual and it said to readjust the TV cable but i can't find one on it. My question is does the TV cable exist or is it all computer controlled? Also what do you guys think might be wrong? From a dead stop it's no problem taking off just when your going and try to go faster. Also when you do floor it it will shutter a little and the the tranny will slip a bit so the engine revs to 3000 but no speed increase. I have no idea whats wrong. Thanks to those who respond. oh yeah it's a 1998 Z71 extended cab with a 5.7 vortec with a 4 speed auto tranny.

Jeremy WI · January 24, 2004

No TV cable on your tranny, all electronic

Chris97K1500 · January 24, 2004

My truck does the same thing. It'll run great from a dead stop. If I'm already cruising and try to hit the gas, like when passing someone, it won't downshift, the rpm's just slowly go up. In my situation I'm wondering if it could be the fact that I've got bigger tires and never reprogrammed the shift points? If not that, I've got no idea. Hopefully someone else will know. Chris

hamel01 · January 24, 2004

Talked to the service garage today and the guy there told me that my Throttle positioning sensor is either bad or out of adjustment and it would need to be hooked up to a scanner to see for sure. Does this sound right to you guys? Sounds like this could be a little expensive?

MN Z-71 · January 25, 2004

TPS could be a problem, not sure how expensive of a fix. Is this a GM dealer service dept. you are dealing with? If so I would recommend that you get an estimate from them and from some other well-known/reliable independent repair shops. GM dealers tend to charge more than an independent shop.

You could probably test it yourself, there should be instructions on how to do this in your service manual. You will need a multimeter to do so though.

The shuddering/slipping could be a sign of a worn out tranny though. When mine went out (at 230k) it still downshifted ok but had a real bad hard shift/shudder on the 1-2 upshift, and all other shifts were really sloppy.

How many miles do you have on the truck?