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Converter Lockup Question

keckjr

By keckjr
in Ask A GM Technician

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keckjr Enthusiast

keckjr

Posted
Posted

I have a 1991 gmc sierra 1500 2wd 5.7L with an automatic overdrive transmission. I want to start off by saying that im not sure if this is an actual problem or just normal operation. This is the first of these models that I have owned and not sure what they are supposed to do. Everything im describing happens in O/D (4th). Anyways, the truck seems to be unlocking the converter when theirs no load on the motor. You can start up a hill and the converter will lock up and pull the hill with no problem, but once you top the hill and the load on the motor goes away the converter unlocks again and will stay unlocked unless you give it more pedal. If you give it more pedal after it locking up it will unlock again to give it more power to pull the hill just like normal. But it just seems like to much slipping. I live in the ozark mountains and this just seems like it would get so much better gas milage and less transmission wear if the converter stayed locked up at all times (in 4th gear) other then when your pulling a hill. No load=unlocked, mild load= locked, heavy load=unlocked (all in o/d). If you have any info it would definitely be helpful, even if its just to say stop worrying its supposed to do that.

anonemouse Enthusiast

anonemouse

Posted
Posted
I have a 1991 gmc sierra 1500 2wd 5.7L with an automatic overdrive transmission. I want to start off by saying that im not sure if this is an actual problem or just normal operation. This is the first of these models that I have owned and not sure what they are supposed to do. Everything im describing happens in O/D (4th). Anyways, the truck seems to be unlocking the converter when theirs no load on the motor. You can start up a hill and the converter will lock up and pull the hill with no problem, but once you top the hill and the load on the motor goes away the converter unlocks again and will stay unlocked unless you give it more pedal. If you give it more pedal after it locking up it will unlock again to give it more power to pull the hill just like normal. But it just seems like to much slipping. I live in the ozark mountains and this just seems like it would get so much better gas milage and less transmission wear if the converter stayed locked up at all times (in 4th gear) other then when your pulling a hill. No load=unlocked, mild load= locked, heavy load=unlocked (all in o/d). If you have any info it would definitely be helpful, even if its just to say stop worrying its supposed to do that.

 

My 4L60E did that for awhile and I found it annoying. I had a local shop install a "Super Servo" and that did the job. Simple and inexpensive to do.

 

Anon

keckjr Enthusiast

keckjr

Posted
  • Author
Posted

Im pretty sure its not the servo, because it stays in overdrive at all times when its doing it. Thats why I think it may be something mechanical or electrical in the converter causing it to lock and unlock at incorrect times. I personally think its electrical because it shifts perfectly each time you pull out, but once you get up to speed and no longer are accellerating thats when the converter unlocks again. It maybe a bad sensor relaying incorrect info to the computer making it unlock at the wrong load. Dont these transmissions have sensors that tell the computer how much line pressure or load it has on it or is it a mechanical linkage. It does have a kickdown cable, but the converter has to know when to lock up the converter and that couldnt tell it. So basically im stuck in a rut until someone can give me some info on how the converter knows to lockup. Please any info would be greatly appreciated.

  • 4 weeks later...
pistonslap Enthusiast

pistonslap

Posted
Posted

First of all let me start by saying this is only an educated guess,because i have only owned one chev automatic.(I just recently bought a 2000 chev 4x4 auto.) Isn't the converter only supposed to lock under load? The reason is to save gas mileage. On my pickup I have a switch to lock up the converter. I was told to use this for towing on hilly terrain.I also was told that I would get less mileage with the converter locked up. If my guess is right the transmission will not go into overdrive with the converter locked, hence the lower fuel mileage.

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