tranny issue while towing?

[Red '97]

My buddy ran his 97 half ton GMC out of gas today. I had to hook a chain to his front tow hooks and my reciever hitch and tow him about 9 miles, doing 45 miles per hour. the whole way, the torque converter wouldnt lock up and the transmission wouldnt shift to overdrive. was it supposed to not lock up? i almost never pull heavy with the truck and this truck probably weighed 5-6000 pounds. i know thats not heavy, but its usually a couple horses that i pull and thats it, so thats why im worried. thanks in advance!

[STROKED_NY_023]

Umm I think you mean unlock... The TC is locked at takeoff. What were your RPMs at 45? And were you in tow/haul ?

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[1Dieselman]

No the torque converter is not locked at take off, doesn't lock until third gear at the soonest unless a switch or program modification has been done. Op it appears that you do not have a chip or anything else to help build power so at 45 mph with the weight you where pulling on stock power I don't think you would see overdrive or lockup especially if you where making some heat in the trans.

[STROKED_NY_023]

Originally Posted by 1Dieselman

No the torque converter is not locked at take off, doesn't lock until third gear at the soonest unless a switch or program modification has been done. Op it appears that you do not have a chip or anything else to help build power so at 45 mph with the weight you where pulling on stock power I don't think you would see overdrive or lockup especially if you where making some heat in the trans.

The E4OD is completely computer controlled and has nothing to do with "stock power". It shifts based on inputs from the VSS, solenoid pack, and line pressure (also measure be the solenoid pack). The TC is locked at takeoff, if it wasnt how would the truck move? The TC is like a clutch on a manual, clutch engaged vehicle moves, clutch disengaged vehicle dosent move.

I have an E4OD service manual if you would like to educate yourself on it.

Back to my question, what were RPM's at 45mph under load?


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[1Dieselman]

I am not going to argue so here's some reading Torque Converters - Diesel Power Magazine How Torque Converters Work Lockup Photo 7 What is a Torque Converter and what does Lock-Up mean? | Got Transmissions
If a stock engine is struggling to make enough power to pull the load the computer may not tell the trans to shift to overdrive which is normally at 40 mph and it won't lock the converter

[STROKED_NY_023]

Originally Posted by 1Dieselman

I am not going to argue so here's some reading Torque Converters - Diesel Power Magazine How Torque Converters Work Lockup Photo 7 What is a Torque Converter and what does Lock-Up mean? | Got Transmissions
If a stock engine is struggling to make enough power to pull the load the computer may not tell the trans to shift to overdrive which is normally at 40 mph and it won't lock the converter

Theres no argument, those are really nice links about TC's but have nothing to do with the OP's problem.

Again more info is needex to diagnose...


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[Red '97]

my rpms were at 1750 or so at 45. it was in third gear, not overdrive, and i didnt have the overdrive turned off, it simply wouldnt shift into overdrive. these things are built to pull a lot more weight than what i had behind it, so thats why im skeptical as to w3hy it acted funny. i could tell the torque converter was unlocked (or locked, either way it wasnt at its normal state in third gear), from the lack of power i usually have and that it would go back to a rolling idle if i let off the accelerator. i still had more than enough power to pull the truck, but my transmission is stock and has never been rebuilt. im biting my nails because i know that its probably not gonna last a lot longer with 250,000 miles on it...

[STROKED_NY_023]

Originally Posted by Red '97

my rpms were at 1750 or so at 45. it was in third gear, not overdrive, and i didnt have the overdrive turned off, it simply wouldnt shift into overdrive. these things are built to pull a lot more weight than what i had behind it, so thats why im skeptical as to w3hy it acted funny. i could tell the torque converter was unlocked (or locked, either way it wasnt at its normal state in third gear), from the lack of power i usually have and that it would go back to a rolling idle if i let off the accelerator. i still had more than enough power to pull the truck, but my transmission is stock and has never been rebuilt. im biting my nails because i know that its probably not gonna last a lot longer with 250,000 miles on it...

Its not a power issue...

Ok so what happened when you gunned it? Did it over rev? At first glance it seems like it is your TC lockup solenoid...

How is it driving now? Honestly at 250k it dosent owe you a damn thing... I would expect a rebuild.

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[JD3020]

Originally Posted by STROKED_NY_023

The E4OD is completely computer controlled and has nothing to do with "stock power". It shifts based on inputs from the VSS, solenoid pack, and line pressure (also measure be the solenoid pack). The TC is locked at takeoff, if it wasnt how would the truck move? The TC is like a clutch on a manual, clutch engaged vehicle moves, clutch disengaged vehicle dosent move.

I have an E4OD service manual if you would like to educate yourself on it.

Back to my question, what were RPM's at 45mph under load?


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So then why is it a called a lock-up solenoid that controls when the converter locks up? If the converter was locked at an idle then the motor would stall out. Try driving a truck with a screwed VB or dropped filter in reverse, it basically tries locking the converter and kills the motor, or your floor it and peel out in reverse. At an idle its unlocked, above 32mph(my stock PCM at least), its locked.


How is the truck driving now? OD light flashing? Unless you were pulling up steep hills all the time it should've locked the converter and shifted into OD. I know when my truck was stock and i was towing heavy on hills it'd rarely leave 3rd because it would have to downshift due to lack of power, but i don't recall it ever not locking the converter, until my converter blew apart.

[jesilvas]

Normal third gear operation can be locked or unlocked TC. Normal, at a stop is unlocked. The TC 'clutches' are slipping past each other, which allow you to keep your foot on the brake in drive. Try that in a manual
If you are driving, slightly push the accel pedal, and the RPMs increase with the pedal, the TC is unlocked. But if the RPMs don't change really but the injector noise does, the TC is locked.
The trans can stay in 3rd at that speed. Normally no, but can. Usually it's under heavier load applications. How hard were you into it?
Also, was the trans cold? It won't lock up the TC until a certain temp.