700R4 - RPM with TCC Locked vs Unlocked? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-10-2008, 10:54 AM
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700R4 - RPM with TCC Locked vs Unlocked?

I have an 85' GMC Suburban 1/2 ton 4x4 with the 700R4 trans (3.42 gears).
It has the 3-wire TCC lock-up arrangement and I am trying to validate the operation of the converter clutch.
The only thing I can tell is that when I unplug the TCC connector at the trans, the RPMs at any given speed in 3rd or 4th gear is about 150-250 RPM higher than when the plug is installed.
Does this sound about right?
For some reason I was expecting something a little more dramatic.
The trans shifts fine otherwise- I just can't tell (even with the tach) when the trans goes into or out of lock-up.
I verified all the wiring and the solenoid is getting 12 volts (I can hear it click when I apply 12 volts and the engine off).
I guess I just need a sanity check before I go tow the kids back to college next week and cook my trans. I think I'm OK but would like some confirmation.
Thanks!
Elm

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Old 08-10-2008, 11:08 AM
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From what research I've done is that 4-prong/3-wire conncetor runs the lock-up. So no plug, no torque converter lock-up. That's the theory I'm working with on my truck...doens't mean it's right.
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Old 08-10-2008, 11:20 AM
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Im very sure it varies from trans to trans but couple hundred RPM is all id expect.
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Old 08-10-2008, 05:51 PM
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HELP-Moderators???

Well what if the trans goes though all 4 gears OK...but when the torque converter is told to lock up(I ran a manual lock-up toggle switch into the cab) in 4th gear, and i know it's locking up...but the RPM's don't drop...does that tell me my torque converter is trash?
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Old 08-10-2008, 11:34 PM
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Quote:
Originally Posted by ezobens
I have an 85' GMC Suburban 1/2 ton 4x4 with the 700R4 trans (3.42 gears).
It has the 3-wire TCC lock-up arrangement and I am trying to validate the operation of the converter clutch.
The only thing I can tell is that when I unplug the TCC connector at the trans, the RPMs at any given speed in 3rd or 4th gear is about 150-250 RPM higher than when the plug is installed.
Does this sound about right?
For some reason I was expecting something a little more dramatic.
The trans shifts fine otherwise- I just can't tell (even with the tach) when the trans goes into or out of lock-up.
I verified all the wiring and the solenoid is getting 12 volts (I can hear it click when I apply 12 volts and the engine off).
I guess I just need a sanity check before I go tow the kids back to college next week and cook my trans. I think I'm OK but would like some confirmation.
Thanks!
Elm
Your RPM drop sounds correct, Stock converters usually don't slip anymore than 200-300 RPMs cruising.
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Old 08-10-2008, 11:36 PM
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Quote:
Originally Posted by metalhead2910
Well what if the trans goes though all 4 gears OK...but when the torque converter is told to lock up(I ran a manual lock-up toggle switch into the cab) in 4th gear, and i know it's locking up...but the RPM's don't drop...does that tell me my torque converter is trash?
Either the converter lockup clutch is toast or the lockup solenoid is.
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Old 08-13-2008, 08:15 AM
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I give a second nod to the solenoid if you think it is wired correctly. I had on 200-4r rebuilt, and scratched my head for a week trying to find what I wired wrong putting it in. I had to drop the pan and swap the solenoid, and that did the trick. I had all 4 gears right, but no lockup in 4th until i swapped.
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Old 08-24-2008, 07:32 PM
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Took the truck down the road one day and lock-up suddenly hit in 4th gear...completely out of the blue, have been running it since and it's running alright. Dropped my number 5 cylinder though, no copmpression so now I'm getting the money to rebuild the engine. If it's not one thing, it's another. Thanks for your help guys. But I think you were right, something was off with the solenoid.
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