lock-up issues, need ideas

B

Big Bertha

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Mar 14, 2013
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My buddy just bought a 98 12v 2500. the transmission is built, alto clutches and steels, billet input and output shafts and a single disk torque convertor, the truck sat for a year or so and we drove it home last night, she pulls nicely and shifts fine but noticed the torque convertor would go in and out of lock up, almost like partical lock up and then full lock up, only changing rpm about 200 rpm, but enought where i notice it and my truck does the same times. we are gonna go through and do a fluid change on everything since its sat for so long and for our piece of mind but any ideas would be great appreciated
 
I think its a tps problem. I just put a lockup switch on mine to fix it.
 
kinda what i was thinking too, i mean i know its either gonna be a bad/loose ground or something small needed adjusted. just wasnt sure since it kept doing like a partical lock up and full lock up
 
If the TC is very tight, there might not be a great difference between locked and unlock RPM when you are noticing the issue. If It's at constant cruising speed this would be the case.
 
yeah it happens when your cruising along at a constant speed, doesnt matter when if its low speed or high way. both of our trucks are doing it, doesnt matter if cruise control is on or not, doesnt matter if your doing 45 or 75. I know the only thing that could possibly be the issue is the tps since its really the only thing that is used for the transmission control and not really even that with a 12v.
 
both transmissions have miles on the rebuilds, plus both of our trucks have aftermarket valve bodies, could it be something to do with that possible, the only reason i ask this is because both our trucks are 1st.......2nd..3rd...... its almost like the transmissions skip second gear and goes straight to third but if we manually shift them its fine obviously. im just trying to think of every possible idea
 
You're going through the same thing that mine has done. I haven't found a solution.
My 1-3 shift was fixed by a combination of things revolving around the throttle valve setting. I have definite shifts now.

The other issue: I can come up to speed where the truck should lock itself. It won't until I reduce throttle. It doesn't matter how much throttle I was giving it, it has to be reduced before the ecm will lock the converter. I think it is a problem with the lockup solenoid and reducing pressure allows it to lock.
Even my lockup switch won't lock up the tcc until I come off the throttle.
I don't mean to sound like I'm crashing the thread. I just wanted to be specific to see if your issue is the same.


From my Not-So-Smart phone
 
If his is in and out both, I would check out the brake switch knocking it out of lockup

From my Not-So-Smart phone
 
no your cool man, I know sometimes its kinda hard to help diagnose a problem from the internet if someone hasnt really put enough info on to really explain the problem. I was going to adjust both our TV and see where we stand after that. Im going to read up on it more on here and how to adjust since most manuals dont say anything really. On my buddies truck I'm still kinda lost on the whole TC doing the whole half lock/full lock thing myself. I dont think it has anything to do with the brake switch because its not fully unlocking, its like a partcial lock. I was going to test the ground and power for the TC and see what I got from there, heard those could cause it to but who knows, appreciate the advice! Gotta love automatics!!
 
This issue is not a trans issue, but it will damage the trans.
It is electrical noise from the alternator getting into the harness and confusing the computer.
The computer thinks you are moving the throttle.

You can test this theory by wrapping the big wire that runs from the alt to the passenger battery area ( ussually this is a brown wire maybe 8 or 10 gauge) with aluminum foil. If it goes away it is electrical noise.

( aluminum foil is almost as usefull as duct tape!!)
 
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thanks, ill have to check into that and try it on trucks, think that heater duct tape would be better
 
Is this true of a system with a pot?
I guess I could unhook the alt. And drive it on the batteries.


From my Not-So-Smart phone
 
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