Engine/Transmission (1994 - 1998) Lock up question!

[PToombs]

Has anyone had a problem with their lock up unlocking when they let off? When I'm on the highway with my '97 and let off the throttle to slow down for the off ramp or because of traffic after about 3-5 seconds I can feel the converter unlock. If I step on it I can feel it lock up again, if I hit it hard it gets ugly, starts to rev and then locks up. I rebuilt the transmission last fall and have about 3-4k on it now. Aftermarket converter, billet, ultra low stall. The TPS is set to about 1. 4 volts and the TV cable is set pretty good too. The trans works great other than this irritating problem.

TIA for any insight you can give me.

 

[budnate]

Crap Pete... that sucks mine just started doing the unlock under light throttle deal going down the road. I feal your pain brother.



I need to go find it again I ran into a good read on taking press readings in 2 places on these transmissions last week, I did not know that, the guy in canada says just because it reads right at the valve body does not mean your getting the right press elsewhere in the trans. it can cause all kinds of shifting and wear issues he said.



I think I was into geno's transmission tech area I was reading it looking for stuff on my transfercase 4x4 switch.



B.

 

[Joe G.]

That is normal behavior and why the lock up switch was invented. An exhaust brake won't work on a stock setup because the lock lets go in a few seconds after you lift. The PCM detects idle throttle position and after a few seconds unlocks the converter.

 

[PToombs]

Bud, let us know if you find it. I hope you get your OD issue worked out. It sounds like you think the pressure is off and making it drop out? Did you put in the updated pressure solenoid and cover? The guy at PATC told me that the cover will warp and leak fluid when you warp on it. Eventually it will leak all the time. I wasn't going to, but I spent the extra and put in the updated cover and solenoid. Beefy piece compared to stock, and the solenoid is way bigger too.

The other thing that comes to mind is the TV cable. I had mine way too tight, and it hit OD and Lock-up at about 50 mph. It kicked down real easy too. Turns out I had it so tight that the pressure was up so far the sensor was telling the PCM I was going 110 and it was time to shift! I set it back to stockish and it goes in around 60-65mph, much nicer to drive now, and my mileage went up some too because it's not lugging on the shift and lock-up.



Joe, thanks for that. I thought it just started doing it lately, maybe I just never noticed it before. I may have to hook up the "mystery switch" again.

 

[budnate]

Pete, glad to here your back up and shifting right, I am good to go also after this last weekend, I dont fully understand where to test the line pressures that Bill K references on the trans but a guy should check as he is right about them being off I suppose, I have not seen what kind of gauge they rigged up to read it with either, I would like to check my trans for fun and see where its at.



I was not throwing any codes and it was only dropping total lockup of the converter at very light throttle sometimes not consistently, basically just maintaining speed going down the road, I wondered if my TPS has slipped a little from setting it last summer, or if I was getting that voltage bleed on the tps wiring causing chatter I have read about,



so I checked the tps voltage, it was right about 12. 5vdc at idle where I had left it, so I hit it with wd40 again through my lube holes and reset it for 15. 5vdc at idle, trans works excellent again but noticed my shifts are less firm, like Bill says adjust one thing and it affects all your other settings, like a cat chasing it's tail with these auto transmissions.



I also changed my alternator this weekend with a Napa life time unit, mine was a nasty looking unit from when the kdp got me and slinged a ton of oil up into to the point it dripped oil out of it last year, it showed it charged right on the money but I wondered if I was getting small erratic wave signals from it that only the computer or oscilloscope would pick up on and act weird, again like I have read on the forums, so just to eliminate that from my thoughts I stuck a rebuilt unit on for piece of mind ... ..... sure would be nice to just twist the key on this rig for a few years with just fuel and oil changes, I baby my stuff and service it like it's the space shuttle, its making me crazy, lol. .



Peace, B.

 

[cerberusiam]

I dont fully understand where to test the line pressures that Bill K references on the trans but a guy should check as he is right about them being off I suppose, I have not seen what kind of gauge they rigged up to read it with either, I would like to check my trans for fun and see where its at.

Here ya go.



#ad

 

[budnate]

Cool,



Thnx B.

 

[PToombs]

Bud, did you get a chance to check it yet?

I was also wondering if you can put a potentiometer in to replace the TPS like on a 1st gen?

 

[budnate]

I am shifting good again, knock on wood!, I have not taken any pressure readings, maybe later in the fall, its go time for fun right now before the snow flies!!



I dont think you can delete the tps with our trucks, dont quote me but I think the voltage swing from the tps affects the transmission shifts where as the 1st gens had a vacuum style of shift for the trans and they can set the voltage to a steady signal and work fine... ... hassling around with my 4x4 now, its dang slow to pull into 4x4 even with all new vacuum cad and switch, thinking I have a small leak somewhere or a pinched line, need to hand trace it all but have not had the time to crawl back under it.



peace, B.

 

[Joe G.]

The TPS only affects OD and Lockup shifts. If you substitute a pot for the TPS you can set the shift point for these shifts where every you want it. If OD is allowed (light off) then the pot will set the OD shift point with the lockup shift happening shortly after that. If OD is not allowed (light on) the pot will set the shift point for OD and lockup will not happen. However, if you use a pot kick down won't work.

 

[PToombs]

Joe, thanks for that info. I thought it was the same set up as on the 1st gens, but I didn't even think about the kick down feature. The TPS works with the TV cable to kick it down? Man, I hate these things! :-laf

 

[Joe G.]

The guys who have replaced the TPS with a pot think it's a great mod. I don't think kick down is that important for our trucks because the result of kick down is usually to spin the engine off the torque curve so you usually get more noise and not much acceleration.

 

[cerberusiam]

The guys who have replaced the TPS with a pot think it's a great mod. I don't think kick down is that important for our trucks because the result of kick down is usually to spin the engine off the torque curve so you usually get more noise and not much acceleration.

That is very dependent on your locale and local constabulary. If you don't knock it out of OD in a lot of places you get tickets. The no kick down is a total pain when dealing with low\no boost situations and needing to accelerate. Mystery switches work great but its still not the same and forget trying to explain the ops to another driver.



The trailers or following cars always get smoked and generally annoyed. If there is a LEO close get ready to have a chat. :-laf