torque converter clutch cycling 99 Silverado NBS

[oldred95]

Just bought this truck from my land lord and I never noticed it when I test drove it but after a 150 mile trip I noticed the converter cycles like mad. It seems to stay unlocked as much if not more then it stays locked. Also seems like if its going to stay locked it will do it when pulling a hill and as soon as I start going down the backside of the hill it unlocks. On flat ground its constantly cycling. Its got brand new Mobil 1 ATF in it and no check engine light. The truck has been babied all its life and only has 127k on it and is in like new condition. I've checked GM Dealerworld and its really not help other then bulletins about testing the TCC control system which I need and am going to do. I'm thinking its valve body wear causing fluid leakage past the valve and its not always staying engaged. It does it at all fluid temps too. Have any of you transmission guru's ran into this issue before? I'm thinking a transgo shift correction kit would fix this problem would it not? I know they address the infamous P1870 slip detected code. It is a 4L60E too.

[PBA]

I carry the PWM eliminator valve from TransGo for this unit, Price is $10.17. You will want to use "LUBEGARD's Dr. Tranny Transmission Instant Shudder Fixx". This works very well for the problem you are having in most cases.

[oldred95]

You think this is a mechanical issue more then a control circuit issue?

I am talking to PFK right now and he had this same exact problem with his tow rig only it has an 80E and it was the Engine coolant temp sensor connector. It was cracked and not getting a good connection and would randomly send a temp of like 20 degrees to the PCM which the PCM said was too cold to lock the converter so it unlocks it, then it gets the correct signal and relocks. Sounds a lot like mine is doing.

Also this truck has been sitting most of the last 3 years and the owner who is also my land lord never had an issue with it and he would not have sold it to me had there been an issue. Also being that there are no codes that makes me thing even more it could be the ECT because the PCM itself is turning off the signal to the TCC solenoid. I'll have to do some checking and see but I hope this is it. It was just flushed and Mobil 1 synthetic ATF put in and I don't really want to buy a bunch of fluid if I have to pull the pan off. I can always catch the fluid but still...

[Fast305]

Originally Posted by oldred95

Just bought this truck from my land lord and I never noticed it when I test drove it but after a 150 mile trip I noticed the converter cycles like mad. It seems to stay unlocked as much if not more then it stays locked. Also seems like if its going to stay locked it will do it when pulling a hill and as soon as I start going down the backside of the hill it unlocks. On flat ground its constantly cycling. Its got brand new Mobil 1 ATF in it and no check engine light. The truck has been babied all its life and only has 127k on it and is in like new condition. I've checked GM Dealerworld and its really not help other then bulletins about testing the TCC control system which I need and am going to do. I'm thinking its valve body wear causing fluid leakage past the valve and its not always staying engaged. It does it at all fluid temps too. Have any of you transmission guru's ran into this issue before? I'm thinking a transgo shift correction kit would fix this problem would it not? I know they address the infamous P1870 slip detected code. It is a 4L60E too.

I am going to say that it is the PWM torque conterter valve. My express acts up the same way. 1/2 the time it works just fine, half the time it doesn't. Mine tends to lock most predictibly when its cold after its sat a day or so. Once it gets driven say 50 miles, it stops locking sometimes entirely. I get the 1870 code set quite often, only if I cruise a constant, steady 45-65 mph. If I drive even remotely aggressive or 70+ I NEVER see the light. I am going to put the Transgo HD2 Shift kit in mine which includes a PWM eliminator valve. It should fix it.

[oldred95]

Originally Posted by Fast305

I am going to say that it is the PWM torque conterter valve. My express acts up the same way. 1/2 the time it works just fine, half the time it doesn't. Mine tends to lock most predictibly when its cold after its sat a day or so. Once it gets driven say 50 miles, it stops locking sometimes entirely. I get the 1870 code set quite often, only if I cruise a constant, steady 45-65 mph. If I drive even remotely aggressive or 70+ I NEVER see the light. I am going to put the Transgo HD2 Shift kit in mine which includes a PWM eliminator valve. It should fix it.

Thats not what this is doing. As long as its past the coolant temp threshold to allow TCC lockup and the speed is about 45 or higher it will go into lockup obviously but it may unlock right after it locked. It seems like as long as I'm gradually accelerating it stays locked for the most part up until 65 mph or so and then regaurdless of whats going on its cycling. By cycling I mean locking and unlocking every few seconds to maybe as long as ever 30-45 seconds. Its not something where it either works or it doesn't more like the PWM hodis causes. Seems to me like it could very well be a coolant temp sensor kicking up the wrong signal for whatever reason be it the sensor or the connector. And Chris the lever concept is being put into full effect on this truck.

[Fast305]

Originally Posted by oldred95

And Chris the lever concept is being put into full effect on this truck.

Thats Ok as long as you still have OldRed.

[oldred95]

Originally Posted by Fast305

Thats Ok as long as you still have OldRed.

Thats the whole point.


So this PWM eliminator hodis turns the PWM TCC apply system into a simple locked or unlocked system, no modulation, no nothing? That comes with the HD2 shift kit?

[Fast305]

Originally Posted by oldred95

Thats the whole point.


So this PWM eliminator hodis turns the PWM TCC apply system into a simple locked or unlocked system, no modulation, no nothing? That comes with the HD2 shift kit?

Sure does, it DOES come with the HD2 kit.

[oldred95]

Originally Posted by Fast305

Sure does, it DOES come with the HD2 kit.

Putting in a hard days work I see.

[oldred95]

Well got a hold of a Tech II and was just thrilled at what I found. No codes of course. Checked my TPS output and it was smooth as butter, trans temp and engine coolant temp inputs were steady and consistant. Ran the TCC solenoid test and the TCC will kind of studder engage and the engine will pull down and almost die a few times and then it finally engaged and killed the engine testing in in stopped in gear. Going down the road it will lock in and the slip speed is 0-5 rpm and the PWM is 95% and the converter is commanded to lock then out of nowhere the slip speed jumps up to 50-150 or so and the PWM is still 95% and its still commanding the TCC on. Looks like its a problem in the valve body/PWM piece of crap. I guess its just not slipping long enough or bad enough for code P1870 to set just yet.


I believe this is the kit I need is it not? How hard will it be to install? I'm not brain dead about automatics but I'm not a professional on them either.

http://cgi.ebay.com/ebaymotors/TRANS...6937QQtcZphoto

Above fast305 mentioned the HD2 kit eliminates the PWM valve altogether but according to the SK kit it fixes the same things as the HD2 kit. I'm a little confused as to which I really need. Also will I need to get a new seperator plate while I'm at it?

[NEUMANNZZ]

Originally Posted by oldred95

Well got a hold of a Tech II and was just thrilled at what I found. No codes of course. Checked my TPS output and it was smooth as butter, trans temp and engine coolant temp inputs were steady and consistant. Ran the TCC solenoid test and the TCC will kind of studder engage and the engine will pull down and almost die a few times and then it finally engaged and killed the engine testing in in stopped in gear. Going down the road it will lock in and the slip speed is 0-5 rpm and the PWM is 95% and the converter is commanded to lock then out of nowhere the slip speed jumps up to 50-150 or so and the PWM is still 95% and its still commanding the TCC on. Looks like its a problem in the valve body/PWM piece of crap. I guess its just not slipping long enough or bad enough for code P1870 to set just yet.


I believe this is the kit I need is it not? How hard will it be to install? I'm not brain dead about automatics but I'm not a professional on them either.

http://cgi.ebay.com/ebaymotors/TRANS...6937QQtcZphoto

Above fast305 mentioned the HD2 kit eliminates the PWM valve altogether but according to the SK kit it fixes the same things as the HD2 kit. I'm a little confused as to which I really need. Also will I need to get a new seperator plate while I'm at it?

I know the hd2 kit comes with an updated pwm valve. It looks like that kit doesnt come with the pwm valve. I would at least get new gaskets for the seperator plate if that kit doesnt come with it.

[oldred95]

http://www.transmissionpartsusa.com/...-000035935.htm


Same kit different description. Is the PWM boost valve the same as the PWM valve for the TCC system? Seems like some sites descriptions say yes it does have the valve and yes it will fix it and others just say it fixes it but doesn't say how. Also while I'm at it don't I want to install a .500 boost valve?

[NEUMANNZZ]

Im not sure what the other kits use to fix the pwm valve. I just now the hd2 kit has a updated pwm valve. If you do get the hd2 kit it will come with the .490 boost valve. I would get the boost valve.
these kits comes with a pic of the updated valve:

http://cgi.ebay.com/ebaymotors/GM-4L...3286.m20.l1116

http://cgi.ebay.com/ebaymotors/_Car-...3756.m20.l1116

[oldred95]

Got a transgo HD2 kit and seperator plate on order. Decided not to get the vette servo for a couple of reasons. First of all I don't want a real firm shift. The shift kit is going to make it plenty firm the way it is. Second I don't know how the torque management and adaptive shift mode and what not will react to it. I've heard it will vary from won't feel it shift to neck cracker shifts. Decided just to fix it and leave it at that.

[NEUMANNZZ]

I put my stock tune back in my truck the other day when I got it smogged. The transmission shifted great, as in smooth and crisp just a little throttle(better then stock) 1/2 to 3/4 throttle was a little firmer. not bad at all. I would of got the vette servo too. just dont put any spacers in the accumulator housing. It will shift good with a stock tune(plus major improvement in downshifting).

[oldred95]

Originally Posted by NEUMANNZZ

I put my stock tune back in my truck the other day when I got it smogged. The transmission shifted great, as in smooth and crisp just a little throttle(better then stock) 1/2 to 3/4 throttle was a little firmer. not bad at all. I would of got the vette servo too. just dont put any spacers in the accumulator housing. It will shift good with a stock tune(plus major improvement in downshifting).

I imagine I'll put it in with zero washers and see what happens. I have yet to completely compile my order list for my 95 and if I feel like the 99 needs a firmer shift I can always get a vette servo and put it in later on. I'll just order one up along with my 95's list of parts.

[NEUMANNZZ]

yeah if you have the habit of WOT foot the adaptive shifting will make it firmer.

[Fast305]

Originally Posted by NEUMANNZZ

yeah if you have the habit of WOT foot the adaptive shifting will make it firmer.

My 97 Express gets rubber on almost every 1-2 upshift, even in traffic. But I drive the hell out of it. 0-85+ on a daily basis. Running the stock 60E and stock tune. Got to love the old adaptives.

[PBA]

Give me a call on this, as I carry the modified Shift kit, predrilled separator plate, and the Corvette servo to "match" your setup. The Corvette servo does more than firm up the 2nd gear shift, it also helps with the 3rd gear accumulation which improves the 3rd gear shift and life of the 3-4 clutches. With what I do to these kits you will have a smooth part throttle 1-2 shift with the Corvette servo. I also add the torlon checkballs to keep from destroying the separator plate. I add additional Viton seals and new accumulator pistons and hardened and oem accumulator pins. When this kit is matched to how you drive and any other modifications you have done, there is a noticeable difference in how the transmission upshifts and downshifts. Once you have added the Shift kit, leave the transmission firmness tables at zero. Any questions on this call me at 909 795-1876. Dana

[Fast305]

Originally Posted by PBA

Give me a call on this, as I carry the modified Shift kit, predrilled separator plate, and the Corvette servo to "match" your setup. The Corvette servo does more than firm up the 2nd gear shift, it also helps with the 3rd gear accumulation which improves the 3rd gear shift and life of the 3-4 clutches. With what I do to these kits you will have a smooth part throttle 1-2 shift with the Corvette servo. I also add the torlon checkballs to keep from destroying the separator plate. I add additional Viton seals and new accumulator pistons and hardened and oem accumulator pins. When this kit is matched to how you drive and any other modifications you have done, there is a noticeable difference in how the transmission upshifts and downshifts. Once you have added the Shift kit, leave the transmission firmness tables at zero. Any questions on this call me at 909 795-1876. Dana

Not trying to steal your thread Kurt, but I am in the same boat with the intermittent lockup due to the PWM valve.

Dana (Pro-Built?),

That sounds like just the package I will be interested in. I am looking to do my Express van soon, dreaded P1870 code and intermittent lockup. I will definately be giving you a call. If I am understanding you right, if I add these components the transmission will shift mildly at part-throttle and beef up as the throttle is increased even with stock shift tables. Another member and I are about to reflash the PCM in the Express. My thoughts are to elminate the PWM of the TCC from the tuning entirely (its easy enough to do) by adjusting the parameters to make the lockup either on or off. The WOT TCC Lockup is as good as gone as well. I have always hated that in the stock routines. Nothing like trying to accelerate @ WOT when the transmission has just shifted into 3rd gear only to have the TCC clutch lock up and bog the engine back down.