99 tahoe (old body) tcc trans converter clutch

[YenkoZL1]

I have a 4L60E tranny in my 99 tahoe. I just had it completely rebuilt just 5k on it. Shift kit, z-packs,vette servo, Sonnax O.D. Servo, and supposively torque converter ment for towing. My trans converter clutch keeps slipping in and out of lock up mode between 40 and 45 mph. I can see the rpm move when it slips in and out and I can feel it. My diagnostic tool shows me real time data and I can see it lock and unlock only between 40-45 mph and the weather has to be above 80 degrees. If its cold out nothing will happen. I have already taken it back to the tranny shop to have it looked at and they swear its not the tranny acting up but something is causing the tranny to do this. I have already done a tune up. Plugs, wires,cap, rotor, crank trigger sensor, camshaft position sensor, TPS etc.. Fuel pressure is perfect and there are "ZERO miss fires". I am completely lost now. What can cause the lock up converter to slip in and out like that? I spent $150 to confirm my theory at the dealer. But they dont think its anything but the tranny. I heard I might need to have the computer flashed once a rebuild is done. Is this true? No codes are being spit out. I did notice when the TCC locks and unlocks the timing and fuel pressure fluctuate. I think this would be normal though. Any ideas would be great!

[MT-2500]

Originally Posted by YenkoZL1

I have a 4L60E tranny in my 99 tahoe. I just had it completely rebuilt just 5k on it. Shift kit, z-packs,vette servo, Sonnax O.D. Servo, and supposively torque converter ment for towing. My trans converter clutch keeps slipping in and out of lock up mode between 40 and 45 mph. I can see the rpm move when it slips in and out and I can feel it. My diagnostic tool shows me real time data and I can see it lock and unlock only between 40-45 mph and the weather has to be above 80 degrees. If its cold out nothing will happen. I have already taken it back to the tranny shop to have it looked at and they swear its not the tranny acting up but something is causing the tranny to do this. I have already done a tune up. Plugs, wires,cap, rotor, crank trigger sensor, camshaft position sensor, TPS etc.. Fuel pressure is perfect and there are "ZERO miss fires". I am completely lost now. What can cause the lock up converter to slip in and out like that? I spent $150 to confirm my theory at the dealer. But they dont think its anything but the tranny. I heard I might need to have the computer flashed once a rebuild is done. Is this true? No codes are being spit out. I did notice when the TCC locks and unlocks the timing and fuel pressure fluctuate. I think this would be normal though. Any ideas would be great!

The old runaroud Dealer says transmission.
Transmission people say engine running.



Proper testing with a transmission /engine capable scanner/labscope should show the problem.

The engine has to be running good and all engine sensors good for the transmission to shift good.

Shift kit stuff does not always help or work right.

The Dealer should have checked and done computer reflashes needed.

Off hand I would check out the engine TPS sensor and signal real close.
The only true test on TPS is replace or check with a good labscope.
Also all wiring and plugins.

Good Luck

[2000CAYukon]

What torque converter did you install in your tranny? The stock converter is designed for PWM engagement. Many of the aftermarket converters that use a Kevlar or Carbon clutch lining can not handle this. PWM can be removed by reprogramming the computer (PCM). Another option is to install a PWM eliminator valve in the valve body. This converts the lockup to an on/off setup similiar to what was used before PWM. I know the PWM eliminator valve comes in the Transgo HD2 kit so you may want to ask your tranny builder if they installed one or not.

//2000CAYukon

[YenkoZL1]

I am not completely sure what torque converter was used. I know it's not a kevlar or carbon clutch setup. I'm not sure what brand they use. All I know is that the tranny shop said it was a heavy duty converter for towing. But I know it's nothing special. I bet it's OEM. I only tow 5000-8000lbs. So what does this PWM eliminator valve do? If it is installed do I then flip a switch manually to get the lock converter to lock and unlock vs it automatically doing it?

[2000CAYukon]

Originally Posted by YenkoZL1

I am not completely sure what torque converter was used. I know it's not a kevlar or carbon clutch setup. I'm not sure what brand they use. All I know is that the tranny shop said it was a heavy duty converter for towing. But I know it's nothing special. I bet it's OEM. I only tow 5000-8000lbs. So what does this PWM eliminator valve do? If it is installed do I then flip a switch manually to get the lock converter to lock and unlock vs it automatically doing it?

The PWM eliminator valve just eliminates the PWM function and the TCC is still locked automatically. Might want to ask the tranny builder if he already installed it or not.

//2000CAYukon

[YenkoZL1]

Ok, so the PWM can be eliminated by either reprogramming the computer or buying the PWM eliminator valve kit. And by eliminating this the converter will still lock automatically. Then whats the purpose of the PWM? This is the first time I've heard of this. Sorry for all the questions.

[2000CAYukon]

This article talks about PWM being added to improve converter clutch engagement and to help increase fuel economy http://www.motor.com/magazine/pdfs/062006_07.pdf

//2000CAYukon

[YenkoZL1]

No PWM eliminator kit was installed. Thanks for the article on the PWM 2000CAYUKON. It was very interesting. The one thing that caught my eye in that article was how the converter clutches changed over time. 1st design 4L60E used a cellulose base clutch in the converter and then the 2nd design changed to a kevlar lined clutch setup. Now from 97-98 they went with a carbon lined clutch in the converter. My tahoe is a 99 same as the 97 and 98 models. Is it possible that the wrong torque converter is in there? If the shop installed a converter with the cellulose or kevlar lined clutches might that be the reason the converter is slipping in and out of lock up mode? The article said that the cellulose and kevlar would not work with the PWM. Am I way off?

[2000CAYukon]

Originally Posted by YenkoZL1

No PWM eliminator kit was installed. Thanks for the article on the PWM 2000CAYUKON. It was very interesting. The one thing that caught my eye in that article was how the converter clutches changed over time. 1st design 4L60E used a cellulose base clutch in the converter and then the 2nd design changed to a kevlar lined clutch setup. Now from 97-98 they went with a carbon lined clutch in the converter. My tahoe is a 99 same as the 97 and 98 models. Is it possible that the wrong torque converter is in there? If the shop installed a converter with the cellulose or kevlar lined clutches might that be the reason the converter is slipping in and out of lock up mode? The article said that the cellulose and kevlar would not work with the PWM. Am I way off?

Some of the LS1 based cars (Camaros, etc) have seen issues w.r.t. TCC lockup with higher stall converters. PWM eliminators have been used to avoid the issue.

Ideally, it would be a good idea to talk the vendor that made the Torque Converter. That way, you could find out what they recommend (PWM eliminator or reprogramming changes).

Another option is to give Dana a call at www.700r4l60e.com. He sells the PWM eliminator but he also very knowledgeable about the 4L60E.

The valve body does have to be removed to install the PWM eliminator valve.

//2000CAYukon