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 Write-Up: Tuning Trick for Failing Torque Converter Clutch (TCC Lock-Up)

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PostSubject: Write-Up: Tuning Trick for Failing Torque Converter Clutch (TCC Lock-Up)   Mon Oct 10, 2011 8:44 pm

The following probably doesn't apply to most, but it involves some discovery, and might be an interesting read. If you have a slipping TC clutch, or a DTC P0741 "TCC stuck off", and you have access to a tuner package, this write-up could help you out.

About 30k miles ago (when my car had ~200k miles) I noticed the TC clutch started to malfunction. Specifically, it started to slip, at first every now and then under heavy load, then getting worse and happening all the time. I confirmed with a scan tool this happened only when the lock-up solenoid was activated. No DTCs, so the PCM thought everything was working fine - that told me it was probably a mechanical problem, probably a worn-out TC clutch. The symptom was a very annoying pulsation when in 3rd & 4th gears, as the TCC engages, then slips, then re-engages rapidly, over and over. After 10-15k miles, It got to the point where the car was basically undrivable at freeway speeds. The correct solution begins with dropping the transmission and replacing the clutch. Whatever the case, typical cost for even diagnosing a problem like this would be at least a $1000. Considering the transmission is out, a rebuild would be a wise decision, which can add another $500-1000 depending on what's needed. So dropping the transmission isn't something all of us want to do, unless absolutely necessary.

In my case, I had a transmission rebuild fairly recently at 151k miles, and the engine/transmission runs excellent except for this TCC problem. I don't know if they typically rebuild the TCC as part of a rebuild, but I do know they replaced the torque converter, just not sure about the clutch. Regardless, I got a good 50k miles out of it (2 years) before any symptoms - this is way past the warranty period on the rebuild - so I felt there needed to be some other option for getting around this.

First, I have some good ideas for why the TCC failed in my case:

1) As mentioned, I don't know if the TCC was replaced during the rebuild, and if so, I can't verify the quality of the parts used.
2) I use an active TCC lock/unlock tune, which I created based on reports found on the DHP board. This in theory increases clutch wear because frequency of the lock-up cycle increases, but I'm not sure how much this contributed, if at all.
3) I do pull a trailer from time to time, and if the load is light I have pulled in OD with TCC lock-up. Looking back, this wasn't a very good idea. For the record, the first time I noticed the problem, I was pulling an empty trailer back home in 4th gear, at a slow speed, thinking the transmission could easily handle it. I should have been in 3rd gear.

So I think one of those, or for a combination of those reasons, the clutch got tired and gave out. As mentioned, the car ran great otherwise. I even tested the transmission with a hard launch up to a high speed - no problems until the TCC locked-up.

I did some research and found that the TCC mainly does two things: increases fuel efficiency in OD, and keeps transmission temperature down over long trips. I knew this from experience, reporting some incredible MPGs over long distances when the TCC was kept locked at low speeds. I also knew about the heat issue, as the very reason my transmission needed rebuilt at 150k was because a dirty valve body prevented TCC lock-up, resulting in a DTC P0741 code. In this condition, the car operates normally for everyday use, but if you drive a long distance (100-200 miles or more), the TC will heat up, and eventually it cooks the transmission. There isn't any getting around that, except to monitor temps and change the transmission fluid more frequently. I tried that, but it caught up with me, as I wasn't using a trans cooler at the time.

I checked the DHP PowrTuner's capabilities and found it could be used to deactivate the TCC lock-up entirely. You normally don't want to do this, as TCC lock-up is crucial for healthy transmission operation and efficiency, but in my case I really didn't have a choice, so I tried it. The way you do this on the PowrTuner is to set all TCC Apply fields to "255 MPH". This ensures the vehicle's speed is never high enough to activate lock-up. The release fields are probably not important, but I set them to "255 MPH" also. I would imagine the same technique works for HPTuners software.

This tuning tweak fixed my TCC problem entirely - no more slipping clutch. The only problem I found was the cruise control has its own TCC lock-up settings, which I attempted to tweak as well, but the PCM does not appear to respond to the new settings, at least not when using DHP PowrTuner. HPTuners may offer an advantage here. For this reason, I no longer use the cruise function, which stinks, but at the moment this isn't a priority for me.

The heat issue I decided to deal with right away, which is why I installed a trans cooler in April of last year. See link for info:

http://rivperformance.editboard.com/t1748p45-write-up-transmission-cooler-install

The cooler did a great job of managing the heat, and so far I've been running without TCC lock-up for about 30k miles, with no issues that I'm aware of, except one, which I'll mention below. As an added bonus, I love how the throttle responds in 3rd & 4th gears. No more waiting for the TCC to release, ever!

Interestingly, fuel economy didn't take a large hit as I'd expected. Over the course of my fuel logging, which goes back about 4 years, I averaged 21.0 MPG with a working TCC lock-up. On the highway, I would see 31 MPG regularly, and mid/high 30s under very controlled trips. Of course, I didn't drive long trips enough to impact the amount of city driving I do, so 21 MPG was avg. With the TCC lock-up disabled, I've watched my average drop to 20.7 MPG over the past year and a half, and I'll add that's running a set of 18" rims w/ 8.5" wide summer performance tires a large part of the year - not the most efficient set-up! On one 120 mile trip, I saw a confirmed 26 MPG with no TCC lock-up. This is definately worse, but not terribly bad.

I did run into one problem when the summer heat arrived. When taking long trips (100-200 miles) on hot days, I discovered an unusual symptom that baffled me for a long time. After an hour or two of steady driving in 4th gear at freeway speeds, the transmission would automatically downshift into 3rd gear for 3-5 mins, then shift back into 4th. Usually (but not always) the cycle would repeat every few minutes for the remainder of the trip. I noticed these shifts were very firm, and checking the scanner showed 96 PSI (or %), the max allowed shift pressure. The condition remained this way until I restarted the car, indicating a type of limp mode. The condition sometimes wouldn't occur at all on cool days. On very hot days, or when I was pulling the trailer, or when climbing hills it seemed to happen sooner. This made me suspect heat in the TC was causing the issue, even though I installed a fairly large trans cooler.

Turns out after some hours spent scanning on long trips, heat was the issue. Even with a trans cooler, without TCC lock-up to deal with the heat, eventually the fluid temp can creep up past the coolant temp, which is between 175-185F. The time it takes varies with the factors mentioned above. The PCM shifts down into 3rd to cool itself, then back up to 4th when things look okay. I was surprised at the numbers: only 190F trans fluid temp causes the downshift, and remember this is only when TCC lock-up hasn't been activated since the engine was started. That's a pretty low number, and certainly not dangerous, but the PCM is looking out for the possibility of thermal runaway, I guess. In 3rd gear, it only takes a couple minutes for the temp drop back to 187, then 185.

I've found that by carefully watching the trans temp, I can usually keep it around 183F. I set an alarm on the scan tool to let me know if I exceed this number, at which time I can back off the throttle a little and watch it go back down. As long as I don't let it get to 189F, I can drive forever with no limp mode. On cooler nights, it's easy to drive - even spirited - for hundreds of miles with no issues.

Anyway, I thought this whole experience was interesting, and it turns out I will be forgoing another transmission rebuild for as long as I can. For everyday driving, I don't have any problem, and during the cooler months, no problem either. It's only on those 200+ mile summer trips that I need to put the scanner on the seat and keep an eye on things, which isn't a huge deal, really. Now I'm really thinking about an Aeroforce gauge, or a some other way to monitor temp value without plugging in the laptop.

Hope this helps someone looking to avoid spending $1000-2000 on a rebuild, just because their TCC lock-up has malfunctioned for whatever reason. You can drive without it if you know how to disable it safely. This probably is not something a shop would do as a service, but if you have access to a tuner, it could at least work as a temporary solution until you have the time + money to deal with the problem.

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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PostSubject: Re: Write-Up: Tuning Trick for Failing Torque Converter Clutch (TCC Lock-Up)   Tue Oct 11, 2011 5:01 pm

I believe the clutch is inside the torque converter. So you should only need a converter, not a tranny rebuild. Still not a simple installation, but not a full rebuild either.
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AA
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PostSubject: Re: Write-Up: Tuning Trick for Failing Torque Converter Clutch (TCC Lock-Up)   Tue Oct 11, 2011 5:20 pm

My thought is, if I'm going to remove the transaxle, I'd rather do it when it's time for the rebuild. Do everything at one time. That might be 50-100k miles from now, or it could be next week, lol.

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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http://www.cardomain.com/ride/657082/4
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PostSubject: Re: Write-Up: Tuning Trick for Failing Torque Converter Clutch (TCC Lock-Up)   Wed Oct 12, 2011 2:56 pm

Interesting write-up Aaron, just wondering why one wouldn't want to deactivate the TCC lock-up for good?
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PostSubject: Re: Write-Up: Tuning Trick for Failing Torque Converter Clutch (TCC Lock-Up)   Wed Oct 12, 2011 3:16 pm

I mentioned above two very important reasons: 1) fuel economy. You'll get about 10 MPG better on the freeway with TCC lock-up. In town in makes no difference, and 2) TC heat management. Without TCC lock-up, your transmission fluid cannot cool effectively on a trip over 100 miles, so you will cook it. For shorter trips, it makes little difference. A trans cooler can help, but even so the PCM can go into limp mode on warm days.

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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http://www.cardomain.com/ride/657082/4
DEMonte1997
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PostSubject: Re: Write-Up: Tuning Trick for Failing Torque Converter Clutch (TCC Lock-Up)   Thu Oct 20, 2011 2:25 am

Great read Aaron. +1 from me.

Interceptor gauge is very handy as I've found with my Regal. Might get one for the Riv someday. smile
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