Cheap way to get the TCC to lock in 2nd.

[jeffreydmet]

Because of last summers heating problems pulling a camper through the mountains I have looking for a way to lock the Torque converter clutch in 2nd gear. I am driving a 99 K3500 CC Dually. I think I have found a cheap way to do it. I have been scouring the Helm manuals trying to understand how the computer is controlling the clutch and stumbled on something.

I found out that if the thermistor in the transmision is working correctly and it senses a temperature over 284 deg F then the trans will go into hot mode, freeze the shift adapts and record in history the code for a hot trans. It will not turn on the service engine soon light.

So what I did was to wire a switch so that a 50 Ohm resistor could be switched in and out of a parallel circuit with the transmision thermistor. What this does is trick the PCM into thinking the trans is close to 300 deg in temp so it works the TCC in hot mode. The goal is to make it think its hot without thinking that the thermistor circuit is shorted. Also I wired in an LED to the TCC solenoid so I could tell when the PCM was calling for the TCC to be locked.

Here's what happened with the switch on. The TCC will lock with the trans shift lever in second when it exceeds about 25mph. Also the TCC is used longer, more frequently and under higher throttle in 3rd and 4th. It still goes off when a shift is made. Also when slowing down the TCC will stay locked until you let almost completely off of the accelerator pedal. Shifts were still smooth.

I did see one thing though that needs to be watched out for. In some situations with a very heavy pull such as accelerating hard up a hill the TCC may continue to slip until it can catch up. What you need to do in this case is slack off the throttle until the TCC completely locks up then reapply throttle. It will then hold the big load.

I have not towed much with this yet but expect it to improve my opinion of my automatic trans. I also expect it to help mileage and definately reduce the heating problem.

Now if I could only keep it locked with my foot off the accelerator until it was slower than 25mph I might like the AT better than a manual.

[kowsoc]

Interesting,...did the speed at which lockup occurs change. Mine locks at about 80 km/h or 50 mph in drive or OD.

[jeffreydmet]

Yes, It looks like it starts locking in 2nd at about 25-30 mph then keeps locked except for shifts on up.

[rjwest]

Got to try this...........

Any more results ? How many miles have you ran this way?

[jeffreydmet]

Haven't pulled my trailer to much yet but so far I like the way it pulls in hot mode. I will be going to Florida over Christmas so should get to try it out thoroughly.

[kowsoc]

What size does the 50 ohm resistor have to be. Did you use a 1/4 or 1/2 watt or does it have to be bigger to prevent burning out? This sounds interesting because if the convertor is locked more often it should save fuel. Slush mode is a definite energy waste!

[Scooby]

Jeff, where did you splice the resistor in?? I have the Helms for my 96, but I havent had a chance to study the TCC circuit.

[MJEasly]

Jeff,

How do you think your solution would work in conjunction with an interceptor device like B&M or other shift improver?

[Johnny B.]

Jeff, I'm curious will this fix work on all years of the 4L80E.

[jeffreydmet]

Kowsoc
The voltage driving the sensor is 5V since V=I*R I=V/R wich is 5/50 = .1 amps. Power is V*I so power is .1*5=.5 watts. You need at least a 1/2 watt resistor. I used two 100 ohm 1/4 watt resistors in parallel.

Scooby
The switch switches the 50 ohm resistor in parallel with the transmision temperature sensor. On my truck ('99 K3500) I connected it with scotch locks between the yel/blk wire on connector 2 of the PCM and the black wire on the same connector. A word of caution though when looking at the Helm manuals and trying to find the wires it is not totally obvious which one you should use. I used a jumper between the transmision connector and the connector on the PCM with a Volt Ohm Meter to be absolutely sure I'm on the right wires. I did this after I got it wrong the first time. It takes longer to find the right wires than to connect the resistor/switch into the circuit.

MJEasly
I haven't used one of these shift improvers but hot mode uses a more aggressive shift. I'm sure GM is trying to shift so that less heat is made from all of the slipping that an auto does.

Johnny B.
I would think any 4L80E that has the temperature sensor would probably have some provision for some sort of hot mode.

[kowsoc]

Great information, thanks Jeff.

[rjwest]

Installed " Resistor " on TFT Sensor....

1996 K3500 ext cab... 3.73 Gears ( was 4.10 )
PRE-RES. TCC Lock up at 50MPH both 3rd and 4th
and would unlock TCC below 60-65 if
to much trottle used....
POST-RESISTOR
Results.. 1-2 shift quite firm, ditto 3-4
2nd TCC lock up at 30MPH
3rd " " " " 40 MPH
4th " " " " 50MPH
I have not reprogrammed the computer after changeing to 3.73 gears. May be why different results or possible early code im PCM...

The shifts seem too harsh for my normal load
3000-3500 Truck Camper. But 2nd Lock up
is Great for PA Hills and 3rd will be good at 40-65
on long interstate Climbs..
Still would like 4th not to down shift, It appears
downshift occurs before TCC unlock.

Will keep working on it...

: Resistor ( 2 100 in parallel gives 298 Deg TFT )
Will try 45 ohms to see if any change.

Also NO codes or History that I could see on
my Laptop/Carcode Program ( Not the best reader )


My biggest problem/complaint with truck is premature downshifts at highway speeds.
It is hard to keep 4th from downshifting.
At about 60mph and below, loaded, at about 6lbs
boost I get a TCC unlock or Downshift ( No Res.)

AT 65mph It pulls max boost 8-9psi no downshift,
2000 rpm and above. Really has more " Guts " at higher speed. ?.. Not good at non-interstate where
at 45-55 I'm in and out of TCC...
was better with 4.10 gears, Stayed locked up longer. Does anyone know If Computer re-program
to 3.73 gears would help?

[jeffreydmet]

rjwest

On my 99 when I went to 3:73 gears instead of the 4.1 I had to reset the VSSB per the 99 reprints. I can't say with certainty but I didn't notice that much difference when I reset the VSSB. It seems the shifts are more tied to engine rpm & load than speed.

But if you haven't reset the VSSB its pretty easy to do. I just cut the right jumpers and soldered some others in per the 99 reprints. I then compared the speed to a GPS and fine tuned it.

[rjwest]

I did re calibrate VSSB, All speeds are accurate with a GPS....

The Lock up speed changed from 45 mph with 4.10 gears
to 50 mph 3.73 gears I agree, tcc lock up must come
from rpm or Tran speed.

I need to do more work to figure out how to use
switched resister.... will work great in 2nd
" shift lever held in second , ditto for third.

4th didn't seem to make much differance, because
it down shifted to third...

I am thinking of putting a momnetary push button
switch on shift lever and just holding locked
when needed....


You Have made a great discovery !!!!!!!!!!!!!!!!!
I tried torque-loc, ( No Good ).
This seems to get low speed hill climbs solved.
Again Great stuff.., Thanks......

[MTTwister]

Reviving an older thread...

Question -
A. Are You all running with the TCC 'locked' all the time?
B. Not swtiched during cold startups or around town?
C. Only switched when warm and on the road?

Note - digging into this, and per my '96 manual - the TFT sensor yel/blk, circuit 1227 - goes to pin C9 ( middle top row) on the BROWN 32 pin connector C1 at the PCM .

The Black ground , circuit 452, goes to pin B12 on the Brown 24 pin PCM connector.
(This is the same connector to install the pin B7 or B8 for the High Idle option. )

Now -
There is also the TCC PWM possibility - Grounding Circuit 418 Brn wire, Pin C5 on connector C3 ( Blue 32) which would -
"stop the converter oil from exhausting, which causes the converter signal oil pressure to increase and move the TCC valve. " THis does set a DTC of P0742 TCC Stuck on , AND sets the MIL light.
"The PCM turns off the MIL after 3 consecutive iginition cycles without a failure." This is a tybe B DTC ( Emissions related...)

Seems like a lot of downside to the latter option, but this could provide 'full-time' converter lockup - When needed - if you stay on top of using this switched option. .

[rjwest]

The BD torque loc forces a TCC lock up. But
it will set a " Limp " mode on 96 and newer
that will screww up shifts ( very severe"

need to turn off ign and back on to clear "limp"
mode......I believe the PCM detects a differance
between input speed and output speed, If not as expeted > Limp home mode set ".

I have the resistor installed, works great for
2nd and third gear Hill climbs, Just wish
4th gear would lock up before 50mph....

[rjwest]

jefferydmet how did tcc lock up work on trip to FLorida????????

[jeffreydmet]

The trip to Florida from IL through AL doesn't give much of a challenge as far as hills. No long pulls in 2nd gear like out West. What I did find out with this trip was that you can use 3rd much better with the trans in hot mode. Mostly I noticed a significant improvement when having to drive 50-60 mph in moderate hills. Without the switch the TCC slips a lot and the trans shifts a lot. In the hills driving slower I like to shift to 3rd in hot mode so the trans doesn't shift to overdrive with the crest of every small hill. In hot mode you can also give more throttle before it will shift down.

I did not need the hot mode when running fast on the Interstate on relatively level roads since the TCC will stay locked until heavy throttle.

My truck has 3.73 rear with 265/85 tires so it wants to shift more than before I changed the gearing and tires. I was pulling about 4k with an additional 2k in the back of the truck.

[rjwest]

Thanks For info. DO you remember what speed
your TCC locked up in HOT mode/?

Mine won't lock untill 50.in 4th

I had a BD Torque Loc installed. It would not work
on my 96. Set an invisable code that caused it
to set " Limp Home " mode. Made " Severe Shifts
untill power off reset.

DO you think HOT mode would cause the PCM to
ignore the TCC locked up at slow speed fault
and allow use of the BD torque loc.

I know it's a tough question, but you seem to be
knowledable on the Tran electronics.


Thanks for follow up.

[jeffreydmet]

In hot mode the TCC lockup is still dependent on throttle setting. The PCM is just a lot more aggressive in using the TCC. I can't remember exactly but it seems to lock 10-15mph lower than regular mode.
As far as the BD torque lock, I'm not sure how it would affect it. According to the helm manual a stuck TCC is not supposed to set limp mode. It does command max pressure which would make shifts harsh.

[TurboDiverArt]

Hey Jeffery,

Did you happen to take any pictures? This seems like great information. My hope is to install a B&M electronic gizmo to increase the line pressure and make shifts firmer. I'd like to install your resistors and use them when in tow mode. My hope is that in conjunction you'd have the best of both worlds. The B&M electronic shift kit would make the shifts themselves more aggressive and apply the TCC harder to eliminate any excessive wear. Your switch would allow the TCC to be applied earlier in 3rd and also in 2nd for hills. I too have a 99. The Torque Lock looks great and even though high in price, would possibly be a good investment if it wasn't for putting the truck into limp mode.

I'd think that your TCC controls with the B&M is almost the ultimate goal.

I don't have a Heml manual so I'm not sure of the wiring. I was hoping that you'd have pictures of the wires you are talking about. If you already have the wires hooked up it would probably be a great illustration. Me thinks this needs a formal write up. If you can provide the details to me I'll document it and pen your name to it.

Email me directly at artpaltz@optonline.net. I'll do all the document work and you can take all the credit for your find!

Thanks,
Art.

[rjwest]

Turbo driver, When I left the resister installed
it caused the shifts to be VERY SEVERE under load.

Besides changing when the TCC locks up , I believe
it also increases pressure, I did not feel comfortable in leaving the TCC ( Hot Mode )
when transmission was shifting gears.
I would probably only use it in second,
or third( Manual selected ) and release it when shifting. when in OD it would down shift
to third with TCC locked, this downshift seemed to
occur just about where it would without TCC locked up by the Resistor. I am guessing that since the resister makes high pressure shifts, the BD unit may not be affective. ( already high press mode.)
I am still experimenting with the " fix" will keep you posted.

[TurboDiverArt]

Thanks,

My thoughts exactly, sort of... My thought was to use the B&M ShiftPlus all the time. This would make the shifts firmer for normal driving and generally tighten things up. I wouldn't use it on the extreme mode, just one setting up from stock. I'd only use the switched resister if I was pulling in manual 2nd or 3rd. When driving normal (non-towing) or in OD I would switch the resister off.

Thanks for the input. Now I just need to figure out how to determine which wires on my 1999 to jumper with the resister.

Art.

[rjwest]

my 96 manuel was as stated in the post ref TCC lock up. If you want my 96 wiring data, for the
resister, i will post it....

[TurboDiverArt]

I'd like to know which wires. I've never pulled my PCM from behind the glove box. I think there are 3 connectors?

Art.

[rjwest]

Turbodriverart, just got in from a 550 mile
trip , 4 am to 730 pm , Get on the books tommorrow and post tommorow night.....

Did get 18.7 mph at 65 ( all flat florida ground)

Best ever.....

[TurboDiverArt]

Thanks, get some sleep! That's good fuel economy!

Art.

[MTTwister]

Per the 96 Manual - the wires controlling the TCC lockup should be :

per my '96 manual - the TFT sensor - yel/blk, circuit 1227 -
goes to pin C9 ( middle top row)
on the BROWN 32 pin connector C1 at the PCM .

The Black ground , circuit 452,
goes to pin B12 on the Brown 24 pin PCM connector.
This is the same connector to install the pin B7 or B8 for the High Idle option"

One question answered -Don't run this switched all the time!

Now - another new thread on the B&M shift improver explained -

[i]"27 ohms is applied in shunt across C11 and C6, which at saturation assume 11 volts causes about 400 ma of current to be shunted away from the pressure control solenoid. That setting may move you to the middle or

[rjwest]

Turbo Driver, MTTwister looks the same as Mine.
Can't find darn manuals.

Take out Glove box, ( squeeze in tabs , pull out)

There ia a shinney silver box with 3 connectors
down left side,
Temp sensor is in first connector ( up front )
it is yellow with black stripe.
Ground for sensors is in second connector back,
it is most forward wire on top row of second conn.. BLACK in color

I used wire " piggy backs " the kind you squeeze on with extra wire. don't have to cut and splice .

2 100ohm resisters ( radio shack 2 per pack)
in parallel, and a switch

you may have to peel back elect tape on harness to get enough room to work. I pulled connecters out
, need to squeeze tabs and use flat blade screwdrive to pry out, so as not to pull on wires.

Good test, run it up to 40 mph in 2nd, swicth on, rpm drop..


Now I have to determine if any of the shift enhancers will over ride the PCM, if they do
and it elimanated the Real Harsh shift.
you could probably leave the Hot mode on most of the time.

May be time for a new thread on this subject. ?

[TurboDiverArt]

Thanks guys. Very clear now. Might try it out this weekend. Need to complete the trailer brake project first....

Art.

[MTTwister]

If anybody cares ;) , I have a question on the B&M shifter thread that ties into this... using the values to lower shift line pressure via the PCM....

So, using this switched value in the circuit requires keeping track of what you're doing - split shifting almost, if you go from 2 - 3rd. Definitely seems ya' only want to use this in manual mode...

Edit - 2/16 - Thinking on how to use this switch - I'm going to investigate a wayto mount a on-off switch on the Gear Shift lever, maybe in the bend, so that it will be 'handy' to switch off before up-shifting out of 2nd, or 3rd. Then maybe a 2nd switch by a tranny temp gauge in an A-Pod to switch in a resistor for the Tranny Line pressure ( x-ref the B&M Shifter thread. )

Too much thinking, not enough doing... :rolleyes:

[ 02-16-2004, 11:04 AM: Message edited by: MTTwister ]

[jdmetcalf57]

Well I finally got a chance to go to Colorado and thouroghly test the hot mode. With the load I pull (7k lbs) I often have to shift to 2nd to make it over passes like Monarch and Wolf Creek. Last year I like to never made it over Monarch. This year by shifting to 2nd in hot mode with the torque converter locked up above 30mph and trying to maintain rpms between 2-3k I was able to pull Wolf Creek (this pass is similar to Monarch) pass with out getting to hot.

[Diesel Dan]

Originally posted by jeffreydmet:
I did see one thing though that needs to be watched out for. In some situations with a very heavy pull such as accelerating hard up a hill the TCC may continue to slip until it can catch up. What you need to do in this case is slack off the throttle until the TCC completely locks up then reapply throttle. It will then hold the big load.Sounds like the converter may be getting weak. I had to install a converter in my '00 due to slippage. While the trans was out I upgraded to the trans-go 4L80E HD2 kit and a aftermarket converter(~$450) and switched over to mobil 1 synthetic trans fluid. Now while pulling 10-11K lbs 3/4+ throttle, accelerating, around 50-55 mph the converter will come in and pull the engine down 150-200 rpm and hold. No slipping or having too let off.

IIRC, the trans-go kit was supposed to help with the converter apply fluid.

Just might have too look into the "resistor upgrage" myself.

[rjwest]

The TCC lock up in 2nd gear is " Great " as stated.

Really pulls in 2nd with 10-12 lbs of boost
( Kennedy boost fooler }

Wish the PCM could be reprogramed for 2nd gear TCC lock up and a lower TCC lock up speed.

[99gmccrew]

Jeffrydmet, It sounds like I had the same problem as you with the trans temp getting too hot towing up grades with a load. I also have a 99 c3500. Nice work on figuring out how to do this cheap fix for locking the TCC. I've got to try this when I get some time. I've been wanting to change my 4:10's to 3:73's but I'm not sure how it will tow my fifth wheel. How much better milage did you get after the change and how much towing capability did you lose, if any? thanks

[jdmetcalf57]

99gmccrew
I went to the 3.73 and put 265/85 tires at the same time which is about the equivalent of 3.5? gears.

I did not gain much mpg. Maybe 1mpg. What is really great about the new gearing is how much quieter when it is cruising at 70mph and about 2100 rpm. Also now I can actually cruise in 3rd if I need to and maintain a decent speed and rpm. Before it seemed like 50-55mph was all you wanted to do to keep the rpms reasonable.

My total payload trailer and truck payload is about 7000 lbs which it still pulls good. Much of hill and it or I will shift down more than before. I have also pulled my horse trailer loaded with my camper behind it (11k lbs)without any trouble but not on huge hills like out west. I'm sure I would still have heating problems with this load out west.

For the type of towing and driving I do I would do this again. Although if I could swing the money the gear vendors od would give more flexability.

[99gmccrew]

I agree about the gear vendor, I've been looking for a good deal on one. Just a little hard to swallow the price tag.