transmission Tc Lock-up And Temp Question

[MasterChief]

When placing the 48re in 1st or 2nd does the TC lock up?



If pulling a load up a hill is it better to place the transmission in 1st or 2nd or just put in towhall and let it shift down on its own for TC lock up?



I pulled my 5er up a 11% grade today on State road 40 in PA. My transmission temp gage hit 275 for just a minute, then I pulled over and let it cool down. I pulled at 250 for about 5-7 minutes. My transmission over temp light never came on. I have my gage sensor located in the hot out line. My toatal weight is 22K. The truck had lots of power, pulled the hill at 2500-2800 rpms, and the turbo never went over 1000 dgs. I put the shifter in 2nd when I pulled the hill, I'm now wondering if I should have let the transmission shift down on it's own, in towhall mode.



I have 32K on the truck and planned on having the transmission oil replaced after my trip. I already had it changed at 15K



Mike

 

[JEstes]

Dang, 275 is a little warm. Good idea on the transmission fluid change. There's not a ton of life left after it sees 275.



Anyway, on your '06 the tow/haul button should be able to toggle between normal, tow/haul, and overdrive lockout. I think one tap is for tow/haul and two taps is for OD lockout. Tow/haul should delay your shifts a little to keep from lugging the engine and it should provide tourque converter lockup for 3rd and 4th. I think it can even lockup 2nd, but I'm not sure.



Putting the gear selector in either 1 or 2 should provide lockup in either gear, but I wouldn't swear to it. My '03 does that, but your '06 might be different. Just drop it into 1st or 2nd next time your at a light and try it. It won't hurt anything.



When I'm pulling something heavy up a hill, I'll either drop the gear selector into 2 or I'll lockout the overdrive just so I can get the TC to lock. The transmission doesn't generate a whole lot of heat when everything is locked up, but when it's unlocked it can overheat so fast it's scary.



BTW, the transmission temp light on the dash doesn't do much other than tell you that you just fried your transmission... . That's assuming it even comes on. The real way to tell is your guage in your cooler line. Maybe one of the transmission gurus can chime in.

 

[nunya]

my 06 when I shift it to 2 will lock the converter and helps keep temps down, I use it on long slow pulls and in town between lights. I have a jake on it too so not sure if that makes a difference?

 

[RPayton]

Have a 04 . transmission hit 220 with my 30 ft. gooseneck (15,000 lbs. ) I dont know how hot is hot but this was going 2 be one of my ? . If n town not a trailer on from stop light 2 light it can get up 215. Is this normal?

 

[TWhiteside]

According the the Service Manual - for what it is worth... ...

"Transmission fluid temperature readings are supplied to the transmission control module by the thermistor. The temperature readings are used to control engagement of the fourth gear overdrive clutch, the converter clutch, and governor pressure. Normal resistance value for the thermistor at room temperature is approximately 2000 ohms.



The thermistor is part of the governor pressure sensor assembly and is immersed in transmission fluid at all times. (exactly where, I don't know)



Transmission Temp Indicator (in the dash cluster)

The transmission over-temperature indicator gives an indication to the vehicle operator when the transmission fluid temperature is excessive.....



Trans Over-Temp Lamp-On Message - Each time the cluster receives a trans over-temp lamp-on message from the PCM indicating that the transmission fluid temperature is 135° C (275° F) or higher, the indicator will be illuminated and a single chime tone is sounded. The indicator remains illuminated until the cluster receives a trans over-temp lamp-off message from the PCM, or until the ignition switch is turned to the Off position, whichever occurs first. "



Hope that helps -



By the way - 275° seems a little hot to me!!!

 

[THogsed]

All this was very helpful, ive installed an ATS TC, ATS VB, & an ATS Co-pilot. I can feel when the TC kicks in in any gear. I also can set when it comes in. My trans temps stay alittle above normal on flat ground or in a pull in 3rd. ( by the way they are pretty solid shifts). when im in 2nd, the temps raise to about 230 till the TC kicks in. I try to have the TC ingage as much as possible when im in 2nd. I was wondering about the temps myself. Thanks

 

[cerberusiam]

ATF+4 is a group 3 synthetic and is rated to short temp spikes to 325 degrees, IIRC. While running at those temps for more than a couple minutes is NOT reccomended, periodic temps at 275 should not be a problem. If you see much of that I would defnitely change fluid a 20k intervals.



The 06 trans should lock the TC in manual second and TH second, however if you were using a lot of throttle to get the speed it may not have locked the TC. Those temps almost sound like the TC never got a a lock command. The computer controlled lockup is a bit flaky as it has a lot of parameters to engage. It engages way to slow for my taste most of the time so I use a lockup switch to hurry it along.

 

[JordanB]

I've asked this question before on the trans temp. My sensor is also in the "hot line" going to the cooler. Mine can hit 250 while idling in gear at a fast food line. Several have suggested this is normal (as did the dealer) on "hot line" side. They say it's the pan temp you should worry about because this is the fluid your transmission sees 1st - as opposed to the fluid coming out of the converter towards the cooler. I'm still concerned myself, but what the heck.

 

[BHolm]

Sounds to me like you are on the right track. The TC will lock in second regardless if you move the shifter or allow the trans to do it. It will not lock in first. So the question was, which is better, first or second via the shifter. If you can get the TC to lock in second, that is best, though if it brings EGTs up because the rpms/speed is too low the trans is going to unlock it to allow the EGTs to come down with the higher rpms. With that much wieght I suspect first unlocked is going to generate heat. Running higher rpm will help some as it wont run on the convertor so much but it sounds to me like a switch to manually control lock-up would be a perfect solution to your problem. Use it early in the pull to stop temps from climbing. Once they get up there, the low speeds you are running wont be enough to bring temps back down. If you can keep it locked up you should have lower temps and longer trans life.



I cooked on in my '03 QC, the light never came on. From then on the truck had a trans temp gauge in the hot line. I think that is the best place for it. It gives you a good idea of when the fluid has been hot enough to warrant a change.

 

[cerberusiam]

I've asked this question before on the trans temp. My sensor is also in the "hot line" going to the cooler. Mine can hit 250 while idling in gear at a fast food line. Several have suggested this is normal (as did the dealer) on "hot line" side. They say it's the pan temp you should worry about because this is the fluid your transmission sees 1st - as opposed to the fluid coming out of the converter towards the cooler. I'm still concerned myself, but what the heck.

Think of it this way, the cooler is capable of taking 90-100 degrees of temp out of the fluid then it gets warmed/cooled some by the engine coolant.



Now, if you are seeing 300 degrees at the hot line you can be pretty sure fluid is returning to the pan somewhere in the neighborhood of +/- 200 degrees. Trans temp should not vary more than 10 percent of the 200 and thats an acceptable range.



What would you see if had the probe in the pan? Only the constant temp of the mix of exisitng fluid and cooled fluid. If you were seeing a constant pan temp of 260 degrees what could the hot line temps possibly be? Using what I have seen for variations somewhere around 350-370 would be in the ball park. With a break down point around 325 degrees those temps would be detrimental to fluid life and you would not be able to calculate what the max was until after it happened.



Watch the hot line temps and when the start pushing over 300 its time to start shifting or slowing. Seems to be a bit more effective than waiting for the reservoir to heat up to a danger point.

 

[JEstes]

It would be neat if someone offered one guage that could check both hot line temps and pan temps... .