GMCtrk

iTrader: (27)

Yeah, if you don't have a tune it's a MUST. Look no further than Charlie Wheatley this guys customer service is impeccable. He's always willing to help and never sticks his nose up at a customer, I've sent him my PCM for retune probably 5 times now at no cost to me.

kbracing96

iTrader: (26)

I don't see any reason you cant tow unlocked in 4 gear, IF you install a large tranny cooler. Turbo 350 and 400's have been used for years for towing and they don't even have lockup converters. And besides, you would only be unlocking it to help get a few more rpm out of it when pulling hills right? With out having to down shift to 3rd and scream at you. I have done that with mine, you just need to have your TCC set to unlock with less throttle % position in tow/haul mode. I have done this with my truck and haven had any issue with it. Seems half way between 3 and 4 put it in a good power band a lot when pulling some hills. If you have a tranny temp gauge, you can keep an eye on it that way too.

jsawduste

Honestly this is what my logic was. Only for pulling grades for a short time. In fact the current set up does it on its own but not effectiveley enough. The convertor tends to hunt a bit between locked/unlocked. And on some of the bigger hills she will downshift to 3rd-bump up to 2700-2900 and hold road speed with not problem. But I have a hunch that with a little more "tuning" the need for a downshift would be even less.

I do have the tranny temp gage and it always runs well below the danger zone. Even in the hottest of weather.

Seems that my combined weight/areo dynamics is just out of the envolope (sp) for everything to work as a team. Just a few more rpm or lbs/ft torque and everything would be working pretty well.

hog

Why over stress your drivetrain, if its a big hill, pull her down to 3rd. Its only for a minmute while you climb teh high. I certainly would NOT let it lock and unlock while loaded.
Priced a 4l85e and torque converter lately? Worth the extra 800rpm for a few moments.
These are GEN 3 engines, they make peak torque at 4000rpm and peak power at 5200+, yet they get lugged at 1800rpm.

peace
Hog

zippy

You will shorten the life of the trans for sure by getting rid of lock-up. The old TH350's and TH400's had converters with around 1400rpm stall speed or so back then to keep them tight enough to try to keep trans temps down. They also had a way lower tow rating than today's trucks in the same form. A 2500HD came with 245/75R16's on it. Stepping up that much in tire size should come with a gearing change. I wouldn't recomend going any bigger than a 265/75R16 unless you intend on changing gearing. There is a reason the 2500HD didn't have a 3.73 gear option, it needed the extra gearing to do work. Putting a taller tire on there just gets rid of what they were trying to do by gearing your 9200GVW truck that way. The newer engines make more torque in the higher rev's for sure, but at only 364 cubes a 6.0L will out pull an old stock Vortec 350 anyday.

jsawduste

Guys, you are making a lot of sense. Good conversation IMHO. Again thanks for all the help.

Ran the numbers based on several factors.
70 mph/tire od from BFGoodrich A/T`s web site/Trans with a .75 overdrive/4.10`s
Assuming 100% lockup here is what we get

245`s- 30.5 dia = 2371
265`s- 31.8 dia = 2274
285`s- 33.0 dia = 2191

Differance between 245`s and 285`s works out to be 180 rpm. Now 180 may not seem like much but guess what ? The truck likes to run unlocked on a gentle grade at around 2400 rpm. Right where it would be if it had 245`s and locked TC.

I am now getting a real respect for what the GEN III motor likes and dislikes. AND the effect of the taller tires. Again it may not seem like much (RPM wise) but when you are pulling 7000lbs plus all the crap in the bed it is proving to be a big differance.

With the 285`s I am simply not spinning the motor fast enough to make enough torque to pull grades without a unlock/downshift. As Ho and Zippy said, ya gotta spin them to make them work the way they were designed, thanks guys.

So here is the plan. The 285`s are getting thin so a tire change is in the VERY near future.
265`s would be a help and 245`s optimum. Plus (with the 245`s) it would lower the truck a bit reducing wind drag.

Talked to Charlie Wheatley about a tune for the PCM. A little more spark/different fuel curve and maybe a different algortihim (sp) for the convertor. Need to discuss this tire size stuff with him again.

What do you guys think ?

GMCtrk

iTrader: (27)

You either gotta spin higher revs or make more power. To me, spinning 2400 rpms on the highway is unacceptable. It's noisy, puts undue stress on the drivetrain, and fuel economy goes down the *******. The only thing holding me back from 3.90 or 4.10 gears from my current 3.42s is the fact that I love cruising on the highway at 1500-1800 on the highway with my 6.0. I know exactly what you are talking about though with being in the power range, and it's only gotta be worse in that big, heavy 2500hd. My vote is to get a tune and add longtube headers. I don't know how much better the 2500 exhaust is than the 1500, but with the power gains I got just from added a cutout post cats, I think the stock exhaust is garbage. I really think longtubes should add a nice gain over the whole power band.

cttandy

iTrader: (12)

I have pulled heavy trailers with many trucks. I have to say, with stock size tires my 4.10 equipped yukon will out pull the neighbors 3.73 454 99 truck and my dads 4.10 350 96 truck. It will down right walk away from them with the same load like they are broke. Now the 454 likes cruising better on the interstate, but my yukon leaves me absolutely nothing to complain about.

At the same point, I really enjoy towing my 89 gmc K1500 with a 350, built 700r4 and 3.42. But you have to know its abilities and respect it. It doesn't begin to compare to the yukons power nor the 454's, but it gets much better over all fuel economy. If respected, it doesn't stress. Take you time, don't hurry it, let the transmission do its job like it's suppossed to. Alot is due to the built trans. It completely changed this little truck over. I am not sure what the guy did to it, but it was $1500 very well spent, (buddy deal).

chevrolet all the way

iTrader: (24)

almost all of your heat in your trans coms from the converter. if you drive 70 mph for a long time out of lockup in a lockup converter your transmission will hit levels of heat to change it the color of mine (see avatar) you may drop out of overdrive but not lockup

nonnieselman

iTrader: (10)

My buddy put a Used Yank SS3600 in his Transam... OF course the Lockup clutch was fried.. I commanded 100% DC for the TCC and it slipped its butt off... So mean while 2nd gear started acting up. Riding down the interstate his TFTs would skyrocket when we hit a hill.. thus his Coolant started rising..
Now we are tryin to kill the transmission before we pull it out..

I know this is a big stall, but if you do want to unlock your converter after you go back to the 245s, just keep an eye on your Trans Temps..