Towing question.

[56pan]

I'm sure this has been addressed here before, but I didn't find it. I've got to tow my son's '79 El Camino on a Uhaul auto transporter trailer from NC to NM. Total weight, trailer and car, about 6000 lbs. My truck is a '93 3/4 ton 2 wh. drive. Goodwrench rebuilt 4L80E with less than 5000 miles on it. 6.5 AMG mil. surplus eng. with 42,000 on it now. A team turbo, Peninsular intercooler, trans. cooler, 130 gpm water pump (supposedly "high flow" single thermostat) and Duramax fan, header wrap on all the hot parts, 3.42 diff. I've got a trans. temp gauge and what I'm wondering is at what temp. should I take it back out of OD to 3rd? I know I'll have to keep it in 3rd over the Smokies, but figured it would be okay to put it in OD on the flat land? This new trans. wasn't cheap and I'd sure hate to kill it. Any input appreciated and thanks for your time. Yeah, I know it's obvious to even the most casual observer that I've never towed long distance before.

[john8662]

You can tow in OD as long as you keep your foot just above where it'll shift down. It's the in, out, shifting that kills OD on any auto.

I don't know how well the ATT will do with your gears and less RPM's.

From what I've gathered this is not a good turbo for low RPM usage due to larger A/R on the turbine and being non-wastegated.

[56pan]

Yeah, the A team turbo builds a little less boost at about 1600 rpm in 4th OD on a level road. But with that load I'll be pulling I figure it will stay at >5 psi. under the same conditions. I've got an EGT gauge and it made a big temp. reduction under boost, and I've seen it up to about 14 psi. That much pressure/heat is why I got the intercooler. My mileage went up a little more than 1 mpg. which I attribute to the reduction in backpressure. I'm happy with it. Thanks for the input about towing.

[phantom309]

I put a manual lockup switch on mine,. it helps to keep temps down,.

anything above 230 deg is working the trans hard,.
below 200 is optimal

[56pan]

Keep it below 230. Gives me something to work with. Thanks. Afraid I'd forget to use the switch and do some damage. 65 and have CRS. (Can't remember s&*t.)

[Robyn]

The 230 F on the tranny temp is a good safe zone.
Get up into the 300F and it takes it out of things real quick.

Usually with a good oil cooler on the tranny it's not hard to keep temps well below the danger zone.

EGT AT OR BELOW 1000 F
Coolant temps below 220 F


The 3.42 butt gears are a killer for towing though, but dropping the tranny into 3rd with the tall gears will not rev the engine all that much and will keep things happy.

Have a safe trip

Missy

[56pan]

I've got 265/75R16 tires on the truck also, so it's actually geared higher than 3.42. Probably keep in 3rd as you advised. Thanks for the input.

[phantom309]

Keep it below 230. Gives me something to work with. Thanks. Afraid I'd forget to use the switch and do some damage. 65 and have CRS. (Can't remember s&*t.)

I,m not sure i explained it correctly,.

when i say i added a manual switch,.it's simply grounding the solenoid for lockup in the trans,.The ecm does the same thing,. so by adding another switchable ground path you can choose to keep it locked up, over riding the ecm,. to use engine braking to help slow downhill,;. and you can keep it locked in second gear for climbing really steep hills,.

When the torque converter is locked it's not building heat,. I also have 3:42 gears and 285 75 16 tires,. it tows nicely in 3rd gear up to 60mph,
over drive after that,.

without the manual lockup switch, it just slides the converter most of the time in overdrive,.

When the manual switch is "off",. the ecm then has full control and can lock or unlock as it sees fit,.

when the truck is empty i don;t use the switch at all,...

I love the 3:42's, at cruising speed,. the rpms are always below 2200 where the gmX turbo's become inefficient,

[56pan]

Okay. The lights were flashing, the bar was down, but the train wasn't coming. I just dug out my factory schematic manual and understand what you've done now. I was thinking you had a switch installed that may not let the brake lt. sw. disconnect the TCC. Your switch is electrically downstream of the brake lt. sw. and in parallel with the grd. source from the TCM. Makes perfect sense. Believe I'll install one too before this trip. Thanks for taking the time to clear it up.

[phantom309]

I was thinking you had a switch installed that may not let the brake lt. sw. disconnect the TCC.

you are correct,. when the switch is 'on' it does keep the converter locked up,.
but the 4L80E is plumbed so it will not lockup in 1st gear,. only second and up,.

4L80E trans' has a (inmho) a design flaw,. it free wheels on overun down a hill with a load on,.. most aggravating,.

If you forget the switch,.it'll remind you quick enough as you pull up to a light,.

[DmaxMaverick]

......4L80E trans' has a (inmho) a design flaw,. it free wheels on overun down a hill with a load on,.. most aggravating......

Not a design flaw. It was an EPA regulation, starting in about 1982 when lockup converters became more common. Easily defeated with programming, or a switch/rewire method. The regulation was later amended (2000-ish), which allowed MFG's to develop T/H modes, among other shift patterns that allowed locked TC more broadly.

[56pan]

Phantom, one other thing about this inline TCC switch: is there a possibility of damaging the transmission if the switch is grounding the TCC solenoid, and the transmission shifts down? Wouldn't that be similar to downshifting a manual without disengaging the clutch? Or do you have to sense a downshift coming and open the switch? I'm assuming you only use this switch on a long flat road where the trans. wouldn't downshift? The freewheeling with the 4L80E is an aggravation, I agree. Thanks for the input and any info.