This ***** can Tow!!!!!

[DesertfoxAZ]

Well, I have a habit of not getting outbid on GovDeals. I just picked up my 5th vehicle this year. Rented a Uhaul toy hauler trailer. I do like the trailer, don’t like surge breaks, but that is because of my own fault.

So, you know the weight limit is 8600 lbs. is that when the car is loaded or unloaded? Wink wink…… drove from Phx to southern CO with an empty trailer 11 hrs there, pretty much stuck it at 75 the whole way there.

The return though was a little more interesting. 16hrs to get back. Pretty much was set at 58 mph on the way back. Stopping about every half tank. Depending on the section, I was getting as high as 12mpg down to 9.6mpg. There were only two points where the car temp got to 235 and Tran was 220. One was the pass on I40 from CO to NM. The other was climbing up from Camp Verde heading south on I17 from flagstaff to Phx.

A real trailer and brakes w/ a controller would have made that drive easier and would have driven about 65 on the way back.

So to address the big blue elephant in the room. I based the weight on a uhaul 10 box truck. The trailer was a little more then I though it was at a hair over 3100 lbs. the trailer was not over weight at all. That being said, I am guess that Tahoe was probably 2 or 3 hundred pounds heavy. Will I do that again, nope. The blue truck can tow more anyways……

 

[DesertfoxAZ]

I will add, I did not have the AC one for the drive back.

 

[Marky Dissod]

It'll tow even better with 3.42 or 3.73 ...

 

[Fless]

There were only two points where the car temp got to 235 and Tran was 220. One was the pass on I40 from CO to NM.

I-40 doesn't touch Colorado...

 

[mikez71]

It'll tow even better with 3.42 or 3.73 ...

Exactly! What I noticed most going from 3.08 to 3.42, was it could hold 5th and 6th easier at low rpms.

Surprisingly, I didn't notice any diffference taking off from the stoplights..

 

[Marky Dissod]

Exactly! What I noticed most going from 3.08 to 3.42, was it could hold 5th and 6th easier at low RpM.

That's what everyone misses - getting to 5th & 6th sooner, and spending more time in 5th & 6th and less time downshifting to / being in lower gears.

Surprisingly, I didn't notice any difference taking off from the stoplights.

Did you get tuned around the same time as getting 3.42'd?
Upgrading the axle gear without tuning leaves the torque mgmt expecting the weaker axle gear;
so the torque mgmt takes its nibble out of the stronger axle gear.

 

[mikez71]

I did tune shift speeds and gear ratio.
It's possible I just don't hit the gas hard enough these days.. but at 50% tps off the line.. not really feelin it..

Reminds me of @swathdiver's AXN and 3.73 swap, where he ran about the same 1/4 mile time as before the swap.

Useless Information

... back in 2018 I looked at the fuel economy of our actual trucks (Fuelly.com and window stickers) and saw that there was virtually no difference between the 2007-2008s with their 4-speeds and the 2009 with the 6-speed. Check more closely. 6L80 trucks typically came with 3.08 axle gear. 4L60...

www.tahoeyukonforum.com

Perhaps the bigger gears in the AXN just sap that much power?

Again, 5th and 6th can actually handle being lugged around, whereas before I would keep slowing until it downshifts.
That's with an empty truck! But low throttle angles...

 

[Marky Dissod]

But did you address torque mgmt?

 

[mikez71]

Are you saying a stock 3.42 geared tahoe has it's acceleration limited by torque management?
Or there are different settings for torque management between a 3.08 and 3.42?

I have not changed torque management.

I have turned traction control off.
I have set ETC opening rate to 100 in all cells.

I have not found any differences between 3.08 and 3.42 tunes regarding torque management in ECM or TCM.

 

[Marky Dissod]

Are you saying a GM OE 3.42 pickup/suv has its acceleration limited by torque management?
Or there are different settings for torque management between 3.08 and 3.42?
I have not changed torque management.

Yes. The difference being that 3.42 can trigger torque mgmt slightly sooner than 3.08 if the tires don't break loose.
In the ecm / tcm there is no difference, the difference is between the transmission and the tires.

 

[mikez71]

Not sure the actual setting. Let me know if you have it, or I will look through it some more!

 

[j91z28d1]

I still don't understand why being in 5th gear with 3.73 vs 4th gear with 3.08 at the same rpm would make any real world difference? overall the same thing and less gear multiplication done in the tranny usually means less heat and less power loss. why they used to always tell people to tow in 1:1 tranny gear.

I just towed thru the mountains with a 3.08 gear, not the rockies and not the big air brake he did. but I honestly don't see why a 3.73 would have helped anything other than raise the rpm when cursing in flat ground at 70.

 

[swathdiver]

The higher numerical gearing puts the engine closer to it's ideal torque powerband and puts more power in newtons to the ground.

 

[j91z28d1]

The higher numerical gearing puts the engine closer to it's ideal torque powerband and puts more power in newtons to the ground.

but it's the overall final drive ratio.

 

[Marky Dissod]

... still don't understand why being in 5th gear with 3.73, vs 4th gear with 3.08, at the same RpM would make any real world difference?

OK, 6L80E, 32" tires, 2125RpM ...
3.73 * 0.852 = 63MpH
3.08 * 1.152 = 57MpH
The 3.08 will likely need to downshift to 3rd to accelerate if towing heavy (unless it's a 6.0L or 6.2L)

overall the same thing and less gear multiplication done in the tranny usually means less heat and less power loss.
why they used to always tell people to tow in 1:1 tranny gear.

They used to tell people to tow in 4L60E's 3rd because GM had a bad habit of weak@$$ axle gears to try to 'game' the CAFE MpG test scoring.
Putting it in 3rd avoids unnecessary 3-4-3-4-3-4 'huntshifting'. Lugging the engine isn't good for the engine either, by the way.
Of course, if one has enough axle gear to avoid huntshifting, both the engine and the transmission will last longer under duress.
A Tow/Haul shift mode (or a well-customized Normal shift mode in some cases) won't increase the tow rating but will prevent excessive huntshifting.

Take note that the 8L90's & 10L80's 2nd gear is roughly equal to the 4L60E's 1st gear. More gear helps the 5.3L when it's time to accelerate, for sure.
('More gear' is also why turbo4cyl & turbo6cyl engines are becoming more common.)

I just towed thru the mountains with 3.08, not the rockies and not the big air brake he did.
but I honestly don't see why a 3.73 would have helped anything other than raise the rpm when cursing in flat ground at 70.

On flat ground, not much difference, ok, but hills will make you see why GM's GMT900 2500 & 3500 suvs & pickups pair the 6L80 with either 3.73 or 4.10.

 

[swathdiver]

but it's the overall final drive ratio.

Yep. But same thing, the lower ratio spins the engine higher and puts it closer to or at its maximum torque at speed.

Here's an example and note the engine rpms in 3rd and 4th gear at highway speeds:

 

[j91z28d1]

Yep. But same thing, the lower ratio spins the engine higher and puts it closer to or at its maximum torque at speed.

Here's an example and note the engine rpms in 3rd and 4th gear at highway speeds:
View attachment 468821

2700 I'm 4th with a 3.08 and 2400 in 5th with a 3.73?

 

[swathdiver]

2700 I'm 4th with a 3.08 and 2400 in 5th with a 3.73?

Yessir, plus 10 rpms give or take for torque converter slip.

 

[Marky Dissod]

Yessir, plus 10RpM give or take for torque converter slip.

Actually, wouldn't there be more slip @ 2700RpM, than @ 2400RpM?

 

[swathdiver]

Actually, wouldn't there be more slip @ 2700RpM, than @ 2400RpM?

Probably. I remember taking note of it once but don't remember how much at different gears, rpms and speeds. On the highway, it isn't much different, not 20 rpms if memory serves.