2001 Yukon XL Towing Help

[hoaxci5]

I tow an open trailer with my Jeep on it to go play at the offroad park. I have a 2001 Yukon XL, the trans has a new valve body from gmtransmissionparts and new(ish) fluid. It shifts fine when not towing, but activating the tow/haul mode it just about refuses to downshift when pull up a hill. Often I end up manually downshifting it to not lose my momentum, does anyone have an insight to what the problem could be?

 

[GmTech14]

It won't downshift under a high load situation like towing, esp uphill. Tow haul mode stretches the rpm range out to keep the engine rpms up for more power, and to keep the torque converter from locking up. I would say what you are expiriencing is normal and working as designed.

 

[hoaxci5]

Eww really? On some of the long grades I'll be full throttle and slow down to 25 (from 50) before it will finally downshift on it's own. If there is traffic around I manually downshift to avoid slowing so much..

 

[Oobray]

That sounds like tuning issues. Don't know what motor you have, but my 8.1 will down shift at around 1,800 RPM under load. But when I know there are multiple grades I'll just keep it in 3rd and it will pull almost anything even pulling my 6k# travel trailer. Pulling that trailer (has HUGE wind drag) I've only seen 2nd gear once. That was pulling Raton pass going from NM to CO and I was doing about 58mph at just under 4k RPM. So there's definitely something wrong and my guess is tuning first and foremost. Or bring it back to the person who did the tranny valves and make sure they're working.

 

[Scoutn79]

It won't downshift under a high load situation like towing, esp uphill. Tow haul mode stretches the rpm range out to keep the engine rpms up for more power, and to keep the torque converter from locking up. I would say what you are expiriencing is normal and working as designed.

What the OP is saying is the tranny won't drop into a lower gear automatically thus raising the RPM, hence the reason he has to manually drop a gear. What you are thinking of is upshift into a higher gear to lower RPM.

Darrell

 

[Scoutn79]

I tow an open trailer with my Jeep on it to go play at the offroad park. I have a 2001 Yukon XL, the trans has a new valve body from gmtransmissionparts and new(ish) fluid. It shifts fine when not towing, but activating the tow/haul mode it just about refuses to downshift when pull up a hill. Often I end up manually downshifting it to not lose my momentum, does anyone have an insight to what the problem could be?

If you run in tow/haul with no load will the tranny work as it should keeping the rpm's up and downshifting sooner?

Darrell

 

[justcuz]

Are you towing in overdrive and expecting it to drop out of overdrive? If you are it sounds like your converter may not be unlocking. Try what scoutn79 is suggesting and see what happens. I can check my 2000 owners manual too.

 

[rayra]

Sounds like by manually downshifting you are screwing things up. It's possible there is something wrong with the transmission, a fluid pressure / valving leak somewhere. But I really don't think the OP is helping the situation by running Tow Mode AND screwing with the shifter.

I also have a vague recollection that you're not to use (Over)Drive if in Tow Mode. But I'm looking for references on that.



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Towing info starts on page 4-50. 4-59 has some stuff about gear selection, but not what I was looking for.



http://www.vadengmpp.com/owners-manual/chevrolet/2001-Chevrolet-Suburban.pdf

Tow/Haul Mode
Tow/Haul is a feature on automatic transmission
equipped vehicles that assists when pulling a heavy
trailer or a large or heavy load. See Tow/Haul Mode
on page 2-31 for more information.
Tow/Haul is designed to be most effective when the
vehicle and trailer combined weight is at least 75 percent
of the vehicle’s Gross Combined Weight Rating (GCWR).
See “Weight of the Trailer” later in the section. Tow/Haul
is most useful under the following driving conditions:
• When pulling a heavy trailer or a large or heavy load
through rolling terrain.
• When pulling a heavy trailer or a large or heavy load
in stop and go traffic.
• When pulling a heavy trailer or a large or heavy load
in busy parking lots where improved low speed
control of the vehicle is desired.
Operating the vehicle in Tow/Haul when lightly loaded
or with no trailer at all will not cause damage. However,
there is no benefit to the selection of Tow/Haul when the
vehicle is unloaded. Such a selection when unloaded
may result in unpleasant engine and transmission driving
characteristics and reduced fuel economy. Tow/Haul is
recommended only when pulling a heavy trailer or a large
or heavy load.

-------

I've towed a variety of things up and over the stiffest grade in CA (the Grapevine) fairly frequently, same drivetrain as the OP, and I've never had the problem he's describing. I have to wonder what the total weight is that the OP is dragging, he could be exceeding the GVWR, contributing to his trouble. Cherokees are about 4500# and that's a substantial trailer. I'd say he's quite likely at least 7000#, plus the Sub, plus loaded for a day/weekend at such a place, he's almost certainly exceeding the 12,000# max recommended combined weight and probably by at least a 1000-2000#.

 

[justcuz]

rayra, do you drop to 3rd coming up the Grapevine and let tow/haul do the rest?
That grade coming out of Oxnard south to Thousand Oaks is a good one too.
I think stock Cherokees are around 3,500 lbs, however with bigger tires and extra gear weight adds up quick.

 

[rayra]

Generally no, a motorcycle trailer, bowrider ski boat. The times with a 14' loaded UHaul trailer I have, up the steep side headed south. And typically with the heater blowing just as a preventive measure.
But I've never experienced the high RPM / slow speed described in the OP. I just don't ride the pedal that hard, don't floor it, and I seem to be able to keep it in the power band. Having very high RPMs with poor groundspeed seems like a torque converter or valving issue. There's a good bit online about such faults in 4L60E trannies. Tips for diagnostics.

This is the second / third topic about folks with these trucks towing heavy loads and having trouble. Most recent was just last month, the guy with the huge mobile home and the very large boat. I think it's some combination of (exceeded) max load and driver habits. Not 'bad design'. Lots of these drivetrains, towing a lot of stuff, all without generating a lot of failures. I think the problems start when people start hauling 6k#+ AND keep it floored trying to force it up the hill. But that's just my 'theory'. Just the common denominators I'm seeing in anecdotes online. I would say my loads have been between 4k-5k# and in some high heats and 100k+ mi transmissions, without trouble. Without even things getting hot, for that matter.