Tow/Haul Mode, 4L80E, 1991?

[Duncan Sterling]

Greetings,

I've just picked up a 91 R2500 Suburban with a 4L80E trans.

I've heard that later models have a tow/haul mode switch, though my truck doesn't.

Can I retrofit this to my trans? Also, I have no way of locking out OD--my shift selector only shows D, 2, and 1.

So the question is, do I need an aftermarket shift kit or controller to get these capabilities?

TIA for any and all responses/pointer/hints,

--Duncan

[HowieE]

The Allison trans used in the new Duramax trucks have tow/hauler not the 4L80s.
What are you trying to do?
Your 40L80 should haul a trailer in OD unless you have a strange rear ratio.
Let have some more information.

[Duncan Sterling]

Originally posted by HowieE:
The Allison trans used in the new Duramax trucks have tow/hauler not the 4L80s.
What are you trying to do?
Your 40L80 should haul a trailer in OD unless you have a strange rear ratio.
Let have some more information. Hmm. OK, I had alway heard that you never want to tow in OD--you're supposed to lock it out so the trans can't "hunt" on hills and cook itself--but I have no way of doing this on my truck.

I had also heard that the 4L80E could fry itself when towing without either using tow/haul mode, or a shift kit that accomplishes the same thing as tow/haul mode. I also have read that the first year version of the 4L80E has some design flaws and that adding a later model valve body or upgrade kit is supposed to help this.

I've currently got #2000 and #3000 trailers, but will probably need to pull a #6000 trailer from time to time, up some pretty steep hills. I have a trans cooler, but it's pretty small and I plan to upgrade to the largest size I can get. I also plan on adding an oil cooler as well.

I don't know what the rear end ratio is, but I plan on finding out today.

My main concern in all this is to avoid destroying this $2500 transmission.

Thanks,

--Duncan

[rjschoolcraft]

I have 220,000 miles on my 4L80E. I tow in OD most of the time. About 100,000 of the total miles is with trailer in tow (maybe more). Not the first problem with the transmission.

[Keith Richards]

You really cant tow in 2nd gear for too long,or above 30 mph.What I do with my older truck with turbo 400 is just start off in 2nd, until rpms get high enough ,then shift manually into D when needed.That method would probably be best for your tranny as well.I just dont understand why your 4l80e does not have:1,2,3,D.I would try driving it in OD while towing that heavy trailer and see how it does before doing any costly mods.good luck

[tanker]

The new 4L80E has the tow/haul button on the shifter. My son just bought a new 04 2500HD w/6.0 engine and he has the tow/haul mode. It includes a passive shift stabilization feature that helps eliminate shift busyness, a shift schedule to contribute to the solid shift feel, improved transmission life, and overall trailering capability. However I'm not sure that will work on an older unit as it is integrated with the computer. smile.gif

[sidedump]

Sounds like the sub came from the factory with a 3 spd trans and some where along a 4L80E was put in. Best bet would be to find a 4spd column. One of the members here should also be able to decode the numbers in your glove box to see what transmission originally came with you sub. There is also a product review for what you asked http://www.thedieselpage.com/reviews/pcstrans.htm
about the tow haul mode.