4L65E tuning and towing

[truethinker]

2003 GMC Sierra Denali - 6.0L, 4L65E

I just picked up this truck a few months ago and haven't really needed to do any towing with it to this point. My family goes to Super Chevy Weekend in Reading, PA every year. Recently the tranny in my dad's HD started slipping in second so I towed his 30' camper for him. Needless to say, its a pretty heavy unit and was a pretty good test on a couple of the mountains.

My only complaint really is that there was a lot of gear searching from 4thu to 3rdthe when driving on relatively flat ground. Also just looking for it to shift and drive better all around.

I made some adjustments to the trans tune for both regular driving and towing and would like some input/advice before I tow the trailer back on Monday. My trans is stock except for a corvette servo and a super hold 4th apply piston and cover. That being said, the second gear shift is still slow most of the time even with the modified tune and corvette servo.

Any suggestions or adjustments to the tune would be greatly appreciated.

[Taz]

Hello TrueThinker,

The 4L60 / 4L65 were never designed for heavy towing - those tasks were better suited to the 4L80. That said, with a few upgrades, proper driving technique, and a “towing” tune the 4L60 / 4L65 can survive a fair bit of towing duty.

If memory serves the fluid flowpath in the transmission is different when the gear selector is placed in the 3^rd position (detent) versus the 4^th or overdrive position - which is why some owner’s manuals of 4L60 equipped vehicles encourage drivers to tow with the gear selector in the 3^rd position.

Again, if memory serves, when the gear selector is in the 4^th position and the transmission is in 4^th gear, some of the fluid is diverted or dumped directly back into the oil pan - probably to reduce parasitic power loss and promote increased fuel economy.

You indicated the transmission had servo upgrades. If you also upgraded the boost valve, have an auxiliary transmission cooler, and a transmission temperature gauge in the Sierra IPC - you should be good to tow.

Heat is one of the main causes of transmission failure. Personally, I view a transmission fluid temperature of 200 F (95 C) as being at or near the upper threshold when towing. Also, the transmission oscillating between 3^rd and 4^th while towing causes increased wear of the 3-4 clutch pack, increases the TFT, and puts significant stress on the stock sunshell.

I will set up a 4L60 tune for towing with the caveat that the gear selector will be placed in 3^rd gear position (all or most of the time). I only alter the Performance mode (Tow \ Haul) tables, that way in Normal mode (when not towing) the shifts will remain smooth and predictable. I also recommend setting up the TC to be locked at all times - at highway speeds, when in 3^rd gear, and when in Performance mode.

Earlier this month I picked up a project vehicle in northern Alabama. I used the above towing technique with a Gen III 4L60 equipped Sierra pickup. For over a 1000 miles (1600 Km) and 18 straight hours (won’t do that again !) the truck was driven with the gear selector in the 3^rd position with the transmission in Performance mode while towing a car hauler (approximately 2500 lb) loaded with a 4000 lb vehicle. This was on various interstate highways at speeds of 55 to 75 MPH.


Regards,
Taz

[truethinker]

Taz, First off thanks for the quick reply and extensive information!

I do have a TFTsensor on the dash And just the factory auxiliary transmission cooler. The boost valve has not been upgrade.

As for transmission temperature, if I'm on the highway it stays at about 150 when not towing. If I'm on back or winding roads it can very easily get near 200. While towing the previously mentioned trailer it's got Up to 220 And stayed pretty consistently around 210

So keeping the gear selector in third will prevent me from ever going into fourth Even on Nice flat roads, correct?

Locedk torque converter clutch sounds like a good idea To me.

And yeah, I know by first hand experience that this is not a transmission that handles much abuse. I blew the 4l60 oit of my 96 silverado twice before swapping a 4l80 nto the vehicle. I unfortunately do not have the time to do such a job on this truck just now

Thank you in Advance for the modified tune and I'm very anxious to see how it will improve things

[Taz]

Attached is the tune you posted - reworked as an example of what I was trying to describe. The shift speeds remain unchanged. The TC will be locked most of the time when in 3rd gear Performance mode (Tow / Haul). I also increased the 2>3 and 3>4 shift pressures when in Performance mode.

If you tow with the shifter in the 3rd gear position with Tow / Haul active - this tune should work just fine. If you place the shifter in the 4th gear position with Tow / Haul active - you will experience an odd shift into 4th gear - the transmission will shift into 3rd gear, lock the TC - then on the 4th gear upshift the TC will unlock at the shift and relock shortly afterward.

I use this type of tune strictly for towing with a 4L60. In other words, on a daily driver I will only flash this type of tune before needing to tow something - followed by reflashing the original daily driver tune after towing duty has been completed.


Regards,
Taz

[joecar]

+1 on what Taz said.

Avoid gear busy-ness, keep it in manual 3rd when towing and when not on highway.

Use a large enough cooler to get TFT below 200F.

Whenever TFT gets above 200F the fluid starts to oxidize rapidly it needs to be changed immediately.

Also: set the Throttle Kickdown tables to 100% all across (prevents interfering with the Part Throttle up/down shift tables).

[truethinker]

Also, I have a set of oem efans installed and just pulled the fan cal numbers out of the parts truck computer but the coolant got a little hotter than I would have liked while coming up over the one mountain

Would someone mind reviewing the fan cal in my original tune that I posted? I had hanged a ew things in the modified tune i posted but I hadnt tried it yet.Thanks guys.

[Taz]

Electric fans were not widely used on Sierra / Silverado until 2005. As a reference you could take a look at the Tune File Depot site www.tunefiledepot.com for a stock truck tune with efans.

Going to guess that event happened with the A/C turned on. This time of year the radiator / cooling fans often can't keep up with the demands of heavier towing without the assistance of a large capacity auxiliary transmission cooler (with its own efan). The efans are tasked with cooling the radiator, condenser, and OEM transmission cooler - equilibrium is often reached at over 210 F.


Regards,
Taz

[truethinker]

Just as I noticed the engine temp hitting 235, it suddenly dropped back to around 195 over a 30 second timespan. My thought was simply that I needed to set the highspeed turn on a little lower. Which I did in the tune I posted. I tried to check the tune deposit but have no internet connection here at the camp . While im able to download an attached tune off of this forum onto my phone and then transfer to my laptop...it wouldn't allow me to download from the tune deposit.

[truethinker]

First off, Thanks Joecar & Taz for the info and tune. It was very helpful in improving driveability and definitely improved towing ability.

Secondly, the 2-3 shift was a bit harsh, especially with a trailer attached. Would that be due to the reduced shift times?(0.35 rather than 0.6). Also, the 1-2 shift is still slow, even with a corvette servo, 0.2s shift time and 10% increased pressure(0.35 and 15% increase in tow/haul.) Do you feel that this indicates worn out parts in the trans(band or clutches) or should I just increase the pressures in similar fashion to what you did with the tow/haul settings Taz?

As for transmission temps. . . I've come to realize that I'm an idiot and overlooked a very important fact. . . When I installed my e-fans I didn't pay much attention to trans cooler location in relation to the fans. Turns out, the cooler is located low and in the middle. Right between the fans. In other words, there's very little air flow through the cooler.

[Taz]

Tuning an A4 is great way to get acquainted with the software, and study "what happens when" (stimulus / response) - with only 3 main variables to manipulate - shift time, shift pressure, and torque reduction (TR).

Daily driving, drag racing, or towing - call for different transmission tuning strategies, for different reasons. When towing, your primary goal is for the transmission to survive, and have as long a service life as is possible. The main enemy is heat. Heat is generated from longer than absolutely necessary shift times, slippage, and deficient transmission oil cooling.

The changes I made to your previous tune were to increase the shift pressure (2>3 & 3>4) - to reduce / eliminate slippage. These were very aggressive pressure curves. To also combat heat, the shift times should be quick, but not "slam bang". To reduce potential shift harshness, which may accompany increases in shift pressure, and decreases in shift time - TR should be increased.

In a towing application, increasing TR has the added benefit of further promoting transmission longevity. The 2>3 shift times in your tune were not overly brief (I've actually reduced these further) - the problem (causing harshness) was insufficient TR. I dropped in 2>3 TR values loosely based on a 2003 Silverado SS with an LQ9 and 4L60.

I only modified the 2>3 Performance mode (Tow / Haul) shift. My goal is provide you with an example of possible options (not a complete tune), so that you will be able to embark on tuning the transmission shifts on your own, to meet with your own personal shift "feel".

Also, the OEM transmission auxiliary oil cooler is not sufficient for towing duty. I would highly recommend a large aftermarket cooler with its own dedicated electric fan.


Regards,
Taz