Upgrading my 1999 Suburban C1500 for better towing performance

Well, sometimes we don’t get to tow with what we want, so we have to tow with what we have. I am looking to pull the ECU out of a junkyard 2002 Chevy Express 1500 with 3.73 rear end and swap it into my 99 C1500 Suburban in order to gain a tow/haul mode. I mention the gearing because I am also swapping out the rear end to that ratio from a 3.42. After this and some easy brake and suspension upgrades, I intend to use this truck to tow a 7000# camper until I can afford the 1-ton passenger van that will replace it in a couple of years. I’m hoping somebody in here has done this swap and gained some knowledge that they would be willing to share.

Hello, and welcome!

I also have a '99 1500 Suburban. This is my second 'Burb as the first rusted away thanks to New England weather and salt. both were originally equipped with 3.42's, 4L60E, and 5.7 engines. The old Suburban was built for economy and some towing. I built a 302 smallblock, short headers and duals, installed a massive transmission cooler, an OEM tow package radiator, a 2200 rpm stall converter. I was able to successfully tow large loads by using a weight distributing hitch and because my trailer has electric brakes on both axles the vehicle always stopped reasonably well. The only issue was the 302's powerband was a bit weak in 3rd at 65-70 mph. But because the engine was built well, I could drop to second gear and run rpm up as high as needed to accelerate or climb hills without problems.

The current vehicle is still running the stock 5.7 while I wait for time to swap the 302 from the other 'Burb. I have replaced the front brakes with a hybrid of parts that allows the rotors and calipers from a 2009 ish 1500. These are large enough that I had to switch to later 17" wheels. I have also replaced the stock master cylinder with an older part to delete the "quick takeup" master cylinder and get rid of the slow, slushy apply that prevents quick stops. I am also planning to build a custom rear spring pack using a mixture of the stock leaves and leaves removed from a 2007 2500HD. I am still trying to work out whether or not the "light 3/4 ton" trucks from around 93 have larger rear brakes than the stock 'Burb. I do intend to stay with the 3.42's because the old truck routinely achived 16-18 mpg during long cruises with no trailer. I would love to have a different planetary set for the trans to get rid of the 1.62 second gear ratio but I'm not sure that will happen.

As far as tuning, the later 0411 will offer tuning options and improved performance over the stock Suburban pcm. I hope to find time to switch my truck to the later pcm some day. It is possible to add a tow/haul button to the stock pcm but the pcm will need some tuning to take advantage of it. There was a chart made by Lextech / Jeff of Pacific Performance forum to help with the pcm swap. He is on this site as well. Lextech's truck was featured in a book on pcm replacements that could be handy. https://www.eficonnection.com/home/p...ontrol-systems

Feel free to start a thread about the swap. Include pictures, too. Everyone loves pictures.

If you plan to tow in 4th, you might think of upgrading the 4L60E transmission. 4th gear stock is not setup to handle a lot of load. A new reverse input drum, a wide 2-4 band, and the Sonnax or Superior 4th gear servo will greatly increase the 4L60E's ability to tow in 4th. And if you're in there, replacing the sunshell with a Sonnax Smartshell and the 3-4 clutchpack with the 2003-up clutchpack and the Sonnax 74140 HD 3-4 clutchpack backing plates will give you a bulletproof geartrain. You can install ALL of these parts with basic hand tools and a decent set of snapring pliers. Just need new pump and servo gaskets and o-rings which are cheap from Amazon or any local transmission shop.

Thanks. I do have a dead 4L60E sitting in my garage. I swapped it out in my driveway with the cheapest junkyard transmission in all of Wisconsin over six years ago, back when the Burb was our only vehicle. When I pulled it the TC off of the one that failed, the rebuild date was in paint pen, and it was within a year of the rebuild date, but I could not reach previous owner for warranty info. I suspect the pump gave out.

I am not sold on spending a lot of time or money on the truck. I really want to do the easiest things that will make the biggest impact. Long term, this truck does not meet my needs regardless of towing capabilities . I really want a 2010 or newer extended passenger Savana 3500 with a 6.0 and 4.10 gears. There are seven of us and we all have bicycles and gear. Something this Suburban will barely tow in 3rd through the relatively flat terrain of Wisconsin, will be easily towed through mountains when I can upgrade to such a van. I dream of just being able to toss bikes in the back and never having to load a roof or hitch rack ever again.

You have me interested in fixing up my other transmission, though, unless it will cost a fortune. I already asked a local shop if they wanted it to rebuild and sell, just to get it out of my garage, and they had no interest in it. The truck has towed a 4500# camper all over the state in 3rd with 9-10mpg, and I did haul a 2003 Ram 2500 cargo van with it on a U-haul trailer. I estimate that was a 7500# load. It wasn't fast. I took my sweet time and it did just fine through the rolling hills of the Kettle-Morraine. At the very least, having a spare transmission assures that I will never need it. I do plan on either adding a trans temp gauge, or figuring out how to use my scan tool app to keep it up when I tow.

I would love to upgrade my rear end to 4.10 full-float, and spindles to accommodate the 8-lug wheels and brakes, slap some stock 2500 alloy wheels on it with some proper 10 ply tires, but my 15" tires are almost brand new and I am not looking to spend a lot or keep the thing for more than a couple more years. Your brake upgrade sounds perfect. I am a little confused about going to the older master cylinder. I've read that the one from a GMT800 is the way to go? I do not mind terrible mileage because I have a company service van and a loaded minivan with all the goodies that gets 25mpg while keeping kids occupied. The Burb hardly ever gets more than occasional use other than towing.

Jeff sent me the spreadsheet to do the 411 swap and I'm going to send it to him for a tune to be optimized for my application. I was thinking about just running it for a while with the stock Express 1500 flash. I mean it has the same engine, transmission, and axle ratio. It has to be right there, right?

I don't plan on getting started until the water that has been pooling up in my garage and freezing is melted and gone. I do want to get all the parts, tools, and info gathered up and ready. Maybe I'll try my hand at youtube. I will definitely start a thread and post up some pics.

I've been using the Sonnax 4L60E build guides lately; this is solid information. Sonnax parts are now available at quite a few online places including Summit Racing, but it always pays to shop around. If you do decide to rebuild it, the necessary tools are around $300 or so, and you can always sell them when you're done. There are some little tricks and things to watch for, so have a knowledgeable person you can consult when you open it up.

One other tip - only take apart one portion of a trans at a time. I once had a guy disassemble a 4L60E I had built for him down to the last nut and bolt looking for what he thought was a problem, then gave it back to me in several totes. I kept a few bits and tossed that whole mess out; it wasn't worth putting back together.

Definately not impossible to swap to the full 1-ton running gear. I did it on my Express van. I actually drove it for a few days with the 3500 rear end and 1500 front end under it. Suprisingly it did not even throw and ABS code.

My 10.5 has 5.13s and I am running a LT265/75R16. With the 85E I tow in OD. My 350 is far from stock. 215cc ported aluminum heads, 215/224 comp cam, 1.7 rockers, thorley tri-ys, full exhaust, coil per cylinder 24x ignition, ported marine intake with 3.8 injectors that flow 42 lb/hr. Also have hydroboost, all the fluid coolers, helwig 1 3/8" rear anti sway bar. 1 ton springs, 1 ton brakes and air bags in place of the rear bump stops.

I tow a large Jayco travel trailer with mine.

Maybe EFI Live ( https://www.efilive.com/latest/cat/download-efilive ) would be an option for tuning either the 99 PCM or 2002 PCM?

Attached are EFL Live files from a 1998 Pickup (the 1999 is very similar) I'm currently working on. The EFI Live files will work with the "Free Version" of EFI Live that can be downloaded in the link above.

For transmission tuning check out Bluecat: https://forum.hptuners.com/showthrea...Table-Software

EFI Live and Bluecat have steep learning curves!

dave w

UPDATE:
My mods have come along nicely. I swapped out the rear end to 3.73, along with all new brake parts. I did the NBS master cylinder swap. I bought the tow/haul button out of a 2003 Chevy Express van. I did the 411 swap with a junkyard 411 from a 2001 Express 1500. My truck started right up after a security relearn and ran better than ever with no tuning. I found that grounding C1-71 did nothing at all. I downloaded PCM Hammer and TunerPro RT and bought a $30 OBDLink interface. Then I did a PCM read with PCM Hammer, found a definitions file on the internet, and used TunerPro RT to open that and the .bin read from my truck. I switched the performance shift trigger to use pin C1-71, made my max speed match my speedometer, and turned off vats. Then I saved the .bin and wrote it to the truck.

I didn’t really notice any difference with tow/haul activated. I will post a new question about proper settings for tow haul, because now it is down to that. I’ve towed heavy trailers with a 2013 Silverado 2500, and the tow/haul was an amazing difference. In the meantime, I am going to open up a bin for a GMT800 Suburban 2500 and compare those tables.

Pretty sure the vans tow/haul switch is a serial type switch, and for the method you're using all you need is a momentary switch to ground. As to the actual tow/haul tables, they're not that different from the regular tables. You have to remap them to be an actual tow/haul table.

I found the button on Tuner Pro that graphs the table values. The stock performance tables are noticeably different in 3D. I’m going to call it good enough until I get my 32’ camper that weighs 5400# empty. Maybe an Airlift system before then. I am still open to hearing specific adjustments that can be made to improve things.

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Originally Posted by Machine_whisperer

I found the button on Tuner Pro that graphs the table values. The stock performance tables are noticeably different in 3D. I’m going to call it good enough until I get my 32’ camper that weighs 5400# empty. Maybe an Airlift system before then. I am still open to hearing specific adjustments that can be made to improve things.

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Get a copy of blue cats and remap the shift points.

For tow haul I set the preference to lock the torque converter in acceleration from 2-4th gear. Do that by setting acceleration lock to 2nd gear in blue cats. With a 4L60E I leave the WOT lockup option off which you do by setting WOT lockup to gear 5. Set the minimum RPM to 1,800 rpm as that will keep the RPM up when accelerating and keep the shift points from allowing the engine to drop too low in rpm. Then again look at the factory Tow/Haul settings for an 02 Astro Van and they will get you close. The overall gearing and powerband of the engine are very similar. For Tow/Haul I would set all the command shift times to 0.300 for 1-2 and 2-3 and set to 0.00 for 3-4. Anything over about 260 ft/lbs of torque should have a 40% torque reduction for 1-2 and 2-3 upshifts.

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Originally Posted by Fast355

Get a copy of blue cats and remap the shift points.

For tow haul I set the preference to lock the torque converter in acceleration from 2-4th gear. Do that by setting acceleration lock to 2nd gear in blue cats. With a 4L60E I leave the WOT lockup option off which you do by setting WOT lockup to gear 5. Set the minimum RPM to 1,800 rpm as that will keep the RPM up when accelerating and keep the shift points from allowing the engine to drop too low in rpm. Then again look at the factory Tow/Haul settings for an 02 Astro Van and they will get you close. The overall gearing and powerband of the engine are very similar. For Tow/Haul I would set all the command shift times to 0.300 for 1-2 and 2-3 and set to 0.00 for 3-4. Anything over about 260 ft/lbs of torque should have a 40% torque reduction for 1-2 and 2-3 upshifts.

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I googled Blue Cats and came up with nothing. Maybe TunerPro will let me do this? Thanks for the info, I’ll take a look at the Astro maps and compare to what I have

Try this - https://forum.hptuners.com/showthrea...Table-Software

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Originally Posted by Kitch

Try this - https://forum.hptuners.com/showthrea...Table-Software

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AWESOME! Thanks! Digging in now.