2003 Chevrolet Suburban Quadrasteer, LB7 Duramax

Chevrolet

Suburban

2003

0

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Mods

2003 Suburban:\r
* Stock 2500 model\r
* Stock Quadrasteer 4-wheel steering\r
* Stock Magnetic Ride Control suspension\r
* Swapped a 2003 LB7 Duramax (federal emissions)\r
* 2003 Allison 1000 with 6-speed conversion\r
* Custom "AutoTrac XHD" transfer case: combined NP1 (263XHD) + NP8 (246 AutoTrac)\r
* Retains stock dual tanks & transfer pump, using the stock diesel ECU to control it all\r
* 2005 Cadillac Escalade touch-screen nav system\r
* Backup camera added to factory nav\r
* Bluetooth, USB, and aux-in added to factory nav\r
* "Ambulance prep package" parts used to retain rear A/C and keep up with desert heat\r
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Everything was done in the family farm shop by my brother & me!

Build story

My brother and I wanted to build the ultimate diesel Suburban, as if it was built by GM. We wanted Quadrasteer (2002-2005), a GMT800 (2003-2007 Classic), and no emissions controls (2001-2003 LB7). In most states, it is illegal to swap to an older engine, so that left us with needing specifically a 2003 federal-emissions Suburban and a 2003 federal-emission LB7 Duramax engine.\r
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After years of looking, we finally found a forest green 2003 Suburban 2500 with Quadrasteer (4-wheel steering) that we could afford. It was sold new in Oregon (federal emissions, yay!), and spent most of its life in California (minimal rust, yay!). We got a good deal on a mildly wrecked 2003 Duramax, and got busy. The main swap was completed in 2 weeks over Christmas 2016, with my brother and I working full time. It has slowly been reaching perfection ever since, as we added the mods noted.\r
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The Suburban was fully loaded for a 2003, minus the sun roof and XM radio. It has power+memory seats, mirrors, & pedals, auto-dimming mirrors (not just the rear view), heated seats, etc. Everything still works perfectly after the diesel swap due to careful integration of the electronics.\r
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The transmission is a mild build Allison 1000 with the Suncoast 6-speed conversion kit. Having the extra overdrive let it get 22.2 MPG on the highway at a constant 65 MPH. It averages around 16 MPG in real-world use, with 18+ on the highway being pretty common.\r
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The Duramax + Allison has only ever been mated with standard 4x4 transfer cases (until the latest model), but I am a sucker for All Wheel Drive. The Suburban actually came with the NP8 AutoTrac transfer case, which works much like a Nissan GTR. It is RWD by default, but can use a clutch pack to send up to 100% of the power to the front wheels if needed. The computer watches front and rear axle speeds, steering angle, and throttle input to calculate how much power to send to the front. It works really well, IMO. You can also force it to full 4x4 (high and low range) or 2x4 (which disconnects the front axle for fuel mileage) if you want. I had a local transmission shop combine the NP8 from the Suburban and the NP1 from the Duramax, and I made the wiring harness. The transmission and transfer case are the only parts not done by my brother or me. Not a skill we have learned yet.\r
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---------- bonus rambling below ----------\r
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That's the gist of it. I can go on for hours about this project, as it has been a labor of love for me ever since we started. Feel free to stop here if you just wanted the basics. Otherwise, read on.\r
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The video is the only one I could find, but it does show off the 4-wheel steering pretty well before I rip a donut. :D\r
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While not a driveway build, per-se, it was all done in the shop on the family farm. We are lucky enough to have a lift and a good selection of tools.\r
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After several years, oil analysis showed traces of coolant in the oil. With 200,000 miles of unknown abuse on the motor, the head gaskets had thrown in the towel. While replacing the head gaskets, I took the body back off and painted the frame, and replaced the increasingly difficult to find mag ride shocks. The stock ones still worked after 15 years, but were getting soft, and I was worried I wouldn't be able to find replacements. Hopefully the paint will protect it from the salt they are starting to use on the roads here in Idaho every winter.\r
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The engine is intentionally kept stock, and I believe it to be emissions legal in every US state (even California)-- despite having no EGR or catalytic converter! That was the point of going to all the effort to find this exact combination of chassis & engine. For closed-course racing events (ahem), there is a 425 HP / 750 lb-ft (at the wheels) tune that moves the Suburban pretty briskly for its size. I find that to be a reasonable limit of power for a completely stock LB7 without dealing with excessive smoke & EGTs.\r
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The Quadrasteer is absolutely fantastic. It turns sharper and parks easier than my car, and puts a smile on my face every time I drive it. The only thing that I dislike (and learned the hard way) is rear wheels will steer ±12° when going forward, but only ±6° in reverse. So you can drive into a situation you literally cannot back out of. Not sure why GM did that?\r
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One thing I am proud of is the fuel system. Most people put a sump in the rear tank so it gravity feeds the main tank, but I wanted to retain the factory setup exactly, mainly to see if I could. It is also technically illegal to gravity feed between car fuel tanks in the US, though that doesn't seem to be enforced. The stock rear tank has a transfer pump in it, along with a fuel level sender. I was able to get the original LB7 engine computer to run the transfer pump just like the gas motor, effectively hiding the fact there are 2 fuel tanks from the driver. You fill them through one port, and the computer shuffles fuel around as needed. The fuel gauge even works like you would expect, with no indications it is transferring fuel automatically between 2 tanks as you drive.\r
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My most recent set of mods was putting in the OEM navigation radio out of a 2005 Cadillac Escalade. It bolts right in, and with a little bit of prodding with a Tech2 scan tool, it works perfectly. To push things over the top, I added a video interface inside the GM head unit to enable a backup camera, and an aftermarket module that adds Bluetooth and USB integration. Overall it works really well, comparable to a mid-range aftermarket stereo, but I retain the factory rear-seat audio and look this way.\r
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Overall, it is just about perfect, and has been an amazing 4 year journey. I still love to drive it whenever I can think of an excuse. I am sure I will keep thinking of mods over the years, but for now, it is in the rare "just enjoy it" stage of the project.

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