GM fullsize AWD Van Info thread

boardrider247

Weekend warrior anarchist
There seems to be a lot of questions and confusion around the GM AWD fullsize van platform.
The purpose of this thread will be to get as much information as possible in one place regarding these vans.
For information on 1996 and newer GM fullsize RWD vans or GM fullsize vans with aftermarket 4x4 conversions (G1500/2500/3500) please see this thread.


I will make a handful of posts at the beginning as place holders and keep them up to date. If I post something incorrect please feel free to correct me. If others post good information I will add it to the first postings to keep it on the front page.

This thread is a work in progress:elkgrin:
 
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boardrider247

Weekend warrior anarchist
Factory GM AWD availability:

GM offered fullsize AWD van's as either a Chevrolet Express or GMC Savana from 2003-2014 model years.

All GM AWD vans came equipt with the 5.3L engine and 4L60E transmission.

A 2500 version was offered in the 2003 model year only. All other fullsize AWD vans were 1500.
I have an 03 Express AWD 2500. The only thing I can find that makes it a 2500 is the rear axle. It's a semi-floating 6-lug Dana 60.

There was never a factory 3500 AWD offering from GM.
However Quigly has offered 2500 and 3500 4X4 converted vans which have been sold at GM dealerships.

AWD was available in either cargo or passenger versions. I have never found a cab/chassis van with AWD, I don't believe they were ever available from the factory. If someone can prove me wrong please do.

I have read (without any real verification) that the AWD van's share a chassis with the AWD Avalanche/Tahoe and that they are a completely different chassis then the 1500/2500/3500 RWD van's. Again if someone has credible information to the contrary please let me know so I can correct this.
 
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boardrider247

Weekend warrior anarchist
Lift options and availability:

Short answer. (but you should read the long answer)
UCA part number is UCAK100009. Straps are LSAK13. Our vans use the same UCAs' as 1999-2006 1500 pickups so any aftermarket UCAs' for that application will fit. For pics see the late December post from NWExpress in this thread. I am running 265/75/16's (about 31.6"), but I know others run 285's(32.8") with a little trimming. Even though you can fit 33"s, for me they compromise gas mileage, braking performance, and wear intervals of suspension more than I would like since my van is a daily driver. You may have to adjust your wheel offset to fit 33"s as well.

Long answer.
I likely understand suspension less than some, but definitely better than I can explain it. I took the time to write the long answer below for anyone looking to lift one of our vans safely (a lot of it applies to any gm front torsion, rear leaf spring suspension), not to say that anyone else is doing it wrong. I am not an engineer, just someone who has been building, breaking and wheeling lifted vehicles on and off for 30+ years. This is my first GM, so do your own research before taking my advice. If you don't, it is on you. If there are mistakes, missing info, etc. please feel free to let me know and I will gladly edit, but you may have to convince me first.

Below are some things to consider before lifting your van that may save you and hopefully others some money and increase safety. A lot of people buying these vans don't have a lot of experience with lifts and offroading, so there is a lot of misinformation floating around in this thread regarding lifts. Unlike most other trucks, there is not a lot of aftermarket support for our vans, and no turn-key solution available (except one that is over-priced and poorly designed) so it is important to understand the basics of suspension when doing your own lift. Two things to keep in mind when lifting a vehicle without going into extensive suspension mods...Everything in suspension is a compromise, and the engineers designed the suspension to balance those compromises to work optimally with some safety margins built-in. Moving the center of gravity of a vehicle up is inherently less stable, but it can still be safe if you know that and keep your lift within the limits of the suspension design.

Torsion keys = Before buying new ones crank the oem keys and see if you get the lift you are looking for without bottoming out...their seems to be a belief that what keys you use effects the spring rate, but it doesn't. A different key allows you to index the torsion bar differently and that is all. It is NOT equivalent to increasing pre-load on a coil spring. The spring rate of a torsion bar is static at a given load no matter where the load is applied in the travel of the suspension, and torsion bars have a relatively flat spring rate within their travel. Each one of our vans rolled off the assembly line with slight variations, so sometimes new keys are needed, but usually only when going for max lift (which comes with a lot of other problems.) Look at your halfshaft angles before you lift, it should be sloped slightly upward toward the hub. Post-lift your halfshafts should be sloping downward at no more than about the same angle. Much more and you will experience much faster wear of CV boots, tie rods, and ball joints. At extreme lift heights you severely limit down travel which can harm offroad performance and is dangerous on the road. Aftermarket keys allow you to adjust to the extremes, usually the OEM keys will allow enough lift while staying within a safe part of the suspension travel. Cranking torsion keys does not change the total suspension travel or where the top and bottom of the travel are relative to the frame, just the static point at which the suspension sits within the travel. By lifting the van you increase up-travel and reduce down travel available relative to ride height.

Front Bumpstops = You may or may not need them...the bumpstops on our vans are designed to act on more of the suspension travel range then "traditional" bumpstops. They act upon the suspension system through most of the uptravel cycle in order to give a more progressive spring rate. than a torsion bar alone. Because there is little to no uptravel before the bumpstop makes contact it also helps to control body roll reducing the amount of work the sway bar and shocks need to do. Look closely at where the bumpstops are located relative to the pivot points of the lever (lower a-arm) and the contact pad. You can see how much of the suspension up-cycle they affect. When you crank your keys you are moving the static point of your lower control arm away from the bumpstop which diminishes initial control of body roll. Z71 bumpstops moves the point of contact closer to the pad providing a progressive spring rate sooner. The compromise is that they will physically bottom out sooner and get rapidly progressive near the top of the travel, slightly limiting the total amount of travel. I have a hightop, travel in and live in really windy places with lots of wildlife, so I like the Z71 bumpstops for crosswinds or sudden maneuvers at high speeds.

Rear bumpstops = With the OEM leaf springs installed the bumpstops act much the same as the front ones, but because of the geometry they act on less of the suspension cycle than the front.. The stock leaf springs also have a relatively flat spring rate, but when you swap to suburban springs you have a stiffer spring with a much more progressive spring rate. The bumpstops move away from the pads, but because the spring rate is higher they are not as needed to control body roll but will still work on the very top of the suspension range as a bumpstop. I left mine stock to maximize wheel travel, but also added a rear sway bar for the same reasons I use Z71 stops up front.

Front Shocks = DO NOT USE SHOCK EXTENDERS, EVER! Cranking or changing the torsion keys to lift a vehicle does not change the total amount of suspension travel or where the bottom or top of that travel is relative to the shock. Those extensions only limit the amount of shock up-travel available to the shock. This likely will cause the shock to bottom out before the bumpstop, causing broken stuff. This is why the extensions almost always break when used offroad. The OEM shocks will work exactly the same post-lift as they did before. Neither the Bilsteins or the OEM shocks are position sensitive, so lifting does not effect their performance. As long as the shock has the correct OEM spec extended and collapsed lengths they will work. If your shocks are still functional there is no need to change them. When they die, or if you want a stiffer ride then it is worth getting the Bilsteins. The 4600 and 5100 series of Bilsteins only differ in finish and valving. The 5100 are valved more aggressively and will give you a more stiff ride feel.

Rear springs/lift blocks = Swapping your rear springs to 3/4t suburban works to increase ride height, spring rate, and travel. It also changes the front to rear balance of the suspension and makes the van ride more like an empty truck. It does unbalances the ride a bit. A custom leaf spring built by a good shop for your load and use is the best, and most expensive option. Lift blocks are an OK way to go if you want to keep the same ride quality, but only when the blocks are minimal and designed for proper the proper pinyon angle.

Rear Shocks = When you swap springs you have effectively changed the spring rate and the total amount of suspension travel significantly. You will need new shocks sized appropriately in order to not limit down travel. The Bilstein suggested in previous posts work. Lift blocks change the distance of the lower shock mount on the axle relative to the upper shock mount on the frame. Longer shocks may be needed to not limit droop, but I have not measured this to be sure that the OEM shocks wouldn't work.

UCA's = I would adjust your ride height (lift) first then get an alignment and see if you get sufficient caster (3+ degrees) without compromising camber. Every van is slightly different and you might get lucky and not need the Cognitos. The higher you go the more likely you will need a way to correct caster. The ball joints in the Cognito UCA's wear out about twice as fast as OEM for me, but they are also much easier to replace. The other reason to get aftermarket tubular UCA's is for tire clearance at steering lock. My 265's did not contact the OEM UCA's, but it could be a problem as tires get bigger. Downside is you will have to pay for a second alignment if you end up installing aftermarket UCA's.

Limit Straps = Mandatory with aftermarket tubular UCA's. The down travel on our stock suspension is limited by the UCA contacting a metal pad attached to the frame. If a tubular UCA is allowed to limit down travel in the same way it will bend and/or break. This could lead to sudden, catastrophic re-alignment of your front wheels at high speeds, which is no fun for anyone. The way I mounted my limit straps (drilling through the shock tower like Cognito suggests for pickups) is not ideal for shock life, see NWExpresses pics for a much better solution.

Any brand torsion keys meant to lift the 1999-2006 GM 1500 pickups should fit the front of the AWD vans.

In the rear simple lift blocks for most any modern 1/2 ton GM product will work.
Or a spring pack from a 1993-1999 3/4 ton suburban can be used. #22-907 they are rated at 2900 pounds vs. the 2200 pound stock springs. The spring pack is 1 7/8" thicker to begin with and adds about 3" of total lift.
 
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boardrider247

Weekend warrior anarchist
Shocks which fit 2-3" lifted AWD vans.

Front:
Fox # 985-02-009
Bilstein #24-186643
Skyjacker #H7003
Rough Country #20045

Rear:
Bilstein #24-221948
Bilstein #24-185615
Skyjacker #H7017
 
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boardrider247

Weekend warrior anarchist
AWD to 4WD transfer case swap
http://www.expeditionportal.com/for...s-Van-AWD-to-4x4-conversion?highlight=AWD+4x4

More drivetrain info


The AWD 1500 Van is officially known as H-1500 or "H chassis" 7300 GVW and all other vans are G-1500,G-2500,G-3500...

They came with a 10 bolt 8.6" rear axle and 7.2" IFS front diff w/ 3:42 gear unless a 3:73 was ordered, G-80 locker optional as stated.....

265-70-17 BFG A/T tires on stock wheels fit my AWD Van with no mods, also similar year OEM 1/2 ton 6 lug SUV and Pick Up wheels fit 1/2 ton AWD Van.......

The AWD transfer case is a Borg-Warner 4473, this is the best info I could find:



Transfer Case Description and Operation
General Description

The Borg Warner (BW) model 4473 RPO NP3 transfer case is a 1-speed, full time AWD, transfer case. The BW 4473 provides 1 operating mode, 4HI full-time AWD. The transfer case has a planetary differential gear set, which provides a 35 percent/65 percent torque split, front/rear, full time. Both axles are constantly being driven for maximum traction, and the best balance of vehicle handling characteristics under all operating conditions is provided.

The BW 4473 case halves are high-pressure die-cast aluminium. The transfer case requires DEXRON®VI Automatic Transmission Fluid (ATF) GM P/N 88861003 (Canadian P/N 88861004), which is red in color.


Object Number: 851792 Size: LF
Click here for detailed picture of above image.

The power flows from the transmission to the transfer case input shaft (1). The input shaft (1) delivers the power to the planetary center differential (4), which splits the torque 35 percent through the differential pinion gears (Cool to the front sun gear (7), through the sprocket drive (2), via the chain (10) to the front output shaft (9) and to the front propeller shaft. 65 percent of the torque is delivered to the rear output, which goes through the differential ring gear (6), which is connected to the rear output shaft (5), and to the rear propeller shaft.

The viscous coupling (3), torque biasing device, has a series of opposing discs which are attached to the front and rear output shafts. 1 set turns with the front axle and the 1 set turns with the rear axle. The viscous coupling has a sealed housing, which is filled with high viscosity silicone fluid. When there is a speed difference between front and rear axles, the inner and outer plates of the coupling turn relative to each other. The silicone fluid provides resistance to the speed difference, and torque is transferred to the axles to equalize the speed difference. The tuning of the coupling is such that binding is not felt in tight turns, on dry surfaces, while being high enough to bias torque quickly to the wheels that have traction in a vehicle slip event. If the speed difference between the axles is high, the viscous coupling can go into hump mode. This occurs when the heat generated by the high speed difference expands the viscous fluid in the coupling, which results in pressure between the plates, forcing them in to contact each other, similar to a clutch pack. In the hump mode, the coupling can bias torque 100 percent to 1 axle. To prevent damage to the viscous coupling, the following should be avoided in the vehicle:

• Do not tow with only 2 wheels on the ground.
• Do not drive with 1 propeller shaft removed.
• Do not drive with a mini spare tire for any extended period of time.
• Do not operate the vehicle on a hoist to diagnose the driveline components.

Customers may have concern that the transfer case is not operating properly, because 1 set of tires spun for a brief period. It is normal for 1 set of tires to spin until the viscous coupling engages. Turning off the traction control switch, if equipped, enhances the function of the viscous coupling. The viscous coupling, as described above, engages by heat. Allowing 1 set of tires to spin or slip for a very brief period, generates heat in the viscous coupling. The engine speed should be kept at a constant speed during the brief spin of the tires. Feathering the engine speed, or hard acceleration, will not allow the viscous coupling to operate properly.
Power Flow - No Wheel Slip


Object Number: 851796 Size: LF
Click here for detailed picture of above image.

During normal operation, 100 percent engine torque is delivered to the input shaft (1) from the transmission. The torque is split 65 percent to the rear output shaft (5), and 35 percent to the front output shaft (9), by the planetary differential (4). Because there is not a loss in traction, or slip in the front or rear wheels, the viscous coupling (3) is locked in place and there is no shear mode or hump mode involved.
Power Flow - Front Wheel Slip


Object Number: 851797 Size: LF
Click here for detailed picture of above image.

When traction is lost at the front wheels, the viscous coupling (3) works in conjunction with the planetary differential (4) to bias the torque more to the rear wheels. The rear torque goes higher than 65 percent, up to 100 percent torque to the rear output shaft (5). The torque at the front output shaft (9) is lowered from 35 percent, to as low as 0 percent torque.
Power Flow - Rear Wheel Slip


Object Number: 851798 Size: LF
Click here for detailed picture of above image.

When traction is lost at the rear wheels, the torque is biased to the front wheels. The torque to the front output shaft (9) goes higher than 35 percent, up to 100 percent. The torque at the rear output shaft (5) is lowered from 65 percent, to as low as 0 percent torque.
 
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DEFENDERBEAM

strategic command
Not a bad idea. Thanks for starting this thread.

I have a 2014 AWD, but it is 100% stock for time being. I will be referring to this over time.

feel free to delete this post to keep the thread clean and simple.
 

justbecause

perpetually lost
i have seen a few people report a factory rear locker was available for the chevy van. if that is correct, how do you identify a van with that option?
 

BigDan

Observer
ok then ,
I might get answers to my questions ....

What are the differences between a 1500 & 2500 AWD in 2003

Will an IFS pick up ( 15000 or 2500 ) diff , fit in place of the 7.2 awd IFS front diff ? ( bolt in place )

thanks
 

Herbie

Rendezvous Conspirator
Another resource for info that I've found very helpful over the years:

GM Upfitter Guides - These are the manuals used by coach/RV builders and they have a wealth of knowledge about loading, official body measurements, Tire data by axle, etc.

The Express/Savanna (and the Astro/Safari) are both considered "Light Duty", so look there, by model year, then check out both the Body Manual and the Electrical manual.

SUPER dense amount of info in there.

page example:
 
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