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Old 11-08-2020, 12:48 PM   #1
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4x4 vs AWD

I'm currently looking at buying an AWD GMC Savanna and would like to learn more about how the AWD thing works. Does the transfer case also use some kind of clutch like a LSD?

Also curious if there are any suspension lifts that allow for more wheel travel (not just lift blocks or spacers) available?

Not looking to go rock crawling but just would like to be able to go where things might get a little bumpy without bottoming the suspension.
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Old 11-08-2020, 02:35 PM   #2
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I think the '03 Savana had a Borg Warner 4473 transfer case. That's single-speed, chain-driven (rather than a clutch pack). You should ask the owner for a pic of the badge on the t-case to make sure.

I have an '03 Astro AWD with a single-speed New Process clutch-pack t-case. It works well in snow and mud, but I do wish it had low range. The best remedy for me would be a New Process 2-speed case. If you wanted to do the same with the Savana, I think the NP246 would be a straight swap for the BW4473.

As for suspension lifts, WeldTec Designs has a few options.
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Old 11-08-2020, 02:52 PM   #3
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I am curious about this too. My Chevy Express 1500 has an additional leaf added to the rear leaf springs to deal with the extra weight of the penthouse top. This added a small lift in the rear, so the front torsion bars were adjusted to level it out. I have not found a lot of lift options for the 1500 other than blocks and torsion spring adjustments, most lift kits seem to be for the 2500/3500.
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Old 11-08-2020, 05:06 PM   #4
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Check out Expedition Forum. There are a lot of threads on the AWD GM van platforms, upgrades, etc.
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Old 11-08-2020, 09:27 PM   #5
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Just did a search for Borg warner 4473 transfer case and found a website describing it as a viscously coupled transfer case with a 35%/65% torque split front to rear.
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Old 11-08-2020, 10:21 PM   #6
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The way I understand is it works using 2 functions.... the silicone-fluid torque converter thingy does the primary torque split, but if it gets hot from slippage, the turbine housing then applies force to the friction plates improving torque transfer, but those plates are susceptible to wear, and if the silicone gets too hot, the turbine housing will leak
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Old 11-09-2020, 04:07 AM   #7
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Quote:
Originally Posted by Vanguy View Post
Just did a search for Borg warner 4473 transfer case and found a website describing it as a viscously coupled transfer case with a 35%/65% torque split front to rear.
Maybe we're saying the same thing. Do you have a link?

The way I understand it is the BW4473 is a chain-driven transfer case with a viscous coupler that apportions torque to the front and rear driveshafts. (See here, here and the rebuild kit here.)

The viscous coupler fits to/is a component of the t-case (see here).

Am I confused?
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Old 11-09-2020, 06:42 PM   #8
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No I just had no idea about the viscous coupling aspect. Do most 4x4 transfer cases have such couplings or are they straight drive units? I've never owned a 4x4 vehicle so still pretty new to all this.
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Old 11-09-2020, 11:10 PM   #9
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I could be wrong but I think viscous couplers are an AWD thing.


I looked up the NP271 and 273, which are popular 4x4 t-cases for the Econoline platform, and I didn't see any viscous couplers there. Nor on the NP205, so I infer that 4x4 is straight drive.


Which brings up the point that AWD and 4x4 aren't the same thing. I mean, you probably already know that, but I have to remind myself sometimes.
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Old 11-10-2020, 06:06 AM   #10
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I guess the advantage of AWD is the ability to use it on pavement..
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