NV136 to BW4472 Swap 2001 AWD

[Mr Bean]

Newbie here. 2 month lurker...I scoured the web, the club, and everywhere to find info on this particular question, so if the info exists, please feel free to point me in the right direction and remove the thread...

I just purchased (actually was nearly given) a pristine 2001 AWD LT from my wife's boss with 150K on the clock. This summer he had $2500 of maintenance performed on it including tranny flush, fill, filter change, new tires, alignment, brakes, cooling system, etc. Van is literally perfect except AWD sporadically works/fails...checking the encoder motor today. Also, don't want to replace the TC fluid with the Autotrak II since I am keen on swapping a BW4472 TC into our van. I don't like the lag time for the AWD to kick in when it does work and I like the idea of a 100% mechanical viscous coupling system without fallible electronics. I already read enough to know I am not interested in a 4WD swap since I drive frequently in the snow. I have access to a donor '98 BW4472 for $300 with fairly low miles on it. All of you '98 and older owners indicate how much you like your full-time AWD system, and us '99-?? peeps have encoder motor, and other issues and a stinky lag time for the AWD to kick in even when it is working properly. So if anyone can tell me if a BW4472 swap into my 2001 would actually be possible without extreme fabbing then I would love to tap you for info. Couldn't find a lot of photos of said TC's to compare...that might help alot. Since the van was obtained for little dinero, we are prepared to put some into it in order to make it work well for us. 2" OV lift is coming. Thanks for any and all help!

-scott
2001 AWD LT White

[mdmead]

I don't have any answers for you, but I'd like to see this swap. I have no experience with the newer cases, but they don't seem as durable or as quick to engage. I'm definitly sold on my viscous case though! I would guess without a tweak to your computer, your AWD light will come on without the proper input from the electronic case. I would guess you could fix this oter ways too....

[Mr Bean]

Is the lag-time occuring as a result of a failing or failed encoder motor? If so, a fresh motor would fix the problem. If the lag still exists based on the design (the time needed to sense rear wheel slip and then engage the front wheels) versus the viscous coupling system using the gelling silicon-based gunk in the pre '99 trucks which seems to be nearly instantaneous as well as 100% mechanical, then I would definitely want to swap in the pre '99 TC. Just not sure how well it would fit and what modifications need to be made to driveshafts, etc.

[rlsllc]

I have a '99 with the NV136 and a '94 with the BW4472. In normal driving, there is no appreciable difference in the two. I did notice that the NV136 was smoother with the Auto-Trac II fluid in it than the red stuff. My '99 must have more preload on the clutch pack than some of the units, as I have never been able to feel it "kick in" or any kind of lag. I've never had the rear tires spin on any surface, unless the fronts were as well. It also goes like nothing else with AWD and a G80 rear with the heavy conversion interior adding traction.

That said, I too prefer the mechanical (non electronic) fluid coupler. It's just simpler. The draw back: run mismatched tires, and it will fail expensively. With the '99 on, it will light the Service AWD light and disable the system if something is wrong.

I think you will need the drive shafts to swap the cases out, I'm thinking they are different lengths. I could be wrong on that, if it weren't so crappy out, I'd measure them for ya.

I do agree that if it just needs an encoder motor (or what ever it's called) to just do that, the NV136 is a good unit. It could be something else, I think it gets info from the anti-lock brake system, namely the speed sensors on the front wheels and the speed sensor on the trans.

[Mr Bean]

Roy? True about the mismatch tires issue with the Borg Warner...I am going to take yours and Aarons (he pm'd me) advice and try to troubleshoot the issue with my NV136...would tire pressure cause the unit to stop functioning? If the fronts were 10-20 PSI different than the rears I assume that changes the diameter enough to disturb the unit? In any case, I purchased three quarts of the Autotrak II stuff today and plan on draining and filling the TC tonight. Interesting that you don't experience lag. I wonder if the lag is indicating something isn't right (so all of the peeps here with the NV136 lag issue might need to give their AWD system some TLC)...that's what Aaron thought. I'll work on it over the next few days and see what I can do to troubleshoot it.

[rlsllc]

I'm not sure if tire pressure would be enough to cause a problem, but anything is possible. TP does affect rolling radius.

As for the lag, I've seen others post about it, and can only guess that it could be manufacturing tolerances, wear, etc. I just know that my '99 doesn't have it, or at least it isn't noticable. It also has enough preload that you can't spin one of the front wheels by hand if it is raised off of the ground and the rears aren't and it's in Park. I'm tempeted to pull the fuse and try it on snow to see how much it takes to spin the rear tires. I may have to do that.

[MountainManJoe]

I don't experience lag problems with my 136 either. Like rlsllc said, if my back tires are spinning, so are the front ones.

[LiftedAWDAstro]

Flush the AutoTrak fluid and run it for a little while. Make sure all 4 tires are the same make, model, size and tire pressure. I never noticed any lag with our 2003 AWD even though we only had it part of the end of the 2006-2007 winter. I also agree that manufacturer tolerances and preloads is what may give some delay to a few and no delay to the rest.

Personally, with winter here, I would run the 136 this winter and figure on a possible swap of the 4472 in the spring/summer.

[Mr Bean]

You guys rock...thanks for your takes on this...I drained and filled TC last night with Autotrak II. The original fluid was bluish-greenish which I do believe indicates Autotrak II was already in it? In any case, my oil pressure was super low yesterday and hardly any oil drained out of the pan...the culprit is super leaky oil cooler lines. So my project today is to remove those baby's...Can't test the TC fluid change until that's taken care of. Been driving my Toyota 4x4 around to get parts and run errands...8 degrees and snowing like it's winter around here...the heated garage is keeping things cozy. Once the truck is fed oil and back on all fours, I'll drive it around...then take it to the dealer to see if they can pull codes on it for the TC. If the encoder motor is bad, I'll replace that and stick with the NV136 for now. Aaron, if you ever come up with the system you pm'd me about, I would love to follow your progress on it. With many of you saying your lag isn't there or isn't noticeable, I'm more comfortable with the idea of keeping the 136...but the other night, when we were driving in the snow, I could easily have the truck sideways before the fronts decided they wanted to help out...

[ihatemybike]

Aaron, if you ever come up with the system you pm'd me about, I would love to follow your progress on it.

Might be awhile, my wife is currently holding me to three vans.

[Mr Bean]

[quote="ihatemybike]Might be awhile, my wife is currently holding me to three vans.[/quote]

I don't blame her. 3 vans is enough cubic feet to store the Library of Congress...

[Mr Bean]

So I took the Astro to the dealer today...and they gave us a complimentary diagnostic read. Only codes were for the MAF sensor and a "non-communication" code from the transfer case. Not sure what that means...should I just replace the Encoder Motor and call it a day?

[LiftedAWDAstro]

You could and if it isn't better, keep a spare in the garage.

[ihatemybike]

"non-communication" code from the transfer case. Not sure what that means...

I would guess a loose connector or bad wiring. Time to crawl around under the van a little.

[Mr Bean]

"non-communication" code from the transfer case. Not sure what that means...

I would guess a loose connector or bad wiring. Time to crawl around under the van a little.

Alrighty then...I searched for loose connections...unplugged and re-plugged everything back in...nothing appears to be loose, cut, torn, or otherwise damaged. What is the sensor that goes into the TC? When I unscrewed it, it was just a plastic sensor with a tiny metal dimple in the end...could that be it? I thing I'll replace the Encoder Motor from Rock-Auto ($148 for GM OEM) and if that doesn't fix, then I'll have a spare like you said.