Chevrolet Express Van - AWD to 4x4 conversion

[drsmonkey]

My brain must have been scrambled when I tried the driveshaft originally. I actually got it to work!
Total budget of $130 
So if anyone needs a good AWD transfercase and front driveshaft it's available for pickup in 53188.
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Wondering if you can answer a few more questions about this swap now that you have a few miles on it. I've got a 1500 awd that I am planning to 4wd when the TC finally dies.
What trans in your van, 4L60e or 4L80e?
Does the tranny shift correctly in 4lo?
Was your VSS originally on the transmission, and did you move it to the transfer case?

 

[blazen71]

It's a 4L60E trans. It will hold first gear way too long when in 4LO, but will eventually shift. You can always start in 2nd gear by putting the shifter in the 2 position. The vss is on the transfercase. I bought a new plug and wired it to the vehicle side and used the "used" vss that came with the t/c. The sensors don't swap between the cases, they are diff threads.

Wondering if you can answer a few more questions about this swap now that you have a few miles on it. I've got a 1500 awd that I am planning to 4wd when the TC finally dies.
What trans in your van, 4L60e or 4L80e?
Does the tranny shift correctly in 4lo?
Was your VSS originally on the transmission, and did you move it to the transfer case?

 

[Len.Barron]

With the tuning from a pickup equipped with a manual shift t-case you can remedy the 4Lo shifting issue. The ECM/TCM needs to see the 4Lo signal coming in via the data bus and it will rescale the shift points based on the 2.72 ratio.

 

[drsmonkey]

Not sure what you mean by "tuning from a pickup" unless Blazen71 swapped the TCM and ECM from the donor truck (which would not work without a lot of work and some custom dealer programming) and I missed it. From what I have gathered from this thread and other sources the ECM/TCM programming on the AWD 1500 does not have the input for the 4lo signal to adjust the shift points (like Astros).

I was hoping that by moving the VSS to the TC output shaft the algorithms in the OEM TCM that dictate shift points would force a shift in 4lo and not throw tranny slippage codes from the discrepancy between the input shaft and output shaft speeds. From Blazen71 it sounds like it works somewhat, if not perfectly. That means you can probably get away using any TC that mates to a 4l60e, fits, and has a GM VSS on the output without switching to an aftermarket stand-alone TCM and get upshifts in 4lo and a somewhat accurate speed.

This also means that Zuren (the OP) might be able to use a kit from Advance Adapters to get a VSS from the output shaft of his TC to get his van to shift in 4lo without swapping his TC again.

 

[blazen71]

i have yet to even need 4LO. Personally I wouldn't even worry about the shifting. It kinda works and that's good enough for me.

 

[TDIJ]

With the tuning from a pickup equipped with a manual shift t-case you can remedy the 4Lo shifting issue. The ECM/TCM needs to see the 4Lo signal coming in via the data bus and it will rescale the shift points based on the 2.72 ratio.

So my experience on my 2007 was that the tuning for the low range is not in the transmission segment, if so it would be as simple as swapping that segment. It is in the body segment, so when we were swapping segments from 4wd silverados I could get the low range to work properly, but it would always disable my a/c and/or throw my battery light.

Ultimately, just swapping segments you would need to find the proper body segment for a truck that had the same type of hvac controls and stuff. It might be doable in that way, but I was not able to find one that didn't cause other problems.

 

[Len.Barron]

So my experience on my 2007 was that the tuning for the low range is not in the transmission segment, if so it would be as simple as swapping that segment. It is in the body segment, so when we were swapping segments from 4wd silverados I could get the low range to work properly, but it would always disable my a/c and/or throw my battery light.

Ultimately, just swapping segments you would need to find the proper body segment for a truck that had the same type of hvac controls and stuff. It might be doable in that way, but I was not able to find one that didn't cause other problems.

Yes, using a BCM(or having yours reprogrammed to match) from a matching (optioned) donor would be required, the 4Low switch signal from the Transfer-case goes to the BCM, it then sends that signal (via Class2 or GMlowspeed data depending on what year van you have) to the ECM. It's tough to deal with the controls that go through both the BCM and ECM on swaps, Tow/Haul is another one of those functions, I have no idea why GM thought it important to send that signal to the BCM, it should go direct to the ECM/TCM then just a status signal via data bus to turn the IPC indicator on..

 

[wjeeper]

Been researching how to get 4Low in my AWD for a upcoming trip this summer. My need for 4Low is more about speed control and keeping the trans temps lower. Just found this thread.......could have saved me some time had I searched here first!

Let me double check that this combo works in theory:

I am planning on running a NP242HD T-case. This t-case has the 6-bolt round mounting, 27 spline input/ 32 spline output, 2WD/4WD/4WD Full-time/N/4Low (I really liked the 4WD Full-time on snowy days when I had a Grand Cherokee) The case I have was from a 2002-2003 V8 Grand Cherokee with select-trac, and is extremely similar to the NP242 units found in Hummer H2's. The Grand Cherokee's of this vintage used the ABS tone rings for speedometer pick-up so the t-case doesn't have provisions for a speed pick-up. In fact the mainshaft doesn't even have the splines cut for the relector ring.

I am planning on running the speedo pick-up in the t-case adapter housing. Yes the speedometer will read 2.72 times too fast in 4Low but I should have all 4 gears in Low and low range will be used on a limited basis. I am hoping the shifts points will be ok as I am sure the 4Low shift points are mapped differently for low-range. I will probably go the route that TDIJ mentioned in post #70, although hacking a speed sensor in DIY shouldn't be a big deal. I will be going the JD Fabrications cable shifter route, its cheap enough!

I foresee needing to rework the driveshafts front and rear. Is there anything else obvious I am missing before I go on a parts buying spree?

 

[blazen71]

If it bolts to the 4L60E, give it a try. I have no idea if it will. But the shift schedule is way off in 4 low. If you can’t figure out how to remap the ECM/BCM as stated it won’t shift until approx 4K rpm. You can start in 2nd gear by simply putting it in 2.

 

[wjeeper]

On paper it should bolt up to the 4L60E. Diameter and spline count are the same as the OE t-case, unsure of the pressure angle of the splines. I am not so set on messing with the ECM and BCM seems like a lot of extra work for not much benifit. Having just 1st and 2nd low is ok for my purposes, not perfect, but I don't plan on using it often.

The more I build on the AWD chassis, the more I wish I started with a 2WD, done a SAS with super duty axles!

 

[blazen71]

You’ll just have to give it the old college try. I hope it works, it’s a cool idea to still have a mechanical awd with hi and low 4wd lock.

 

[wjeeper]

Have also thought about going the Northwest Fab Doubler route. This would add low range to the stock case and keep the stock t-case, not sure how the viscus coupler would like the extra torque though.

 

[blazen71]

I do like the ingenuity, but my $.02 is to just start with the np241 and see what you think. I did the swap for about $120 total. I used 4hi in the snow this morning. Worked great!

 

[Len.Barron]

I do like the ingenuity, but my $.02 is to just start with the np241 and see what you think. I did the swap for about $120 total. I used 4hi in the snow this morning. Worked great!

I agree, a GM NP241 is the simplest fix and they are bulletproof, I ran one for years in my LS2 powered rockcrawler then a couple years back swapped to the jeep rubicon NV241OR with the 4 to 1 low...it was more of a commitment because the output shaft of my 4L65e had to be swapped to the jeep 23spline configuration....4 to 1 is a game changer..

 

[wjeeper]

Oh the 241 swap is bullet proof, proven, well documented way to go without a doubt.

Big reason I am chasing the 242 dream is I have one sitting on the floor in the garage. From my junkyard surfing it appears that the 242HD shares a lot of parts commonality with the 241.

If you can’t figure out how to remap the ECM/BCM as stated it won’t shift until approx 4K rpm.

If the speedo pick-up is between the trans/ tcase do you think the shifting still be holy crap out of whack? I know the low vs high range shifting mapping is way different. I really hate that they felt the need tie the ECM and BCM together.

I will save the 4:1 for my willys crawler