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Discussion Starter · #1 ·
Let's start by stating that I am not the be all end all of AWD conversions. I did 3 of my own trucks and I can only comment on how my conversions went but not if "this" transfer case will work in whatever truck you have.

AWD what is it and why would I be interested?
An All Wheel Drive conversion is main done to increase the traction of our trucks. Basically we start with a 4wd or 4x4 truck and swap in an AWD transfer case and change some stuff on the front end. GM did this with the Typhoon & Syclones, and stuck a turbo on it just for fun. These turbo trucks really hustle and without the extra traction would be a handful. Even those of us with a 2wd or a 4wd IN 2wd, merging into traffic on wet pavement can be a frustrating experience.

Pushing a 2wd truck to the limit is usually reached early as the rear wheels break loose. This of course means that the truck has reached the limit of cornering as you can't push it any harder into the corner without totally spinning out. This is where AWD becomes more than just a straight line modification. With the extra traction available, a front tire must also break loose before the truck will also lose traction in the rear. This means that corners can be taken faster for those of you interested in track or auto-x, not to encourage spirited driving on the street :D

So this began with my 89 4wd Jimmy. I wanted a simple no frills AWD conversion, just like the Typhoon. At the time I had planned a V8 swap, hence the AWD V8 moniker. I chose to use an AWD transfer case out of an Astro/Safari van. The early ones are non-electronic, I don't know when they went to electronic, about '95 but someone can correct me. The non-electronic transfer case only has a VSS sensor on it, no other wires or sensors. Bravadas work too, we just have more AWD vans up here than Bravadas. Different years and whether van or Bravada, you have 2 transfer case available. The 1372 with a 27 spline rear output and the 4472 with a 32 spline rear output.

As far as I know any AWD of these transfer cases will fit any auto or manual in our trucks. IF you are doing a V8 swap and are interested in AWD but only want a manual transmission, you will need to consider how your transmission will hold up to a V8 with added traction. There is a T56 conversion to a 4wd/AWD transfer case but it is ultra expensive, several thousand last I heard.

When you remove your 4wd transfer case and compare it to the AWD transfer case you will see that the coupler shaft is longer than the AWD's, don't worry it will fit fine.

4x4 transfer case


AWD transfer case


Don't worry about the difference in depth, the AWD transmission output shaft is the same as the 4x4 transmission.

Again, 4x4 transfer case top, AWD transfer case below.




Swapping in the AWD transfer case is a straight forward bolt up to the transmission, but because the output of the transfer case is clocked higher it can hit the floor or fuel lines.



Note: If you are using a transmission from a 4x4, you need to know that the transfer case shifter that you removed, was bolted to the intermediate housing between the transmission and the transfer case. These bolt holes go right into the housing leaving an opening for dirt & water to get in, and oil to get out. I applied sealer to the bolts and screwed the bolts back in. Not needed with push button 4wd trucks.


Once you have your AWD transfer case installed you can remove and plug the vacuum lines.

Tip for the 4wd guys with a persistent transmission oil leak on trucks with a floor mounted transfer case lever, these bolts come loose and will leak oil, remove the bolts one at time and seal them.

Next post, modding the transmission mount.
 

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Discussion Starter · #2 ·
This is what you will likely have if you don't mod the cross member.


My '89 & '99 Jimmy required a simple mod to the cross member, the '95 for some reason bolted in with no mods to the cross member?? It may be floor height differences between years. So I can't tell you what years may or may not need the transmission cross member modded, but it's a simple mod but does require a wee bit of welding.

You can try installing your cross member and mount after you install the transfer case, but if it's tight against the floor or fuel lines you will have to mod the cross member, here is what I did.

What I did was drop the mounting surface on the cross member 1/2". I did this by splitting the mount surface horizontally on both sides. Then I laid a 1/2" bolt in there to space it lower. Welded it back up.

Here is the stock transmission cross member.


Here is the modded transmission cross member.


I cut the sides vertically and across the bottom. I cut a 1/2" bolt and used it on the bottom to bridge the gap.






The transfer case will now sit 1/2" lower.

This is the lower transfer case mounting bolt, normally you can get a socket on it without removing the cross member. However, once you lower the mounting plate, you cannot get a socket on it. If you grind the upper edge of the mount down just below the bolt, you will still be able to remove the transfer case without removing the cross member. No pic of the notch.


As far as the drive shaft is concerned, if you match the smaller or larger slip yokes with the same style transfer case it should fit. My drive shaft was the correct length.

So now we have the transfer case installed and the cross member modded so it's all mounted and tight.

Let's move on to the front axle.
 

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Discussion Starter · #3 ·
With and AWD transfer case you MUST have a connected front axle. The transfer case uses a viscous type clutch to direct power to the front and rear. If you have no connection to the front axle the viscous coupler will be in constant slip and over heat and seize. Your truck can be driven easy for some time if needed but don't be too quick to try burn outs with only rear wheel drive. Also not that if the front axle is uncoupled or the front drive shaft is absent, you cannot leave the truck standing in PARK or in gear for a manual, it WILL roll on an incline as the viscous coupler will slip!

Some guys have left the 4wd front axle in place and leave it coupled. I chose to swap in an AWD front axle as I believe the 4wd coupler is designed for low speed and limited use, not constant.

I removed my 4x4 front diff and swapped the Astro right axle & tube over to mine. I swapped the Astro pinion flange over to the 4x4 diff, the 4x4 front shaft is different. You MUST know how to do this as over tightening WILL cause major damage to the diff bearings! If the ratio is the same and you know the gears & bearings are good in the Astro, just swap the whole thing in. All years 4x4 & AWD front diffs will work. The early Astro uses bolt on front axle shafts and later used slip in shafts, I don't know the years, but you can easily swap the parts over. The 4x4 uses 6 bolt flanges until '97 and slip in CV joints 98+. You can swap the later slip in diff if you use the slip in axle shafts. You just have to match bolt on with bolt on, and slip in with skip in.

The front diff is the most difficult, you have to remove the axle shafts, and this requires removing the front spindles. I however DID manage by unbolting the axles shafts and pulling them up out of the way and cutting the lower mount as shown. This allows the pinion shaft to just drop down. Not shown, I have overlaid a piece of metal extending to the suspension bolt to the left. I welded this to the piece I cut off, it greatly simplifies removing the diff!


Starting in 1998 S10 4wd and Astro AWD used CV shafts that pop out of the diff. You must remove the spindles to remove the CV shafts before you can pull the diff. You can use ANY AWD from a van or a Bravada of S10, they all fit, just be aware of the axle type. You can use your S10 axles in a van front diff.

My 4x4 diff with the Astro axle & tube installed on the right side.


Now I have to point out here that I swapped the AWD front diff pinion flange over to the 4wd diff. So far in my experience the front universal type on the front drive shaft is a CV type. I have read that some AWD or part-time AWD's use a spicer, or cross style U-joint here, I have not seen this and can't confirm if it's required or not, but if it comes on a vehicle that can be switched to AWD while on the highway, well then I guess it works.

Front drive shaft.
If you are getting swap parts of an AWD Bravada or S10 the shaft will be the correct length. If you are getting the front shaft off an AWD Astro/Safari then it will need to be shortened as I did. I took it to a drive line shop and they charged me $80. To get the correct length I bolted it up to the transfer case and shoved the CV joint as far back as I could while holding the shaft under the front diff pinion. Take a measurement from the protruding pinion shaft sticking out of the flange and to the current CV flange location, then allow a 1/4" more for install clearance. The transfer case and front diff do not move relative to each other so the CV will run midway in it's travel.

Now you can remove all the 4wd stuff, hoses and the vacuum servo for the axle disconnect on the 4wd. The servo is located under the battery box.



Now what to do if your fuel lines are in a bad place now, next post.
 

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Discussion Starter · #4 ·
In my '99 Jimmy I have to deal with the fuel lines. My '89 and my '95 I did not, I don't know what years you do or don't have to deal with this.





Unfortunately you will have to remove the transfer case to do this! Maybe you will be able to see by my pics if your fuel lines are in the same location as mine.

While my transfer case was in I marked out the preferred line routing.


The lines before I rerouted them.


I removed the transfer case and rerouted the lines. I wish I had some of those nice AN lines but alas only simple high pressure Fuel Injection hose and fuel injection hose clamps. I bought a Dorman fitting for the fuel filter and supply and return lines, total, about $30 for all.


Make sure your lines are not rubbing on the transfer case or the floor.

A note about the front drive shaft, watch the end of the automatic shift shaft out of the transmission. If you engine mounts are broken or have shifted the front drive shaft can tough the drive shaft tube. You can try loosening the transmission mount and jiggle it to the passenger side, or elongate the mounting holes. You can also take a cut off wheel to the end of the shifter shaft if needed.
 

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Discussion Starter · #5 ·
So that pretty much is it. With this information you should be able to do the swap easily in a weekend, faster if you have done this kind of work before.

Driving an AWD truck
Well it's a lot of fun to say it simply. If you have been frustrated by lack of traction you will be amazed and possible have a permanent smile on your face :D

You will now be able to gas it to merge into traffic without worry of wheel spin.
You will now be able to jump on that go pedal with that V8 in your truck without screeching tires drawing attention of the boys in blue.
You can do wonderful spinning donuts if you can break the back end loose.
You can get by on summer tires in the winter unless the snow is higher than your ground clearance. I drove my truck with summer only rated tires in foot deep snow with no problems. I only have about 6" of clearance.
And my favorite, I can hit the gas when pulling out to make a left turn on wet pavement and STAY on the gas when the rear end DOES come loose, it will just hang out a bit but the front of the truck will pull the truck forward even with the back end loose.

Things you CAN'T do.
You can't do brake stands.

Things you MUST do.
You must have the same size tires on all corners.
You must check your tire pressures on occasion.
Your spare tire must be as close to the same diameter as your tires as you can get.

Your truck will now understeer when you have reach its limit. You may have other suspension mods that may change this to some extent. If you are not crazy about this, like I am, you may want to consider a rear sway bar upgrade to help the back end transfer weight to the front, helping the rear swing out a bit. Remember that the front driving wheels will always be there to keep the front of the truck moving in the direction you want to go. On dry pavement I have never reached the limit, maybe at the auto-x. One wet pavement, with the tires I'm running, I can corner faster on wet pavement than I could in 2wd on dry pavement!

Brake balance is improved as locking up the rears requires that the front also experience lock up.

While rolling, or idling in gear while the wheels are turned, you will experience some "resistance" to roll as the transfer case is resisting the drive shaft speed difference.

So that my friends is about all I can think of at this time. Other members please jump in with your experience and comments.
 

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awesome! ive been waiting for this write up for a while. i have been debating doing this conversion one day. i love awd drive mated with lots of power.
 

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2.2 Extremist
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Silly question but, it would be possible to do the AWD conversion with a manual correct?
 

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Discussion Starter · #12 ·
Silly question but, it would be possible to do the AWD conversion with a manual correct?
If the S10 has a 4wd transfer case, you can swap an AWD transfer case in it.

If you are planning a V8 swap the transmission you use must accept a 4wd transfer case, so a T56 won't work, without a ton of money to adapt it.
 

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Cornerin Demon
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If the S10 has a 4wd transfer case, you can swap an AWD transfer case in it.

If you are planning a V8 swap the transmission you use must accept a 4wd transfer case, so a T56 won't work, without a ton of money to adapt it.

that sucks... manual awd would be hella fun :(


btw, do you have any idea how much TQ the awd components can take? whats the weak link, the xfere case?
 

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Discussion Starter · #14 ·
In case I didn't make myself clear, yes you can turn a manual transmission 4wd into a manual AWD, you just can't do it with a T56.

I've read of many 10 second LS1 AWD trucks running with no breakage.

The front diff is likely the weak link.
 

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Hardhead
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Interesting concept. What year Bravadas came with AWD? Have you ever tried wheeling with this setup? I have plans to do the 5.7 swap and am currently gathering the pieces I will need. This would be beneficial to the swap as well. I did have plans to use a manual 231 transfer case but this may be better. I already have a cast iron front differential for my swap with a Bravada tube and axle to use.
 

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Discussion Starter · #19 ·
The AWD transfer case is not the best for wheeling. It has no low range and continual slipping may overheat the viscous coupling. The front axle swap is popular for off roading as it is always engaged and you have no issues with the front axle not engaging.
 

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Hardhead
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So do the guys that do quarter mile stuff use this setup? You stated that you've heard of 10 second trucks running these? So if I understand this correctly it should work well in a mud racing truck as well. Sound feasible?
 
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