Transfer case swap to a 2 speed - manual shift

[LiftedAWDAstro]

Here is a collection of pertinant posts and information to help with anyone doing a swap from AWD to a manual shift 2 speed transfer case. This information was originally posted in the http://www.astrosafari.com forum.

As originally posted by sandfly:

Everyone talks of replacing the awd with a 4 hi-lo t-case with elec shift. What about a manuaul shift T-case with a shift between the front buckets????

Reply by Rockwerx:

Manual shift would be great! You may be able to put the control linkage in a few places so that it is easy to engage.

Go for it! Do you have a T-case yet? I have an NP243 which is the electronic shift model. I think that an NP208 and an NP241 will work. They are manual shift models.

Reply by atljwpepper:

I'm new to the forum myself, but perhaps I can help you out.
I've been running a NP231 out of an S-10 blazer for over 3 years now. It was a simple bolt-on to the 700R4 trans. The only difficulty is with the shifter, adapter between the transfer case & the trans, and the drive shafts.

The transfer case is a lot lower in its relationship to the floor of the astro than the S10's transmission tunnel and T-case. This requires raising the shifter bracket, and extending the shifter rod. Pretty simple, but it requires a little welding.

Problem two, if you don't get the transmission/T-case adapter that comes with the NP231, you must drill and tap the holes in the original astro T-case adapter. The astro's adapter actually has provisions for the three holes necessary. Pretty simple, but it's a lot less of a hassle to use the S10 one.

The NP231 that I have actually requires a larger rear slip joint than what the astro has. I simply replaced the astro's with the S10's on the rear drive shaft. Don't forget to have the rear shaft rebalanced and you might as well put in new U-joints.

For the front shaft, I used the S10 version with conventional U-joints. I only had to have the front shaft lengthened and rebalanced.

I am also running a front assembly out of an S10 with 4:10 gears. This allows me to disconnect the front drive shaft when I don't need it. I also used a cable adapter to engage/disengage the 3rd member. The front assembly boths in with no modifications to the subframe or the axle shafts.

Needless to say, the rearend must also be regeared to match the front. I find that 4:10 gears work great with my needs. I really enjoy the increased towing ability. It puts the engine in a better part of the power band on hills.

I converted my astro to 4x4 for a couple reasons.

1) My T-case and front drive shaft were broke when I bought the van.
2) There are thousands of NP231 S10s on the road, so parts are readily available and inexpensive.
3) The astro is my support vehicle for my Rock climber.
4) The conversion was done for under $800 US dollars using recycled parts.

I've driven my van into many areas that require 4-wheel drive with great results. In reality, the Astro is no Rock Climber, but the look on bystanders when they see an Astro covered with mud, slinging debre 8 feet into the air while coming over a hill is priceless.

I'm sorry for the long post, but I've always wanted to pass a lot of this information on to others that have considered the swap. This conversion has never let me down and its very unique. I am so confident of this conversion that I shipped my van to South Korea where I am serving in the US Air Force and have been driving it hard for the past two years.

Michael

[LiftedAWDAstro]

This was posted by me when I did my 231C swap:

I swapped in a 231 case out of a 1993 S-10 truck. It is a manual shift transfer case. I had to have the front driveshaft modified but the rear was the correct length. http://home.earthlink.net/~dharp1971b/id4.html

Reply by 96SafariSLT:

I have pretty much decided to go with the NP231C TC. My only question left is this. It is my understanding that the rear drive shaft hooks right back up into the 231C with no mod, the front needs lengthening though. If, until I get all the needed mods done, I just hook up the rear drive shaft and put the the selector in 2wd will this be ok? Or is there a problem with the transfer case possibly getting out of 2wd with no shifer attatched. Is it okay to drive around without a front drive shaft hooked up to the 231C?

Reply by CD0156:

No problems runnin 2wd until you get the front shaft made up. Dean (LiftedAWDastro) did that on his.

Posted by LT4Astro:

Received my ebay $75 NP231C transfer case yesterday. Got questions about it. Looks like what I want..has an electronic VSS sensor, and feels smooth and shifts thru all ranges. Guy advertised it as a '91 4.3 automatic Blazer T case...first question, was the electronic speedo (VSS) used on 91 Blazers?
The numbers on the case are: model # 1565 3414, and the case castings are: C16117L and 09104.
Has a 27 spline input shaft and electronic VSS which I need on my 94 Astro. Could anyone verify what this T case is? It has '91 markers on the assembly stamps. My guess is that it's what the seller indicated. Could be a 92 year model vehicle use. I'd like to know what to buy parts for since there is a small problem...
Bad news is that it appears to have been dropped on the top of the case, perhaps during shipment..and maybe before, and the vent is broken off (believe I can remove it if it's press fitted?)...also the upper bolt hole casting is slightly misshapen...the bolt hole is an easy fix...what about the vent?
Does pull out like a dipstick tube?

Reply by LT4Astro:

Thanks for the info Bill. The numbers I listed on the previous post were taken from the round red tag with a screw right in the middle (1565 3414). Also has the 231C imprinted...I was looking for exact year model vehicle it may have been removed from. The fact that the 91 had VSS likely indicates that that is what it is. All the listings showed speedo cables up to 91, VSS in 92 and up? The reason I bought it was because it's a NP231C with a VSS. Hoping their interchangeable!
Input looks like 27 spline count...haven't counted the rear yet. Appears to be same as front.

Reply by LT4Astro:

FWIW, the vent fitting on an NP231C is separately available...just in the unlikely event your 231 gets rolled over and the vent broken off. Mine got dropped (apparently) by UPS while in shipment. Ordered one, and as soon as it arrives I'm gonna get the T case installed. Now watch it snow a foot deep while having the front driveshaft modified. Is high-tech silastic working long-term as a gasket replacement on the transfer case?
Any problems related to removing the engine-to-transfer case brace? No place for it to bolt onto an NP231. Reckon it's not needed due to being in 2WD most of the time.

[LiftedAWDAstro]

Reply by Lockdoc:

The brace will be removed permanantly. I don't know what the heck high-tech silastic is, but RTV works great! What are you using for a shifter?

Posted by LiftedAWDAstro:

Just as Lockdoc said, the brace from the AWD t-case to the engine is to be pulled and hung on the shop wall! The vent tube is just pressed in and seals with an O-ring. As for the output, your AWD case could be either 27 or 32 spline although I think most were 27 spline. If the 231C case is from an auto tranny equipped truck, it will probably be 32 spline. All you will need to do is buy the correct spline slip yoke for an Astro/Safari. Swap that onto your current rear driveshaft and you will be good to go. The front driveshaft will either need a spacer block or to be modified.

Reply by LT4Astro:

Well, sometimes these things go well and sometimes they don't. Got the T case bolted up, but there's no way the front driveshaft is going to line up...it's splitting the upper aspect of the trans cross member. The replacement T case is definitely an NP231C, and it fits the adaptor and driveshaft without issue. However, there is interference above the T case/body crossmember that will not allow the transmission motor mount to be reinstalled. I had to loosen the crossmember (cannot easily remove or modify due to torsion bars) to remove the trans mount from the BW4472. Looks like the 231 needs to be "clocked" up, or rotated about 2" or maybe 3". Anyone have an knowledge about trans adaptors? Are there different adaptors? Would the adaptor from the Blazer reposition the case? There's a good website that shows a 231 being installed into a 97 (98?) Astro..the pix seem to show a lot more room than my 93 for the upper part of the T case. The rear driveshaft fits the splines...have not tried to install the driveshaft since the T case will have to be removed anyway. Are there various NP231s? Maybe I have the wrong one. Any thoughts on this problem would be appreciated. Unlike the pix of the 97 adaptor, where the trans attaching bolts are outside the adaptor, mine are inside the adpaptor.

Reply by LT4Astro:

It just hit me. The van with the pix of the T case install has a lift kit (body lift?). That would account for the additional space between the motor mount and body. Tell me it ain't so!
Had a typo in previous post...my van's a 94...not a 93. I would've thought they are all about the same.

Posted by Lockdoc:

Pics always help but, my front shaft hit the crossmember when I first installed the 231C. My tranny mounts were very worn dropping my trans down about 3\4 inch. Replaced those and also added some washers to the smaller mount that mounts to the crossmember for clearance. If you don't have any body lift you need to pound out or cut the brace above the tcase for clearance.

Pics posted by atljwpepper:

[LiftedAWDAstro]

Reply by LT4Astro:

Thanks guys! Now to decide whether to mod the body crossmember or lift it? I can work it out now knowing the T case is correct. Wealth of info on this site!
I like the idea of an S-10 front shifting diff.

Posted by Lockdoc:

Here are some pics of the Suburban shifter. You want to make sure you get the linkage with it also. I like the stock look it has.







Posted by V8Astro Captain:

I welded in my filler panel from the notch I cut in the body. I thought that this would be easy compared to a 2" body lift. Cheaper yes...easier, probably not. I'm spoiled since I've been working in a shop for the last few years. I can't tell you how easily I get pissed when I have to roll around on the floor to work. That plain sucks





The stock Astro AWD front driveshaft next to a '91 Blazer front DS.

[LiftedAWDAstro]

More pics from V8Astro Captain:







It's all done! I got my driveshafts back yesterday. The guy said he never wants to make another front DS like that again. lol. Apparently the OEM wall thickness on the main tube is almost 3/8". All new Spicer u-joints and front flange.

for the sake of bandwidth I sized the pics to 640x480. Some of the pics are a bit fuzzy...sorry...I was trying to take them in the dark...

I spaced the trans mount up 1/2" to get me a little front DS to crossmember clearance. It's still close, but it's ok after a run around the neighborhood. What do you guys think?










In the end they used a new a front flange to mate to the Astro front diff (special order of course), the Blazer slip joint, a new main tube and the Blazer rear yoke with the matching u-joint. My rear DS was lengthend 2" total.

The specs are 34" flange to yoke center. Spicer u-joint p/n 1200. Spicer flange p/n R223149.

[ryanhettenbach]

has anyone tried this swap on a '02 style van? I'd like to do the swap after my 2" lift but I don't want to mess up the trans or ECU electronics by doing so.

[twinbratz]

Since I could not find any info on the NP231c swap into a newer Astro I did a trial and error job on my 2002 AWD cargo. Started with a 1988 231c with the vss sensor. It bolted up to the trans without any problems. No cross members had to be modified. Both front and rear driveshafts had to modified. Rear is the original astro shaft which was lengthened and the front was a 90 S10 front shaft that was modified to fit and is now a hybrid of the astro and s10 shaft. It has about 1" clearance at the cross member. At first I did not hook up the front or rear drive shaft speed sensor. For some reason the antilock brake warning light would come on. Since all 3 speed sensors on the AWD transfer case work the same I decided to hook up the wires from all 3 speed sensors to the single speed sensor on the 231. since the computer is reading the same speed input from all 3 circuits the AWD warning light does not come on and the Antilock brake warning light has not come back on. Antilock brakes work fine. Speedo reads accurate and transmission shifts fine. I used the shifter out of my old 1989 K5 Blazer. It does not go though the full range on the indicator on the shifter cover but when I installed it I put notches on the z pattern guide plate that the shift lever travels along with my dremel. When I change from 2W hi and pull back to 4W hi the shifter drops into the notch and moves toward the seat. Same for neutral and 4W lo. I even used the stock K5 shift rod and it moved the shifter even with the front edge of the seat. easy to find in the dark.
I have been driving this setup for 6000 miles in the last 2 months without any problems. Had a slight vibration from the rear shaft so I put wedges under the rear spring pack to correct the pinion angle. Everything looks stock and this little delivery van goes anywhere. I'm sure glad I ordered the 3.73 posi option back in 2002.

[T.Low]

Since I could not find any info on the NP231c swap into a newer Astro I did a trial and error job on my 2002 AWD cargo. Started with a 1988 231c with the vss sensor. It bolted up to the trans without any problems. No cross members had to be modified. Both front and rear driveshafts had to modified. Rear is the original astro shaft which was lengthened and the front was a 90 S10 front shaft that was modified to fit and is now a hybrid of the astro and s10 shaft. It has about 1" clearance at the cross member. At first I did not hook up the front or rear drive shaft speed sensor. For some reason the antilock brake warning light would come on. Since all 3 speed sensors on the AWD transfer case work the same I decided to hook up the wires from all 3 speed sensors to the single speed sensor on the 231. since the computer is reading the same speed input from all 3 circuits the AWD warning light does not come on and the Antilock brake warning light has not come back on. Antilock brakes work fine. Speedo reads accurate and transmission shifts fine. I used the shifter out of my old 1989 K5 Blazer. It does not go though the full range on the indicator on the shifter cover but when I installed it I put notches on the z pattern guide plate that the shift lever travels along with my dremel. When I change from 2W hi and pull back to 4W hi the shifter drops into the notch and moves toward the seat. Same for neutral and 4W lo. I even used the stock K5 shift rod and it moved the shifter even with the front edge of the seat. easy to find in the dark.
I have been driving this setup for 6000 miles in the last 2 months without any problems. Had a slight vibration from the rear shaft so I put wedges under the rear spring pack to correct the pinion angle. Everything looks stock and this little delivery van goes anywhere. I'm sure glad I ordered the 3.73 posi option back in 2002.

Sounds like a job well done. Thats good info about the sensors and warning lights. Thanks.

[cd0156]

This is great! I am sure it was a pain to retrieve and repost all this, but I will have to go and seek out my write up on the newer vans since there seems to be some questions.. I had removed the entire AWD computer and harnesses in mine, and had pics and info on it.. The fuse can just be pulled to eliminate the light if you do not want to remeve the entire harness and computer though..

The above post is correct though, no cutting involved or anything. The only thing to watch is the mounting style (Tcase to tranny) my original case had threaded studs that went through the trans and then nuts that secured it, while my new tcase (NP231C) just had threaded holes.. Simple fix though, just go to home deopt or something and get some grade 8 bolts with the proper threading.. Just check this BEFORE you start!! I had pulled the shafts, unbolted the tcase and removed it before I noticed, so I had to reassemble everything to go to the store and get the bolts!!

The other thing I wanted to add is that on the 99+ the electronic tcase is longer than a manual case, which is why the driveshaft nees to be shortened, BUT the 98 and older with the mechanical AWD is a shorter case with VERY similar dimensions to the NP231 cases... SO.. find yourself a rear shaft out of an older AWD van and it will work. I have been running a 97AWD stock rear driveshaft for years now with no issue. As for the front, I just had to have the end cut off and a new Joint welded on the end, MUCH cheaper than paying for two entirely new shafts!

[gres67gs]

Hi Guy's

Are you leaving your stock front differential or are you changing out the axle tubes for blazer style lockup? are there any draw backs to using the AWD front diff (less traction)

Thanks
Frank

[T.Low]

Hey Frank ,good to see ya made it here.

I haven't touched my front axles yet. But anytime I get into technical 4x4 conditions I'm always thinking "easy does it" and the word "FRAGILE" ticker tapes across the front of my mind in flashing neon. SO far, so good, though, (knock on wood).

Yes, I have thoughts of a staight axle swap.

Just my 2cents.

[LiftedAWDAstro]

Most of us leave the Astro front diff alone. The S-10 driver side axle only gives the disconnect feature and in theory will save a couple tenths in mileage. There will be no traction difference in switching to the S-10 disconnect. The front diff will remain open in both cases and really only gives 1 wheel traction at any one time. (especially when you need it!)

But anytime I get into technical 4x4 conditions I'm always thinking "easy does it" and the word "FRAGILE" ticker tapes across the front of my mind in flashing neon.

Couldn't agree more...here are pics of the front diff out of the SPB. I was driving it like this and had no idea it was bad until after I did the SAS. The 4.11 pinion has very little contact area on the ring gear and apparently I chipped the teeth during one of my wheeling trips...I was always quite easy on the throttle just for this reason.

[WVKayaker]

So I guess the rule is take it easy on these AWD's?

[LiftedAWDAstro]

Yeah pretty much...Lockdoc has blown apart 2 front diff's with 3.42's in them.

[doyoulikeithere]

Hey folks, thought I'd throw my 2 cents in here.
I recently put my project van on the road after a few modifications.
I have a 1987 factory 5 speed 2wd van, and a well used 1995 VinW AWD van with a dead tranny and other issues.
I also happen to have a stockpile of other parts from an astro I stripped last summer, and another "5 speed" van that I stripped for parts too!
So, I had an extra 'Astro' 5 speed to play with, and I bought an s10 4wd T5 for like 50 bucks for parts.
My goal was to convert my 1987 5 speed 2wd van into a part time 4wd with an NP231C, an Astro T5 Trans, and an S-10 Front axle. I had to take apart the S10 trans for: a main-shaft, tail-housing & top-cover assy. I swapped the main-shaft and housing, and it now accepts a transfer case. easypeezy. My rear AWD drive-shaft is a bit short so I will need to have it lengthened. (actually, I will shorten a 2wd shaft I have around)
The front drive-shaft was easy. Neither the Astro nor the s10 shafts would just fit, so I looked around a bit. Then I used a nice thin solid shaft straight out of any late 70's early 80s Jeep CJ. My front shaft is 32.5 inches with the GM T5 Trans and an NP231C. I've got an S10 axle with a U-Joint yoke on it, instead of an Astro flange. 3.73:1

My biggest clearance issue was that I have a clutch Slave Cylinder on the drivers side of the bell-housing. It sits right smack dab in the same spot as the front drive-shaft wants to be. I came up with a pretty easy solution with more pros than cons. I modified the engine mount brackets to sit the engine up 2 inches higher. I had also put in a 2" body lift, so pro #1, no cutting the fan-shroud. Excellent, I like that one. Pro#2, the oil pan is 2" further from the earth, and all its sharpness. :-k Pro #3: The drive-shaft squeaks past now with a safe clearance. Pro #4: I know there must be some cons but don't much care anymore at this point.
Because the engine was raised 2" I had to raise the transmission mount up too. Anyways the super skinny Jeep CJ front drive-shaft and the custom engine mount brackets meant that I didn't have to slice into the frame or the cross-member anywhere at all. I made my transmission mount so I could slide in or out 1/8 inch shims till I get a nice drive-line angle. I will shim the rear axle a few degrees if needed as well. seems ok so far though. I plan to install double U bolt plates from an S10 instead of the rusty crusty clamps that hold the Astro axles on, from the factory. The front drive-shaft only gets used in the dirt, for me, so its not a high speed use item. I doubt I will find that it vibrates even if the drive-angles have changed a wee bit.