Well, it's done. After months of planning and acquiring parts from around the country, I will never again be vexed, by another NP136.
Why did I go through with this? I had three NP136 cases malfunction. They were: AWD locked stretching chain, Clutch plate failure and AWD locked causing loss of power/mpg. I removed the front axle the last time this happened and drove 2,000 miles home. That beach run was nice for 20 minutes. Given my history with the NP136, I knew it would die at some point.
Why should you do this swap? Do you do anything more than drive on paved roads? Do you want reliable engagement without the need of anything electronic? Do you want amazing handling at all speeds? Do you want 1-3 mpg less? Then..this is the swap for you.
A full day if you have all the parts. 3 hours for Hardware swap and 1-3 hours for electric work
You will need:
1)A working BW4472 TCase. Available from your local junk yard or someone here on the site.
2)Front AND Rear driveshaft
3)Choice of motor oil for the BW4472 (I used 5W40 Rotella Synthetic)
4)Transmission jack or motorcycle jack. I guess you could use a regular jack but don't recommend it
5)Transfer Case Seal. The seal is paper (really) and easily rips. Without this, you will spill ATF on startup. I heard it's a dealer only item
6) Torsion bar from the same year astro as the donor Tcase. The NP torsion bar will not work.
7) Wiring and sensor clip from donor van for VSS. The NP and BW use different style VSS sensors.
1) Full complement of sockets up to 18mm and box end wrenches
2) Big pan to catch transmission fluid when separating Tcase. When you tip T case, it will dump blue fluid like a stuck pig. I used a concrete mixing tub from Home Depot $14
3) Lots of rags and clothes you are willing to dispose of
4) A muscular friend to help balance the Tcase
5) A warm day or garage
6) A tray to collect nuts and bolts
7) Transmission Jack/Regular jack and wood pieces
1)Drive shaft yoke from the earlier astro. I didn't have this and ended up grinding out the yoke on mine. The bearings are slightly larger on the 99 and older astro.
2)New VSS sensor for 99 and older Tcase.
3)Transmission rubber/poly mount. You have to remove it..why not replace it? We didn't..but wish we did.
Things that will swap:
1)Bolts from both drive shaft flanges will change over
2)Torsion Bar Bolts
3)Nuts/Bolts from transfer case
What was expecting:
1)AWD light would illuminate -it didn't
2)VSS would swap over-it didn't. Without a VSS, your transmission will go into limp mode. That means second gear and a very slippy 3rd.
3)Van will slowly roll down a hill without front driveshaft-it did. Scary to see 4000lb van move at a millimeter/second roll downhill in Park
Here are the steps:
1) Put both ends of van on jack stands
2) Shake van like dickens/jump on it..etc to make sure it isn’t coming off of stands.
3) Remove Front and rear driveshaft. It’s helpful to have the friend put the vehicle in and out of Park in order to rotate/lock drive rear driveshaft. On your own for the front.
4)Remove Tcase. First, we removed the hardware from the transmission mount, lifted the transmission up via the regular jack and wood (gently) and then removed the hardware that was now accessible. Take it slow and look around. Remove Torsion Bar. Remove all electronics. There are two VSS sensors and one addition sensor.
We put the jack under the Tcase and removed all the hardware between the Tcase and transmission.
5 )Once all hardware is removed, balance the T case and gently pull it away from the Transmission. Remember the studs in the Tcase are threaded.
6)Drain NP136 into pan
7) Swap studs into BW4472 case. Gently… We used two nuts per stud and slowly backed them out and then put them into the new case using some thread locker. Not a lot of threadlocker…
8)Install Gasket. I used some Transmission installation grease to hold the gasket in place. Seemed to work well.
9)Place T Case on motorcycle jack. Line up. We put grease on studs for ease of sliding through.
10) We sort of manhandled it in to position. Bolt up. Tighten down. Getting a torque wrench in there could be tricky. We just tightened down in a “every other” pattern”. Bolt up torsion bar
11) Check all hardware is tight
12) Lower down transmission and bolt up transmission mount. Fill Transfer case with oil.
You can attach both drive shafts now or do electric. I opted to add driveshafts
13)Add front drive shaft and rear driveshaft.
14) If you opted to use the existing yoke on your van, you will need to grind out the yoke to receive the larger bearings on the driveshaft. I DON’T RECOMMEND THIS. I recommend to getting the right yoke. We ground it out…and it worked ok.
Take your VSS connector you got from the junkyard and wiring. This is the fun part. You will need to determine which VSS connector from your van actually is the speed sensor. I simply put some connectors on the exposed wires and tested it. When the speedo worked, I was golden. I then used heat shrink to connect the wires. My polarity didn’t seem to matter. YMMV.
Now, you will have a lot of wire left over from the NP136 connections. What I did was tie it all up and tape it into the frame with zip ties. See photos.
Last edited by Meterpig
on November 27th 2015, 11:02pm, edited 1 time in total.