4X4 Manual to Automatic Transmission Conversion

[RipMeyer]

Copied from Spencers Website


Manual to Automatic Conversion (with a bit of humor)

When we got this truck we didn't know what was wrong with it, only that it would not move. We got it started and quickly figured out it was something in the transmission or transfer case. It ended up being a toasted output shaft and coupler. This was cool to us as my wife has bad knees and couldn't push the damn clutch pedal anyway. For that matter I could barely push the manual clutch to the floor. So off we went into the hell that is a manual (SM465) to automatic (TH350) conversion. I decided to go with a TH350 instead of a TH400 because I felt the little small block had enough work to do pulling around a over 5000lb truck without making it do even more work by running the power robbing TH400. If I had a big block in this truck my decision would have been for the TH400.

Looking back this was not such a bad little adventure. I didn't know what I was doing and nobody I talked to could give me a straight answer on how to make the swap. I wasted months chasing my tail looking for the marriage unit that would hook up the mighty New Process Model 205 transfer case to the TH350. I looked in the junkyard and all over on the web with no luck. I found out the part you need to ask for is a stock Chevy 1979 or 1980 K5 Blazer transmission to transfer case adapter and Power Sleeve.

What you need:

1979 K5 Blazer transfer case adapter unit - $252.00 Trans Parts Inc.
1979 K5 Blazer Power Sleeve - $65.00 Dealer
Transmission dip stick - $7.50 Trans Parts Inc.
Transmission kick down cable - $7.50 Trans Parts Inc.
TH350 Transmission - $63.00 from the junkyard (got it on a ½ off day)
K5 blazer TH350 short 27-Spline output shaft - $Free at junkyard with the transmission
TH350 rebuild kit - $89.00 Carparts.com
Book on how to rebuild a TH350 - $12.00 at Pep Boys
Torque Converter - $Free with transmission at junkyard
Flex plate $12.00 from junkyard
Floor Shifter - $45.00 off of ebay
27-Spline Input Shaft for NP205 - $101.25 Drive Line Service
Gasket and seal kit for NP205 - $21.25 Drive Line Service
Transmission Cooler - $10.00 at junkyard
The total cost was about a little over $700.00.

How I did it

Remove all the manual stuff and the transfer case. The worst part of this was getting the clutch pedal assembly out. What a pain. All the other stuff was real easy.

Support the engine with a jack. I used a block of wood under the rear of the engine as the jacking point.

Let the truck sit for at least 3 months while you chase your tail looking for advise on how to do the swap and finding out what parts you will need will need. Go the local 4x4 "experts" and find out they don't know nothing 'bout nothing.

Half ass figure out what you are doing and start buying stuff.

Go to junkyard. (on ½ off day if you can wait) Find a 4x4 Blazer with a cracked (ruined) TH350. Find perfectly good TH350 in a van two isles down. Pull transmission from van and then drag it back to the Blazer to compare the two. See the Blazer transmission has a different output shaft. Tear down the Blazer transmission in the dirt in 105 degree heat to get to the output shaft. Find an almost new flex plate and torque converter on a gutted old farm truck and grab those too. Note: Make sure when you loosen the last bolt on the torque converter that your head is in it's path when it lets go so you can have cool scar on your forehead to talk about later. Make sure you get all the bolts that go to the flex plate and the torque converter or you will probably end up cutting some longer ones down make them work.

Buy book on how to rebuild a TH350 from Pep Boys.

Get a TH350 rebuild kit from www.carparts.com

Tear transmission apart and throw old output shaft in the trash. Make sure you do this before you realize that the van and the Blazer had a different type of bearing on the output shaft forcing you to go to Trans Parts and get the right one.

Take at least a week to put the transmission back together. Note: DO NOT lay finger on the transmission unless you have had at least two beers to settle your nerves. Worry about whether you did it right for the next couple of months while you look for a transfer case adapter.

Call Advanced Adapters and try to get the adapter you think you need. Find out you have been smoking crack and that the only thing you need from Advanced Adapters is . . . nothing.

Call Drive Line Service and get a new 27-spline input shaft and a gasket set for the NP205. Have a friend help you pick that cast iron beast up and put it on the tailgate of the truck for a proper teardown and shaft swap. Drink two beers and start tearing it apart carefully. Realize there isn't a damn thing in there you can hurt and begin to work more aggressively.

After calling everyone you know besides the dealer and getting prices from $300 to $500 dollars for the transfer case adapter break down and have a buddy (Rick at Trans Parts) order it from the dealer for you for about $250.

Have your wife get the power sleeve from the dealer for you.

Go to junkyard and find a transmission cooler. We ran 3/8 aluminum line from the transmission through the frame rail up to the cooler and back. You'll need a small tube cutter and flare tool for this.

Flush the torque converter with some fresh fluid and then mount it and flex plate up to the motor.

Install the transmission into truck. It's real heavy for one person to do. But after it sits on your chest for a while and it gets real hard to breath you will find the motivation to get it up there.
Attach the transfer case adapter to the transmission and then install the old cross member and the old transmission mounts. No drilling is required, nor are new transmission mounts or a new cross member. This is contrary to popular belief.

Mount the NP205 and then install the drive shafts. Yes the drive shafts bolt right up See the difference in the length of the adapters? Well that makes up for the difference in the length of transmissions and the stock drive shafts fit perfectly.

Fill the NP205 with nearly a gallon of gear oil. Man that thing is huge!

Install the dip stick, kick down cable, and vacuum lines. Throw about 4 quarts of AFT in the transmission not knowing that it actually takes about 11.

Install the shifter of your choice, or budget in this case. Here is the automatic shifter in the mounting location we choose for it on the floor. I put it a little too close the transfer case lever but it works just fine.
Fire it up and check the fluid.

Road test it.

When we first drove the truck the transmission shifted so smooth you could barely even feel it shift. After about 300 miles it started shifting a lot firmer. I guess it had to break in a little. We are very happy with the results of this conversion.