Converting a 4 speed to an automatic

[Mike Phillips]

Anyone ever switch a 4 speed Blazer over to an automatic?

This would be removing a four speed transmission (SM465) with granny low hooked up to a  NP205 transfercase and replacing it with either a Turbo 400 or a Turbo 350, whichever would be the best fit/mate.

Mike

[Captkaos]

Either will fit the motor.  The TH400 would be stronger.  The output shaft would have to be a match to the T-case.  If I remember right the manual has different splines than what was offered in the autos.

[76_Scottsdale]

I just did a similar swap except I went to a 700R4. Your NP205 has a 10 spline input shaft , so you would need to install a 10 spline output shaft on the tranny. Keep in mind though to swap to a TH400 the TCase has to be machined to account for the larger bearings on the input shaft, but a Th350 with the right output shaft and adapter would bolt right up.

[VileZambonie]

Have you thought about a 700R4/NP208 swap?

[Mike Phillips]

I just did a similar swap except I went to a 700R4. Your NP205 has a 10 spline input shaft , so you would need to install a 10 spline output shaft on the tranny. Keep in mind though to swap to a TH400 the TCase has to be machined to account for the larger bearings on the input shaft, but a Th350 with the right output shaft and adapter would bolt right up.

I don't want this project to get complicated so I'd prefer to go the route that is completely bolt up.  I don't actually plan on doing much 4x4 stuff, especially rough stuff, mostly just a daily driver so Turbo 350 should be fine.

I did a normal tranny swap on my Milk Truck when I had it going from a Turbo 350 that completely gave up the ghost to a Turbo 400 and for that all I had to do was move the tranny crossmember mount about an inch and have the driveline cut and lengthened or shortened, don't remember now.



 

[Mike Phillips]

Another question...

Since the truck has a floor shifter, thus no column shifter, I could either R&R the column and replace with a column mounted shifter for an automatic or install a floor shifter.

The floor shifter sounds like a much easier way to go, perhaps a B&M or even a Lokar shifter.

Opinions?  Recommendations?  Suggestions?

Here's one of my favorite trucks... sold it a few years ago...

1971 3/4 Ton Chevrolet 4-Wheel Drive
396 Big Block Chevy - Big cam, 750 Holly Double Pumper, 2" Diameter Headers
Turbo 400 Automatic Transmission Short Shaft with a baby driveline to the Transfer Case
2-Ton Military Transfer Case
Corporate Rearend with 4:11 gears and Detroit Lockers
Dana 44 Front End with 4:11 gears and Detroit Lockers
12" I-Beam Rear Bumper with 4 foot Drop Hitch (To pull the Drag Boat)
4" Diameter Driveline Tubing Roll Bar
Custom Stainless Steel Fender Lips on front fenders to be legal
Custom Suspension Lift, Frame Lift and Body Lift.  Top of truck was about 7' 8"


This grainy photo was taken on the beach in Seaside, Oregon where it's legal to drive on the beach.

[VileZambonie]

If you're going to be using it as a daily driver the 700R4/208 is the best choice. You could probably buy a parts truck with that driveline dirt cheap giving you everythign you need.

[HAULIN IT]

Mike, I did this swap several times. Vile is on the right track I feel, get a rusty truck/frame with driveline maybe less motor sitting beside someones house. That way you have ALL of the parts. You can go to the salvage yard/friend & piece it together, but it would be simpler if you had the truck as a donor. As Kaos said, your t-case is a 205 10 spline male. To use a 205 t-case, you will need a rare th350 (26?)spline 205 t-case & support/adapter, if you want a th350. Or rarer 205 or do machine work for a th400. Your driveshafts will work. If you use a 203 t-case you will need different length shafts, but are much easier to find.The 208 can be a good option also. Changing the pedal assy. & column & gear indicator is no big deal (if you have the parts), the clutch safety switch wires(green) become it nutral safety switch wires. I feel getting the parts & "doing it right" is the way to go.Any Questions, Just Ask, Lorne   

[Mike Phillips]

Hey thanks for all the great advice guys, this morning I didn't think I was going to need your advice but it looks like I do now.

eBay Item:  260202972438

Me = showcargarage

I'm so excited!

[VileZambonie]

Mike didn't you have a 2wd blazer? BTW I saw that blazer on ebay...I'm always lookin

[ccz145a]

Most excellent!

[Mike Phillips]

Mike didn't you have a 2wd blazer? BTW I saw that blazer on ebay...I'm always lookin

Yes, I'm sad to say I wrecked it but I've found a new owner who's going to give it a good home, he's a Blazer guy too.

[Mike Phillips]

If you're going to be using it as a daily driver the 700R4/208 is the best choice. You could probably buy a parts truck with that driveline dirt cheap giving you everythign you need.

Okay, so if I understand you correctly, you're saying to remove both the transmission and the trasnfer case, these two items,

the four speed transmission (SM465) with granny low and a near indestructable NP205 transfercase

And locate a 700R4 transmission and a 208 transfer case?

Was kind of hoping to leave the transfercase since it's supposed to be in great condition.

[Mike Phillips]

If you're going to be using it as a daily driver the 700R4/208 is the best choice. You could probably buy a parts truck with that driveline dirt cheap giving you everythign you need.

Okay, I've only owned old trucks, this 1975 will be the newest truck I've ever owned, so if I want to find a 'parts' truck, which model and years will I be looking for?

We have a lot of wrecking yards around here and of course CraigsList, eBay and the trader papers are full of parts and parts trucks.

[Mike Phillips]

Since I haven't seen the truck in person, I'm guessing the transmission and transfer case are the "mated" style.

My 71 Chevy in the picture above had a 2 ton Military transfer case and a Short Shaft Turbo 400 with a baby driveline from the tranny to the transfercase which allowed for more lift.

If the current transmission is a mated style, then I'd really like to go the path of least resistance and that's to install an automatic transmission that will bolt right in its place.

At this time it's vitally important that I make the change so I can start driving it ASAP as I can't drive a manual transmission car as I have an artificial leg due to a little accident with my Drag Boat.  You can kind of see it in this picture where I'm wet-sanding a car called "The Titanic"



So I really need to make the swap not as fast as I can as I have an old Ford truck I can borrow but the sooner the better.