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Tech question - trans swap

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aquaelvis

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I finally found a used set of tires and I'll be going ot get the K5 on Thursday! :D
One of the things I want to do is switch the trans. It has a 4 speed now and I'd rather have an automatic.
So if anyone is bored and wants to school me on the swap I'd appreciate it.
I was told I should look for a good donor blazer from '73 to 78? (wheel bases are the same- can use the drive shafts) Correct? Or is it easier to just get new drive shafts?
Do I want a turbo 350 or something else? (400 or 700r4?) I need to know what parts I will need. What transfer case? (203 or 205? difference?)
I was thinking of just doing a floor shifter. In the future I may want to switch the column but right now I think the floor shift would be the easier way to go. (I'll keep an eye out for a stock column from an auto)
I want to start getting the parts together and looking for deals on donors so any help would be great. (keep it simple... I've never done a trans swap)
 
4 speed is pretty short, so you'll need the driveshafts from the donor as far as I know. Do you want an overdrive? What engine is in the truck? I've never physically done a trans swap, so hopefully someone more knowledgeable will chime in.

Basically:

TH350 - 3 spd, no overdrive (PRND21)
TH400 - 3 spd, no overdrive, stronger than the TH350
TH700r4 - 3 spd with overdrive, (PRN(D)D21) (Will need proper kick-down/TV cable adjustment so as to not roast the trans, a fluid cooler is a good investment)

NP203 - Full Time 4x4, Chain driven, heavy.
NP205 - Part Time 4x4, Gear Driven, not so heavy.

Unless you're running a big block, you probably don't need the TH400, but it can't hurt. Most on here will say that the 205 is the better t-case, I'm running a 203 with a part-time modification in my K5 with no problems, so that's up to you.

While the wheelbases are the same, the length of the trans/t-case combo changes, so the driveshaft length will change. So if you have a donor with the trans/t-case combo you want, get the driveshafts and crossmembers as well.

Hope this helps.
 
It has a 350.
Not sure if I need an OD... lots of cars and trucks have the t350 so I assume OD is not needed.

Can we have a little transfer case for dummies? (I know, I know... I should know this)
NP203 - Full Time 4x4, Chain driven, heavy.
NP205 - Part Time 4x4, Gear Driven, not so heavy.
Click to expand...

What is the deal with full time 4x4 VS part time?

Does anyone know for sure what years have the same WB as the '72?
 
aquaelvis said:
It has a 350.
Not sure if I need an OD... lots of cars and trucks have the t350 so I assume OD is not needed.

Can we have a little transfer case for dummies? (I know, I know... I should know this)

What is the deal with full time 4x4 VS part time?

Does anyone know for sure what years have the same WB as the '72?
Click to expand...

I have a TH350 in my '73, only time the overdrive would be nice is when cruising at 70 on the highway, which I don't do very often, so having no OD doesn't bother me.

For the NP203, the Full-time 4WD means that the front driveshaft is always turning, the front hubs have drive slugs, and that there is no 2WD (unless you have unlocked front hubs, and put it in one of the Loc positions, which is bad for the t-case, or you put in a part-time kit). the shift pattern is Low-Loc, Low, Neutral, High, High-Loc. When in the normal High or Low positions, there is some slippage/difference allowed between the speeds of the front and rear axle speeds, which means you can run it on the street. Once in one of the Loc positions, the power output/speed is locked to 50/50 front and rear, and the t-case no longer acts as a differential. This t-case is cool for icy or rainy conditions in full-time 4WD.

For the NP205, Part time means that the shift pattern is 4-Low, Neutral, 2-High, 4-High. Which means regardless of having lockouts or drive slugs in the front axle, running in 2WD will only turn the rear driveshaft, which is cool on the street, and then you just drop into 4WD when needed.

As for the wheelbase question, I'm assuming it's for driveshaft lengths, and I have no clue.
 
Just a note, if you have a sm465 and the floor shifter, your old column is worth some good $$$.

What you want to do with the truck should dictate what trans you choose. I've done a trans swap the other way since I wanted the manual. You'll need a new radiator or a separate external trans cooler and plumbing. If you stick with the floor shift, that's probably the least hassle especially if you keep the clutch pedal on the floor and don't try to swap it out.

If you drive over 55mph anywhere, I don't see how you cannot need an overdrive unless you have the 3.08 highway gears or stock tires. I had a th350 with 3.08 gears and it still would get too hot on the freeway if I drove longer than 20 minutes at Ca highway speeds ( 65+)
 
Not trying to be rude. But use the search function, there's a ton of info on tranny swaps already here. You could spend a whole day reading through it all. It all boils down to personal preference and how much $$ you want to spend.
 
First off, the wheel base between 69-72 blazers is different than 73-91 blazers.

Second, i've been told that the SM465/205 is the exact same length combo as a TH350/205 so no driveshaft mods are required. You should PM RyanB as he swaps between 465 and 350 all the time and he's who told me they are the same lengths. I'm sure the crossmember sits in a different location based on which combo you're running but that's an easy cure.
 
4X4HIGH said:
First off, the wheel base between 69-72 blazers is different than 73-91 blazers.

Second, i've been told that the SM465/205 is the exact same length combo as a TH350/205 so no driveshaft mods are required. You should PM RyanB as he swaps between 465 and 350 all the time and he's who told me they are the same lengths. I'm sure the crossmember sits in a different location based on which combo you're running but that's an easy cure.
Click to expand...

And this is why I hoped someone else would chime in. Thanks!
 
IIRC the wheel base on the 69-72 blazers is 102" and the 73-91 blazers are 106.5"
 
4X4HIGH said:
IIRC the wheel base on the 69-72 blazers is 102" and the 73-91 blazers are 106.5"
Click to expand...

Actually it's 104" and 106.5"

Can't believe I actually knew something that Scott didn't :yikes:

That will never happen again!


:D


:usaflag:
 
Greg72 said:
Actually it's 104" and 106.5"

Can't believe I actually knew something that Scott didn't :yikes:

That will never happen again!


:D


:usaflag:
Click to expand...

Sorry i let you down Greg, this wasn't engine related tech so excuse my lack of knowledge in this department. :D

I thought i remembered that the 1st gens had close to a 4" difference in wheel base, guess i was wrong. :p:
 
Ditto what Chef Bear said.........the SM465/205 adapter is longer making up the difference in length. Crossmember stays in the exact same spot.
 
I found a guy who is parting out a 78 K5. It has a turbo 350 & NP205. He wants $450 for the tranny and t-case. Says it is all running.
So if I decide to do it, I need the trans, t-case, drive shafts, cross member and what else?

Should I get the column or pedal assy? I don't think I want to mess with it right now but down the road I might want to switch the column but I think I'd rather have one from a 72?
For right now with my time and skill I'd be happy to get the swap done and the K5 back on the road.
 
You will need the column or a floor shifter since a 4 speed column can't be used with an auto trans.
 
If you do switch columns, you want a 69-72 column. The later stuff is way different. You should be able to find an auto column for pretty cheap.
 
Any 69-72 column from an automatic should work right? (truck, blazer, 2 or 4 wd?)

Anyone know a cheap/easy way to set up a floor shifter? Is there a model or year that will work? (other than buying something new off the shelf)
 
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