Auto to manual tranmission swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BigRed Beast · 11-08-2009, 12:18 PM

Hey...

Have a '72 4x4 Blazer with a TH350 fitted to a stock 350. My son--it's his first car--wants to swap the tranny to a stock 4 speed--a 465? We lucked in to a donor track, another '72 Blazer with said 4 speed,so we thought it best to pull the parts off the donor and have them checked out prior to pulling the driver apart.

The question de jour is whether we go through the "new" tranny and its mated tranfer case, and bolt them in as one, or do we bolt the tranny up to the driver's transfer case? Would the TH350 be bolted to a 205 and the 465 bolted to a 208?

I searched the forums--I can't believe no one's done this and written it up, but the search engine in our forum gave me no matches (!), so here I am. Any been-there-done-that advice would be welcomed!

DB

Critter · 11-08-2009, 02:21 PM

I haven't done it personally, but I can tell you that the two transfer cases aren't 100% identical. The manual tranny NP205 should have a 10 spline input shaft to match the 10 spline output of the sm465. The 350 style np205 should have a 27 spline input shaft to match the th350 output. These parts can be swapped out between cases (which should be identical), but you have to tear the np205s down pretty far to do it. Not too hard, just takes some time and patients.

EDIT: Just reread your post. As long as both the drive trains are stock 72 setups then what I said applies. I'm pretty sure the sm465 was offered in front of a np208, but it wasn't until sometime in the early 80s when the np208 was introduced, and it would have been a 32 spline setup.

Lots of good info here...

http://www.advanceadapters.com/resources.html

BigRed Beast · 11-10-2009, 10:59 AM

So, the best way to do this would be to take the mated transfer case and 4 spd tranny out, service them, then remove the TH350 and transfer case and replace with the donor stuff. Nice to have a donor, for sure.

BTW, where are the ID #'s for the transfer case located?

My son and his buddy spent 5 hours on Saturday and 4 hours on Sunday working on the removal from the donor. They were up to their ears in muck--just trying to find the bolts was an adventure. They ended on Sunday with the cross members out, the flywheel cover off, drive lines off and the transfer case out--and about ten pounds of greasy dirt piled around them. This weekend they go after the tranny--or so they say. Quite the job, definitely more than they bargained for!

Thanks for your input...

11-08-2009, 12:18 PM	#1
BigRed Beast Registered User Join Date: Aug 2007 Location: Parker, CO Posts: 140	Auto to manual tranmission swap Hey... Have a '72 4x4 Blazer with a TH350 fitted to a stock 350. My son--it's his first car--wants to swap the tranny to a stock 4 speed--a 465? We lucked in to a donor track, another '72 Blazer with said 4 speed,so we thought it best to pull the parts off the donor and have them checked out prior to pulling the driver apart. The question de jour is whether we go through the "new" tranny and its mated tranfer case, and bolt them in as one, or do we bolt the tranny up to the driver's transfer case? Would the TH350 be bolted to a 205 and the 465 bolted to a 208? I searched the forums--I can't believe no one's done this and written it up, but the search engine in our forum gave me no matches (!), so here I am. Any been-there-done-that advice would be welcomed! DB __________________ Big Red Beast 1972 Blazer CST AC/Auto/4x4 "Project" 1997 F 350 CC Powerstroke "The Great White"

11-08-2009, 02:21 PM	#2
Critter Future TOTM Winner Join Date: Aug 2006 Location: Bulverde, TX Posts: 2,692	Re: Auto to manual tranmission swap I haven't done it personally, but I can tell you that the two transfer cases aren't 100% identical. The manual tranny NP205 should have a 10 spline input shaft to match the 10 spline output of the sm465. The 350 style np205 should have a 27 spline input shaft to match the th350 output. These parts can be swapped out between cases (which should be identical), but you have to tear the np205s down pretty far to do it. Not too hard, just takes some time and patients. EDIT: Just reread your post. As long as both the drive trains are stock 72 setups then what I said applies. I'm pretty sure the sm465 was offered in front of a np208, but it wasn't until sometime in the early 80s when the np208 was introduced, and it would have been a 32 spline setup. Lots of good info here... http://www.advanceadapters.com/resources.html __________________ 72 Chevy CST K5 HIGHLANDER BLAZER Getting a 6.0,NV4500,NP205,14BFF (Currently laying all over the place in little pieces) 72 Chevy swb step-side "LS" 6.0 Here's a build thread of sorts 2002 HD2500 Crew Cab, 8.1L Allison 4x4 Daily Driver Check it out www.lsdyno.com Last edited by Critter; 11-08-2009 at 02:28 PM.

11-10-2009, 10:59 AM	#3
BigRed Beast Registered User Join Date: Aug 2007 Location: Parker, CO Posts: 140	Re: Auto to manual tranmission swap So, the best way to do this would be to take the mated transfer case and 4 spd tranny out, service them, then remove the TH350 and transfer case and replace with the donor stuff. Nice to have a donor, for sure. BTW, where are the ID #'s for the transfer case located? My son and his buddy spent 5 hours on Saturday and 4 hours on Sunday working on the removal from the donor. They were up to their ears in muck--just trying to find the bolts was an adventure. They ended on Sunday with the cross members out, the flywheel cover off, drive lines off and the transfer case out--and about ten pounds of greasy dirt piled around them. This weekend they go after the tranny--or so they say. Quite the job, definitely more than they bargained for! Thanks for your input... __________________ Big Red Beast 1972 Blazer CST AC/Auto/4x4 "Project" 1997 F 350 CC Powerstroke "The Great White"



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