68 k20 4 speed swap to automatic - The 1947 - Present Chevrolet & GMC Truck Message Board Network

neil alan wicks · 04-25-2008, 08:12 AM

Hey buddy's will my stock 4 speed 1968 k20 trans fer case bolt up to a automatic transmision with mounts and drive line mod's.?? or what is the best way to to swap 4 speed for an automatic transmision????

sweet70beast · 04-27-2008, 08:09 AM

The simple answer is no. The t-case adapter is different between the two and the 4 speeds output shaft has (I think) 10 splines and the auto has (i think) 30 splines. It will take some scrounging but the thing to do is find a trans, adapter and t-case and even driveshafts from an auto truck. If you get one with a 205 t-case your stock driveshafts might work if the overall length of the auto/t-case and manuel/t-case is the same. If you get one with a 203 t-case I think the driveshafts have to be shorter because the t-case is longer. If you get one with a 208 It has a slip yoke so your driveshafts won't work.

**special-K** · 04-27-2008, 01:31 PM

I don`t believe the Rockwell case was ever mated to an automatic.I could be wrong.If they were it would be a rare find.Just find a complete auto/trans conversion.I`d buy a donor vehicle to get the whole deal.

sweet70beast · 04-27-2008, 06:05 PM

I forgot that these had rockwell t-cases, so yeah the only way to do it is an entire swap. 4wd didn't get automatics until 71 before that all GM 4x4s were manuels.

**special-K** · 04-28-2008, 03:14 PM

`70 had TH350/NP205s.

Robert1970C20rstbukt · 05-05-2008, 07:37 AM

Yep my K20 Suburban came with a 350/TH350/NP205 when it was new.

1969 GMC · 05-05-2008, 05:37 PM

Quote:

Originally Posted by Robert1970C20rstbukt

Yep my K20 Suburban came with a 350/TH350/NP205 when it was new.

I understand his point, though. There was never a Rockwell tcase behind an automatic. FWIW, I thought you could get an auto in a '69, because of the K5.

**jerry moss** · 05-05-2008, 05:45 PM

some of the early K/5s had dana t-cases so auto trans might have been an option.

04-25-2008, 08:12 AM	#1
neil alan wicks Registered User Join Date: Jan 2006 Location: morrow bay , ca Posts: 5	68 k20 4 speed swap to automatic Hey buddy's will my stock 4 speed 1968 k20 trans fer case bolt up to a automatic transmision with mounts and drive line mod's.?? or what is the best way to to swap 4 speed for an automatic transmision????

04-27-2008, 08:09 AM	#2
sweet70beast Registered User Join Date: Sep 2006 Location: Shelley Idaho Posts: 876	Re: 68 k20 4 speed swap to automatic The simple answer is no. The t-case adapter is different between the two and the 4 speeds output shaft has (I think) 10 splines and the auto has (i think) 30 splines. It will take some scrounging but the thing to do is find a trans, adapter and t-case and even driveshafts from an auto truck. If you get one with a 205 t-case your stock driveshafts might work if the overall length of the auto/t-case and manuel/t-case is the same. If you get one with a 203 t-case I think the driveshafts have to be shorter because the t-case is longer. If you get one with a 208 It has a slip yoke so your driveshafts won't work. __________________ 1970 Nova 327/T5 (my 1st car) 1971 K-20 350/350/205 (winter DD) 1953 GMC Suburban 1968 Chevy Bel Air 1976 Chev C-10 1972 Skylark (suncoupe) 1 of 3943 made

04-27-2008, 01:31 PM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 68 k20 4 speed swap to automatic I don`t believe the Rockwell case was ever mated to an automatic.I could be wrong.If they were it would be a rare find.Just find a complete auto/trans conversion.I`d buy a donor vehicle to get the whole deal. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

04-27-2008, 06:05 PM	#4
sweet70beast Registered User Join Date: Sep 2006 Location: Shelley Idaho Posts: 876	Re: 68 k20 4 speed swap to automatic I forgot that these had rockwell t-cases, so yeah the only way to do it is an entire swap. 4wd didn't get automatics until 71 before that all GM 4x4s were manuels. __________________ 1970 Nova 327/T5 (my 1st car) 1971 K-20 350/350/205 (winter DD) 1953 GMC Suburban 1968 Chevy Bel Air 1976 Chev C-10 1972 Skylark (suncoupe) 1 of 3943 made Last edited by sweet70beast; 04-27-2008 at 06:07 PM.

04-28-2008, 03:14 PM	#5
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 68 k20 4 speed swap to automatic `70 had TH350/NP205s. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

05-05-2008, 07:37 AM	#6
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	Re: 68 k20 4 speed swap to automatic Yep my K20 Suburban came with a 350/TH350/NP205 when it was new. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck

05-05-2008, 05:45 PM	#8
jerry moss Born Psycho Join Date: Feb 2001 Location: brentwood,cal,usa Posts: 4,936	Re: 68 k20 4 speed swap to automatic some of the early K/5s had dana t-cases so auto trans might have been an option. __________________ jerry moss 72 cheyenne super K20- tilt,tach,vacuum,speedwarning,buckets,shoulder belts,am/fm,tow hooks,bumper guards,toolbox,aux. fuel tank,posi front and rear,plus other goodies!!! SOLD 69 suburban K20-tilt,tach,vacuum,speedwarning,buckets,shoulder belts,am/fm,4 inch all spring lift,4 speed, 14 bolt full floater, dana 44 HD,warn winch,posi front and rear,tow hooks,plus other goodies. 73/80 chevy/gmc K20 SB400,turbo 400,205,tilt,a-c,gas hog. 77 K/5 cheyenne blazer-daily driver/beater. SON HAS IT NOW BRENTWOOD,CALIFORNIA

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