1972 c20 3/4 ton - The 1947 - Present Chevrolet & GMC Truck Message Board Network

C203/4 · 01-08-2007, 03:35 PM

can anyone tell me how to tell what kind of transmission is supposd to be in my truck? i know it is a short shaft, and has the square 350 pan on the one in it now, plus a drain plug, not original i am assuming, will not shift into third, and i want to replace with a th350 short shaft, but not sure if that is good enough, no towing, or hauling, just regular daily driver. anyone near Austin texas have a nice used one untill i can get mine rebuilt?

Longhorn Man · 01-08-2007, 03:38 PM

if it has a kick down cable, it's a short shaft TH350 (which DID come stock with a drain plug)
If there is no kickdown, it's a TH400.

Robert1970C20rstbukt · 01-08-2007, 11:49 PM

That's a TH350, the one in my '70 K20 Suburban is original and it has a drain plug also. I don't think there was a short tail TH400, at least I've never seen one. The 400 in my truck is a 1967 long tail.

**WorkinLonghorn** · 01-08-2007, 11:56 PM

That's the only problem,that it won't shift into 3d?

poorboy · 01-09-2007, 12:41 AM

A short tail t400 came in alot of pass cars. There are long tail 400's that came in some trucks and older wagons anf 400's that came in 3/4 and 1 tons with no slip yokes.

skchevota · 01-09-2007, 12:46 AM

My 70 originaly had a short tail 400.... But it had a big block too.

RVFR · 01-09-2007, 01:10 AM

pretty sure mine is a short TH400 but its connected to a BB in a longhorn

72armyswbtruck · 01-09-2007, 02:35 AM

Go with a cheap $400 dollar rebuilt transmission from autozone, that's what my 350 replacement cost me

**WorkinLonghorn** · 01-09-2007, 08:49 AM

Who says you need a bebuilt? Unstick the governor,check the modulator.Check vac line to modulator. All real easy stuff,maybe 1 hour max.-cougar

C203/4 · 01-09-2007, 05:44 PM

yes the only problem....

**WorkinLonghorn** · 01-09-2007, 08:07 PM

Take the vac hose off at the modulator (on the trans). Any fluid? Then you need a new modulator. Uncrew it and screw in a new/used unit. Check the line for leaks.A vacuum leak on the modulator line will cause it to not shift up. Then if it still doesn't shift up take the round cover off the governor on the side of the trans.and free up the governor,cause they occasionally get stuck with grit. It will now shift up.
If not,post again.-cougar

01-08-2007, 03:35 PM	#1
C203/4 Registered User Join Date: Oct 2006 Location: Austin Texas Posts: 60	1972 c20 3/4 ton can anyone tell me how to tell what kind of transmission is supposd to be in my truck? i know it is a short shaft, and has the square 350 pan on the one in it now, plus a drain plug, not original i am assuming, will not shift into third, and i want to replace with a th350 short shaft, but not sure if that is good enough, no towing, or hauling, just regular daily driver. anyone near Austin texas have a nice used one untill i can get mine rebuilt?

01-08-2007, 03:38 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: 1972 c20 3/4 ton if it has a kick down cable, it's a short shaft TH350 (which DID come stock with a drain plug) If there is no kickdown, it's a TH400.

01-08-2007, 11:49 PM	#3
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	Re: 1972 c20 3/4 ton That's a TH350, the one in my '70 K20 Suburban is original and it has a drain plug also. I don't think there was a short tail TH400, at least I've never seen one. The 400 in my truck is a 1967 long tail. __________________ 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

01-08-2007, 11:56 PM	#4
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,883	Re: 1972 c20 3/4 ton That's the only problem,that it won't shift into 3d? __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

01-09-2007, 12:41 AM	#5
poorboy Senior Member Join Date: Jun 2006 Location: Oregon City, Or Posts: 758	Re: 1972 c20 3/4 ton A short tail t400 came in alot of pass cars. There are long tail 400's that came in some trucks and older wagons anf 400's that came in 3/4 and 1 tons with no slip yokes.

01-09-2007, 12:46 AM	#6
skchevota Registered User Join Date: Oct 2006 Location: Evans, Colorado Posts: 530	Re: 1972 c20 3/4 ton My 70 originaly had a short tail 400.... But it had a big block too.

01-09-2007, 01:10 AM	#7
RVFR New Member Join Date: Jan 2007 Location: Olympia, WA. Posts: 21	Re: 1972 c20 3/4 ton pretty sure mine is a short TH400 but its connected to a BB in a longhorn

01-09-2007, 02:35 AM	#8
72armyswbtruck Registered User Join Date: Feb 2004 Location: Idaho Posts: 4,033	Re: 1972 c20 3/4 ton Go with a cheap $400 dollar rebuilt transmission from autozone, that's what my 350 replacement cost me __________________ "Remember, They can Kill You, but they can't eat You, That's against the law!!!!!!!!!"

01-09-2007, 08:49 AM	#9
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,883	Re: 1972 c20 3/4 ton Who says you need a bebuilt? Unstick the governor,check the modulator.Check vac line to modulator. All real easy stuff,maybe 1 hour max.-cougar __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme. Last edited by WorkinLonghorn; 01-09-2007 at 08:49 AM.

01-09-2007, 05:44 PM	#10
C203/4 Registered User Join Date: Oct 2006 Location: Austin Texas Posts: 60	Re: 1972 c20 3/4 ton yes the only problem....

01-09-2007, 08:07 PM	#11
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,883	Re: 1972 c20 3/4 ton Take the vac hose off at the modulator (on the trans). Any fluid? Then you need a new modulator. Uncrew it and screw in a new/used unit. Check the line for leaks.A vacuum leak on the modulator line will cause it to not shift up. Then if it still doesn't shift up take the round cover off the governor on the side of the trans.and free up the governor,cause they occasionally get stuck with grit. It will now shift up. If not,post again.-cougar __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

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