New Game Plan...th350 behind L6 250? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bluec10 · 02-01-2007, 02:51 PM

Ok, so I got a new brainwave. I have a TH350 out of a '76 GMC. The trans wouldn't shift in to 3rd when I took it out so I'm rebuilding it, mostly for the heck of it.

I was wondering if anyone else has put a TH350 behind a L6 engine. The truck currently has a three-on-the-tree trans. I have an automatic steering column that I want to install anyway. What else do I need to watch? What about driveshaft length?

Longhorn Man · 02-01-2007, 05:23 PM

they came like that..so I don't see any big deal in it.
Can't tell you about d/s length
You'll need an automatic X-member
tranny mount
cooler lines
rad with cooler or a dedicated tranny cooler
Linkages for the shifter
I'd just use a toggle switch for the back up lights personally... get one with a red LED in the end of the toggle so you won't forget they are on and look like a retard

67ChevyRedneck · 02-01-2007, 05:44 PM

^ I've been guilty of that quite a few times

I'd get everything mocked up and see where you're at with the driveshaft. I don't know about the th350, but when I put my 700R4 in (it had a 3spd manual) I had to change the yoke that went into the tranny, don't know if the 3 speeds and th350 are the same.

Ozark Tim · 02-01-2007, 06:40 PM

I owned one like this years ago and it is still in the circle of friends. You will need the shift linkeage set up from a 4X4 because the transmission will mount further rearward on the frame when coupling to a 6-cyl than it does with a V8. All the 4X4's with V8's are set back the same amount so it is my understanding that youd need that. As for the drive shaft, you will need to measure the distance from the center of the input yoke or U-joint at transmission now to the center of the central u-joint. Then after your install is complete measure and calculate the difference. Once that is done the drive shaft will need to be modified by a drive shaft shop and the correct input shaft for an automatic will need to replace the current one. It will be a shorter drive shaft overall. Back up light switch should be on your automatic column and other than the possibility of needing a new wire connector should be manageable. The worst thing I remember was that the original engine in mine was made for a manual tranny so there were no mounting holes in the block for a starter that is used on automatics. Maybe youll be lucky and yours is pre drilled and tapped. Tranny lines and a cooler or radiator with cooler provisions will also be required along with the correct cross brace and mount. The cross brace should fit to pre made holes already present.
Good luck with your project.
OT

02-01-2007, 02:51 PM	#1
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	New Game Plan...th350 behind L6 250? Ok, so I got a new brainwave. I have a TH350 out of a '76 GMC. The trans wouldn't shift in to 3rd when I took it out so I'm rebuilding it, mostly for the heck of it. I was wondering if anyone else has put a TH350 behind a L6 engine. The truck currently has a three-on-the-tree trans. I have an automatic steering column that I want to install anyway. What else do I need to watch? What about driveshaft length? __________________ Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.

02-01-2007, 05:23 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: New Game Plan...th350 behind L6 250? they came like that..so I don't see any big deal in it. Can't tell you about d/s length You'll need an automatic X-member tranny mount cooler lines rad with cooler or a dedicated tranny cooler Linkages for the shifter I'd just use a toggle switch for the back up lights personally... get one with a red LED in the end of the toggle so you won't forget they are on and look like a retard

02-01-2007, 05:44 PM	#3
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	Re: New Game Plan...th350 behind L6 250? ^ I've been guilty of that quite a few times I'd get everything mocked up and see where you're at with the driveshaft. I don't know about the th350, but when I put my 700R4 in (it had a 3spd manual) I had to change the yoke that went into the tranny, don't know if the 3 speeds and th350 are the same. __________________ Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride American Born, Country by the Grace of God 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! Last edited by 67ChevyRedneck; 02-01-2007 at 05:45 PM.

02-01-2007, 06:40 PM	#4
Ozark Tim Registered User Join Date: Aug 2004 Location: Oakville, MO Posts: 1,018	Re: New Game Plan...th350 behind L6 250? I owned one like this years ago and it is still in the circle of friends. You will need the shift linkeage set up from a 4X4 because the transmission will mount further rearward on the frame when coupling to a 6-cyl than it does with a V8. All the 4X4's with V8's are set back the same amount so it is my understanding that youd need that. As for the drive shaft, you will need to measure the distance from the center of the input yoke or U-joint at transmission now to the center of the central u-joint. Then after your install is complete measure and calculate the difference. Once that is done the drive shaft will need to be modified by a drive shaft shop and the correct input shaft for an automatic will need to replace the current one. It will be a shorter drive shaft overall. Back up light switch should be on your automatic column and other than the possibility of needing a new wire connector should be manageable. The worst thing I remember was that the original engine in mine was made for a manual tranny so there were no mounting holes in the block for a starter that is used on automatics. Maybe youll be lucky and yours is pre drilled and tapped. Tranny lines and a cooler or radiator with cooler provisions will also be required along with the correct cross brace and mount. The cross brace should fit to pre made holes already present. Good luck with your project. OT

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