Swap TH350 for 700R4 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bluec10 · 01-16-2004, 12:55 AM

Someone has got to have done this...

The TH350 in my '76 is getting pretty tired. It's leaking from the back end and there's a bit of slippage in reverse.

I could pick up a TH350 pretty easily, but I was wondering how easy it would be to swap in a late 80's TH700R4. Has anyone done this? Will it require a new driveshaft? Different linkages and cables?

bigblock73 · 01-16-2004, 01:05 AM

I did this swap. But I am not finished (in the middle of a body off resto), but can tell you what I know.

You will have to slide back the trans x-member and drill new holes to mount it. You will also need to modify your carb in order to run the TV cable required for this trans. Bowtie Overdrives has an excellent site with tons of information, might want to swing by there.

The trans cable should be fine, and I believe the driveshaft should swap out as well. You will need to calibrate your speedo with the appropriate trans gear as well.

That is a quick rundown, maybe others will chime in as well.

Opper77 · 01-16-2004, 03:24 AM

driveshaft will need to be shortened, the x-member will move, most (?) 700r4 have electronic lockup converters I think so you'll need a module or something to control that if you want that feature(unless you have a th350c already) , maybe a new flexplate depending on your bolting arrangement, speedo gear I think only changes with rear end gears, but I could be wrong there....I haven't got to that point on mine yet either....

I'm going from a 700r4 to a th400 so I'm backwards from you, but I think mostly the same things change

maineiac · 01-16-2004, 09:56 AM

It depends upon if you have a short shaft 350 or long. I just went back to a 350 when my 700r4 went to lunch but my drive shaft was not cut the only mods that had been done was to move the cross member back and use the holes that were the back for the front and drill 2 new for the back. The 700r4 is actually just an inch or two shorter than the long shaft 350 so the drive shaft will be okay if you have a long shaft not sure if you have a short shaft if you might have to cut it or get one from a junk yard. Lots of people here have done it I am one of the few that went back to originall just too many ponies for the early model 700r4. If you go to www.73-87.com and check out the info there.

Steve

bluec10 · 01-16-2004, 02:19 PM

Thanks for great info guys - the links look very helpful.

mcmlxix · 01-16-2004, 03:43 PM

What is the length of the drive shaft from center of U-joint to center of U-joint on a short bed with a stock TH350/v8 combo?

01-16-2004, 12:55 AM	#1
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Swap TH350 for 700R4 Someone has got to have done this... The TH350 in my '76 is getting pretty tired. It's leaking from the back end and there's a bit of slippage in reverse. I could pick up a TH350 pretty easily, but I was wondering how easy it would be to swap in a late 80's TH700R4. Has anyone done this? Will it require a new driveshaft? Different linkages and cables? __________________ 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.

01-16-2004, 01:05 AM	#2
bigblock73 yeller Join Date: Oct 2001 Location: Twin Cities Posts: 13,824	I did this swap. But I am not finished (in the middle of a body off resto), but can tell you what I know. You will have to slide back the trans x-member and drill new holes to mount it. You will also need to modify your carb in order to run the TV cable required for this trans. Bowtie Overdrives has an excellent site with tons of information, might want to swing by there. The trans cable should be fine, and I believe the driveshaft should swap out as well. You will need to calibrate your speedo with the appropriate trans gear as well. That is a quick rundown, maybe others will chime in as well. __________________ Jeff 73-87.com 73-87.com Facebook page 73-87 cab corner 6x9 speaker brackets for sale 67-72 cab corner speaker brackets for sale 47-54 cab corner speaker brackets for sale

01-16-2004, 03:24 AM	#3
Opper77 Ob-Gyn Kenobi Join Date: Aug 2003 Location: Edmonton, Alberta Posts: 489	driveshaft will need to be shortened, the x-member will move, most (?) 700r4 have electronic lockup converters I think so you'll need a module or something to control that if you want that feature(unless you have a th350c already) , maybe a new flexplate depending on your bolting arrangement, speedo gear I think only changes with rear end gears, but I could be wrong there....I haven't got to that point on mine yet either.... I'm going from a 700r4 to a th400 so I'm backwards from you, but I think mostly the same things change __________________ '85 GMC Shortbox... I used to have a firm handle on life....then it broke off.

01-16-2004, 02:19 PM	#5
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Thanks for great info guys - the links look very helpful. __________________ 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.

01-16-2004, 03:43 PM	#6
mcmlxix Collector of Projects Join Date: Apr 2003 Location: Las Vegas Posts: 3,106	What is the length of the drive shaft from center of U-joint to center of U-joint on a short bed with a stock TH350/v8 combo? __________________ Rich 1972 K5 Blazer CST Click HERE D60 BIG BRAKE UPGRADE Click HERE

01-16-2004, 09:56 AM	#4
maineiac Registered User Join Date: May 2003 Location: South Carolina Posts: 104	It depends upon if you have a short shaft 350 or long. I just went back to a 350 when my 700r4 went to lunch but my drive shaft was not cut the only mods that had been done was to move the cross member back and use the holes that were the back for the front and drill 2 new for the back. The 700r4 is actually just an inch or two shorter than the long shaft 350 so the drive shaft will be okay if you have a long shaft not sure if you have a short shaft if you might have to cut it or get one from a junk yard. Lots of people here have done it I am one of the few that went back to originall just too many ponies for the early model 700r4. If you go to www.73-87.com and check out the info there. Steve

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