Tranny education - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DoobieBrother · 04-28-2007, 11:14 PM

I'm doing some planning for an upcoming tranny. My tranny knowledge is minimal at best. From what little I've read so far, I think I want a 700R4. Here's the question, though. Right now I have a 350 in the truck. I haven't fully decided whether that will stay and be rebuilt to be a lot more than it is now, or of if there it will eventually be replaced with a big block. I don't want to do the tranny twice. So, the question is, are the sizes and bolt patterns the same. Or if I put a 700R4 in now on this 350, will I be screwed if I turn around and do a big block for it. So same bolts, new bell housing, or some other situation all together?

jeffspower · 04-28-2007, 11:51 PM

SBC & BBC are the same bellhousing pattern. You might have to drill 3 new holes in the flywheel of the BBC for the 700r4 converter bolts, depending on what flywheel you have. You can't run the BBC Qjet as it doesn't have the "arm" to hook up the TV (detent) cable.

mnunn454 · 04-29-2007, 09:35 AM

Some other differences between the TH350 and 700R4:

- 700R4 is a longer tranny. Requires mod or replacing the tranny cross member and shortening the driveshaft.
- 700R4 has a throttle valve cable that connects to bellcrank on the carb. The TH350 usea a vacuum line. The TV cable is a "challenge" to get adjusted right. Failing to do so can shorten the 700's life, or kill it completely.
- Stock, both tranny's are about the same strength, but it's a little cheaper to upgrade the TH350 for BBC strength than to do the same for the 700.
- TH700's are less tolerant to overheating than a TH350. Aux tranny cooler is strongly recommended.
- Don't get a 85 or 86 TH700. They're weaker than the 87 and up models.
- Besides the overdrive, the TH700 has an electrically controlled converter lockup that'll save you additional fuel on the highway.
- Stall converters for the TH700 are more costly and less plentiful (2nd hand) than the TH350/400 converters.
-700R4 tranny has a lower low gear and a higher high gear, so depending on your current ratio it may require a ring and pinion swap to keep the engine in it's best operating range.

Hope it helps.

**special-K** · 04-29-2007, 10:06 AM

I gots me some edumacations,too.

piecesparts · 04-29-2007, 10:41 AM

I took my 350C out of the 84 and installed a 700 in it's place, the length difference was ot that much different, but since I had lowered the truck, I did have to change the driveline. There are two differnt lengths of 350 tranny tubes and if you have the longer one, the changeover is not that bad. The mounting bracket will have to be moved for the rear tranny mount and the changeover for the cable is needed, but that is not hard. My tranny is mounted behind a 400 plus horsepower stroker motor and it is handling it well. However, I went ahead and replaced the planetary and clutches in it to ensure the longevity. I would recommend a tranny upgrade BEFORE you insatall it to be ready for the big block. I changed my rear end gearing from a 3.42 to a 3.73 gear and I get around 2500 RPM at 70 MPH, that puts me right in my power curve for the engine. It is one of the best things I ever did for the truck.

04-28-2007, 11:14 PM	#1
DoobieBrother Registered User Join Date: Aug 2006 Location: US Posts: 184	Tranny education I'm doing some planning for an upcoming tranny. My tranny knowledge is minimal at best. From what little I've read so far, I think I want a 700R4. Here's the question, though. Right now I have a 350 in the truck. I haven't fully decided whether that will stay and be rebuilt to be a lot more than it is now, or of if there it will eventually be replaced with a big block. I don't want to do the tranny twice. So, the question is, are the sizes and bolt patterns the same. Or if I put a 700R4 in now on this 350, will I be screwed if I turn around and do a big block for it. So same bolts, new bell housing, or some other situation all together?

04-28-2007, 11:51 PM	#2
jeffspower Well, Whoop-dee-do! Join Date: Mar 2003 Location: Easton, Mo. pop.- me & scarcely a few others Posts: 2,302	Re: Tranny education SBC & BBC are the same bellhousing pattern. You might have to drill 3 new holes in the flywheel of the BBC for the 700r4 converter bolts, depending on what flywheel you have. You can't run the BBC Qjet as it doesn't have the "arm" to hook up the TV (detent) cable. __________________ '68 GMC shortbox 4x4 350/SM465/T221- bought it in '83 SOLD '72 K20 500 Cad/TH400/NP205 SOLD '92 Chevy 2500 6.5 mech TD 4L80E crusty daily driver '72 Monte Carlo... sweet low mile toy '11 Dodge Challenger IE 392 6spd... midlife car

04-29-2007, 09:35 AM	#3
mnunn454 Registered User Join Date: Dec 2006 Location: Rhode Island Posts: 602	Re: Tranny education Some other differences between the TH350 and 700R4: - 700R4 is a longer tranny. Requires mod or replacing the tranny cross member and shortening the driveshaft. - 700R4 has a throttle valve cable that connects to bellcrank on the carb. The TH350 usea a vacuum line. The TV cable is a "challenge" to get adjusted right. Failing to do so can shorten the 700's life, or kill it completely. - Stock, both tranny's are about the same strength, but it's a little cheaper to upgrade the TH350 for BBC strength than to do the same for the 700. - TH700's are less tolerant to overheating than a TH350. Aux tranny cooler is strongly recommended. - Don't get a 85 or 86 TH700. They're weaker than the 87 and up models. - Besides the overdrive, the TH700 has an electrically controlled converter lockup that'll save you additional fuel on the highway. - Stall converters for the TH700 are more costly and less plentiful (2nd hand) than the TH350/400 converters. -700R4 tranny has a lower low gear and a higher high gear, so depending on your current ratio it may require a ring and pinion swap to keep the engine in it's best operating range. Hope it helps. __________________ 69 C-10 SWB Fleetside 454/TH400 (For Sale) http://67-72chevytrucks.com/vboard/c...ct=1299&cat=12 70 El Camino 454 TH700 29 Model A 4-DR Sedan Deluxe Last edited by mnunn454; 04-29-2007 at 09:36 AM.

04-29-2007, 10:06 AM	#4
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,858	Re: Tranny education I gots me some edumacations,too. __________________ "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 ~

04-29-2007, 10:41 AM	#5
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: Tranny education I took my 350C out of the 84 and installed a 700 in it's place, the length difference was ot that much different, but since I had lowered the truck, I did have to change the driveline. There are two differnt lengths of 350 tranny tubes and if you have the longer one, the changeover is not that bad. The mounting bracket will have to be moved for the rear tranny mount and the changeover for the cable is needed, but that is not hard. My tranny is mounted behind a 400 plus horsepower stroker motor and it is handling it well. However, I went ahead and replaced the planetary and clutches in it to ensure the longevity. I would recommend a tranny upgrade BEFORE you insatall it to be ready for the big block. I changed my rear end gearing from a 3.42 to a 3.73 gear and I get around 2500 RPM at 70 MPH, that puts me right in my power curve for the engine. It is one of the best things I ever did for the truck.



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