th350 vs 700r4

[al's71gmc]

I've got a 71 gmc that i drive daily, and am fixing it up as I go. I'm wondering about swapping in a 700r4 to replace the turbo 350. My main reason for considering this trade is the extra gear and maybe a little better mpg. This truck fairly screams going down the hiway. Is this a swap that can be done without major modification? Any other issues I should be concerned about? Is there another 4 spd auto that would be a better swap?

[pjmoreland]

I replaced my TH350 with a 700R4 about 6 months ago. I am extremely happy with the 700R4. The first gear is nice and low which is a lot of fun, and overdrive really makes my truck run smooth on the highway. I went from about 12 MPG to about 16 MPG. I have a 3.73 differential, which I think is ideal for a 700R4.

I'd recommend taking a look at this FAQ thread:

http://67-72chevytrucks.com/vboard/s...d.php3?t=33266

[al's71gmc]

Thanks for the info. It would be great to get the extra 30% milage. I'd also like the lower gear for climbing, or rather for coming down. Even in low range I have to ride the brakes pretty hard on steep downgrades. Does the 700r4 hookup to the transfer case allright?
I just got this truck a few months ago. It has a recently rebuilt 350 engine and the tranny rear seal was leaking from sitting for awhile. I put in some seal conditioner and the leak has all but stopped. I just got some new procomp 305/70/16 mud terrains, and ordered a 4" lift for it yesterday. I've got a lot of interior work to do, as well as some body work and paint.
So many improvements to make, so little time, and even less money!!

[Gray Ghost]

The 4L80E is a much better/stronger tranny but there are fit issues with some trucks. If you are running more than 325 ponies under the hood I wouldn't advise the swap to the 700. There are folks who claim they can be buiolt to withstand the power, but I have yet to see one handle it in the real world. You are also looking at substantially more $$$ to repair that 700 versus the 350. The last 4 spped auto I had rebuilt cost me $1600.

I've had two 4 speed trannies from the 80's era and will never touch another one. I think of 'em as the same quality as a 305....they make GREAT boat anchors.

[68Stepbed]

The 200-4R is actually a better tranny according to the trans shop I use. The 200-4R will fit right in place of the TH350 with no mods. You will have to cut the driveshaft and move your tranny mount.

[BubbaGreen]

Go with the 700R4, its a relativily easy swap.
You will need a bracket that mounts near the carb for the TV-Cable.
If you can locate a "caprice" style tailshaft on the 700R4, you can use
the auto-xmember in the TH400 position. You may need a longer speedometer cable.
If you have a short bed, go to a one-piece drive shaft.
The 4L80e requires a seperate computer to control, unless you have unlimeted funds, stick with a 700r4. Just keep in mind, if the original 700r4 comes from a "car" it may have shorter splines inside the trans compared to a "truck" 700r4. It really makes no difference, but you need to know this if you have driveshaft made. I have done this and its worth the effort. Even if you dont find a "caprice" tailshaft, you can still use the stock crossmember....but, you will need to drill holes apprx 1-3/4" back from the TH-350 holes, the upper ones can be difficult at best (with a cab in place) bottom ones arent too bad. Check out www.bowtiedrives.com -or- www.700r4.com same website, different name, has a lot of good info. The 700r4 is a good trans if its built ok -AND- the end user sets up the TV cable correctly. Another note, the 700r4 uses a lock-up converter, be sure and add the circuitry to deal with this on a NON-computer controlled vehicle.

[Tx Firefighter]

My "real world" experience is that a properly built 700 is plenty durable.

My trans shop, Phoenix Transmission (click the link for their website, they advertise in all the magazines too), builds them to withstand up to 575 horsepower with a full warranty. They do cost good money to get one built strong though.

[Gray Ghost]

Whatever you do don't get the 2004r in any form unless you buy one right out of a Grand National or GNX (They were different trannies altogether than the normal ones you found in the A/G bodies). They will not hold up in a truck, period.

I've only heard two people tell me the 200 was better than a 700 and I just read one of 'em today in this thread....it is just not true in any light. If that were the case the 200's woulda been available in Vettes and Camaros. The strongest HP car it ever came in was the MCSS at 170 hp.

I had someone rebuild my 2004r to withstand 400 ponies...we had put the 330 hp crate in the MCSS...the tranny blew on the first shift. That's the one that cost me $1600 to rebuild the second time. They just won't take the hp or torque. If you must get a 4 speed from the low hp smog era, please make it a 700.

[al's71gmc]

thanks for all the reply's to my query. i emailed a shop that sells on ebay, and he quoted me $1120 for the transmission, converter, shipping and handling, TV cable, filler tube and dipstick, converter bolts, cable corrector for my carb, and conversion kit.
there are a fair number of folks i've talked to who don't like the 700r4, and several who do. i'm thinking for my driving habits and the hp i'm pushing(around 300), it would be a good swap. this truck is my daily and with gas prices where they are i drive it pretty slow and easy. besides, this is my baby. i've wanted one for 20 years, and finally got it. the most strain would be when i'm out climbing, and that's not an everyday thing.
so now this swap will get added to my list. but it may be awhile before it happens. my 17 year old son has a 72 1/2 ton 4x4 that needs a new motor this summer. i want it to be done,(drivable) by the time he starts his senior year.

[pjmoreland]

12 MPG @ $2.75 per gallon = $.23 per mile
16 MPG @ $2.75 per gallon = $.17 per mile

You'll save $.06 every mile you drive. At that rate the transmission will pay for itself in about 20,000 miles. Personally I think it is worth it just because it will make your truck more of a pleasure to drive.

[pjmoreland]

You'll also have to get your drive shaft shortened. That should cost you somewhere between $50 and $100.

[Gray Ghost]

Good luck with the project....keep us posted on your progress.