spokewrench

I was considering the popular 700r4 swap so that I can run 370's in the rear and still retain hiway driveability. My questions are: what is involved with the swap, does it fit right in? I understand you get a lower 1st gear? what is the final drive ratio in 4th? How about the shifter swap from 3 to 4 speed? Do I need to buy another torque convertor? About how much does it cost excluding labor? how about the kickdown is it electric?Any good sources for swap over parts? Any general info would be appreciated. 1970 vette.

Spoke-

Allan71

Bowtie Overdrives builds 700s and sells kits to install in the Corvette. It might be a better idea to get some of the installation parts from Bowtie and then find a local tranny builder to get your tranny from in case you have any warranty issues later on. Only a 1988 or newer tranny with all of the HD updates should be used but most high performance tranny shops know this. The early 700s were plagued by many failures behind higher horespower engines so find a racing tranny builder who will stand behind it. The 700 with the 3.70 axle sounds nice. This will give you a 11.32 overall first gear compared to the 7.64 you have now, and your final drive even with the 3.70 will be only be 2.59 due to the .70 to 1 4th gear in the 700. This would equate to about 2250 rpm at 70 mph. You will need to change your front yoke on your driveshaft to a later Turbo 350 or Muncie yoke and your driveshaft will need to be shortenend about 2 1/2 inches but measure carefully to be sure. The kickdown is really controlled by something called the TV Cable and this must be set up and adjusted correctly or the tranny will not last. Bowtie has this kit also. Here's a link to their page and a link to a rpm/speed calculator. Just fyi the ratios are (700) 3.06, 1.63, 1.00 and .70 to 1; (400) 2.48, 1.48 and 1 to 1.


http://www.700r4.info/Conversions/68...6881vetp1.html

http://idavette.net/tech/ratioc.htm

MIKER

Go to smokemup.com http://www.smokemup.com/utilities/calc/mph_range2.cfm to compare gear ratios/transmissions.

Go to Bowtie Overdrives www.bowtieoverdrives.com to buy parts for the conversion.

In August 2001, I completed the installation of a 700R4 into my ’80 along with a new 383.
Not counting the price of the transmission itself, here is a list of the things that I did and the parts that I purchased.

- Dipstick tube and indicator for 700R4 from Bowtie overdrives ~$22.
- Adapter kit for TV cable to stock Rochester carburetor, from Bowtie overdrives ~ $45.
- Changed from electronic speedometer sending unit to a mechanical gear driven unit from Bowtie overdrives ~$45.
- Had the drive shaft shortened and new U-joints installed at local shop ~ $100.
- The drive shaft yoke from the TH-350 worked in the 700R4
- Modified stock cross-member. (moved the mounting pad ~2” back and moved emergency brake cable over away from the U-joints.)
- Modified the original TH-350 shifter bracket that mounts to the side of the transmission pan. (The distance between the pan bolts on the TH-350 were ~3 ½” apart and the pan bolts on the 700R4 are about 3” apart).
- The stock speedometer cable is supposed to be able to reach the extra couple of inches required. I can’t verify this, I had to purchase a new one because my old one was broken. The new one came out about 12” longer than the old one. (almost too long)
- I will modify the shifter guide plate located in the console below the shift lever to allow placing the shifter into 1st gear. I’ll save this for another time because it is not critical.

I don’t know if the transmission lines from the TH-350 will work or not because mine were so butchered up from previous repairs that I am replacing most of them with new steel lines using compression fittings.

All in all, the modifications for the swap weren’t nearly as bad as I thought that it would be. I worried most about the cross-member modifications but a talented friend using a welder, cutting torch and tape measure made short work of it.

I’m just guessing, but if you have all of the parts and access to the tools needed, I think that you could tackle it in one weekend with help from a friend.

As far as transmission selection, I’ve always heard to go with a 1988 or newer model 700R4. The prices can range from as low as ???$ for a used one up to ~$1200 for a new or rebuilt one.

I currently have 3.08’s which are way too tall. I am changing to 3.73s.

spokewrench

WOW Thanks for all the detailed info I'll definately look inot this swap.
SPOKE-

jdunne

MIKER,my 700r4 with 383 and 3.08 already overpowers my tyre traction on hard launches,that is with good 255.50.17 tyres.....i have a 3.55 diff as a spare but suspect i will spend the whole of first and most of second gear wheelspinning......impressive look but very expensive in tyres........my 383 is set up for max low rev torque,i wouldnt try it past 6500.....not yet dynoed but i am told it is making 400 ft/lb from 2000 rpm..........may be yours is set up for higher rpm power and will benefit from the higher gear ratio...john :chevy

PatsLs1vette

also check out jvette73 he just got done doing it also.