Swapping the 350 transmission for the 700

[jcarle]

I want to swap transmissions to save on gas by having the overdrive. My question is what does it all entail. I saw in a vette parts supplier that they have a swap kit that included changing the shifter counsel. I would like to keep that looking original. Is that possible? Also, is there a used vehicle that I could get the transmission from for a quick swap or do I have to buy a transmission designed for that swap? Any help would be greatly appreciated. I know people have done this, because I have seen two cars for sale with that modification.

Thanks for your help in advance.

Jon

 

[Twin_Turbo]

If you get the tranny from a car different than the vette you will need a new tailpiece. Also, non-vette 700R4 trannies don't allow WOT in OD. They shift back to 3rd so you'll have to change the governor too.

Marck

 

[mmvette80]

Go to the thread that reads 700R4 conversion driveshaft installation. There is a bunch of info to read about the swap. The tranny I bought came from Bowtie Overdrives. They say that their trannys are from 88-92 Vettes.
As for gas mileage I tried doing a highway mileage test. The only problem I have is there isnt a open highway where I can just cruise on. I have to stop and turn around every 50 or so miles. This past week I tried, I drove between 55 and 65 mph. I filled up the tank and went. I got 200 miles and still had three quarters of the tank left. I would guess a non stop run would give at least 400 miles on a tank. Once I cruise over 65mph is sucks gas do to the coeficient drag.

 

[chevyaddict]

Conversion troubles

We tried to do this similiar conversion on our 86 Dually. Isn't it true that the 700R4's have more electrical stuff going on with them as well? After we did ours the pump (we think) went out after about a week. We were uncertain if it was just the tranny or if it was infact that we didn't have the electrical stuff hooked up. I know those overdrives have something that makes them disengage when you hit the brake on deacceleration; there are other things too. So, how would you hook this electrical stuff up? Or do you need to?

 

[Twin_Turbo]

The 4L60E (basically 700R4) has more electrical stuff. The 700 only hsa electronically controlled lockup. You can install a switch. the kit is available from Painless.

Marck

 

[Scott81]

Jon-

I've done the swap in a 1981, it's one of the better things I did to the car. Gas milage increased even with a rear gear swap to 3.55's. I drove from Florida to Kentucky and back and got over 20mpg, and would have gotten more if we weren't trying to set a speed record

Basically get a trans from a 88 and up car, Bow Tie Overdrives or any source you choose and have it rebuilt now while it's out rather than in the middle of summer when you want to have some fun. Painless Wiring has a vacuum switch controlled lockup harness but they only sell them through distributors like Summit and JEG's. This harness is only good if you have a stock or mild motor, I had to remove mine due to a large cam and go with the BTO harness. You'll also need to either buy a driveshaft from an 82, have one made, or cut yours....I believe it's 3 inches. You'll also need to either modify your crossmember or buy the custom one so that the e-brake works and the trans bolts up. You can either buy a shifter conversion kit or just notch you old one as well, but the kit gives you directions and a new gear indicator bezel. It's not a hard conversion at all, it just takes a little thought and preparation. Spend some time on the 700r4 site, it has plenty of good information.

Here's a little info on mine Tranny Swap

 

[mmvette80]

Nice pics Scott81!
You just gave me flashbacks. I wasnt fortunate enough to have a car lift. How nice is that crossmember! I was thinking of going with the 3.55 gears also. What are your RPMS at 70mph with those gears.

 

[jcarle]

Thanks

Thanks for the help everyone. I think I am going to try it.
JOn

 

[Scott81]

Nice pics Scott81!
You just gave me flashbacks. I wasnt fortunate enough to have a car lift. How nice is that crossmember! I was thinking of going with the 3.55 gears also. What are your RPMS at 70mph with those gears.

Thanks! I don't have a lift either, I'm just on good terms with a couple people in town and the tranny shop owner is a great guy who let me in the shop to take pictures of the swap. The crossmember is great, it was a no hassle deal just bolt it up and go, no cutting, measuring, welding. I'm still not sure of my rpm's yet, I've been lazy and haven't changed my speedo gears out but I believe at 70 it's around the 2100-2200 range. BTO has a calculator on their site you can plug in tire and gear numbers to get the exact rpm ranges if you'd like to know sooner than waiting for me to get off my butt and change gears

 

[mmvette80]

How is the launch with the 3.55's. Can you get traction? I purchased all the tranny components from BTO. The hardest part was setting the TV cable. What meathod of cooling did you use. I have a aftermarket into the radiator. It works pretty good. How does the tranny shift under normal throttle? 2nd into 3rd is pretty hard.

 

[Scott81]

When I had the stock motor it imprved a bit, but the motor was a dog no matter what gears I had in it. The 700r4 and gears together made things much better but having a stock motor isn't going to give you a drastic improvement on take off. Now that I have a 383 the car goes like a Corvette should, even though my motor is a bit much for the street. My take offs now can boild the tires if I'm not careful, I can get traction, but I have yet to make it to the track to see what happens from a dead stop to full throttle. For cooling I'm just using the stock setup cooling lines into the radiator. My tranny shifts nice and firm, I actually had to have them reset the 1-2 shift as it was just too much...a real neck snapper. The 2-3 is firm but not too bad. With the shift kit and a few other adjustments you can actually set it up firmer/softer depending on what you want.

The reason I went with 3.55 gears and the 700r4 was based on recommendations, mostly from Art at Van Steel. This combo gives me good cruising rpm's on the highway as well as quicker take offs in the city, I wanted a nice middle of the road combo.

 

[79blueshark]

Just for the info, B&M has a torque converter lockup device also. I wanted to get away from the vacum setup painless offered. This one runs off the speedometer cable so you can tailor the lock up to MPH for the road or track. Its also adjustable on the fly. Mounted mine in the glovebox so I can adjust for the red light to red light runs with the Mustangs. It also connects into the brake/cruise control feed to disconnect the lock when the brakes are applied.

 

[Hib Halverson]

Putting a TH 700R4 in an 79 should be quite easy because that transmission was OE in 82. What you need is a 700R4 with a Corvette tailhousing along with the trans mount. The shifter and a few other stock items.

It was said earlier that the 4L60E is the same as the 700R4 with the additon of some electronics. Well...that's a bit of an understatement. The 4L60-E is a computer controlled transmission and it would not work without the engine computer that goes with it.

What you need is a 4L60 which is pretty much the same as the 700R4 but you need the C3 tailhousing and trans mount. A C4 4L60 will not adapt without changing the back of the trans.

Lastly, the 700R4 has a 3.06 low gear. I'd put the trans in first and see how the car drives before I'd change the axle ratio. You may find that a 3.08 or 3.36 axle is more than adequate.

You'll need an 82 Corvette driveshaft.

As several people have posted, you'll also need to address the 700's lock-up converter. That said, I memory serves me well, I think there were some very late TH350s that had lock-up converters. Maybe your 79 has one of those. If so, you probably can control the 700's converter with the existing hardware.

 

[bans25]

I am in the middle of a 700R4 conversion in my 78' and I am running into 2 problems

1) The trans dipstick is hitting the pass side trans tunnel (very little look there... the tranny is also very close..

2) the 82' driveshaft is a little short, only about an inch, maybe a little more of the yoke goes into the trans.. Im concerned thats not enough..

Did anyone else see this?

thanks

-Bill
P.s. both the dipstick tube and crossmember are from bowties..

 

[mmvette80]

The dipstick was a pain. I didnt bolt it to the tranny I just let it rest up against the firewall.
The yolk should show about 3/4 of a inch. I had the old driveshaft shortened and checked with the company on how they wanted it measured.
Did you get to the TV cable adjustment? Thats where the real fun starts.

 

[mmvette80]

Here is a picture of the TV placement. Hope it helps.

 

[mmvette80]

This shows the dipstick.

 

[mmvette80]

The tranny will be tight at the cooling lines! Did you get the 2200 stall converter?