The Stovebolt Site Forums The Shop Area Driveline Rear end ratio with automatic conversion.

Hey all. Still planning this project and have another question. Going with either a 700r4 or 200 4r. Wondering if anyone is running either of those and what ratio rear you're using? Thanks.

I thought you were keeping the factory automatic?

I think the 700R4 is preferable .... I've got a 700 with a stock 3.90, keeps the pulling power and gives good highway speeds at lower RPM with the OD

Bill

Joseph, I've got 2 54's ones a 3 speed column shift. Way too much stop and go here in Miami plus left leg gives me problems occasionally (broke it in 84).

It all depends on what engine you are running & somewhat on the diameter of the rear tires. Either of those trans. are good choices. The 700 r4 is stouter & the 200r4 is lighter & shorter.

Wrenchbender, I'll be using the 235 with cam, headers and intake or a 261 (if I can locate one).

Red58, what engine are you running?

283 for me

Bill

The stock ratio ought to work good with either one of those o-drive automatics. It takes some special adapters to put them behind a 235.

Wrenchbender. Thanks for the input. Will prob use Langdon's adapter to make it work. Hope to find a 261 to put in. Either way will need to adapt the automatic.

4.11 with the 700 gives a 2.88 final in OD and the 3.90 gives a 2.73. Great road gears for an empty truck although a 261 might be able to pull a light load geared that shallow.

I've had an 85 Chevy K10 with a 700R4, a 95 Blazer with a 4L60, and currently an 04 Trailblazer with a 4L60E. They all had 3.42 gears, and I'll tell you that they ALL needed steeper gears. I wouldn't use the 700R4 or 200 4R, without at least a 3.73 rearend especially in an old bolt. I know the 261 has more torque than a 235, but you still are only going to have 150 HP max. You would probably be happiest with a 4.10 gear.

If you go the 700R4 or 200 4R route, do yourself a favor and get a shift kit from Transgo or Superior. It'll be well worth it. A better 2nd gear and OD servo will always help too, it'll help hold the trans in gear better and help with the "engine flare" that both of those trannies are known for.

Thanks. I was sort of thinking the 3.90 was what I wanted. Good to hear I was in the right ballpark. Now just need to figure out which rear to look for.

The easiest swap is a '55 first series. Be sure to get the springs too. It will bolt right in like it was made for it.

I have 3;73 gears with a 700r4 tranny. It works great, lots of torque, and great gas mileage on the highway. I am running a 350 zz4 crate engine making close to 390 hp and I get 21 mpg on the highway. Sure worked out fine for me.

I have a 700R4 I plan to connect to a 350 and have a Firebird rear end (2:73). What do I need to ensure the 700 operates properly -- a shicft kit or electronic switch of some sort? Where do I find them? Thanks for any help.

Talk to the guys at Bowtie Overdrives. They can help you figure out what you need.

I'm a little worried about your axle ratio choice.
If you're running 28.25" tall tires (e.g. 225/75R15), then your 60 mph cruise in OD will be about 1360 rpm. I'll bet that's too low for your motor's torque band. I think you'll be better served with a 60 mph cruise rpm in the 1800 - 2000 range.

regards,
Leon

I agree the 2:73 is to low for the 700R4

A 3:42 or 3:73 works good.

If you have a pre-92 700R4 or 4L60, You'll need a TV (kickdown cable) connected to the Carb. You'll probably want to get a torque convertor lockup kit too. On a side note, If you get a Transgo NOYOYO shift kit, you won't have to get the lockup kit. It has a check ball and spring kit that lets you run the transmission without the lockup function. I would also recommend a transmission cooler. I would stay away from the 2.73 gears. You'll never have enough RPM for the overdrive to function properly. Go with 3.42 or lower, preferably a 3.73 or 3.90.