Rear Axle: Anyone running a 700R4 GM Trans?

[LarkTruck]

Wanting to know what a good all-around rear differential gear ratio would be to use with a 700R4 transmission.
Probably will be doing more around town-short trip driving, but want to have good highway gears as well.
Any thoughts?
Thanks.
Jim S.

[sweetolbob]

Wanting to know what a good all-around rear differential gear ratio would be to use with a 700R4 transmission.
Probably will be doing more around town-short trip driving, but want to have good highway gears as well.
Any thoughts?
Thanks.
Jim S.

Jim

Most Big GM cars with the 700R4 ran 3:42 gears with 235R 15 tires. The later pickups were 3:55 and 3:73 with an occasional 4:10 with 265 R16.

If you are using a relatively small motor, I'd stick in the in the 3:55 and higher number gear sets. The 700R4 has a quite low first gear to get you started.

Here's a calculator to let you look at the effects of changing ratios (rear and tranny) with tire size vs RPM and MPH.

http://www.wallaceracing.com/gear-speed.php

My 83 Avanti with a .67 final geared 200R4 runs about 2300 RPM at 70 Mph. 26" diameter tires.

Bob

[41 Frank]

I run a 4.09 ratio with my 200 4R with 225x70 15 tires and turn 2500rpm @ 70mph in lockup convertor mode. Final ratio works out to a 2.74 to 1. 3600# car

[bezhawk]

I think a 3.92 would be ideal. My Blazer had a 3.73 with the 4.3 v6 and worked ok, but it needed a bit more gear to head into a stiff wind or climb a grade (when in overdrive). You probably want around 2300 or a bit more at 60 mph so you will have the torque to maintain speed without having to shift down too much.

[KGlowacky]

I ran a 3.24 in my 46 Chev PU and it was OK but I remeber thinking probally a 3.55 would have been better. Live in Houston so step grades are not a issue. I did have the trans rebuilt to where it was not electronic anymore.

[61Lark]

My daily driver is a 92 Caprice that has a 700R4, 190hp 305 cid, and 2.56:1 gears. On paper the car should be an absolute dog, but it gets off the line pretty well thanks to the steep first gear and gets around 27 mpg. If I remember correctly the 94-96 Impalas used 3.42:1 rear ends.

That being said, I've considered doing the swap on my R1 Avanti and have even purchased the adapter. I'll probably go with a 3:31:1 or 3.54:1, but I want a little more performance. If I was doing it more for mileage I would even consider the 3.07:1.

Nick

[Gunslinger]

My '70 Avanti has a 700R4 installed in place of the original Borg-Warner. The shop that installed the crate engine (350HO) and the 700 had the transmission built to the specs of the engine and rear end (3.31). It can smoke the tires in most gears if I want to...and it took a bit of driving to get used to taking off without spinning the tires.

Some say the 200R4 has a better spread of gears...maybe so but I don't know. Every car has its own requirements with its specific engine/rear axle ratio, etc. I do know 700R4 transmissions are generally stronger than the 200R4 (excluding the Buick Grand National GS). 200R4's can be built as strong as a 700, but the 700 is already strong, plus neither is difficult to find on the market as candidates to be built for anyone's needs.

Some have reported clearance issues that required transmission tunnel modifications with a 700, and a 200 wouldn't require that, but I encountered no such problems on my car.

[StudeDave57]

totally weird!!!!

Dad and I were talking about this stuff just yesterday!!! I plan on using one of these trannys in at least two of my cars, you see. All we have to go on is what Mike did with his Hot Rod '59- a 400SBC/700R4 combo with a 3.07 TT. That car is scary quick, and still to this date has an unknown top end to boot...

Thanks for posting folks!!!

[bezhawk]

Dad and I were talking about this stuff just yesterday!!! I plan on using one of these trannys in at least two of my cars, you see. All we have to go on is what Mike did with his Hot Rod '59- a 400SBC/700R4 combo with a 3.07 TT. That car is scary quick, and still to this date has an unknown top end to boot...

Thanks for posting folks!!!

You are talking about a much larger engine with lots more torque.
A Stude is best suited to cruise near 2500 rpm on a 289. (in my experience)
A 3.07 would be undriveable in overdrive....or at the very least you would be constantly shifting.

[StudeDave57]

You are talking about a much larger engine with lots more torque.

That was sorta my point. The '59 doesn't give us much to go on given the HUGE difference between the two sources of power. I'm going to be watching this thread hoping to hear from folks with StudePower and a 700R4 so as to better judge what I oughtta do. My long range plans look like this~

• a '57 Parkview with an "R1+"
• a '57 sedan with a GH and/or R3 combo of sorts
• and (maybe) a '58 Packard with a 'hot' 289

I had been thinking that a 3.31 would 'work' in those cars, but that I might want to go a bit lower if need be. Parts are out there should I need them. I'm lookin' to use the cars mostly for cruisin' 'round the Country and what-not, but the wagon would also need to tote a trailer from time to time. Any thoughts?



StudeDave '57

[PackardV8]

Based on real world experiences with an R1 289 and 700R4:

For R-series enguies, the 3.73 is a good compromise. Numerically lower gears, i.e.3.55, 3.31, 3.07, load the engine heavily at low RPMs. With an R1, it will usually begin pinging before it shifts down.

All-around use, especially with an R1 or R2, 3.73
Flat ground, like Houston, maybe 3.31, only if the engine is a standard engine with low compression, the numerically lower gears can work. It will cause a lot more downshifting on grades
Mostly in town and secondary roads, with a low compression engine, 3.54

One absolute piece of advice if installing a 700R4 - go to BowTieOverdrives and pay their really high price for the throttle valve bracketry and instructions. I'm an experienced engine swapper and fabricator and I couldn't get it right on my own. Their stuff is worth what it costs.

Second advice - go to a Pik-n-Pull and buy a GM floor shifter.

jack vines

[mrjazzmillcreek]

I have a 700r4 in my 1966 Daytona with the original 283 engine and 3.31 rearend. This is an excellant combo,makes it one of the best driving Studes ever/

[sbca96]

With a warmed over Stude 289 I was running a 3.31 TT axle in my '60 Hawk. No issues.
I could spin them through 1st and 2nd, and bark 2nd pretty much on demand. My Impala
SS with 265 hp engine runs a 3.08 axle, and my 275 hp Camaro had a 2.72 axle. Impala
weighs in at 4200 pounds and the Camaro is 3600 pounds.

My experience.

Tom

EDIT: I am running that same axle in my Avanti now, with a stock 105k mile R1 and the
TKO 5 speed manual. It has an OD, which I have pulled grades with in OD.

[studegary]

Wanting to know what a good all-around rear differential gear ratio would be to use with a 700R4 transmission.
Probably will be doing more around town-short trip driving, but want to have good highway gears as well.
Any thoughts?
Thanks.
Jim S.

From this post, I do not see what the vehicle is (weight/aerodynamics) or what the engine is (HP, displacement, torque). These things would have to be known to give a good answer to you.

[PackardV8]

My Impala SS with 265 hp engine runs a 3.08 axle, and my 275 hp Camaro had a 2.72 axle.

Tom, you, of all people know the computer control of EFI and ignition makes all the difference. What gear a computer controlled engine can pull is not in any way applicable to what a fifty-year old carburetor and distributor can pull.

jack vines