New Rear End vs. 700R4 ?

[kyull67]

I have 3:73 gears and a TH350 transmission now. Should I put in the 700R4 or just swap the rear end for something with higher gears for the highway? Also what should I expect to pay for a used rear end and what gear ratio should I look for? Thanks.

[lilpup69chevy]

well i'd go for the overdrive myself but i like the 3.73 gears, if your thinking of switching gears i'd go for some 3.07 gears which is what a lot of these trucks had

[Smitty]

I put a 700 in mine and then screwed up when I had the rear end rebuilt. Instead of staying with the 3:73's that worked real well I went with 3:50 simethings and it still runs good. But took a little mileage benefit away.

[JameslovesJammie]

I would keep the 3.73 and go with the 700r4. Your first gear is deeper than with a 350, so it will launch better, PLUS the overdrive. Can't go wrong!

[kyull67]

Originally Posted by JameslovesJammie

I would keep the 3.73 and go with the 700r4. Your first gear is deeper than with a 350, so it will launch better, PLUS the overdrive. Can't go wrong!

That's what I was thinking, but my project budget is a little low now. College sucks.

[dingo_dan_22]

How tough would it be to swap to a 4160e? I have two rebuilt ones but am afraid to throw them in.

[Vince M]

The 4L60E is electronically shifted but other than that it is basically the same as a 700R4. You would need an aftermarket controller if you want to use it.

[Purduegmc]

Has any done the 4L60E and if so what controller did you use and how much did the controller cost? Lots of questions. By June I am going to have an overdrive in my truck.

[piecesparts]

I installed 3.73 gears in my truck and my Son's truck. Both trucks have the 700R4 tranny's and the combos are real responsive. The Son's truck had 3.08 gears in it after the 700R4 had been installed and the mileage really sucked bad. The truck only got 11 to 12 MPG and struggled on hills and city streets. We installed the 3.73 gears and the mileage picked up to 14 MPG. The truck drives well ow and has plenty of power. My truck had 3.42 gears and I took it to the 3.73s for more launch at a stand still. I average 15 to 16 MPG with a stroker motor.

[Rokcrln]

For now I would go with the 700R4 and then down the road when you can swap in a set of 3.43's to your rear end. I have this combo in my 71 "project slow build" and can't wait to try it out. I had 4.10's and a hydro 350 before and since the first gear in my 700R4 is 20% lower than the 350 was I dropped my rear end by 20% as well and still have the 30% OD in 4th. So now it is 50% OD in 4th compaired to what I had before but I still have the same Gear ratio in first as before. Should be a win win.

Kevin
LFD Inc.

[Alvin]

Originally Posted by Rokcrln

I had 4.10's and a hydro 350 before and since the first gear in my 700R4 is 20% lower than the 350 was I dropped my rear end by 20% as well and still have the 30% OD in 4th. So now it is 50% OD in 4th compaired to what I had before but I still have the same Gear ratio in first as before. Should be a win win.

Kevin
LFD Inc.

Easy for you to say!

[piecesparts]

It is all in the RPMs on the road. Depending on what diameter of tires that you run, the motor will run down the highway between 200 and 2500 RPM with a 3.73 rear end and a 700R4. That is about optimum for a Chevy V-8 and a 4000 lb truck. If you go lower than that in RPMs, then you will work the motor harder to climb even a small grade or if you have a cruise control, it will work harder to overcome hills. That will kill off the gas mileage, my osn's truck (with the 3.08 gears ran at 1900 RPM with the 700R4) and it had lousy gas mileage. When we took the truck to 3.73s we gained gas mileagae and the truck now cruises at 2500 RPm at 70 MPH. We are running 295/50/15 tires on the back of the truck. My truck had the 3.43 gears and with the same tires and a 700R4 tranny it ran at 2200 RPM at 70 MPH, The cruise on my truck did not work as smooth as I wanted it to. By going to the steeper gears, I gained a smooth cruise control operation and still maintained about the smae gas milage as what I had with the 3.43 gears.

[Longhorn Man]

a 3.07 gear would give you 2500-ish RPMs on the freeway, and cost WAY less than a 700R4 (You mentioned being a student, and I'm assuming you don't have 1000 bucks for a tranny swap) Not to mention, the TH350 or Th400 are stronger trannys and would last longer

[kyull67]

Originally Posted by Longhorn Man

a 3.07 gear would give you 2500-ish RPMs on the freeway, and cost WAY less than a 700R4 (You mentioned being a student, and I'm assuming you don't have 1000 bucks for a tranny swap) Not to mention, the TH350 or Th400 are stronger trannys and would last longer

Correct, any idea how much I should expect to pay for a rear end?

[Longhorn Man]

I would expect to pay 100 bucks for one in the junk yard.
No more than 150 from a member personally. When you replace therear axle, you should consider your drums. I know you say it stops fine, but if you think you'll be goin to 5 lug sometime... then you should consider getting the 5 lug rear now... otherwise, you'll be spending money on the rear again.
I just went through your domain page... not a bad lookin truck... you should post more photos of your g/f though.. she looks way better than the truck does. (Just messin...mostly)

[Purduegmc]

On the 307 gears, what would the approximate mpg be? Just a ball park guess would be helpful.

[kyull67]

Originally Posted by Longhorn Man

I would expect to pay 100 bucks for one in the junk yard.
No more than 150 from a member personally. When you replace therear axle, you should consider your drums. I know you say it stops fine, but if you think you'll be goin to 5 lug sometime... then you should consider getting the 5 lug rear now... otherwise, you'll be spending money on the rear again.
I just went through your domain page... not a bad lookin truck... you should post more photos of your g/f though.. she looks way better than the truck does. (Just messin...mostly)

I'll let her know she looks better than the truck and then maybe she won't be so jealous of the time I spend on it!

[72MARIO]

ld just swap a 3:07 rear in. I wish I never put a 700R in my truck. Way too expensive to build. I will never see the fuel savings from it with the added cost of instaling it.

My 84 has a 700 and 3:42's I get better MPG with it in 3 or drive. Because it brings the motor up into the Cruize range of th cam.

[Longhorn Man]

mario has learned what I've been preaching here for years.

[68CHEBY]

You would have to drive alot of miles to justify the cost of the tranny swap for the savings in fuel that is for sure. If your getting 14mpg now and picked it up to 17mpg, based on a 20 gal fuel tank(even number) you could drive 60 miles farther on one tank of gas, but 60 more miles at 17mpg is only 3.53 gallons of gas and at 2.50 to 3.00/gallon you would only save 7 or eight bucks per fill up. (man I hope I did my math right!)

[mnunn454]

My Opinion:
TH 700R4 = costs more up front, longer physically than the TH350 therefore harder to install, harder to properly adjust, and more prone to temperature related internal damage. On the upside, it has a 20% lower low gear, 30% overdrive, and a lockup converter. GM designed it specifically to get heavier vehicles moving more easily. Works well with your 3.73 gearing, thereby avoiding the cost of a rear gear change. Best option performance wise.

TH350 = cheaper up front to rebuild or buy. No PITA TV kickdown adjustments required. A little sluggish in low gear on a heavy car/truck unless you use a stall converter. Less fuel efficient on the highway. To re-gain highway efficiency would need rear gear change (cost for that varies $200 to $1200) making ROI/payback hardly worth the effort/cost.

Either option is going to be fairly expensive unless you can get the parts cheap and just bolt them in. In that case, I'd favor the TH700/3.73 option, and put up with the installation and long term care/maintenance headaches.

JMO