Overdrive...

[twmattox]

Has anyone tried the GM 700-R4 transmission yet? These things are heavy duty, lower first gear ratio, have overdrive, and the adapters are readily available to hook them up.

It seems to me that overdrive would offer two possibilities. First, with stock axles, considerably greater highway mileage. Second, alter the axle ratios to get more useable power during takeoff/lower speed applications and not sacrifice during on road usage with mileage...

[joe]

Originally posted by twmattox:
with stock axles, considerably greater highway mileage. If youre talking about the 2.73 stock gearing in the 80-91's forget OD. The OD will never be engaged. You'll be so low in the powerband the AT will constantly be kicking back down to high gear. If you're swapping gears to a lower(higher numerically) set up then it'll work but not with stock 2.73 gears.

[89grand]

True, with 2.72's and an overdrive with like a .7:1 overdrive gear you would have a final drive ratio of around 1.9:1. I have problems sometimes now turning enough rpms on the highway to make enough power to get up steep grades without the tranny shifting into 2nd gear to make power, it would be worthless with an overdrive. Now on the other hand, if you want to run something like 3.73's or lower then an overdrive would make a lot of sense, and take off would be great with low gears coupled with the 700R4's low 1st gear.

[The Anti-Chrysler]

Late model 700's (4L60) are great, but it's not a direct swap in. First, you'd need a bellhousing adapter, some sort of flywheel adapter, a GM TV cable, stand-alone converter wiring, a t-case converted from rear slip yoke (GM) to fixed yoke, or an adapter to use an AMC NP case, a relocated crossmember, and then the driveshaft lengths would most likely have to be changed (front longer / rear shorter). I had considered the swap but figured I'd just wait until I could throw in a full GM powertrain.

Again, you'd need the 3.31 ratio at least or higher for the swap to make any sense.

[FSJ Thing]

Doesn't Wart Hawg have a th700r4 in his wag?

[Wart Hawg]

Not in my Wag, it's in my Jimmy. Since I've gotten the TV cable adjusted correctly it's great, but then again that Jimmy has 3.73 gears in the rear axle.

[Bobbo]

How about a aftermarket OD, I hear good things about some of them, but never heard about one in a FSJ?

[joe]

The above applies to OD trannies or any other form of OD.
If your axle gearing is compatable with OD it's prolly cheaper to swap in a OD trans. Aftermarket OD's can get spendy and used ones are hard to find. I've got a Gear Vendor splitter/OD unit for a Ford and on GV's web site this model for the BW1345 tcase is $2700 new. :eek:

[Mikel]

I just bought a AA Ranger for my M715 quite cheaply. The only problem is that this thing is set up for a Toyota engine and tranny. A standard BOP bellhousing (and a few new holes) will mate the Ranger to my 455. Putting the Ranger and the T98 together will be a bit trickier, but I think I can get away by re-splining the T98's input shaft to the smaller Toyota splines. 27% overdrive :D

[pb]

Would overdrive work with 3.07 gears?

[Cecil14]

Originally posted by pb:
Would overdrive work with 3.07 gears?Not with any decent sized tires. If you run 27" or so tires you'd probably be pretty good. I don't imagine my s-10 has much lower gears than that and it's got overdrive. Stock it had 205/75R14 tires though, like 25" maybe.

Anthony

[joe]

I wouldn't risk the investment for an OD with 3.07 gears. A 27% OD will give you a 2.24 axle ratio...that's pretty high.
My xj with 3.54's/OD works fairly well but kicks out of OD a lot here(not flat ground) but still worth having OD. I personaly wouldn't think about OD unless you have at least 3.31's but YMMV ;)
With 3.07's you could get the same OD effect on the hwy by going larger than stock tires...to a point. With 3.07's your mpg's is prolly already as good as it's going to get.

[pb]

right now my mileage is 7 city, 9 highway at 70-75mph. I have 29" tires on right now, and just put the perfomer intake and holley carb on. I haven't checked the mileage yet, but i don't think it is much better.

[joe]

Pb you should be getting better mpg's than that. I get 10 with a 360/Roch Qjet/T18 and 4.09 gears. My last truck with 360/Edelbrock 1405/AT/4.09 gears also got 10.
Your motor is near dead or you have some vacuum, carb, tune issues. Time for a major tune up I suspect.