Any ideas on an overdrive?

[ibnfe]

Alright, I'm frustrated. I've done tons of searching all over the place and I can't find any overdrive options. I sure would like to be able to cruise at 75-80 mph in my rig without breaking 3000 rpm. Any ideas on how to get some type of overdrive setup that does not involve changing out my entire drivetrain setup? I'm willing to modify Tcase and driveshafts, but I would like to keep my 727. Any ideas at all? I'm about ready to give up on this mod. Help please!

[James 007]

From what I've found so far, nothing w/ a 727TF. Only thing is the 700R4...

[joe]

If you're running stock axle gearing in the 85, OD is a waste of time, money and fuel. Even worse if you're running larger than stock tires. If you're running 3.73's or lower(numerically higher) it'd be a feasable plan but other wise no.
I've two got vehicles with 3.54 gears and OD and both are a lot lighter than a FSJ. The AT equipped one constantly kicks out/in of OD. It's just too hilly around here with those gears and OD. The manual rig you can't even put in OD w/o immediately switching back to 4th gear except on a few short and perfectly flat stretches of I-5 and then not for long.

[andy d]

Joe's reply is why you wont find much in the archives. the easiest way to keep the rpm down is taller tires. that will make the accelleration suffer. you must go for mpg or performance, the 2 are mutually exclusive in a fsj

[ibnfe]

Can't go much bigger on tires without MAJOR mods. The 3000rpm is with my 38's on it. I hit 3000rpm at about 65 with my 35's on it, but I refuse to get rid of my 4.56 gears. I love the low end. Matter of fact, I love my Jeep, period. But I would really like some lower cruising rpms when I hit the road to head into the hills. I have the Jeep setup exactly how I want it, no regrets or surprises so far. I just want some lower cruising rpm's if I can get 'em. Thanks fellas.

[derf]

Originally posted by ibnfe:
Can't go much bigger on tires without MAJOR mods. The 3000rpm is with my 38's on it. I hit 3000rpm at about 65 with my 35's on it, but I refuse to get rid of my 4.56 gears. I love the low end. Matter of fact, I love my Jeep, period. But I would really like some lower cruising rpms when I hit the road to head into the hills. I have the Jeep setup exactly how I want it, no regrets or surprises so far. I just want some lower cruising rpm's if I can get 'em. Thanks fellas.Unless you do a lot of custom fabbing, you're stuck with high RPMs at highway speeds.

If you want good street performance AND low highway RPMs, you need overdrive. There's just no way around it.

There are some aftermarket overdrives available out there that bolt on between a tranny and t-case. But all of them would take a lot of custom fabbing to work with your 727 tranny and NP t-case.

However, if you don't mind losing some street performance, there is one thing you can do. You can install a Klune V (http://www.klunev.com) underdrive and drop your axle gears to 3.31s. The Klune V is basically another t-case without a front output that sits between your tranny and t-case. When you order it, you get all of the adapters you need to fit in your application.

With the Klune V, you can still shift your existing t-case into low but you can also downshift the Klune into low as well, multiplying their effects. That gives you good crawling ability with highway friendly gears. But you're restricted to shifting it like a regular t-case so no joy on the street.

Trust me, I've researched this to death. I've driven myself nuts calculating speeds and RPMs with all of the gear/tranny/tcase combinations in an effort to find a good crawl ratio, low highway RPMs and decent street performance in one package. It's just not possible with a 727 tranny. At best, you can have 2 of the 3 but that's as good as it gets without swapping out trannies.

[ August 10, 2002, 11:41 AM: Message edited by: derf ]

[andy d]

Originally posted by ibnfe:
Can't go much bigger on tires without MAJOR mods. The 3000rpm is with my 38's on it. I hit 3000rpm at about 65 with my 35's on it, but I refuse to get rid of my 4.56 gears. I love the low end. Matter of fact, I love my Jeep, period. But I would really like some lower cruising rpms when I hit the road to head into the hills. I have the Jeep setup exactly how I want it, no regrets or surprises so far. I just want some lower cruising rpm's if I can get 'em. Thanks fellas.,imho,4.56 and 38s are major mods. that was not in the post i responded to. whats left is some sorta o.d. that will cost a lotta dough and prolly require a driveshaft shortening and a re-balance

[Marvin Gates]

Ibnfe, have you checked out "Gear Vendors" in El Cajon, Ca ? they make overdrive and under drive. Just a thought. MG :D :D :D but its not cheap!

[mdill]

Ouch, looked a gear vendors page, time for a new poll how many
on the list paid more for there fsj than what a gear vendor oved drive
cost ? (2695.00)

I think the 700r4 is the best bet, on first glance the 518 would be
a good choice as all the lines from the 727 would all come out in the
right place, but it is pretty long and there is not much aftermarket
support for the adapters.

Mike D.

[Marvin Gates]

I said it wasn't cheap, how bad do you want or need overdrive? MG:D:D:D

[James 007]

Gear Vendors won't work... I've already spoken w/ their tech & he sez there won't be enuff rr driveshaft.

From what I've found so far, ...there isn't a feasiable way getting an "overdrive" without changing trannies. Only 2 options... 700R4 w/adaptor or 42RH beefed up.

[ibnfe]

Thanks for all the response fellas. I was thinking I was the only one who had ripped my hair out on this one. I think the gear vendors price tag is a bit stiff for the results I'll get, even if it would fit up. I guess I'll have to wait until something else hits the market, or maybe I'll look up my old machinist fabrication buddy and see what kind of custom setup he can come up with. If I have any luck with him, I'll let you guys know. I know he has made custom underdrives for some folks, I can't see why he couldn't come up with a custom overdrive as well. Wish me luck...

[derf]

Originally posted by ibnfe:
Thanks for all the response fellas. I was thinking I was the only one who had ripped my hair out on this one. I think the gear vendors price tag is a bit stiff for the results I'll get, even if it would fit up. I guess I'll have to wait until something else hits the market, or maybe I'll look up my old machinist fabrication buddy and see what kind of custom setup he can come up with. If I have any luck with him, I'll let you guys know. I know he has made custom underdrives for some folks, I can't see why he couldn't come up with a custom overdrive as well. Wish me luck...Good luck. And let us know if you come up with something. I'd hate to have to resort to a tranny swap on mine...