Overdrive Options??

[khurst]

What is the best way to go about an overdrive install in a 1989 Grand? I have a 401 AMC V-8(just installed) with the stock 727 Tranny and a NP-229 tranny and have installed lock-out hubs. My wife drives it every day and we would like to start using it on long-hauls here in Texas but the Gas(10-11 MPG) is killing me. I need specifics and anyone's past experience? BTW I use it occasionally for towing(about 3,000 lbs) and it has 3.54 gears with 32X11.5's and a 4" lift. I am trying to keep the interior section a close to stock as possible--IOWs no after market ****ers.
Thanks, Kirk

[coolram]

The 401 combined with 3:54 gears(did you install these because I thought 3:31s were the deepest availible for '89)curb weight of 4500lbs,32's and a 4" lift at highway speeds don't make for good gas mileage no matter what you do.And your wife knows not to engage 4wd without locking the hubs I hope.I know this isn't much help but i can't think of any way that would pay off mpg or $$ wise for you.

[TexasJ10]

I think that Coolram is on point. There are no cost effective overdrive options that could be justified with gas milage increases. You could probably pick up a little milage, without sacrificing too much acceleration, by changing to 3.31 gears with the 32's, and for the cost of an overdrive tranny, you could pick up a little milage boost going to tbi fuel injection. TPIGUY, could make a custom TBI system for the 401 for $840. His web site is at http://www.customefis.com/jeepgwfi.html Just my two cents.

BTW, I am working on putting a NV4500 into a project J-10. It is a manual 5 speed with overdrive. I am using it more to offset the planned 4.56 gears than to improve milage however.

[Chero77]

I agree with the above. There is no cost effective overdrive option. However, there are other advantages besides gas mileage such as being able run 75-80 on the freeway without the engine screaming like a trapped animal. For about $2k, you could go the 700r4/np208 route, which would allow keep up with new trucks with ease. Having F350s run right up on your bumber and then whip by at 85 or so gets pretty annoying after awhile.

[Joe Guilbeau]

Overdrive for the Chrysler 727 Tranny?

What about the Chrysler 518, supposedly it is a 727 w/overdrive, but I suppose that the tail shaft is different.

Anyone out thee have any knowledge of this?

JAG

[AM Woody]

the Chrysler 518, supposedly it is a 727 w/overdrive, but I suppose that the tail shaft is different I think this is more or less true. I don't know about interchangeability of parts between the Jeep and Dodge 727 transmissions. But as a Dodge truck guy, I do know these O/D units are expensive and can be troublesome. Also, they are electronically switched, so there'd be some wiring and figuring out to do.

There doesn't seem to be a magic bullet with these things. When you upgrade something expensive like gears, trans or EFI you gotta figure out how long it's going to take you to break even saving a buck or two every tank of gas...

[The PIG Smith]

Yes, I have '97 Dodge Dakota Sport 4WD drive and HATE that OD tranny!! I've had it in the shop for adjustments so many times...GRRR!

I would install a Powerguide 2 speed tranny before I would use another Mopar OD unit!

[Mbsk01]

What about those overdrive units available form Gear Vendors? Not useful in 4wd, I assume, but may help when driving long distances.

[Zac]

Could you just change the ring and pinion so it was lower like a 2.7 or something? To help on gas mileage you should get smaller tires.

[ffej]

Np229..manual hubs :eek:

[joe]

OD with 3.54 gears and 32" tires will be useless. If you do have 3.54 gears(after market install) that is because stock is either 2.73 or 3.31's at best and OD would be even more useless with those gears and 32's.
If you run an OD AT it'll constantly be kicking out of OD and going back into 3rd/high which has the same ratio as your non-OD tranny (1:1 ratio).
I have an OD AT in an XJ with 3.54's and stock tires(28.5 or so) and the OD is "acceptable" on flat land. With 32" tires it'd never run in OD, the engine rpm would be too low in the power band. I also have a CJ with a manual trans and OD/3.54 geras/30" tires and out of 85,000 miles the OD(5th gear) has maybe 50 miles on it. Pulled that off somewhere in Kansas I think? My 83 Chero has OD/2.73 gears/30" tires and out of 160,000 OD has "zero" miles on it. Guess that combo was thought up by some college boy "engineer" who didn't exactly shine in math. :(
Anyway bottom line...unless you're running at least 4.10 with those 32" tires installing an OD trans will just be a waste of money cause you'll never get to use the OD part.

[Heimeken]

I disagree, My 360 accelerates fine at 1800 RMPs going uphill, I'm sure I can too benefit from an overdrive tranny. These engines are great at low RPMs. I'm running 35" tires on a T176 and Stock 3.31 gears which gives me some sort of overdrive. Of course my low gearing sucks but that's another topic. When I grow up I want to have a J10 with an NV4500, 3.73 or 4.10 gears and 35" tires as a daily driver, should get descent MPGs. My wag is for wheeling.

[WillyPete]

there's some company that makes a manual valve body for the 4l80e GM tranny. it's a 4 speed HD auto, basically a th400 with a 25% OD. if you get a novak or AA Adapter and flexplate and this valve body, you could run the 4l80e sans all the electric stuff. you'd have to control the shifts tho. still, it's a thought.

i forget the exact name of the company, i will dig around for it if you're interested smile.gif