Rear end decisions

[NCtrueconservative]

I don't want to beat a dead horse cause this has been discussed in numerous threads (all of which I have read). Anyway, went out the chally today and lifted one tire in the air, made sure the other didn't move and counted how many times the dshaft turned with one turn of the wheel. Pretty sure it turned a little over 1 and a half times, which that times two would make it around a 3.23 (no sure grip).  I then crawled under and started wire brushing off some of the crud that had accumulated over the yeras (what I found below was a bright red color all over the rear end?) Anyway, found out that I had a 489 case  Soooo, here comes decision time. Lets talk performance first. A nice peppy 340 is up front, 727 trans. I can't think of a case where I would ever take the Chally on a long long trip. During the summer, I do go down to the strip and run my truck 2 or 3 times a month so I would want to be able to hold my own down there with it. Every other road around here is a 55, not many freeways. I wanna be able to get up and go, put some power to the ground, don't really care about gas mileage. Show its just a rip around town, and a run on the strip or two  Big question: Stay with the 3.23's if thats what they are and put in a sure grip unit? OR get me a set of 3.55's, 3.73's, or 3.91's, sure grip of course. I would be willing to trade my chunk of gears for another chunk with those gear sets in it for sure, if someone wants an open 3.23 to go on the freeway. So what do you think? 3.91's too much? Anyone ever run 3.73's? 3.55 experiences? Now, lets talk cost. I'm limited in funds, but I want something that will work good for sure. How much would it cost to get a posi unit put in my 3.23's roughly? Would it be that much more in labor to order some higher gears and have them put in my existing case? How hard is it to replace gears at home? I have done a bunch of the work myself on this car and could save myself a bundle if I do it myself, but have never taken out a rear end and replaced the gears. Anyway, any help would be appreciated, and if anyone knows of a wanted trade, or some higher gears that your not using, lemme know

[dodj]

If it were me, with an auto 340, I would go with 3.91 gear. Your other questions,..... I am unqualified to answer.

[74challenger03]

Iwould also go with the 391s

[NCtrueconservative]

Iwould also go with the 391s

Appreciate the opinions gents  thats two for 3.91's

[TinCuda]

Good question.   I would also like to see a step by step guide to install a posi.   I am looking at 3:55 gears but I am on the highway more than the track.


.,

[Katfish]

I'll vote for 3.73s.  I originally had 3.55s and went to 3.73's when I put the Dana in.

I also have 340/auto, it works great around town, but cruising 70mph on hwy can be annoying for any drive over 1hr.

[NCtrueconservative]

I'm just trying to think of where I will take my baby when it gets on the road (fingers crossed this spring). I would drive it on the weekends. Might drive it on hour, hour and a half trips, but where I would be going, there is nothing higher than a 55mph road. I'd have to go off the mountain to hit a freeway. "Highways" down here are maybe 4 lane at the most and 55 at that. I think I would enjoy higher gears like 3.73's or 3.91s

[LAA66]

 4:10's maybe? I use that ratio when driving the canyon roads (4-speed).

[brads70]

I'm just trying to think of where I will take my baby when it gets on the road (fingers crossed this spring). I would drive it on the weekends. Might drive it on hour, hour and a half trips, but where I would be going, there is nothing higher than a 55mph road. I'd have to go off the mountain to hit a freeway. "Highways" down here are maybe 4 lane at the most and 55 at that. I think I would enjoy higher gears like 3.73's or 3.91s

This will help to determine RPM at hwy speeds.
http://vexer.com/automotive-tools/speed-rpm-calculator

[NCtrueconservative]

That RPM calculator is pretty cool. Just want to get the best power I can out of my 340. And I'm guessing higher gear=more power even though it would roar like a dog on extended trips in like a 70 mph zone

[brads70]

That RPM calculator is pretty cool. Just want to get the best power I can out of my 340. And I'm guessing higher gear=more power even though it would roar like a dog on extended trips in like a 70 mph zone

The more gear you put in it the quicker it will be, problem is drivability and what you will tolerate RPM wise on HWY driving. Me with 3:55 gears /727 and 255/60/R-15 tires I'm at 3000 RPM'S  at 65-70 mph. When I drive to Carlisle 7 hour trip it does get a little "much" for me. That's why I'm looking at OD options. That and I have to stop for gas every 2- 3 hours. Just depends what you want to do with the car.

[NCtrueconservative]

any idea on how bad it is to change out existing gears with new ring and pinion and sure grip unit? I'm guessing its no walk in the park. Better to look for a whole pumpkin I would reckon

[LAA66]

any idea on how bad it is to change out existing gears with new ring and pinion and sure grip unit? I'm guessing its no walk in the park. Better to look for a whole pumpkin I would reckon

 

 Two hours to swap pumpkins, Plus you have the option if planning a long trip. Don't need sure grip going down the hiway.

   

[jimynick]

I had a 67 Valiant with a 340, 4 speed and 3:91's and it'll put a grin on your face. The engine speed, if I remember correctly was fairly high; I want to say about 3600 @ 60-65mph and the gas mileage is not great. BUT, if it's a local toy, that may not be a big factor. I had a friend with 4:10's in a 340 Dart and it was too much in my opinion, for a street car. Either Popular Hotrodding, Hot Rod or Car Craft had an article on gear swaps in a 8 3/4 Mopar only a month or so ago. If you searched their web sites, I'm sure you'd find it. Don't forget the crown gear bolts are lefthand thread! Good luck. 

[Challenger III]

  My last Challenger had 3:91 gear 8-3/4. It was quite a bit of fun on the street!