68 Charger rear end gears. What do you have and what do you recommend?

[yamanut1970]

I had great luck with the recommendations I received for replacing my motor mounts so I thought I'd see where I go with this!

I have a '68 Charger R/T clone. I had the 440 done two years ago. The block was line bored, decked and bored .30 over. The crank was balanced. Had Speedpro 10.5:1 pistons installed. An Edelbrock top end kit with aluminum heads/intake and cam were installed. It's topped with a Holley 780 and is using the stock cast manifolds, 2 1/2" exhaust with Magnaflow open chamber stainless mufflers.

The motor works great!........BUT

I have a distant memory of my uncle taking me for a ride in his '68 R/T with a 383 Commando in it. I remember that car stuffing me back in the seat helpless to touch the dash no matter how hard I tried to lean forward to get it. which brings me to the title of this thread.

The rear gears are 3.23's. I realize that I will be sacrificing my currently stellar gas mileage ;) but I'm contemplating changing the rear gears. It's an automatic and very rarely leaves town (little to no highway) Can you let me know what you're running, have run, liked and hated.

I have been looking around online and seen whole carriage assemblies and there seems to be 3 different part numbers 489, 741 and 742. I'm guessing these refer to the pinion shaft diameter?? How can I tell which I currently have in the car?

Thanks and sorry for the short book!

 

[MikeyT]

Well, it kind of depends on what you want them for... 3:23's are a great gear, but if you feel you want more oompf off the line, a 3:91 or 4.10 is good. I know lots of people run 3.55 as a best of both worlds...

All three units work very well, but the 489 and 742 foir some odd reason are preferred... However the 741 has a pinion shaft almost as big as a ford 9 inch, so go figure. i personally like the 742 because you don't need crush sleeves.. However all are good.

Mike

 

[Seax440Dodge]

I went from 3.23's to 4.10's.............................. annnnnnnnd I absolutely hate it... while they are great if you don't plan on any highway driving at all, it gets annoying real, real quick


as far as ID'ing the carriers...

You can tell by looking at the center section, on the driver's side you'll see the casting numbers like on this one:




Last 3 digits say what it is, this is a 741, as you can see (a 489 will also have a big 9 cast in it where the X is on the 741)

 

[Lenny Arsenault]

I really like your charger looks exactly like the one my sisters x husband use to own. They bought a brand new Yellow RT, 440 four speed, with a black top, 3:55 gear dana, black interior, same rims with red line tires. You don't see to many yellow chargers around I think they look great. My brother inlaw did race it stock at first ran about a 9.50 seconds 1/8 mile next year added a few things like headers, more gear, aluminum intake, holley 750, went about 8.50 then wanted to go real fast and had it bored, balanced, lots of head work, not exactly sure about all that was done but, the car didn,t go one tenth of a second faster after spending about $3,000.00 on it back in 1971 and gave up parked the car with 29,000 miles and just sat there and rusted into the grave never to be used again. What a shame was such a great looking charger.

 

[HYRDGOON]

I had a thread where I essentially asked the same question and do similar type driving as yourself. Here's the thread and replies if it helps

http://www.forbbodiesonly.com/moparforum/showthread.php?56617-Gears-3-55-vs-3-73

 

[The Beep]

I have a 68 Roadrunner with a mild 383 4 speed. A few years ago I went from 3:23's to a 4:10's. The difference was crazy stupid! Gas mileage sucks way more and rev's went up to over 3k at 50 mph.

The car has no headrests and I can kill passengers at will!

I freaking love it!

 

[69redrunner]

69 roadrunner with a 4 speed...fender tag says car was built with a 3.91 was replaced at some point with a 3.55. Just under 3k on the tach @ 65mph with 15" tires

 

[Dennis H]

3:54 Dana here. Sweet Charger. Love the color and the smoldering.

 

[Kerplunk]

I went from 3.23s to 3.91s and its a good gear around town, a bit too low to be doing a lot of highway driving, but good for what I do. The difference in acceleration however, while notable was not jaw dropping.
Also, Id look for a good centre section and use that with the new gears, and keep your current centre section so you can swap back and forth if you wanted to.

 

[68 HEMI GTS]

3.91 is a good street/strip gear, just don't plan on driving 80mph down the freeway and you'll be fine.

 

[moparcanuck]

3.91 is a good street/strip gear, just don't plan on driving 80mph down the freeway and you'll be fine.

x2

 

[yamanut1970]

Can I ask what you ended up going with?

 

[68 Sport Satellite]

I had 3.91s in a 742 case in my 68 satellite column shift small block auto. It was fun around town, but just an hour on the freeway at 70mph was too much for me. I kept the 742 case and swapped in 3.55s. Great on the freeway. Pretty decent around town. Then I drove my buddy's 440 car with auto and 4.56 gears and when ya get on it it'll snap your neck back. Sweet. Sucks at freeway speed in a big way though. I will be swapping in a 451 big block soon and then with my 3.55s it should be just right. May get a set of 4.10s with a separate case and carrier for swap and go fun.

You also will see 3.73s offered but I have heard that was not a ratio offered for our cars at the time yours was built.

You said not much freeway driving. I say go for 3.91s or 4.10s especially with your auto trans.

 

[HYRDGOON]

I'm pretty sure I'm going to go with the 3:73's when I can finally get around to it... Seems like a good compromise gear as I do a little bit of highway driving but not often.

 

[soundhd]

I suggest searching for a rear gear charts on the internet.........they will give you info like rpm's at any speed using your tire size. You have to decide what kind of driving your going to be doing, long trips, short trips, combination of the two, street & strip, etc.....
Everyone's needs are different...

 

[moparcanuck]

This is a good one: http://vexer.com/automotive-tools/speed-rpm-calculator

 

[yamanut1970]

Thank you everyone for your advice. I was able to get my hands on a 489 case with 3.91's and sure grip for a great price. I'll be installing it in a couple of weeks and will post up my take on the differences. Oddly enough, I purchased if from someone who switched to 3.23's (what I currently have) because he wanted better mileage and the ability to drive longer distances on the highway!

 

[am3rican]

I have a 440 6-pack with 3-spd. I currently have 4.10 and can tell you that it is great for the drag strip but horrendous for the highway. The car roars at 55mph. But I can tell you that my passengers want 'oh ****' handles. Launches are violent and will snap your head back.

 

[Meep-Meep]

The gears should pretty much go with your cam and basic engine tune. And all that depends on what you built the car for. 3.55 is a great street / strip gear with a mild cam. You will use the full potential of the motor in a 1/4 mile run and it's not unbearable on the hwy. If you do a lot of hwy driving, which you said you don't, then I'd go taller like 3.23's or even 2.94.

 

[moparcanuck]

A lot depends on your tire diameter as well. Most of us are running larger diameter tires than what came on the car. For example, running a 3:23 with a 28" tire (not stock size) will give you a final gear ration of 3:00.

Here's how to calculate your final gear ratio when you are not running stock tires: http://www.4lo.com/calc/geartire.php