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Rear axle ratio advice
https://slantsix.org/forum/viewtopic.php?t=7065		 Page 1 of 1
Author:  DiggerDave [ Tue Sep 30, 2003 11:02 am ]
Post subject:  Rear axle ratio advice
Need some advice from those experienced. My 16 year old son & I have been preparing his 1973 Duster for his soon to be daily driver. This is a slant 6, single barrel stock power plant with standard automatic. We upgraded the front brakes to disc and just replaced the 7 1/4 rear end with an 8 1/4 (open diff.), mostly to get the matching larger bolt pattern, but to handle later power upgrades as well. The 7 1/4 rear had a 2.76:1 ratio and the 8 1/4 has a 2:45:1 ratio (it came from a 318 '74 Dart 4-dr). We plan to put 15" wheels & a bit lower profile tires on at least the rear.

My question: will the slant have difficulty moving this car with the intended set up? We are not yet looking for racing ability, but economy and driving experience for now. There are plans for upgraded intake and exhaust sometime in the future, and a lower limited-slip gear ratio likely to accompany it. But, not much room in the budget for now, unless absolutely necessary to make the driving bearable.

I have to applaud my son for choosing a 30 year-old mopar over the newer fancy and faster rice burners of his friends, and am trying to do what I can to allow him to keep his head up in his choice to be different.

Any help is welcomed and appreciated.
Author:  Super6 [ Tue Sep 30, 2003 11:23 am ]
Post subject: 
With those 2.45's, highway cruising (once you finally got to speed) would be nice, but around town that gearing would be too sluggish, in my opinion. Even the 2.76's were probably a bit sluggish, I know they are too steep for my tastes in my truck.

Personally, I would go with 3.23's for a good balance between around town 'get-up-n-go' and highway cruising. Stepping up to 3.55's with a 3 speed would probably make for more highway rpm's & noise than you could bear for a daily driver.

My .02

-S/6
Author:  Dennis Weaver [ Tue Sep 30, 2003 11:53 am ]
Post subject: 
Yeah, I had 2.45's in a '75 Scamp with a 318. It was a dog. Factor in a slant 6 and relatively tall tires on 15 inch wheels, and it's gonna be like starting out in third gear ;)

One possibility: If you are going through the transmission anyway, you can retrofit some A-999 type planetaries which will lower first gear from 2.45:1 to 2.74:1, and second from 1.45:1 to 1.54:1. The factory did this so they could run ridiculously high (2.21:1) gears in cars like the LeBaron, Dippy, 5th Ave and such... It would help some with that 2.45 without having to swap rear gears.

"DW"
Author:  DusterIdiot [ Tue Sep 30, 2003 1:19 pm ]
Post subject:  Weight + Drag + Gears= slug....
I currently have a '74 duster with a 7 1/4" 2.76:1 rear ratio in it and even with the nicer 3.09:1 first gear in the A-230 floor shifted manual I have to burn clutch to get the 3350 lb slug to motivate...

For your application and 'utility' of street driving 3.21's in the 8 1/4" will be fine and provide nice off the line performance (even when the engine is cold and 'cranky'), and will retain your mileage...

Unfortunately due to the change in the diff. casing for 2.45 and lower...To use any thing longer (2.76-4.+) you need a new case, if you bought a new sure grip unit you won't need it...also if playing it cheap and can bear a little gear whine, find a pre 1994 dodge truck in the local yard with a 10 bolt round cover rear, check the ratio, check for 'sure grip', pull the gears, casing , and speedo gear and find a reputable rear-end shop that can put your gears in....

just something to chew on...

-D.Idiot
Author:  kesteb [ Tue Sep 30, 2003 5:10 pm ]
Post subject: 
I am currently running 2.45s in my '65 Dart. I also have a 4 speed, a tried \6 and 15" rims with 26" diameter tires. It handles the gear OK, really steep hills are a problem (lots of clutch slipping). Moderate hills are OK and it runs very nicely on the freeway. Mileage is so so, mostly because you have to rev the engine out to get any speed around town.

On a recent trip to Bo WA. I was able to keep up with the candians and their bimmers. At 75 and 80, the engine is just loafing. And the candians get this worried look when a beat old '65 Dart is passing their new bimmer.
Author:  Dennis Weaver [ Tue Sep 30, 2003 10:51 pm ]
Post subject: 
My Kermit loves breezing lazily by bimmers and other associated glitzy country club crap with annoying driving lights.

"DW"
Author:  DiggerDave [ Wed Oct 01, 2003 10:17 am ]
Post subject: 
Thanks fellows for the advice, it seems my fears of sluggishness may be realized.

DusterIdiot, you might have brought some light to the subject with your truck axle idea. My father has a 1976 dodge club cab with a shot 360 and I am sure it has a sure-grip. Just need to check the axle type and gear ratio. Been trying to get him to junk the truck since it quit running 6 years ago. If the axle/carrier is the one we need, it might be the reason to tip the scale to deal with the truck.

If not, we live in Ocean Shores, Washington, with the highest hill at about 12 feet and most of his longer distance driving would be on the highways with increased speed and the problem may not be as noticeable.

Do you guys have any advice for easy mods to get more lowend torque to help pull it off of stops with the high rear end? I would think that the exhaust system is one thing to attack first. Any help?

Thanks
Author:  kesteb [ Wed Oct 01, 2003 12:58 pm ]
Post subject: 
I had my Dart up to Ocean Shores a few months ago and had no problems getting around. I have a love/hate realationship with these gears. They work really, really nice when on the freeway. You also have to work the gear shift a little bit more when around town. Beware of really steep hills, expecially if you get stopped on them (E. Denny in the Capitol Hill area of Seattle comes to mind). It is quite amusing when you are still in 1st and the rice bucket next to you has shifted twice. You have to get used to being passed on city streets and I feel there is really not that much differance then running a set of 2.7s.

Do you know who owns the puke yellow big block valiant? I saw it in front of the taffy store when I was up there. It looked very interesting, and I dont' see how anybody can cram a 440 into a '61 valiant.
Author:  DiggerDave [ Wed Oct 01, 2003 3:39 pm ]
Post subject: 
I have seen the valiant a number of times over the last two years but it has never been stopped in order to talk to the fellow. It sounded fairly healthy when running, but I just guessed it had a small block. It would take some oats to churn those back meats on it though. I'll keep a sharper lookout for it, but I am only there on the weekends, as I work in Mukilteo during the week. I see that is somewhat near your neighborhood.

Oh. Been on Denny several times and know what you mean. My fear would be climbing Queen Anne Hill. Anyway, aren't those rice-rockets behind you on the hills for resting back on as you get your clutch to workin' And grabbin'.
Author:  kesteb [ Thu Oct 02, 2003 2:41 pm ]
Post subject: 
Tempting, but I value my tail lights to much.
Author:  Guest [ Thu Oct 09, 2003 6:01 pm ]
Post subject: 
For what it's worth, we're putting 3.91:1 gears in my 18 yr old son's 60 Dart. My theory, he'll be a hero from zero, but no real top end with the 5500 chip Dad put in the MSD 6AL.

Just my $0.02

Gilly
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