I read through a bunch of articles trying to gain some insight but everyone seems to be a bit more savvy on the specs than I so I would appreciate a little education 101 on my 7.25. I'm got a 63' Dart 170, /6 225, 76' A833 OD while everything else is stock. I thought I had a 8.25 rear end but learned I have the 7.25. There's lots of talk about changing the gears. I don't race the car is my daily driver, I take trips once in awhile mostly highway driving. Are there any changes I should make to my stock gears that would improve gas mileage? That would be the only thing I'd want to address, it seems to be in good shape, no noise and sounds good when I jack it up and spin the wheels. If it aint broke don't fix it I say but if there are any advantages in making changes I'd like to know what they are.
Thanks in advance,
Brian

What ratio is your 7 1/4"? Selections of new gears are limited, but there are several ratios available in complete rear ends.

You can also change the effective gearing with tire height. Watch the tire/wheel weights and width.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

You need to find-out what gear ratio is currently in the car.
Most likely, it is a 2.93 ratio.

The ratio is stamped on the side of the housing but it takes a good amount of cleaning and a sharp eye to find it.
The ratio is also stamped into the side of the inner ring gear but you have to pull-off the rear end's cover to see it. (you will need a replacement gasket if you remove the cover)
DD

See:

http://www.slantsix.org/forum/viewtopic ... atio#96927

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Were would one find the ratio stamped on an 8 3/4" rea rend? If I have to I can jack & count, but would rather rub & read.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I just got a new gasket because I'm planning to replace the old one so I will check the ratio and get back to ya'all. I did just purchase 14" rims with good tires on them my original 13" tire size was 185/65/13 and the tires I got on now are 195/75/14 a whole inch larger in circumference. So that might be a reason to change the gear ratio ? Again talk to me like a 4 year old regarding the differential, I'm just learning.
Brian

I just did some research and found a couple companies with 7.25 parts information. According to their info my ratio is 2.93,3.55,3.90.or 4.10 those are my options from 1963 to 97. Now that I know I can get any of these ratios and still pending is the identification of mine, with my wheel size 195/75/14, or maybe 195/70/14 and a 1976 A833 OD behind a 225 stock is there a ratio that will work to my advantage for economy. No racing or tricks just straight cruising.
Brian

Okay guys, I pulled my differential cover to change the gasket and looked for some numbers, couldn't find any even on the outside case on the little wing. I counted the teeth of the large gear that stands upright, forgive my lack of proper identification, it had 41 teeth. Does that mean it is 2.93 ratio?
Now is this a good ratio for my car with the transmission I have and wheel size as posted in previous posts.

Brian

If there are 14 teeth on the pinion, yes, you have 2.93 gears. 41/14=2.92857... It's a fine ratio for economy, but high gear gear in the A833OD can't be of much use behind the 170.

BTW, the large gear is commonly known on these shores as the ring gear. East across the big pond it's the crown wheel, but here we don't name things after the monarchy.

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Joshua

The 2 7 1/4's I own have a tag on them. Hanging on the rear cover. I have 3:23's in my 72. Nice street gears.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

hello bubs- was reading your thread. interesting combination, 63 dart, 170 inch engine, 4spd. od trans and 2.93 diff. that would give you a final ratio in od of 2.15. thats the same deal in the 76 feather duster - think that was the best possible ratio combo for mileage, mine gets 25-32. only differences with yours is the 170 engine which is a little less powerful than the 225 in the feather and i think the feather is a little lighter than your 63. how does it run on the flat in od at lets say 35mph? the feather runs comfortably in od at 30 . plymouth also made a 2.45 diff. always wondered how that would run with the od in a duster. that would give a 1.78 final drive which might be too tall to drive comfortably even with a 318 v8 but that engine would negative the gas mileage. what do you think? regards bob fisher

The Feather Duster is much heavier than a 63 Dart. I would guess at least 600 pounds. 185/65r13's would measure just under 23" and the 195/70R14's would be just over 25" tall. That is a big difference, without changing the speedo gear in the trans your speedo will be reading way lower than you are actually going(about 10%). You can go too far when it comes to gearing in respect to fuel milage, if you get your rpm's too low you will not have enough torque to pull the highway speed and end up loosing milage.

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Thanks for al the posts guys, the discussions really help to answer my questions. By the way 170 is my model number, I have the 225 /6 under the hood. When I pulled the cover off my differential it looked like new, all the teeth look the same none broken and everything moves nice and smoothly. Just seems amazing for a 44 year old car which happens to be an awesome car.

Brian

sorry, dub post

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http://imageevent.com/jeffc
62 D100 225 3sp lwb
64 D100 A318 727pb custom lwb
66 D100 A318 4sp lwb
68 D100 B383 727 swb
65 Belveder A318 727 4d
65 Dart GT LA273 2bbl 904
73 Scamp 225 2bbl 4spOD
Old iron or no iron

_________________
http://imageevent.com/jeffc
62 D100 225 3sp lwb
64 D100 A318 727pb custom lwb
66 D100 A318 4sp lwb
68 D100 B383 727 swb
65 Belveder A318 727 4d
65 Dart GT LA273 2bbl 904
73 Scamp 225 2bbl 4spOD
Old iron or no iron