UPDATE!

After about three months of waiting and searching i finally got my hands on an 8 1/4 from an m-body station wagon with 3 speed auto and a 318, i took off the cover when i got it home but i couldn't find out the gear ratio, shouldn't it be stamped on the ring gear?

So my question for anyone reading this is... what kind of gear ratios did m-body station wagons get when equipped with a 318 and auto trans ?

I found a tag on one of the cover bolts but all that is written on it is "1406"


For the love of god i hope it ain't one of those 2.45 ratio units, they wouldn't have been cruel enough to use such a wimpy gear in a wagon right?

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79 sportsman window van 318 4bbl

It's easy to figure out what the ratio is. It should be stamped on the ring gear, and it seems odd that yours isn't. IIRC, the ratio should also be stamped on the housing around the carrier somewhere (or is that only 7.25"?).

If nothing else, grab some chalk, and do the old "How many turns of the pinion does it take to make 1 revolution of the ring gear?" trick.

~THOR~

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1984 D100 Shorty Custom
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Count the teeth in the ring and pinion gears, divide the ring gear tooth count by the pinion number.
Example: 44 / 18 = 2.44444 or 47 / 17 = 2.7647
DD

Will do! thanks Doc.

THOR: Yeah i cleaned her up real nice and still couldn't find it, so i'll go ahead and start counting those teeth.

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79 sportsman window van 318 4bbl

Whoa! hold on a minute, i counted 47 teeth on the ring gear but 21 on the pinion 47/21 = 2.2380 so unless i miscounted the teeth (checked three times) that means my ratio is 2.23

I'll probably check again tomorrow in the daylight for the hell of it but providing the ratio realy is 2.23 can it be changed? or is this rear end like the 2.45 carrier units that can't have the gears swapped.

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79 sportsman window van 318 4bbl

Very well could be; my buddy had an 81 mirada, 318, 8-1/4 rear and it was a 2.2x ratio. Also my Moms 84 5th had that ratio (at least its not a 2.45 so it should be alright, huh?)

Well doing a little more digging around this great site, i found some posts mentioning 2.24 and 2.45 carrier units being incompatible with any lower gear sets.

All though some posts lead me to believe i can swap in a carrier from a 94 and down truck 8 1/4 then use what ever gear set i choose, anyone know if this has been done before?

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79 sportsman window van 318 4bbl

Yup; common swap; except that the highest year I believe is a 96 dakota not 94. Lots of B vans used that rear end too; just knock the "exciter ring" off, that triggers the ABS brakes; while it won't hurt anything; there may or may not be clearance in your older housing for it.

Groovy.

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79 sportsman window van 318 4bbl

Well the swap is nearing completion, found a carrier with new ring and pinion 3.21 had a local drive-train place set her up right and now all that has to be done is a brake bleed and of coarse obtaining the right drive shaft.

So providing i can't find a stock replacement, how much does the 7 1/4 shaft have to be cut down for an f-body ? i read some were that 1.6" has to be taken off but that was in regards to a 74 Dart.

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79 sportsman window van 318 4bbl

sounds about right; I did a 7-1/4 to 8-1/4 swap in a 90 Dakota and that #cut off the shaft sounds about right. It don't matter the chassis; any time you go from a 7-1/4 to an 8-1/4 (unless you're also changing to a different model tranny too) in a given vehicle that number is gonna stay constant.

Good stuff thanks man.

Can't wait to get this puppy back on the road and see what the new gears are like.

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79 sportsman window van 318 4bbl

When I swapped out my 7¼ for an 8¼I had the shop take off 7/8". I found that # here somewhere, but I'm not too sure where. Mind you, my car is a '70 dart, but it should still be the same change.

Nat

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

Well a few days ago i had it shortened 1.6" and after i got it home and installed a new u-joint , i stuck her in there and it seemed to fit just like it did when hooked up to the old 7 1/4 rear.


The 3.21 gear set is real nice for this heavy old f-body.

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79 sportsman window van 318 4bbl

hell razor, check out [url]moparstyle.com[/url] go to the FMJ Body section and look for my post on "rear end ID ". if your still slant powered, I would reccommend sticking with a 8 1/4", 8 3/4" is over kill in my book. I too own a F-body, '79 Volare 2dr, so I know how difficult info can be to find sometimes. remember any FMJ part from '76-'89 will interchange with your car. If you have any questions please feel free to ask


-Mike

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