3.21 8 3/4

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RPMLegends18

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Hi All,
Im new here, but have posted at BBD a couple times. I have a 74 2 door Swinger orginal slant six. I got a 360, bought a v8 k-frame $125 and swapped it in. A buddy of mine built me a 727 and I was planning on running the 7 1/4 rear end until I found an 8 1/4 and hopefully an 8 3/4 well I did just that, got an 8 3/4 out of a 72 Duster for free. The tag on the rear diff cover says 3.21 is that a good gear, like good for torque or is that more of a high end gear? Its a non sure grip.

Thanks,
Ryan
 
3.21 never heard of it..i know 3.23-3.55 are the gears i wanted for my street/strip combo..bc lower...no go...higher..when cruisin, high rpms... unless you're stick or have an overdrive tranny...3.55 is ideal..3.23 is fine..
 
that is a good high way gear use it its free and strongser than the 7 1/4
and with the one legger you can do some serious corner burn outs and not lose it as bad as with a posi :cheers:
 
well its written on the housing 3.23 and theres a little metal tab on one of the bolts for the diff cover thats stamped 3.21, so I assumed the gear was actually 3.21 just marked a 3.23... probably wrong though.
 
what are you building up for...if ur wnatin to do drag..i'd recommend at least 4.11...but if it's gonna be street...you're is fine...you can always get an open carrier 3.55 quite cheap...everyone wants posi..but unless you do burnouts constantly and need both wheels goin..or if it's a drag car..you shouldn't need it...
 
stupid me, i thought it was an 8 3/4...I will have to measure it, actually were do you measure it? thats probably why i thought it was an 8 3/4
 
Are you sure it's 3.21 (and are you certain it's an 8 3/4?, 8 1/4's had a 3.21 ratio) if it is an 8 3/4 look at the tag again, maybe it says 3.31. There was a ratio of 3.31, as refrenced on these 2 different web sites.

http://www.geocities.com/MotorCity/Flats/1549/index3.html

http://members.tripod.com/~Mojo_Page/chry875.htm



EDIT: Just realized after I posted that while I was writing you posted some other info.
The fact that it has a cover instead of the big carrier chunk proves it must be an 8 1/4.
The 2 links I provided will supply you plenty of info.
 
I am not sure, the car is out at our shop. we live in the city and my grandparents have a place out in the country with a shop and its out there on the car hoist. So on my day off on wednsday when I go out there I will snap some pics and count the bolts.
 
or easier yet...does it HAVE a rear differential cover?? the 8 3/4 rears were solid in the back, and opened in the front. My guess is it is an 8 1/4. and it is possible you have 3.21 gears, thats what my 8.25 came with.
 
I'd like to say that if the engine has a good torque curve down with a decent start in the curve down low, the gear ratio isn't to bad. It will make an OK street gear for messing around. Do not make the tire to tall or spinning the wheels will be hard.
 
No problem. Tht gear will have long legs and go well in the top end or in passing on the Hwy.
Your not going to be killing the comp. to well, but it will be good to drive.
 
My friend has 2.73 gears in his 69 firebird and that thing is a pig off the line..should I expect any better from these gears?
 
the 3.21 should be a lot better than 2.73s. 2.73s are pretty much highway gears no low end but will pull 140 if the car will do it. The 3.21 should be an ok street gear i have them in my duster and im happy i could do with 3.55s but the 3.21 is fine for now
 
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