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  #1 (permalink)  
Old 07-24-2007, 03:21 AM
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mopar gear cases

hey guys my appologies if im asking a question thats been asked already.

i have two mopar chuncks: one is a 741 casting with 3.23 gears that i would like to run with 26 inch tall tires.

the other is a 489 casting with an auburn pro series posi unit with 3.91 gears that i currently run with 28 inch tall tires.

my question is: can i take the the posi unit out of the 489 casting, and put it in the 741 casting??? or are the bearings or unit different between the two castings???

i want to put the posi unit on the 3.23 gears because on the free way..... 60mph is my cars comfortable speed....

OR would it be better to get a set of 3.55 gears? and continue to run them with the my 28 inch tall tires?

FYI::: im driving a 73 dodge challenger powered by a sb 360 with a 340 cam, headers, edebrock performer intake, 750 holly carb, msd ignition system. the tranny is a 727 torqueflite with a 2500 stall converter. sadly i have a compression ratio of 8.5:1, but at least i get to run on cheap gas ...... $3.25 a gallon where im at

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Old 07-24-2007, 12:42 PM
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I think the 489 has a bigger diameter pinion. But that is just from memory, a long time ago.
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Old 07-24-2007, 12:54 PM
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Any sure-grip unit (there is no such thing as a "posi" in a Mopar,sorry to pick nits) out of any 8 3/4 Mopar diff will swap between carriers.I believe however,the side bearings are different '70 and later,but no biggie.I think I'd go with the 3.23's,just my opinion.
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Old 07-24-2007, 01:06 PM
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i just wanted to put the "sure-grip" in the 741 case.... just dropp it right on in there... bearings and all.... all i would do is just take the 3.91 ring off and putt on the 3.23 ring. could i do that?

oh also, 26 inch tallers are a cool size for 3.23's yea?
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Old 07-24-2007, 01:16 PM
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3.55's bad idea??? i would most likely save more gas with smaller tires huh???
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Old 07-24-2007, 01:17 PM
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Go to Cuda-Challenger.com I sure they can answer
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Old 07-24-2007, 02:20 PM
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Quote:
Originally Posted by Arillious
i just wanted to put the "sure-grip" in the 741 case.... just dropp it right on in there... bearings and all.... all i would do is just take the 3.91 ring off and putt on the 3.23 ring. could i do that?

oh also, 26 inch tallers are a cool size for 3.23's yea?
Yup,should be a bolt in.I'm not saying the 3.55's are a bad idea,they'd probably be an excellent gear with those tires,but since you already have the 3.23's I think I'd use those...I had a car some years ago with a very similiar combo (I don't know the tire height,but I think they were a 255/60r15 if memory serves) and it pulled down nearly 20 mpg on the highway.
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Old 07-24-2007, 02:56 PM
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aaah i see what you mean. cool

the 3.23 gears belong to my gf's 68 dart; so i would be borrowing them, meaning i would have to take my chunck out, seperate my ring from the surgrip, then take out her open diff, seperate her ring from it then assymble my stuff with her's.... blah blah blah.... and then where her car is up and running, repeat the process and put the stuff back how i got it. lots of work.

i have an extra 489 case laying around with a open diff 2.76 gears in it, but my draw back is having to purchase a sure-grip and different gear set not to mention all the bearings needed.... geeze! total chunck rebuild.

i guess the smart thing to do would be to try and find another chunck with a suregrip and gears for cheap
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Old 07-24-2007, 03:36 PM
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Oh,I see where you're at.A pile of work,to be sure.
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Old 07-24-2007, 03:40 PM
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It's worth it in the end
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Old 07-24-2007, 04:12 PM
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Maybe I'm just stupid, but it seems like you plan to just swap ring gears between the carriers?
If so, NO you can't just trade ring gears.....the ring gear has to stay with the pinion it's with.
JA
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Old 07-24-2007, 06:18 PM
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lol jhonnya i wanted to just swap the 3.91 ring gear on the suregrip with the 3.23 gear, but then i would put it back in with the 3.23 pinion in the 741 case

thats one nice car bart! can wait till my cuda gets like that

sorry, but off topic question... whats the transmission kick down linkage do??? if my linkage was on a two barrel carb could i use it on 4 barrel holley? askin because i just found out mine wasn't hooked up right, so now when im in, say first gear and so forth, when the rpm start to get really high (if i let it get that high, by not shifting) i hear a little air noise... nothin scary but it sounds like air blowing faintly. now i have the linkage hooked up correctly and the tranny automaticaly shifts better.

any input on that comment?

i know its off topic just though id ask

Last edited by Arillious; 07-24-2007 at 06:26 PM.
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