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Discussion Starter #1
Hey ya'll, a fellow member on this board has for sale a posi unit and 3.92 gears from a 98 dakota with a 8.25 rear end. My 99' has the 8.25 with 3.55's and is open...my questions:

1) is a case change necessary if going from oem open to posi?
2)oem posi clutches aren't too durable and a rebuild kit is $90, don't know how hard that is to install either???
3) do i have to remove ring and/or pinion to install the posi unit or no?
4)if i have to remove ring/pinion, about what does it cost to have a shop put it back in to set the right angle, pitch etc?
5)I know lower gears will provide better towing, take-off's etc but how much will it hurt my mileage with a bone stock 5.2? I drive 500+ fwy miles a month so it's fairly important but i also occasionally tow a 5,000lb 21ft' scarab boat.

Regards, -Dan


PS, my bad on the title it's 3.55 NOT 2.55...hit the wrong key
 

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unless your swapping out axles completely then you will have to take your ring and pinion out to put in the 3.92
 

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in your case I'd just swap rear ends and be done with it. less work than swapping guts

yes the differential carrier would have to change to go from open to posi as the clutches are incorporated into the carrier but the housing does not have to change.
 

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Hey ya'll, a fellow member on this board has for sale a posi unit and 3.92 gears from a 98 dakota with a 8.25 rear end. My 99' has the 8.25 with 3.55's and is open...my questions:

1) is a case change necessary if going from oem open to posi?
2)oem posi clutches aren't too durable and a rebuild kit is $90, don't know how hard that is to install either???
3) do i have to remove ring and/or pinion to install the posi unit or no?
4)if i have to remove ring/pinion, about what does it cost to have a shop put it back in to set the right angle, pitch etc?
5)I know lower gears will provide better towing, take-off's etc but how much will it hurt my mileage with a bone stock 5.2? I drive 500+ fwy miles a month so it's fairly important but i also occasionally tow a 5,000lb 21ft' scarab boat.

Regards, -Dan


PS, my bad on the title it's 3.55 NOT 2.55...hit the wrong key
Just last week I got 19.2 on my 5.2, taking it easy, no ethanol gas. It has had a cam change, roller rockers, headers and high flow exhaust, looser converter, computer change, modified OE intake, and 10.5" wide tires. :drive:
 

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Discussion Starter #5
in your case I'd just swap rear ends and be done with it. less work than swapping guts

yes the differential carrier would have to change to go from open to posi as the clutches are incorporated into the carrier but the housing does not have to change.
thank you very much, that's what i was wondering! Sounds like a headache not absolutely necessary haha
 

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Discussion Starter #6
Just last week I got 19.2 on my 5.2, taking it easy, no ethanol gas. It has had a cam change, roller rockers, headers and high flow exhaust, looser converter, computer change, modified OE intake, and 10.5" wide tires. :drive:
that's good mileage! What gears? I'm rethinking my 3.55's they're not too bad except when towing trans how to downshift up the slightest grade...
 

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that's good mileage! What gears? I'm rethinking my 3.55's they're not too bad except when towing trans how to downshift up the slightest grade...
I intended to post that they are 3.55's. That is not typical, usually I am in the 17's. I was driving to get as good of mileage as I could.
 

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Discussion Starter #8
yea that's what i figured, thanks for sharing!:) I think i've made my decision...considering it's not an off-road truck nor is it a drag-strip king, i think the open rear end is fine for my application and switching gears is too much of a PITA unless i had more motives such as heavy towing or 1/4 mile showdowns. Thanks everybody for the advice, -Dan
 

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yea that's what i figured, thanks for sharing!:) I think i've made my decision...considering it's not an off-road truck nor is it a drag-strip king, i think the open rear end is fine for my application and switching gears is too much of a PITA unless i had more motives such as heavy towing or 1/4 mile showdowns. Thanks everybody for the advice, -Dan
If you just want the posi with your 3.55 gears, it's a pretty easy job. The hard part would be the gear setup (pinion gear, in particular), which you don't have to worry about when you only change the carrier.
 

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Discussion Starter #10
Yeaa, what i found was a 9.25 3:92 lsd rear our of a dakota r/t for $100! i know the driveshafts are the same length and that my brakes will bolt up...i think i'll need different u bolts but what else should i be on the look out for or aware of?
 

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Old Fart
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Yeaa, what i found was a 9.25 3:92 lsd rear our of a dakota r/t for $100! i know the driveshafts are the same length and that my brakes will bolt up...i think i'll need different u bolts but what else should i be on the look out for or aware of?
Is it a posi? If so, take the cover off and look for pieces of clutch plates in the bottom of the housing. Turn the pinion yoke slowly and feel for any roughness in the bearings. You shouldn't feel any. If everything looks good and feels good, it's probably in good shape.
 
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