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Currently my 9" rear end is out of my m code conv. I am considering converting it to a posi. It is a 28 spline 3:00 ratio unit. What do I need to do to change it? Do I buy a third member from another car or simply buy a posi unit to fit in mine. If I went to a 3:25 or 3:50, would I notice much acceleration difference and how would that complicate matters? Any advice would be helpful. Any one have a unit?

Jim
 

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You don't need a new housing. You have a few options. If you go with new stuff, the easiest but most expensive would be to buy a complete center section with a posi carrier and the ratio you want. Or a cheaper route, you might be able to find the package you want used since the 28 spline axles are more common. Another would be to get a posi carrier alone, a new ring and pinion in your chosen ratio, and a rebuild kit with shims and crush sleeve and rebuild your existing center. I've never successfully set one up for the street that didn't humm. On the oval track cars it wasn't an issue. You absolutely must get the mesh of the ring and pinion right or it will humm.

If you need to have a pro set it up after you purchase the components, you might be up in the price range of a complete unit purchased as one.

I don't think you'll see all that huge of a difference between a 3:00 and a 3:25. Moreso with a 3:50. A jump to a 3:89 or so will be very noticable. Either way, expect to see a noticable difference in your gas mileage GOING DOWN.

Mark
 

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I recommend the new "soft" Detroit Locker. You can buy the differential in 28 or 31pline from Summit for about $400 and install it in your existing center section.
 

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I just bought a Detroit Locker from www.Ring-Pinion.com
It is for a 28 spline, it ran $449. I have 3:70 gears and I went from a 3:00, it was very noticeable, but the RPMS are very high, too high for long trips.

RayJ
70 XR7
 

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I keep a 2.75 for road trips and have other ratios for the drag strip. It's easy to swap after you know the drill.
 

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I have one set up with a Powertrax locker and 3.25s, One Ford trac-lock with 3.50s, 2.79 open (road trip! :D ) and one I haven't taken apart yet from a 68 BBF Tbird. My Chebbie buddy is pretty green when I swap gears to fit the event!
I prefer the 3.25s but I regeared my C6 for a lower 1st gear ratio.
 

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Oh Boy

Now you guys got me all confused,I have my 4.11 posi out of the car I found a set of 3.50s I am was going to put in .But I got the original 3.00 sitting on the shelf makes me want to do the swap thing its just the 4.11s arnt the best to do some freeway driving MMMMM................gotta think......:confused: :confused:
 

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Dan,

3:50's are great all around gears. I've been running them in mine since '94. I tach right around 3,000 rpm on the freeway with a C6 and 27" tall tires. It would be a tremendous relief from your 4:11's yet still allowing some get up and go.

I, too, have the stock 3:00's set up ready to go and only change to them when I go on those power tours and am racking up over 2,000 miles in a weeks time.

Just my thoughts... I think you have plenty of time to decide which direction you want to go.

Talk to you soon,

Mark
 

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My Cleveland tachs at 3000 RPM at 70+ mph. That is plenty of revs for me at speed. I use a 3:00 ratio open (for now), and a factory 4 speed. I can't remember off the top of my head what size the 14" Big-O tires are, but stock height or close to it.

Steve C.
 
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