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Old 09-06-2010, 02:08 AM
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8.5 question

couple months ago i got this 75 firebird pont400 4speed come to find out they put in an auto rearend.i think its got under 2.42 what ratio should i go with an should i upgrade the 28 spline axles

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Old 09-06-2010, 03:35 AM
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Quote:
Originally Posted by 87fubar
couple months ago i got this 75 firebird pont400 4speed come to find out they put in an auto rearend.i think its got under 2.42 what ratio should i go with an should i upgrade the 28 spline axles

The Carrier in your 8.5" will accept 2.56 & Numerically Lower gears. You'll need another Carrier for 2.76 & Numerically Higher gears.
3.42 is a decent gear for street without turning to high rpms while cruising.
3.42's & 3.73's can be found cheap used as they came in many cars/trucks. Used Posi's also.
For strip use 3.73, 4.10 etc..
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Old 09-06-2010, 09:23 AM
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I build many of these rear ends. With the 4 speed and 400 I recommend a 30 spline Eaton Posi or Duragrip and 30 spline Moser axles. The 3.42 gears are very popular for people who drive their cars a lot. 3.73 is all right if you won't be on the highway. Use quality parts. Don't try to save money by getting bargan brands. Don't forget a good installation kit.
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Old 09-06-2010, 09:23 PM
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would it be just dif axle bearings to fit 30 spline axles or would i have to do somthin to the housing
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Old 09-06-2010, 09:27 PM
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Quote:
Originally Posted by 87fubar
would it be just dif axle bearings to fit 30 spline axles or would i have to do somthin to the housing
The axle bearings will be the same, the 30 spline axle just doesn't get skinny down at the spline end like the stock 28 spline axles do. They both fit in the same bearing.
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Old 09-06-2010, 09:31 PM
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Quote:
Originally Posted by 87fubar
would it be just dif axle bearings to fit 30 spline axles or would i have to do somthin to the housing
The 30spl axles use the same bearings, no mods needed. The Eaton Posi Carrier does use a different Carrier bearing, these would be changed anyway.
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Old 09-06-2010, 09:59 PM
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what kit should i look for the 30spline carrier
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Old 09-06-2010, 10:11 PM
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Quote:
Originally Posted by 87fubar
what kit should i look for the 30spline carrier
Kit will have HD at end of Part #.
http://completeoffroad.com/i-161333-...duty-rear.html

http://www.ringpinion.com/ProductDet...px?ProdID=1665
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Old 09-06-2010, 10:17 PM
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thanks all for the info helped alot
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