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28 spline vs 31 spline Rears

Mosesatm

Well-known member
Joined
Jan 18, 2005
Messages
9,009
Are all 2.79 rears 28 spline units?

Which units have 31 splines?
 

robert campbell

Well-known member
Joined
Apr 10, 2007
Messages
4,321
Arlie,
To my experince The rear end in you car should be an 8 inch vice a 9 inch. 390 or 428 cars mostly have 9 inch rear ends. Some "J" code cars may have a lower (3.50 to 4.11 ratio) which may be a nine inch a posi and have 31 splin axls. All in how the buyer checked the option sheet. Any thing could happen.

To my knowledge all 2.79 rear ends of the 8 inch variety are 28 spline. Many 9 inch open rear ends and some posi 9 inch are also 28 spline. The lower ration 9 inch, 4 pinion, traction lock (posi) rear ends mostly or all have 31 spline axels. Hope this helps.

Rob
 

68gt390

Well-known member
Joined
Feb 22, 2004
Messages
2,021
Location
Columbus, Ohio
Arlie;
Rob is right online. Even a lot of your big block cars are 28 spline even though they have the 9" rearend. It depends on your gear ratio. The easiest way to identify them is look at the end of your axels - they have an oval shape to them. If they are hollow on the end they are 28 spline and if the oval is filled in and solid they are 31 spline if that makes sense to you. That's how it was explained to me. Again, it would all depend on your rear end and gear ratio.


Don :wink:
 
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