Pinion spline on 489 case

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68 Coronet RT

68 Coronet RT

68 GTS # 508 in Registry
Joined
Nov 5, 2015
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Upstate New York
I'm looking to replace the 3.23 gears with a set of 3.91 Richmond Gears but they list 2 different pinion splines. One is a 10 spline and the other is a 29 spline. It will be going into a 68 340 automatic GTS. So without tearing it apart how can I find out which spline it is so I can order the gears. Thanks for any input !
 
If you take off the nut and washer you can see the splines without removing the yoke.
 
Long shot way to tell the difference is the size of the pinion nut, 1 1/4 is 10 spline, 1 1/8 is 29 spline........although I kinda look at it doesn't really matter what is in there right now as when you buy your new gears, buy a yoke that matches spline count of the pinion you buy, problem solved.
 
From Dr. Diffs site..........
If a 1 5/16" or 1 1/4" socket fits your original 8 3/4" nut, you have a 29 spline pinion. Otherwise, your 8 3/4" has a 10 spline pinion.
 
Daves69 said:
From Dr. Diffs site..........
If a 1 5/16" or 1 1/4" socket fits your original 8 3/4" nut, you have a 29 spline pinion. Otherwise, your 8 3/4" has a 10 spline pinion.
Click to expand...

According to the previous owner the case was rebuilt with less than a 1000k on it when I purchased the car and he thinks it's the 10 spline but not sure as he had someone else rebuild it. I just might have to wait to tear it apart to see.
 
I don't understand this. You asked a question and twice people have told you that the way to tell without tearing it apart is to see what socket fits the nut that holds the yoke on. If it takes a 1-1/8" socket it's a 10 spline. If it takes a 1-1/4" or 1-5/16" socket or it's a 29 spline. And it doesn't matter if it were rebuilt 1000 times the result is the same
 
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