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Discussion Starter #1
what was the orginal rear end size for a 1969 Mustang Mach1 "M" code aka 351w with fmx trans. My dad said it was a 9in bust some guy we met claimes it wasnt. And also what is the gear ration in the rear end? Sorry i am not a rear end and trans guy but i do know a motor.
 

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I pretty sure it would have been the 8", the big block cars got the bigger 9" and the 428 super cobra jets were upgraded to the heavier 31 spline axles. The 351 engines (H and M codes) aren't big blocks but if by chance your car did come with a 9" it would have been the lighter duty 28 spline, same as the 8".


There were several axle ratios available, and you'd have to look at your door tag if it's still there and original to the car or order a Marti report on your car.
 

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Discussion Starter #3
yeah my dad claims its a 9" and he swears by it. but i will look again when i get it back from paint.
 

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If your willing to crawl under the car look at the bolts on the 3rd member there is a little metal tag if its there get the numbers off it.I have heard mach1s same with a 9 inch only but im not sure on it.
 

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Discussion Starter #6
ok well its in paint so i will check when i get her back
 
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