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Discussion Starter · #1 ·
I have a 67' Mustang that came with a 289 and a 4 speed. I would like to know what type of rear end I may have in it as I do not know the tale tell signs between a 8" and a 9". I really need to put different gears in it. Because the previous owner obviously had it re-geared. I am currently running about 2,800 rpm at 60 mph. And passing anything but a gas station. I would like to upgrade to a 9" if I am currently running an 8" as I am now running a 351 mildly built, and do not want to overwhelm the axle with the wide tires I run in back. I have access to a 78' cougar xr7 that has a 351 And I would believe a 9" as I could have it reworked to fit the Stang. Although I can have it for free it is 400 miles away at my dads. And I can not eyeball it side by side with my Mustang to see if there is any real differences. Or if I am running a 8", will it stand up to the 351 and 10" wide tires? If that is the case what ratio should I be considering?
 

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9" Rear end id, The 8" will hold up to a 351W mild build easy. If you are worried about the axles the 9" uses a 28 spline axle also. there is not many that have the big 31 splines in them.
your running 2800 rpms at 60 mph what gear are you thinking about going to. it looks like you are running a 3:00 rear gear now. The way you can get your rpms down more at 60mph is adding a over drive transmission.
 

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9" Rear end id, The 8" will hold up to a 351W mild build easy. If you are worried about the axles the 9" uses a 28 spline axle also. there is not many that have the big 31 splines in them.
your running 2800 rpms at 60 mph what gear are you thinking about going to. it looks like you are running a 3:00 rear gear now. The way you can get your rpms down more at 60mph is adding a over drive transmission.
I would think it has a lower gear, just compared to what I know is in mine. I have a 3.50:1 gear now, and I turn 2700 RPMs at 65 MPH.




With a factory 289, you would more than likely have the 8", and as MustangOne said, you should be fine with it unless you're making around 400hp.
 

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Discussion Starter · #4 ·
I looked at the housing. It seems to have the bubble in the middle for the ring gear. I was told that only the 9" have that and that the 8's are just round in shape. The reason I ask is because on the next build I am going to go crazy on the engine. So If I have a 9" then awesome! But if not it will be happening in the next year or so. I must admit that this is my only Ford, although I love it to death. My background is with GM's so I am trying to increase my knowledge on all cars. So any thing you can tell me would help.




I don't care if its Ford,Chevy, Mopar... If it puts a smile on your face and rubber on the ground then your doing right as far as I'm concerned. Ya know? :)
 

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Discussion Starter · #5 ·
Anyone have any input on the radiator post I did a few days ago?
 
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