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Discussion Starter #1
Hi,


I would like to know if the 8" rear axel of my early 65 Mustang with a 289 (bored out to 306) and a C4 transmission can be easily swapped out against a 9" rear axle.


If not what needs to be changed?
 

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AFAIK, you'll need new spring perches and a new yoke/u-joint. Other than that, not sure.
 

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You would need to find a 9" of the correct width, 57.25" IIRC. If the spring perches are in the correct spot then it's a bolt in situation. But looking at your seemingly mild engine build there really is no need to swap. The 8" is typically good to 500 hp or so.
 

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8" & 9" refers to the ring gears within the center section of the rear end. Those gears themselves are not interchangeable. You need to replace the entire rear end housing, basically from wheel to wheel, including the center section. 9" rear ends are very popular for their strength, but likely overkill.
 

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What are you trying to accomplish? Is the current rear axle an 8"? Is it making noise or indicating it needs rebuilt/repair?
 

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My problem is as mentioned before I cant seem to find the housing including a fully rebuilt 8" cener section
This statement makes it unclear what you're trying to accomplish, or why. So you don't have an 8" rearend axle? Do you have a rear axle at all? And why do you want to change from an 8" to a 9"? Will this be a drag car? Or do you just want more un-sprung weight in the rear end (not that anyone would)?

More info please...
 

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Discussion Starter #9 (Edited)
Hi Scott,


my problem seems to be that the place where the axle shafts are pushed into the housing there is excessive play as can be seen on this video:




I have an 8" rear axle with a 2,80 ratio but that cant be found anywhere. Rebuilding this here in Germany is too expensive.
 

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Why do you feel you need a 9 inch? The 8 is is strong enough unless you are making serious power or are dumping the clutch at pretty high rpms. TJ on ebay make 8 inch rear that will handle most people's needs.

Sent from my SM-G935V using Tapatalk
 

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That would be the spider gears making that noise not the ring and pinion. I’d suggest pulling the differential out and inspecting it to see what needs to be replaced.

You seem to be fixated on 2.80 gears. That ratio was not available in a 9” axle. The general ratios in a 9” would be 2.50, 2.75, 3.00, 3.25, 3.50 The 8” would be 2.79, 3.00, 3.25, 3.50. I wouldn’t think twice about going to 3.00. First though pull and inspect the differential and see what’s going on.
 

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Are you sure that axle is installed all the way in? Can we see it from the side view? Some back and forth is normal on an older high mileage rear. Stick with what you have and repair it if something is broken. Someone offered you a core if I remember, get it and rebuild it your self with the help of utube. Or buy one rebuilt and ready to install from TJ. The 9 inch rebuild videos are basically the same for your 8 inch unit. Are you able to pull the center section third member if it is in fact broken internally?
 

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You are better off fixing the axle you have, or at most replacing the "pumpkin".

If you want to upgrade to the 9", you'll need a 9" differential, and the correct housing for the 65-66. Yeah, I know the originals were different each of those years, but a repro will do. You'll need 9" axle housing brake lines, the correct hose for dual exhaust, and you'll need to have the driveshaft shortened about an inch IIRC. Your brakes, axles, cables, and U bolt/plate assemblies will do.

 

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If you can still find them, the 1957 Ford 9” rear end fits the 64-66 Mustang. The width is the same and thebperches are in the same location. Also, the late 70’s Lincoln Versailles 9” rear ends have the same perch width but overall width is 1/4” wider. You’ll need to change either driveshaft yoke or pinion yoke to with in your Mustang. Also, most Versailles rearends has 2 something gear ratios and aren’t great for a performance car. You’ll want to upgrade.
 

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Not trying to hijack the thread but related topic. I was told my car has a 9" rear end how do I confirm this? Supposedly from a Shelby
 

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TJ on ebay make 8 inch rear that will handle most people's needs.

Sent from my SM-G935V using Tapatalk

Do you have a link to this seller? I'm in the middle of shopping for a new 3rd member as we speak.


OP: 2.80s (open) was the stock gearing in our cars, and you are correct - you cannot find 2.80s anywhere. There's a reason for that lol. Your best bet is to have the diff rebuilt by a reputable shop but with 3.00 gears. If you're concerned about remaining concours - replacing the 8" with a 9" is NOT the way to go, as it's readily identified by judges, and was not available in '66. But judges cannot see your gears hint hint...
 

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I have the correct 9 inch axle with the taper tubes listed on here on for sale. The stock 8 inch can go with it or without.
 

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That video leads me to believe there is an issue with the spider gears. Since you're in Germany I have no idea what to suggest to you as I do not know what is available to you. Do they have ford explorers in Germany? If so you can make an 8.8 rear from it fit relatively easy, if you can cut, grind, weld. Good luck.
 

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In your previous thread member "rhutt" offered to give you a complete 8" "pumpkin", "third member", "center section", "chunk" or "differential"- whichever you prefer to call it. Everything you need is included in this part- the ring & pinion, the spider gears, differential gears, etc. Since finding the parts and somebody in Germany to work on your rear end seems to be impossible I would take rhutt up on his kind offer and bite the bullet on having it shipped to you. It is very heavy and shipping will be expensive. I have mailed parts to member "josep" in Spain and USPS was less than half the price of UPS. I think USPS has a limit of 75 pounds weight so you need to find out how much the part and shipping container weigh. I mailed a 64 pound box to josep and the cost was $310 USD vs. $740 at UPS.
 
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