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Old 06-08-2015, 10:11 AM   #1
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9 inch rear end

I've got a 67 with a 289 and a stock 8" rear end 2.80 gears.
The motor is probably in the low 300HP range.

I have a 9" rear housing. The question is:

Should I build it as a small 9" and use my existing 28 spline axles and brakes? or Should I build the standard 9" with the 31 spline axles?
I am trying to keep the costs down and I don't plan on any dramatic HP increases anytime soon.
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Old 06-08-2015, 01:18 PM   #2
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The axles will be the weak point with whichever setup you go with. But you'll have to spend quite a bit more or search junkyards longer to upgrade.


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Old 06-08-2015, 01:40 PM   #3
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The axles will be the weak point with whichever setup you go with. But you'll have to spend quite a bit more or search junkyards longer to upgrade.


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You mean searching for 31 splines?
How much HP do you think a locking 28 spline axle can handle?
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Old 06-08-2015, 02:24 PM   #4
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No I mean the 28 spline axles are going to be the weakest part of the 9 inch rear end. I'd upgrade to 31 spline and not worry about it, but that is just me.

I'd say the 28's would be good for around 300-350 hp, but it's not so much the hp that will break them, but a combination of hp, torque, and traction. You may be completely fine with 28's, it just really depends on the application.






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Old 06-08-2015, 03:33 PM   #5
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Quote:
Originally Posted by fstbck70 View Post
No I mean the 28 spline axles are going to be the weakest part of the 9 inch rear end. I'd upgrade to 31 spline and not worry about it, but that is just me.

I'd say the 28's would be good for around 300-350 hp, but it's not so much the hp that will break them, but a combination of hp, torque, and traction. You may be completely fine with 28's, it just really depends on the application.




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I knew going 31 is the way to go, I guess I was just trying to save some cash. But I it's better to go ahead with 31 and have it take a little longer and not have to worry about it. Thanks.

Do you know if the drum brakes are the same for 31?
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Old 07-31-2015, 09:39 AM   #6
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Quote:
Originally Posted by Aggiesrok View Post
I knew going 31 is the way to go, I guess I was just trying to save some cash. But I it's better to go ahead with 31 and have it take a little longer and not have to worry about it. Thanks.

Do you know if the drum brakes are the same for 31?
This thread is over a month old...............don't know what you've done but it all comes down the what's in the pumpkin...............if you have a locker or posi then I'd go with the 31 spline...................if you don't have either...........I'd stick with the 28 spline..........it's torque that will break the axle, not HP.
My Maverick turned 9.80's in the quarter with 544 lbft of torque with a 9" with 31 spline axles..............the motor had 644hp and the rear end was originally put in the car in 1979 to compete in the 79 Winternationals.
9" Fords are hard to beat...............unless you are using a Dana60.
Drum brakes are the same...................
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Old 07-31-2015, 11:15 AM   #7
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Thanks
I went 31, I've got the housing, axles and case cover. I need the center section and I'm going posi. My last issue is gears. It's a DD, so nothing crazy. Im thinking 3:25. I'd like to go 3:55, but it's a C4, so no OD.


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Old 07-31-2015, 12:19 PM   #8
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Thanks
I went 31, I've got the housing, axles and case cover. I need the center section and I'm going posi. My last issue is gears. It's a DD, so nothing crazy. Im thinking 3:25. I'd like to go 3:55, but it's a C4, so no OD.


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Ok, just a couple of questions then.
Are you commuting mostly on freeways or city roads.
What size tires and wheels are on the car.
What have you done to the motor?, cam, headers, heads, intake, carb and ignition.

I'll tell you from experience that 3.55's will be a lot more fun to drive than 3.25's. I put 3.55's in my 66GT with a mod'd C4, nothing drastic..........just a nice street C4. The motor was an original 289 HiPo with headers and made 366HP at the crank.....different carb and heads.

Or, you could use the 3.25's and put a stall converter in the car..........nothing drastic..........which would wake it up off the line.........a lot!
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Old 08-01-2015, 01:10 AM   #9
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It's mostly city, but with some highways (it's Texas).
225/50/17
The engine is a 289 block, 302 heads, roller tip rockers, mild cam, 4bbl 600cfm carb, edelbrock alum. performer, tri Y headers. I've only had the car about 2 years and haven't been in the engine to know the exact cam. Had the heads out to drill and tap for screw in studs and replaced the intake and rebuilt the carb.

I had 3.55 on my 07, they were great.


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