9" Rear Assembly - '66FB

You could see if you can find a57-59 ford 9" at a junk yard. They are a bolt in. They are mainly small bearing housings and that will allow you to use your stock axles and brakes. All to need to do is get some new spring plates or re-drill the ones you have because the 9" has a 3" axle tubes and the 8" has 2.5". You will also need new u-bolts to holder all together. I have done this swap a bunch of times and it works great. If your lucky you may even find one with 3.89 gears. If you do find one, you have to have a third member with a oil plug in it or you will have to drill and tap one as the housing does not have a plug in the back.

You could also look for a Versailles or Granada 9 inch from the mid-late 70's.

hivewax said:

yes, i've been following the Sticky - Rear End Swap FAQ

EDIT: anyone think i can rebuild the 8" with a stronger 3rd member? any links?

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8 inchers aren't worth the time. There are stronger 3rd members and axles avaliable, but they'll be more expensive than a stock 9" which is stronger.

5 years ago I did a budget 9" swap, had a shop fab a housing for me for $250 and got a posi 3.25 9" pumpkin off ebay for $350. Reused my 8" axles and had myself a cheapo custom rearend, which has held up pretty well so far.

IF that company you saw has complete packagse and have a good reputation, that might be worth a look. $650 for complete setups (flange to flange including 3rd members) would be a pretty sweet deal.

A well-built 8", such as Currie's repro Traction-Lok, is a 4-pinion 28 spline unit, probably stronger than the stock 9" used on 64-66 K code Mustangs. The 8" is the same design as the 9", they even shared some internal parts.

The 64-66 8" housing and 64-66 9" housing used the same U bolts and plates.

Although the 64-66 8"and 9" were specified with different axles, they were in fact interchangeable 28 spline units, with only a slight difference in the thickness of the shafts, with turned out to be no big deal.

The 64-66 8" housing and 64-66 9" housing used the same drum brakes. The only exception was the GT350, which was fitted with the 2.5x10 Fairlane station wagon units.

Your link would charge about $1400 for a complete assembly, without brakes.

If your driveshaft turns without moving the car, your diff is blown. Check out Currie's 8" T-lok before you decide what to do.

The 8 inch rear and the small bearing 9 inch have a lot in common as stated above.

-Same axles
-Same bolt pattern for brakes
-Same axle tube diameter (can use the same U bolts)
-No change to driveshaft length required (if you have the correct flange)

On my '70 I re-used the brakes, driveshaft and U bolts when I did the 9 inch swap.

The big bearing 9 inch is different:
-larger axle tubes
-different bolt pattern for brakes
-different axles

hivewax said:

why would the bolt pattern change? 5x4.5" bolt pattern is most common for 5-lug Ford.

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He's talking about the brake backing plate bolt pattern, not the wheels.

I was at a similar decision point last year, trying to decide if I should swap the 8" to a 9". After talking with some more knowledgable people, I decided to save the money and kept the 8", but upgraded my open diff to the newer 4 pinion Traction-Lok with 3.80:1 gearset (I have a T5 and this is a great setup). I also have a 347 making around 400 FWHP and the rearend is not having any problems holding up. I figure the T5z would give out before the rear. I don't beat on my car, but I like to have some fun with the occasional burnout. So far, so good. I got the new diff for $600 from a vendor at Carlisle. Everything was new including bearings, gearset etc. I figured I was looking at roughly $2k for an equivilant 9" setup (going new, not used), so I am well ahead of the game if the rear holds up. Just another data point for you to make your decision.

I recently built up a new 9" two years ago. it was a full sized ford housing I had narrow two fit my 66fb. it includes strange 31spline axels. cobra auto ubolts plates and 11" drums with Torino big bearing flanges. thing of bueaty and strength. forget about an 8 and don't buy a curry. have your built your way. just my .02$

hivewax said:

i think with the T10, the high RPM's thru all gears are what's hurting the 8" rear on top of the 289 stroked 347. a T5z would be less abusive to the rear.

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The rpm seen by the rear end is only dependent on its gear ratio and the tire size. Taller transmission ratios only lower the engine rpm.

The 9" under my car came from either a '57 or '59 passenger car. I think I probably have less than $500 in it including brakes, new axle bearings, u-bolts, and the 28 spline 3.50 T-Lok center. It's not the strongest 9" by any means, but I only have a single plane 9:1 302 with an aluminum flywheel and rarely abuse it.

'57-'59 Ford/Lincoln/Mercury passenger cars will have the correct width 9-inch rear end to fit your '65/'66 Mustang. These rear ends will have the small bearings --same axle bearing size as all Mustangs '65-'73. You can swap your '65/'66 Mustang 8-inch axles drum brake assemblies onto these 9-inch housings.

The '57-'59 Ford station wagon and Rancheros will have the same width 9-inch housings as the regular F/L/M passenger cars, but will have large axle bearings instead. These rear ends also have the large bearing pattern drum backing plates and these are not interchangeable with the small bearing rear end housings.

This is important because finding new drum brake replacement parts for the old '57-'59 Ford 9-inch 11" x 2" brakes is very difficult. With the small bearing 9-inch housings, you can use your 8-inch rear end brake parts. With the large bearing 9-inch rear end, you're basically out of luck.

Another major problem is even finding a '57-'59 Ford big car 9-inch rear, or a '75-'80 Granada 9-inch drum brake or 9-inch disc brake rear end, or a '77-'80 Lincoln Versailles 9-inch disc brake rear end. If you do find one, it's likely to be very expensive and also likely that many of the parts will need replacing. --Not that none of these rears exist in any of the salvage yards anymore, but many salvage yards don't operate like they did just 10 years ago. Anymore, most are just simply scrap metal yards and useable/rebuildable cores quickly end up in the crusher and forever lost.

There are 8-inch rears that take a lot of abuse and then there are those that get broken with essentially stock engines. It's just a coin-toss as to how long one will last. A beefed up 8-inch is strong but a 9-inch will always be stronger and has the parts availablity to be several times stronger than the that of the strongest 8-inch.

You can search the salvage yards first to see if you might be lucky enough to locate the 9-inch that's right for your Mustang, but my advise would be to buy a custom width housing and some good custom 31-spline axles then hit the salvage yard to get a 31-spline 3rd member from a Ford half ton pickup. The pickups ['73-'85] commonly came with 3.00, 3.25, 3.50 and 3.70 rear end ratios. --you might even get lucky and find a 4-pinion 31-spline Traction-lok differential in one.

After that, outfit it with some modern disc brakes and you will be in business.


9-inch rear end info links from my website:

The Ford 9-inch Rear End

Differential Types

Third Member Cases

Third Member I.D. Codes

RPM-charts

Torque Multiplication

im doing the same thing for my 65 falcon. I have an 8" i am going to buy a currie 9" form summit $300. im getting no leaf pads, (using clamp ones form dirt track racing). small bearing (like stock, so i can use my stock brakes for now) then im going to use the same axles and use my dads 411 gears from his 65 k model mustang.