Rearend Swap info - FAQ

any info on the widths of 8.8 through the years?

from 83-93 4 lug except for cobra's, turbo coupes. width?

8.8 from a ranger years ...Width?:shrug:
8.8 94-98.... width measurement from rotor-rotor?:shrug:

8.8 99-2004.... 1 1/2" wider than a 94-98 width
8.8 2005-2008... way to wide!
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Since there are no dumb questions . . . 9" pinion is centered?

Hey all,
Something I didn't see here yet, and it seems hard to find mentioned anywhere - I understand that an 8.8" rear has a centered pinion, but does a 9" for a vintage Mustang? Specifically, there are a few questions:

-Side to side, is a '64.5-66 9" pinion centered?
-'67-70 9" centered?
-'71-73 9" centered?

I am thinking of ordering a Currie 9+ rear (down the road, no rush) and their handy-dandy calculator is asking for this info.

Thanks :SNSign:
The pinion is centered. The carrier is about two inches offcenter. That's why one axle is always about four longer than the other. Unless you plan on some custom setup, you could just tell Curries that you want stock length axles and housing for your model year. They have all that info in their database. Just for reference, here are the axle lengths according to my Hollander junkyard book.

65-66 67-70 71-73
left 26 5/64" 27 5/64" 31 7/8"
right 30 1/8" 31 1/8" 27 13/16"
Really? I didn't know the stock was off-centered. I had heard a lot of things about the Explorer being off-center, and people would need to shorten one side of the housing.

Is it the same for 8" as well? Or, are the measurements you gave just for the 9"? (I would think they're all the same width...but you never know)
The PINION is centered on the old ones (8-inch and 9-inch), the RING is off-center (as is the diff since it bolts to the ring), that is why one axle is longer.

Some 8.8s have centered pinions like Mustangs, but some don't like Exploders, errr, Explorers.
Spring perch distance the same for '65-66, 67-70, 71-73?

Hey all,
Just ordered my crate 9" from Currie and they claim the spring perch distance is the same for '65-66, '67-70, and '71-73, but I see on other sites that it is different - 52" for 65-66, 54" for '67-70. Reason I'm wondering is that I ended up ordering the '65-66 57.25" crate rear because I wanted it er on each side. We'll see soon enough when I get it, but while I wait I thought I'd throw it up here. (and maybe provide the answer when I get it :rolleyes: )
Hey all,
Just ordered my crate 9" from Currie and they claim the spring perch distance is the same for '65-66, '67-70, and '71-73, but I see on other sites that it is different - 52" for 65-66, 54" for '67-70.

Those 52 and 54" measurements are the overall bare housing width, not the width of the spring perches. The spring perch width was the same from '65-70(maybe '71-73 too, I don't know). For example, the 1957 passenger car 9 inch is a direct bolt in for the '65-66 Mustangs. I have one under my '68 and it was a direct fit except for the wheels sitting inboard 1" on each side.

Check out ultrastang's site:

that makes sense. What threw me off is this quote from the Kevinstang site. Reading it, it is easy to get the impression that he is talking about spring perch distance here on different year Mustangs, but what he is really taking about is Fairlane vs. Mustang. It stands to reason that if the housing is 57.25 or 59.25 flange to flange there's no way the spring perches would be 52 to 54 inches apart. Common sense, I guess.

"I can tell you for a fact, the distance between spring perches is different between Mustangs and Fairlanes.Spring perches must be cut and re-welded inorder for the swap to be performed. The “rough" widths I keep in mind for Mustangs are the following: 52” for 1965 to 1966 (the same width as 64-65 Falcons and 62 to 65 Fairlanes)(as in the Mustang line, most however never received a factory 9 inch), 54” for 1967 to 1970 (same as 66 to 69 Fairlane,Torino,Comet & Cyclone non station wagons)*cars with 351 and up engines received 9 inch units-as did some 302 4V cars-(mainly GT's in 68 with optional gear ratios)* and 56” for the 1971 to 1973 Mustangs/Cougars- (cars with 351 engines and up receiving the 9” housings).Keep in mind as mentioned, the Fairlane spring perch distances were not the same as the Mustang. All the Galaxies I have seen from throughout the 1960’s used the 9 inch rear, regardless of engine size. "
Currie wheel flange at 2.8", Wilwood brake hat at 2.78"

Ok, here is an interesting one not covered here yet - wheel flange diameter. I have my Currie Track 9" rear end with Wilwood brakes that I am putting on it. Problem is, the hats from Wilwood (and from Baer, so this is a Currie issue, not a Wilwood or Baer) is about 2.78" diameter, where Currie's wheel flange / hub center is about 2.8" diameter, and the wheel stud shoulders are a little too thick as well.

I'll give Currie a call tomorrow AM, but what did I get from Currie with my 9+/Track 9"? Is there a spec that this large-diameter wheel flange, large-diameter wheel stud shoulder rear axle fits? Or did they just do something off-spec and expect the brake mfrs to machine their hats to fit it?

Edit: I talked to Currie this AM, and they said to take the axle to a lathe and take it down to 2.78 - they said that Wilwood recently went from 2.8 down to 2.78, and that a spacer could always be used to get up to 2.8. Baer's kit came with just such a spacer - wonder why Wilwood doesn't do it this way?
Interesting. I was going to buy a unit from Currie but freaked at the price they wanted for the one I spec'ed, A 9" with locker and 31 spline axles didn't seem extravagant to me but it was going to cost over $2.5K.

I went the cheaper route and sourced a small-bearing factory-9 out of a big block 1970 Cougar, purchased a blueprinted center chunk, my own axles from Summit, then spent many hours with a wire-wheel and sent it to the powdercoater. The axles, the trac-bars, the springs (I did have to buy new U-Bolts), and my WilWood rear discs fit the housing perfectly.
Edbert, that's good info. So it looks like Currie is doing things a little larger to fit aftermarket kits like Baer. (a Baer rear disc hat would fit perfectly on the Currie, and they include a center spacer to fit the original 2.78" diameter.)

Currie really should do it in the 2.78" diameter and include a spacer to fit the bigger 2.8" ID kits out there.
Hey all, so I'm not the smartest when it comes to rear ends, how can I tell if I have an 8" or 9" rear end on my 70 with a H code 351C?

The easiest way to tell one from the other is to jack up the car. Once under the car, with an 8" rear, you can remove the bottom two housing retainer nuts with a socket & ratchet. With a 9" rear, you can only remove these two nuts with an open or box ended wrench.
As mentioned on the first page....The u joint from a 8" and a late 50s 9" are both 1310s, and allow you to swap without changing the shaft or u joint might be wrong. When i did my swap, I could have sworn i used a conversion joint for the rear.

The 9" was from a 59 Fairlane if i remember....
Rear end width list that I have.... By far not complete but it has quite a few on it.

Information overload....assistance requested

Hi folks...been a while since I have been on. I need have a '66, 289h, with the orriginal "8 rear. My question is this, what is the easiest swap for a locking rear and does it require a housing swap? Also, is there a a locking rear available which will allow me to keep the same ratio (or simmilar for highway driving)? Any and all advise is welcome...Thanks.
Hi folks...been a while since I have been on. I need have a '66, 289h, with the orriginal "8 rear. .....

1.) what is the easiest swap for a locking rear and does it require a housing swap?

2.) Also, is there a a locking rear available which will allow me to keep the same ratio (or simmilar for highway driving)?

1.) "Easiest" would be to shell out for a complete 28-spline 8" locking center section for your current rear end.

2.) You can put whatever ratio you want on the carrier.