REAR SWAP

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CM360

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I'm familiar with the F body--66/67 B body 8 3/4 swap. Anything exist for the '81 Cordoba? Thanks
 
Might be a different driveshaft length for a J body vs the F and M
 
AMC Diplomat said:
Might be a different driveshaft length for a J body vs the F and M
Click to expand...
I thought you'd never ask!!! (LOL)

1980 and 1981 Parts Books scans attached

1980.jpg


1981.jpg


EDIT
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What an absolutely atrocious/abysmal rendering of the uploaded images you guys...yikes...I can't read any of it...PoS forum functionality, seriously...in today's age there is literally ZERO reason to downscale images!!!
 
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Actually, the axle width changed from 58.5" to 59.5" in 1980. This makes the 1968-70 b-body axle a better fit in J-bodies.
 
That looks like different measurement locations. M body is in the 54-55 range which makes it a match for early B body. Later B body and C body is too wide.
 
Yeah the 68-70 B body 8 3/4 should work fine in your '81 Cordoba, just might need to mess with the driveshaft length a bit.
 
So I'm a bit confused. Who is right? "Actually, the axle width changed from 58.5" to 59.5" in 1980. This makes the 1968-70 b-body axle a better fit in J-bodies"( as per SRT Mirada) or FMJ are the same?
 
Yeah I'm with you on the confusion - seems like there's conflicting info on whether the J-body changed dimensions in '80 or if it stayed the same as F/M bodies.
 
Link: Rear end question

Screenshot 2022-02-01 215813.png

Flange to flange, drum to drum, and perch to perch DID NOT CHANGE in 1980 for FMJs

What allegedly changed was tread to tread, 1" total or 1/2" difference on each side.

In the end this is irrelevant to an axle bolting on, the key measurements are the same for ALL FMJs
 
No, flange to flange DID change an inch. That's been documented before and I saw that first hand putting a 79 axle in my 88. The only way tread to tread could change and nothing else is if offset or width of the wheels changed. And I think they did go from 6" to 7"? I'm guessing the axle width change had something to do with that or the body change between 79-80 and wider might have also fit the J bodies better?

But axle width isn't 59. It's only 52.something inches from backing plate to backing plate.
 
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Chrysler considered track width to be middle of the tire tread to middle of the opposite tire tread. This roughly equates to brake drum surface to brake drum surface at the wheel mounting, assuming the same wheel offsets.

The following F/M/J-bodies have a 58.5 inch track width:
  • 1976 - early 1980 (through January 2, 1980 builds) F-bodies
  • 1977 - early 1980 (through January 2, 1980 builds) M-bodies
  • Early 1980 (through January 2, 1980 builds) J-bodies
This includes both 7-1/4" and 8-1/4" axles. The same two size axle housings are shared among the aforementioned vehicles.

After January 2, 1980, the following F/M/J-bodies have a 59.5 inch track width:
  • 1980 (after January 2, 1980 builds) F-bodies
  • 1980 (after January 2, 1980 builds) - 1989 M-bodies
  • 1980 (after January 2, 1980 builds) - 1983 J-bodies
This includes both 7-1/4" and 8-1/4" axles. The same two size axle housings are shared among the aforementioned vehicles.

The 7-1/4" axle had changes including, among others in the differential, a wider differential section, different cover with 10 bolts and 1/2" longer axle shafts per side. The longer axles caused the wider track. Reference Technical Service Bulletin (TSB) 03-01-80.

The 8-1/4" axle housing and axle shafts were extended 1/2" per side. With the longer axles and housing tubes, the track matched the new 7-1/4" axle.

The spring perch center to center spacing remained the same 44.46” for both track width axles. The axle width flange to flange also increased with the track width increase.

The 7-1/4" axle changed again in 1982 with the larger 8-1/4"axle tubes added (with a taper down section) to the 7-1/4"center section along with C-clip retention to allow the same axle shaft bearings to be used with both axles, plus the same spring mounting hardware. Reference Technical Service Bulletin (TSB) 03-01-82.

For more information on the 7-1/4" axle changes, including the TSBs, see 7.25 to 8.25: post #20.
 
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I think the difference is the charts usually use flange to flange for sizes because it's a fixed measurement.

Flange to flange of early F/M is 54.340. And perch is 44.46

Flange to flange of later is an inch wider.

Early B body 8 3/4 is usally listed at 55" flange to flange and 44" perch. Which is why that's usually what people say is the preferred 8 3/4 axle to use.

The C body axles noted a few posts above is 59.2" flange to flange (NOT tread to tread) and 47.3" perch which is too wide.. C body. Big car. No surprise there.
 
Ok, so the difference is track width

Today I learned something new!

In the grand scheme of things, 1/2" on either side isn't that big of a deal unless you're running wider wheels and tires
 
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