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Large Bolt Pattern on the Rear Axle
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Author:  SpaceFrank [ Mon Dec 17, 2012 7:56 am ]
Post subject:  Large Bolt Pattern on the Rear Axle
After completing the front disc brake conversion on my '64 Dodge, I will have LBP on the front. I'll most likely be going up to 15" wheels. The next obvious question is how to get the same bolt pattern on the back.

Is there a documented way to convert the rear to later 10" drums? Or would this be more trouble than it's worth? Are there any vehicles that came with 9" drums with large bolt pattern? If that is the case, it sounds like the easiest swap.

Alternatively, what would you folks suggest for adapters/spacers? It would need to be robust enough to handle road racing, albeit at the relatively low speeds expected from a Slant 6 A-body.
Author:  Joshie225 [ Mon Dec 17, 2012 8:26 am ]
Post subject: 
The easiest thing to do is put in a large bolt pattern rear axle. You cannot put LBP brakes on your 7 1/4" axle, but if you were a masochist you might be able to have your drums and axles redrilled, but then you'd still have 9" drums.
Author:  SpaceFrank [ Mon Dec 17, 2012 9:18 am ]
Post subject: 
Well, there's an '84 (I think ... maybe '87) Fifth Avenue in the local scrap yard with what appeared to be 10" drums on the back. That's the car I grabbed most of the front disc parts from. It had a 318, Wikipedia says it came with either a 904 or 727, and Rockauto says it has a 8.25" rear end.

Rockauto also lists the same U-joints for the '84 Fifth Avenue and the '64 Dart, awesome! Looks like my driveshaft will hook right up, as long as the length of the differential housing isn't much different.
Author:  Matt Cramer [ Mon Dec 17, 2012 10:03 am ]
Post subject: 
Quote:
The easiest thing to do is put in a large bolt pattern rear axle. You cannot put LBP brakes on your 7 1/4" axle, but if you were a masochist you might be able to have your drums and axles redrilled, but then you'd still have 9" drums.
IIRC, this is more along the lines of impossible rather than merely masochistic. The SBP rear axle flanges on my '66 appeared to be just large enough to fit the existing wheel studs - there wasn't enough flange to drill for the LBP pattern.
Author:  SpaceFrank [ Mon Dec 17, 2012 11:27 am ]
Post subject: 
There's the question of track width when swapping axles. Allpar.com gives a rear track width of 59.5 for the '84 Fifth Avenue. A couple of different sites both list 55.6" as the rear track width for early A-bodies.

If I'm not mistaken, track width is the center-to-center distance between the tire treads. I wonder what kind of offset both of these cars' stock wheels have. I'd really like to be able to use the same wheels front and back on the finished product.
Author:  Reed [ Mon Dec 17, 2012 11:48 am ]
Post subject: 
Quote:
The easiest thing to do is put in a large bolt pattern rear axle.
FYI- Joshua used to competitively road race a slant six powered 66 Dart. I would listen very closely to anything he tells you about upgrading the brakes and handling of your early A body.
Author:  SpaceFrank [ Mon Dec 17, 2012 12:07 pm ]
Post subject: 
Quote:
Quote:
The easiest thing to do is put in a large bolt pattern rear axle.
FYI- Joshua used to competitively road race a slant six powered 66 Dart. I would listen very closely to anything he tells you about upgrading the brakes and handling of your early A body.
Nice! I'm getting this '64 Dart ready for 24 Hours of LeMons next year. I know of at least one other team racing an A-body in California, a '72 Valiant I think.

I definitely like the idea of swapping axles, especially since I know where I can get one cheap. If it ends up being a little wide, I'll either get some higher-offset wheels for the rear or add fender flares.
Author:  Reed [ Mon Dec 17, 2012 12:29 pm ]
Post subject: 
Swapping in a rear axle from a non-a-body vehicle (such as a Fifth Avenue) is not the easiest solution. You need to find a large bolt pattern rear axle from a 1973-1976 a-body (Dart, Valiant, Duster, Scamp, Swinger).
Author:  GTS225 [ Mon Dec 17, 2012 3:28 pm ]
Post subject: 
Was there ever a definitive answer to the question of a 5-lug Dakota 8.25 rear going into an A-body?
Just a thought.

Roger
Author:  DusterIdiot [ Mon Dec 17, 2012 5:49 pm ]
Post subject:  Standard
Quote:
I wonder what kind of offset both of these cars' stock wheels have.
Mopar used to be something like 4.25-4.5" offset on the late 14/15" wheels.

-D.Idiot
Author:  Joshie225 [ Tue Dec 18, 2012 8:20 am ]
Post subject: 
A 5th Ave rear axle is much too wide. You'll lose outboard tire clearance even with FWD wheels like the Intrepid ones I used when I put a '67 B-body 8 3/4 under my '66 Barracuda.

The only large bolt pattern axle which is a direct bolt-in (excepting the parking brake cables) is a later A-body 7 1/4. Since you are going to go road racing I would not use a 7 1/4 unless it were free and probably not even then. If you aren't up for welding on new spring perches then you're after an A-body 8 1/4 axle and hopefully one from a 6 cylinder car so you aren't stuck with 2.45 gears like most V8s had. Another option is a Ford 8" axle from a Maverick or Granada/Monarch. The Granada rear end is a little wider than stock though so you end up not having the same room outboard of the wheel and tire, but it's only 1/2" per side. You can usually use your stock driveshaft with the Ford 8", but it requires a conversion U-joint plus a stock Ford U-joint. Lou and I have done this.

Wheel offset and backspacing is simple once you understand how wheel measuring works and offsets are expressed. A road wheel is actually 1" wider to the outside edges than where the tire bead mounts so a 7" wide wheel is 8" wide overall, 5.5" wheel is 6.5" wide overall, etc. On a zero offset wheel there is an equal distance from the wheel mounting face to the inboard and outboard edges of the rim. A 7" wide zero offset wheel (8"/2) therefore has 4" from the mounting face to the inboard and outboard edges of the wheel. The inboard measurement is called backspacing. Chrysler used a small positive (inboard) offset on their larger wheels at least. Negative offset has more wheel outboard of the wheel mounting face. The 15x7" police car wheel has 4 1/4" backspacing. This is 1/4" positive offset as a zero offset wheel would measure 4". You see this positive offset expressed in millimeters on most modern wheels. For instance my 17x8" Ford wheels are ET30 (+30mm or 1.18") offset. Being an 8" wide wheel which is 9" to the outside we divide 9 by 2 and then add the offset to get the backspacing. 9"/2=4.5" +1.18"=5.68" backspacing.
Author:  SpaceFrank [ Tue Dec 18, 2012 9:24 am ]
Post subject: 
Ouch. Thanks for the info, Joshua. It looks like we're back to the drawing board. I'll keep my eyes open for a later A-body or one of the Fords you mentioned.
Quote:
Was there ever a definitive answer to the question of a 5-lug Dakota 8.25 rear going into an A-body?
Just a thought.
Yes, what about this? Dakotas are probably easier to find.
Author:  brummett [ Tue Dec 18, 2012 9:43 am ]
Post subject: 
Quote:
Swapping in a rear axle from a non-a-body vehicle (such as a Fifth Avenue) is not the easiest solution. You need to find a large bolt pattern rear axle from a 1973-1976 a-body (Dart, Valiant, Duster, Scamp, Swinger).
Be careful with using later-model axles, too. I once tried swapping in a rear from a Volare into a '63 Valiant. The width was close enough, but it wasn't a bolt-in because A-body leafs have a big pin that sticks up and goes into a hole in the spring perch that locates the axle and keeps it from squirming around on the spring. I don't remember the details, but the Volare rear had some other way of accomplishing the same thing. I was able to locate another rear from an A-body, so I never bothered to solve the problem.

I'd imagine a Diplomat/5th Ave rear would mount the same way as a Volare/Aspen rear, since they are similar cars.
Author:  Reed [ Tue Dec 18, 2012 10:19 am ]
Post subject: 
Quote:
Quote:
Swapping in a rear axle from a non-a-body vehicle (such as a Fifth Avenue) is not the easiest solution. You need to find a large bolt pattern rear axle from a 1973-1976 a-body (Dart, Valiant, Duster, Scamp, Swinger).
Be careful with using later-model axles, too. I once tried swapping in a rear from a Volare into a '63 Valiant. The width was close enough, but it wasn't a bolt-in because A-body leafs have a big pin that sticks up and goes into a hole in the spring perch that locates the axle and keeps it from squirming around on the spring. I don't remember the details, but the Volare rear had some other way of accomplishing the same thing. I was able to locate another rear from an A-body, so I never bothered to solve the problem.

I'd imagine a Diplomat/5th Ave rear would mount the same way as a Volare/Aspen rear, since they are similar cars.

Aspens, Volares, 83-up Fifth Avenues, Lebarons (through 83), Diplomats, and 81-83 Imperials were F/M/J body cars, not A bodies. You have proved my point- the easiest swap to large bolt parren rear axles is to swap in an assembly from a late A body. 73-76 Dart, Valiant, Duster, Scamp, Swinger. Axles from other bodies or models are more difficult to install.
Author:  SpaceFrank [ Tue Dec 18, 2012 11:24 am ]
Post subject: 
I don't mind doing some fabrication when it comes to the leaf spring mounts. I just want an axle with the right width so I don't have to run ridiculously offset rear wheels. Unfortunately, the 5th Ave. rear axle appears to be about 4" wider than the A-body's.
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