Slant Six Forum :: Rear end ID'ing

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Rear end ID'ing https://www.slantsix.org/forum/viewtopic.php?t=4590	Page 1 of 2

Author:	pierre [ Thu Dec 05, 2002 12:14 am ]
Post subject:	Rear end ID'ing
I am thinking about buying a rear end from someone that I think might be a 8.75 but I can't be sure exactly untill I see a picture, which won't happen for a while. So I am trying to dig up more info on what it may be in the meantime. All the guy told me so far is that it came out of a 1973 Duster with a V8, and has the bigger drum brakes (I'm assuming these are the 10" vs the 9"?). Also It has 15" rims on it but I figure that's easily changed so I can't guarantee those are the original wheels on the axle but I'm pretty sure they are. I was embarrassed when I took my duster (with its current 7.25") into the shop to have new exhaust done. When it was on the lift the guy looked at the rear end and just laughed

Author:	Red [ Thu Dec 05, 2002 5:10 am ]
Post subject:	rear end ID
You already know what a 7-1/4" looks like. You can tell the difference between the other two at a glance: if it has a removable, 10-bolt cover on the back of the center section, it's an 8-1/4". If it has no removable cover, it's an 8-3/4" (instead, the bolts will be on the front of the center section---drop out 3rd member). If you're lucky, the little gear ratio tag will still be under one of the bolt heads. 1972 was the last year the 8-3/4" was manufactured, so you're probably going to find that it's an 8-1/4", but there's a chance somebody could've swapped one into the Duster, so you'll have to eyeball it. 8-1/4" is plenty strong, it's just nice to have the ease of gear change that an 8-3/4" allows. ---Red

Author:	Pierre [ Thu Dec 05, 2002 9:02 am ]
Post subject:	axle swap
Going on the notion that it is a 8 1/4 Does the same hold for 7 1/4 > 8 3/4 swaps, that the driveshaft will need to be shortend since I'm mating it to my current 904? Also, can there be any guesses made as to the bolt pattern on the axles? I want to use my original 14", 4" boltpattern wheels if possible. Doctor Dodge, if your reading this... Know of any places around this area that will do the shortening? I work about 1 mile away from Great America for the time being, and live on the other side of the Altamont. Also, whats your favorite wrecking yard in this area? Gonna be needing the U-bolts and other hardware for this swap as well.

Author:	bud L. [ Thu Dec 05, 2002 3:08 pm ]
Post subject:	shortening?
I believe the only instance of axle upgrades I've run into, where you don't have to shorten the drivshaft, is going from a 9 1/4 to an 8 3/4.

Author:	Red [ Thu Dec 05, 2002 3:35 pm ]
Post subject:	drive shaft shortening
I just swapped an 8-1/4" onto a '71 Dart with a 7-1/4". Yes, the driveshaft must be cut down and rebalanced, because the axle mounting position doesn't change and the 8-1/4" center section is longer than the 7-1/4". I got mine cut and rebalanced for around $50. The guy did a good job (no shudders or shakes at any speed) but this guy is all the way out in Watsonville (almost to the coast from you), so that won't do you much good. Generally, they just want you to measure and mark where you want it cut and they'll do the rest. Any axles after '72 will be 4.5" bolt circle. That's desirable, really, as it will give you a much better selection of wheels to choose from (Ford wheels are same bolt circle, so there's alot more after market). I was upgrading to front disks at the same time, so I've got 4.5" BC, 14" all the way around now, and like it much better. I assume you want to keep the small BC in back because your're keeping them in the front and don't want to have to carry 2 different spares? Pick-n-Pulls nearest you: Newark (7400 Mowry) Oakland: (8451 San Leandro Street) Hope this helps. ---Red

Author:	Red [ Thu Dec 05, 2002 3:41 pm ]
Post subject:	drive line shop
Used to be an outfit in Concord called Drive Line Service (200 Bates Ave. Concord 510-682-3340). Try them and see if they're still there. This kind of stuff is their specialty, but I haven't a clue what they'd charge you. ---Red

Author:	Pierre [ Thu Dec 05, 2002 4:04 pm ]
Post subject:	pick n'pull
There is one on Berryessa which is less then 5 miles from great america. But I've had my best luck finding A bodies in the pick n'pull in stockton. Rear end/disc brakes is a secondary project.. getting carb straight and soon to be efi when clifford comes out with it will be primary

Author:	slantzilla [ Thu Dec 05, 2002 5:26 pm ]
Post subject:
'73 and up axles will only be large pattern if the car was a disc brake car. Drum brake cars were still small bolt.

Author:	Doctor Dodge [ Thu Dec 05, 2002 8:09 pm ]
Post subject:
Bayshore Truck Service in San Jose has a good driveshaft machinest and equipment. There is also Draveline Service of San Jose, off of Almaden, I like Bayshore better. 2 "Pick n, Pulls" in SJ but the RWD Mopar section is getting pretty thin these days, good to keep checking because they move lot's of cars through those yards, new stuff every few weeks. DD

Author:	DusterIdiot [ Thu Dec 05, 2002 10:06 pm ]
Post subject:
One odd mopar thing to note when ID'ing rear axles at the junkyard.... If scavenging used gears from a 77+ FMJ body be careful, around 1979 Ma put a 10 bolt cover on the 7 1/4" rear-end, all 8 1/4" rearends have a circular cover on them.... good luck, -D.Idiot

Author:	Pierre [ Sun Dec 08, 2002 4:43 pm ]
Post subject:	rear end off a '63 ?
Guys - Found a 1963 (or labeld by pick n'pull at a 63) with the vin beginning with "8233" Now according to a webpage I found that decoded these, the first 8 means its a chrysler V8, and the 2 following means its either a dart 200, 440, 300, or Imperial The engine/tranny was already taken so I couldn't see if it indeed was a V8. I used an improvised measuring (cowel gasket off of a random car) and backplate to backplate distance of the rear end was about the same as a 7 1/4 found on a 71 duster. It was deffinately not 3" longer then the 8 3/4 was supposed to be relative to the 7 1/4. I measured it to be about 1/4" longer, but I attributed this to the rubber just stretching slightly. The car looked similar to pictures of a chrysler 300 J I have found online. Any idea if this rear will fit in my 7 duster without any resizing?

Author:	Pierre [ Sun Dec 08, 2002 4:44 pm ]
Post subject:	err, correction
that should be my 71 plymouth duster

Author:	Red [ Sun Dec 08, 2002 6:22 pm ]
Post subject:
Pierre, Unfortunately, Doc's right about the SJ yards: the selection of Mopars ain't what it used to be @ those P-n-Ps. Same goes for the one out near me. ______ Doc and/or Slantzilla--- My spotty understanding of A & B-body Mopar axles and BCs goes kinda like this: 7-1/4"---(1960-19??) 4W drum A-bodies: all small BC 7-1/4"---(1973 only) front disc A-bodies: all small BC 8-1/4"---(1969-1973) B-bodies only: all large BC 8-1/4"---(1974-19??) front disc A-bodies: all large BC 8-3/4"---(1965-72) all small BC (the ones on A-bodies, that is) Am I even close? Would appreciate corrections of any incorrect or incomplete info above. Were there any small BC 8-1/4"s? I've never noticed any, but then, I've never wanted or looked for one. Don't pay much attention to the post '76 RWD cars either, so I don't know the scoop on them (thanks for the tip on the later cars, D.Idiot). Boy, a variation chart like the one you guys did for engines, heads and cranks would sure help keep all this straight (cross-referencing axle type, engine type, body type, brake type and BC). Then again, there's no guarantee that the components on a car that old are going to be the original configuration anyway. For practical purposes, I suppose all you really need is reasonably good vision, a tape measure and the ability to count to 10 to sort them out. Thanks, guys. ---Red

Author:	slantzilla [ Sun Dec 08, 2002 8:00 pm ]
Post subject:
Red, as far as I know, all '73 and up disc brake A-bodies were large pattern. All A-body before '73 were small bolt, disc or drum. All '73 and up drum brake were small pattern too. My '76 disc brake Duster had a large pattern 7-1/4" in it with 10" brakes. They bolted right on to the 8-3/4" that I put under the car.

Author:	Pierre [ Sun Dec 08, 2002 10:36 pm ]
Post subject:	Incase I dont find a bigger A-body rear....
What do you guys think of getting the original 7 1/4 rebuilt to a ~3.21 ratio? Will it be able to handle that? Also, any modifications need to be made to the 904 to get it compatible? What are other things I need to consider when doing gear ratio changes? Also... interms of getting a non A-body mopar rear end (any rear end ever made, for that matter...) to fit, what do I need to look at, other then makin sure the wheels are under the fenders while the differential is lined up with the diveline, and the shock/leafspring mounting?

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