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| Please indulge another drum -> disc conversion question https://slantsix.org/forum/viewtopic.php?t=55577 |
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| Author: | sunspark [ Tue Jun 10, 2014 9:14 pm ] |
| Post subject: | Please indulge another drum -> disc conversion question |
I know this has been hashed probably a million times already, and I have searched and read, so please indulge me. I have a '73 low-option swinger special, "no power anything", drums w/4" BP wheel mounts, 3 spd floor shift manual (a-250) and 7 1/4 rear end (don't know the ratio...need to check) that I run as a DD. I'm soon to receive practically all of the 4.5" BP front disc components from a '74 Duster donor. Since the front will move to a 4.5" BP, I'd like to know my options for moving the rear to the same. From what I've read, I take it this isn't simple (even possible?) for a 7.25 rear. I'd really like to keep this as "bolt in" as possible (e.g., no housing/axle/drive shaft shortening, adaptors, perch welding, etc.) So, am I looking for an 8.25, 8.75 axle assembly from a '73-up disc equipped A body? Were disc equipped A bodies backed by 7.25 axles/housings? Basically, what are the simplest, least expensive options for moving the rear to 4.5 BP? Many thanks. |
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| Author: | Rick Covalt [ Wed Jun 11, 2014 3:37 am ] |
| Post subject: | |
Yes they built 7.25" Big Bolt pattern rears. That should be a bolt in if you find one out of a late A-Body. Rears are not that desirable so they are cheap An 8.25, would be a bolt in except for having the drive shaft shortened. More desirable, not as cheap 8 3/4 won't be a cheap swap no matter what. There were no big bolt A-body rears. So you would need custom axles and the drive shaft shortened. Did I mention they aren't cheap!..  Good Luck, Rick |
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| Author: | DusterIdiot [ Wed Jun 11, 2014 5:16 am ] |
| Post subject: | Yep... |
Quote: Yes they built 7.25" Big Bolt pattern rears. That should be a bolt in if you find one out of a late A-Body
Exactly, your '74 duster Disc Brake donor would have come with this automatically with 10" drums...if it was a HD optioned car then it would have had the 8.25" rear.
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| Author: | sunspark [ Wed Jun 11, 2014 9:08 am ] |
| Post subject: | |
Yeah, after waking up this morning, I realized it was a pretty ridiculous post, and confirmed by searching for rear axle assemblies on car-part.com. Guess it's time to scare up a 7 1/4 or 8 1/4 a-body rear (or at least 7 1/4 LBP axles). I'm not going to take this car in a direction that would require an 8 3/4, just DD use. Thanks all! |
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| Author: | sixinthehead [ Wed Jun 11, 2014 9:42 am ] |
| Post subject: | |
One note - in the 7 1/4, lbp axles use a much larger bearing and corresponding 'stepped' shape that won't fit into a sbp housing, so you would have to swap the whole rear. It's not that hard to do, so no worries. |
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| Author: | Reed [ Wed Jun 11, 2014 10:42 am ] |
| Post subject: | |
If you change out the entire rear axle assembly, don't forget you will also need new u-bolts and new lower shock absorber plates due to the increased diameter of the axle tubes. The donor Duster will have the shock plates and you can get new U bolts at a spring shop, hardware store, or online. |
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| Author: | sunspark [ Wed Jun 11, 2014 11:26 am ] |
| Post subject: | |
Wow. Thanks. Lots of good, useful info, here. I'd actually prefer to swap the entire assembly opposed to doing axle swaps so, given that there are differences btwn the two (that I didn't know about), I now know my preference is actually a requirement. Didn't know about the shock-plate difference, either, so thanks for that info bit, too. Unfortunately, the donor car is several hundreds of miles from me, so sourcing could get a little tricky. I don't know the details of the donor other than it was a disc-equipped '74 duster. Trans type and rear end are unknowns. I'll check w/the owner and, if all lines up, see if he's willing to sell/ship the rear at a doable price. I wonder, as that may be more effort than he's willing to go. Question: if I find a 7 1/4 LBP unit and the ratio is different, is it technically possible to swap gears btwn the two, or are there differences within the differentials as well? Again, my thanks! |
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| Author: | sixinthehead [ Thu Jun 12, 2014 6:39 am ] |
| Post subject: | |
Yes, the guts will swap. |
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| Author: | sunspark [ Thu Jun 12, 2014 8:23 am ] |
| Post subject: | |
<nod> Thanks. 'ppreciate all the help. |
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| Author: | Reed [ Thu Jun 12, 2014 8:29 am ] |
| Post subject: | |
Be advised that depending on the gear ratios involved you MIGHT have to swap the rear axle gear carriers as well as the gears. the 2.7 and higher gear sets use a different carrier than the 2.9 and lower. The 8 1/4 rear axle I installed in my brother's 74 Duster has a 2.2 gear ratio and I am going to swap in a set of 3.2 gears but I am going to have to swap out the gear carrier as well. |
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