Swap out 7 1/4 RE for an 8 1/4 RE

[lancer770]

I would like to find out which entire rear end and axle unit would be the easiest and require the least modification to swap in my son's 76 Duster. The 76 had the larger bolt pattern and I'm trying to apply the KISS strategy to this swap over. Is there a bolt out(of a salvage car) bolt in(to the 76 Duster) rear axle out there and what car would it come out of. It wouldn't have to be a perfect swap, relocating lspring brackets and the like is do-able I just want the right span for the total unit with the proper bolt pattern. Any ideas? This is to be a street legal driver.

 

[valiantwagonguy]

Just get one from any disc brake A Body (74-up) and it's a 1 hour bolt in jobThese rears are all over the place and again like the rest of the six cyl stuff we are at a huge advantage 'cause no one wants them and they are dirt cheap.

 

[dusterdon]

Just find a 8 1/4 rear out of any abody. You'll need a new or shortened driveshaft due to the different dimensions of the nose of the new rear. You might even get one out of the car the rear came from.

 

[Ace]

Before trying to answer your question, I think I'd have to ask "why are you doing it?" If the 7 failed and this is just a straight repair/replace, then why worry about it, just use the same parts?

OTOH, if you are building towards some higher performance and don't mind cutting/welding perches, then you have already contradicted yourself, because it stops being simple at that point. In this case, I would try for an 8 3/4. The A-body units are pretty rare nowadays, but you should be able to get a C-body narrowed 2.5" each side for $175-200 and have a very stout setup. Granted, even the C-bodies are getting hard to find in the boneyards these days.

I guess my point is the 8 1/4 option is a compromise in both ways. Probably gonna require some modification anyway (driveshaft, whatever), AND not the best in terms of strength either.

 

[dgc333]

Though not a strong as an 8 3/4 an 8 1/4 is still a stout rear end. If your power goal is less than 400 then there is no reason to not use it. Even if you goal is over 400HP it is easier to up grade than getting involved with cutting down housings, axles and moving spring perches.

Disk brakes on the front of an A-body is not an indicator of an 8 1/4 either. Slant 6 and 318 cars came with 7 1/4 rears even when they had disks as standard. It was optional on these cars and was standard starting in 73 on performance models when it replaced the 8 3/4.

Having a drive shaft shortened and balanced should cost between $50 and $75 at a local drive shaft shop.

 

[Ace]

Yeah, you certainly can't argue with the cost factor. It is costing me a total of about $1k to do the driveline work on my Duster: C rear narrowed/tubed/braced, Yukon axels, new 3.73 geras, Powertrax locker, and of course the driveshaft work. And I already had the donor car.