7 1/4 Vs 8 1/4

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DesertRat

DesertRat

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I just bought an 8 1/4 complete A-Body rear end with SG.
The seller tells me it is 48+ inches ID flange to flange and
the 7 1/4 is 51+ inches ID flange to flange. There is only
1 1/8" clearance from my tire sidewall to the leaf spring.
Am I going to have a tire to spring problem??????
Thanks in advance-Douglas
 
I took an 8 1/4 from an A body. Don't know the dimensions.

I put American Racing 200S wheels from a van with 225/50x15 tires and had to flatten the fender edge inside the wheel well on one side. No leaf spring problems.

I can do some measurements on the 8 1/4 I have on the shelf, and the car if you need it. It's a 72 dart.

fastmopar
 
I think you should be OK?

It all boils down to your rim offset. When they started using the 8 1/4 on the later years the cars had not only larger rear 1.4s for bigger tires, but the axles were narrowed a bit. I think you will be OK.

Can you set it up on the springs and do a mock up with your tires.
 
D.R. I'm in the same boat as you. I thought this was a no-brainer and posts done-to-death, but the more I search, the more I wish I had gone a different way. From what I've been able to figure out, drive shaft needs to be shortened 1.6"; spring pads are in the same place, but offset of wheels to the outside are a good thing; lots of discussion about 2:45 gear and smaller origional rears need different gears/limited slip units (need to research this further)...not clear on u-joints...As you, I was hoping to hear from someone who had actually done a BBP 8 1/4 swap into a '67ish b'cuda that had a 7 1/4".
 
i would just measure everything before you do the swap. measure from the axle flange to the spring. or about where the spring would be if you cant mount one. then lay a straight edge across the tire and measure from that edge to the back of the rim, where it meets the flange. that will give you an idea if it will work. or mount the wheel on the 8 1/4 and see how close it is to the spring perch.
 
DesertRat, since the 8 1/4 is actually narrower than an A-body 7 1/4'
53.20" vs. 51.40" (1.8" total or .9" on either side) it should be an easy fit. I
did a 7 1/4 to and early 8 3/4 (same measurements as above) in my
'65 Valiant with no problems. Have a good day.
 
DesertRat, I did the 8 1/4 swap into my 68 Barracuda with no problems. You will have to take your driveshaft to a shop and have it shortened (the diff is a little longer on the 8 1/4), keep your original parking brake cables and swap them into the 8 1/4, you will also need the shock mounts and u-bolts for the 8 1/4 ( larger axle housing) I cant remember my off-set but I have less than an inch clearance between tires and springs. The only hard part was breaking the brake hose fitting loose from the body after 40 years without tearing it up to much, good luck.
 
I know this is the case for the 7¼ and am pretty certain it's true for the 8¼ as well. If you have a 2.45 or 2.21:1 gear ratio in the diff, there's going to be complications getting a lower gear set installed. No problem with the 2.76 and numerically higher ratios. I did the 7¼ to 8¼ swap with no problems. Besides the axle, I swapped the driveshaft and used the clamp hardware from the 8¼.
 
Is the seller talking axle flange or backing plate flange? A lot of 7 1/4" rears were wider for cars that originally had 9" brakes. 10" brake 7 1/4" rears and all 8 1/4" rears should be the same.

I seem to remember the Mopar Chassis book explaining this in some detail. I don't have a copy handy, but perhaps somebody who does can post the facts.
 
Been awhile since I checked this thread, thanks for the input guys. I picked up the rear end last weekend (blowing out my back in the process;-) All I got was the rear end, now I will need to dig up shock plates and u-bolts as I did not get them. Shortening the driveline, no big deal. I unloaded the rear end from my pickup by myself and now my back hurts so bad I can't work on the car. Hoping to heal soon. I know the rear end is from a 74 Duster and is a 3:21 SG so I have high hopes!
Rat
 
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