Rear axle swap (7 1/4 to 8 3/4) - driveshaft?

-
hellfirechrome

hellfirechrome

Well-Known Member
Joined
Aug 7, 2009
Messages
363
Reaction score
31
Location
Tahoe
Howdy! Just yanked the stock 7 1/4” from my 65 Barracuda and am transplanting an A body 8 3/4”. Behind the (mostly) stock Slant 6/904.

Q1: how much does the driveshaft need to be shortened? I saw a formula a while back I know it’s just math, but can’t find it now.

Q2: anything I need to worry about in dimensions/driveshaft angle, or will it be about the same? (I have adjustable spring perches so I’ll dial it in before welding them on, see pic!)

Thanks in advance!

A3F821CF-757E-45ED-9759-0537BC4C137E.jpeg
 
Do you have a place that can cut/make one? They should tell you what you need to know or dennys driveshaft i believe has it on their website.
 
Factory shafts differed by 2.03" between the 7.25 and 8.75 rears, all else being equal; but double check that when you mock it up before you have yours cut. Also check your pinion yoke on the 8.75 to make sure it takes the same u-joint as your current shaft, so you know whether you'll have to run an adapter u-joint or just have a different (compatible) end installed when your shaft is cut; your choice on that.
 
Last edited:
I just put a new drive shaft in my car 3 weeks ago. There are local shops in every town, and could be cheaper and most already have the parts. Go on Denny's and pull the build chart and follow the directions. Take that sheet to the drive line shop and they will be able to cut and weld the flange back on. Should be about 200 for them to recondition (cut/weld/new Ujoints/ paint) your drive shaft and a brand new one is about 500.
 
When I did that swap I actually found the correct one in the junkyard, but that was 30 years ago... they are like hen's teeth because very few cars had an 8-3/4 behind a 904, and that was only from 67 to 69.
 
Thank you all for your advice! I think it sounds wise to just get the car put back together and measure the old driveshaft in place, against the new rear end yoke. I wouldn’t want to take the risk of something not being stock that I can’t see, and paying the price literally.

Measure twice cut once, right fellas?
 
mvh said:
When I did that swap I actually found the correct one in the junkyard, but that was 30 years ago... they are like hen's teeth because very few cars had an 8-3/4 behind a 904, and that was only from 67 to 69.
Click to expand...

A few months back I bought a slant six, 904 car that had an 8 3/4 in it. Yes very strange. Either a special order or they ran out of 7.25's that day. Never found a complete build sheet to confirm but it appeared to have never been apart....same with the rest of the car. I found two build sheets and BOTH were missing the part with the axle code.
 
You must log in or register to reply here.
-

Back
Top