7.25 to 8.25 Swap Questions

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Nick96

Nick96

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Hey guys, so I'm picking up an 8.25 rear end this weekend! It should be more than sufficient to handle the 350 HP my 360 swap will be putting out. I'm upgrading from the stock 7.25 SBP to 8.25 BBP. I put in the effort to find a rear end from another A body, so my assumption is that this will be a fairly simple swap as everything should just bolt right up (expect the drive-shaft) , am I wrong about this?

Also, the 8.25 doesn't have leafs attached to it, will I be able to simply use the leafs from my 7.25? Your help is appreciated!

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You will also need 3" u-bolts & shock plates, the 7 1/4" differentials have a smaller diameter tube.

Depending on the axle ratio, you may also need a transmission speedometer pinion with the correct tooth count for your speedometer to read correctly.

Driveshaft length may also be an issue.....

Your leaf springs will be fine if they are in good shape.

If not, great time to add an extra leaf on each side.
 
Yep. I did the same swap to my car.
Had to have the driveshaft shortened and I bought new u bolts.
 
That was dead on.

Your driveshaft WILL need to be shortened.

IMO, I would also order new springs and my advice is to get them from ESPO.com. While you wait for those, order the new U bolts and shock plates. While waiting for everything to arrive (for myself) I Took the time to remove all paint and rust from the rear and it’s parts to refurbish and paint. Man-O-man did that look good once it was installed.

Once everything arrives, after there installed, you can measure for the driveshaft.
 
It’s been a while but I believe I also replaced the plates that the ubolt goes through.
 
So I just ordered the shock mounts to accommodate the larger housing. I ordered the universal plates from Speedway, people in the reviews section said they worked fine for their 8.75 swaps, but the plates don't come with studs to physically put through the shock bushing. Could you guys point me to some studs.

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Speedway has universal 3" u bolts in various lengths, and shock wise, those plates are designed for a bolt, so just use a bolt with a appropriate size bushing to attach the shock.
 
Also, since your swapping in a 8 1/4, a really sweet easy brake swap is to jeep grand cherokee rear disks....it's basically a bolt on deal!
 
I'm in for more information on this as I am also thinking (or have the opportunity) of picking up a 8 1/4.

so question: would the driveshaft from the car that the 8 1/4 rear end come from make it pretty much a plug n play deal? with just having to buy the new plates and u-bolts?
 
I put an 8 1/4 A body with SG unit in my Barracuda. Bought correct shock plates and u-bolts used from a member here. I just rebuilt my leaf springs at the time and
everything went together really well. Had to have a custom driveline built as I installed a GV overdrive. It's a good swap.
 
prican_2000 said:
I'm in for more information on this as I am also thinking (or have the opportunity) of picking up a 8 1/4.

so question: would the driveshaft from the car that the 8 1/4 rear end come from make it pretty much a plug n play deal? with just having to buy the new plates and u-bolts?
Click to expand...

My understanding is that so long as the 8 1/4 you install came from another A-Body and the your transmission tail length is the same as the donor car, you can use the driveshaft from the donor. If the transmissions are both 904's there won't be an issue, but if I'm not mistaken (which I could be), if the transmissions are 727's or manuals, or completely different from each other, you'll have a mish-mash of different trans-lengths and you'll have to shorten your driveshaft anyway.
 
Nick96 said:
My understanding is that so long as the 8 1/4 you install came from another A-Body and the your transmission tail length is the same as the donor car, you can use the driveshaft from the donor. If the transmissions are both 904's there won't be an issue, but if I'm not mistaken (which I could be), if the transmissions are 727's or manuals, or completely different from each other, you'll have a mish-mash of different trans-lengths and you'll have to shorten your driveshaft anyway.
Click to expand...

Not quite. The Dodge Dart (111”) and Dodge Demon/Dart Sport (108”) had different length wheelbases. If you took a driveshaft out of a 318/904 Demon and installed it in a 318/904 Dart, and both had a 8 1/4 rear end, you would be short. If you did it the other way around, you would be long. A bodies had different wheelbases so it’s not as simple as taking a driveshaft out of any Abody with a 904 and 8 1/4 rear end and putting it in any other A body.

7.25" to 8.25" driveshaft?
 
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She looks good! Completely rebuilt the brakes, inspected the center section and installed a new cover gasket. Buffed the rust off and gave her a nice respray of Rust-Oleum semi gloss black.

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So I have a question, and I apologise if this should be thrown under an engine swap thread, but I'm installing this 8.25 to:
a) accommodate wheels without adapters and upgrade to BBP.
b) handle a bit more power than my 7.25.
I'm wrapping up the engine build on the 360 that will be replacing the S6 currently installed. My question is, I will be swapping out the S6/904 combo for a 360/904 set up, my understanding is that all 904s have the same tail end length, if I swap in this rear end prior to completing the engine swap, would my driveshaft length be incorrect when the 360 is in if I measured according to the positioning/length of the current S6/904?
 
It's so cheap and easy I can't understand anyone rebuilding a drum setup for these rears!
 
Nick96 said:
So I have a question, and I apologise if this should be thrown under an engine swap thread, but I'm installing this 8.25 to:
a) accommodate wheels without adapters and upgrade to BBP.
b) handle a bit more power than my 7.25.
I'm wrapping up the engine build on the 360 that will be replacing the S6 currently installed. My question is, I will be swapping out the S6/904 combo for a 360/904 set up, my understanding is that all 904s have the same tail end length, if I swap in this rear end prior to completing the engine swap, would my driveshaft length be incorrect when the 360 is in if I measured according to the positioning/length of the current S6/904?
Click to expand...

The driveshaft should be the same length for the 360/904 as it is for slant6/904.
 
Can anyone help me figure out how much I need to shorten my driveshaft?
 
Needs to be shortened by 1.5”. More details are in the link in post #12.
 
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