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7 1/4 to 8 3/4

Posted By: Confusedcuda

7 1/4 to 8 3/4 - 11/04/08 04:55 PM

Hi guys, I am going from a 7 1/4 to a 8 3/4 in my 67 barracuda. Can I use my 7 1/4 U-bolts or do I need to get new ones? Also I have a 904 tranny, does anybody know how much shorter my driveshaft will need to be? Is there a standard measurement or do I need to wait till I get the rear end installed and then measure. It is a 67 barracuda with a 904 that was a 273 now a 340, Thanks.
Posted By: Hotwheelsjr

Re: 7 1/4 to 8 3/4 - 11/04/08 05:09 PM

Yes, you need new U bolts and yes, you need a different drive shaft -- there is a 2.26" length difference between your tranny and rear you are going to have to make up just swapping the rear.
Posted By: B5 Bee

Re: 7 1/4 to 8 3/4 - 11/04/08 05:23 PM

You'll also need new bottom shock plates.
Posted By: RangerDan440

Re: 7 1/4 to 8 3/4 - 11/04/08 05:29 PM

...and an e-brake cable
Posted By: RapidRobert

Re: 7 1/4 to 8 3/4 - 11/04/08 09:58 PM

Quote:

or do I need to wait till I get the rear end installed and then measure.

that's the best way, since there's always a stackup of tolerances that way its exactly where you would like it to be.
Posted By: Confusedcuda

Re: 7 1/4 to 8 3/4 - 11/04/08 10:01 PM

Okay, the housing I am buying is supposed to have the perches on it and in the correct position. Is that what you mean by shock plates. I also have a place that will shorten my driveshaft, that should work,right. Thanks...
Posted By: RapidRobert

Re: 7 1/4 to 8 3/4 - 11/04/08 10:13 PM

Quote:

Is that what you mean by shock plates. Thanks...

the shock plates are the flat metal plates under the axle tubes on each end that the u bolts go down into & which the lower end of the shock(s) bolt to which as mentioned are different on the 8&3/4. My suggestion would be to get the 8&3/4 rear bolted in there,jack it up off the ground at the center of the 8&3/4 then butt the driveshaft all the way into the trans & measure how much needs to be taken off & add 3/4-1" to that figure.
Posted By: Reggie

Re: 7 1/4 to 8 3/4 - 11/04/08 10:18 PM

Quote:

Okay, the housing I am buying is supposed to have the perches on it and in the correct position. Is that what you mean by shock plates.



No, the perches are welded to the axle and they have holes that lock the axle onto the locator pins on the springs. Large u-bolts go over the axles and through the shock plates which bolt on under each spring.

Attached picture 4792517-B_BodyRear.JPG
Posted By: Confusedcuda

Re: 7 1/4 to 8 3/4 - 11/05/08 12:28 AM

Okay, so it sounds like I need to get some 8 3/4 shock plates. Thanks for all the info. I will take some more if anyone has anymore.
Posted By: Confusedcuda

Re: 7 1/4 to 8 3/4 - 11/05/08 12:30 AM

If I butt the driveshaft all the way to the tranny, and then add 3/4'' to 1'' won't it be too long?
Posted By: 68cuda27

Re: 7 1/4 to 8 3/4 - 11/05/08 12:46 AM

If you you butt the driveshaft all the way forward, you need to substract 3/4-1" from the dimension.

Good luck, I did the change from 7 1/4 to 8 3/4 earlier this summer. Make sure you use the vented bolt to attach the rear brake hose to the axle housing.
Posted By: RapidRobert

Re: 7 1/4 to 8 3/4 - 11/05/08 01:45 AM

[quote then butt the driveshaft all the way into the trans & measure how much needs to be taken off & add 3/4-1" to that figure.

if 2" needs to be taken off then add 3/4-1" to that figure so ie 2&3/4-3" needs to come off. At least that's what I thought I was saying but you got it.
Posted By: Confusedcuda

Re: 7 1/4 to 8 3/4 - 11/05/08 03:29 AM

Thanks to all who replied. Excellent info..
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