8.75 A body U joints?

-
805moparkid

805moparkid

Slant and AFX Guy
Joined
Oct 29, 2008
Messages
11,498
Reaction score
282
Location
Anthem AZ
i have a 68 dodge dart with the 7.25 or 8.25 diff (don't know the difference) and im trying to upgrade to an 8.75. i found one with 3.91's that needs a rebuild and axles. what u joints does me slant car use? with the right yoke on the 8.75 will it just bolt up?? driveshaft modes??
 
805moparkid said:
i have a 68 dodge dart with the 7.25 or 8.25 diff (don't know the difference) and im trying to upgrade to an 8.75. i found one with 3.91's that needs a rebuild and axles. what u joints does me slant car use? with the right yoke on the 8.75 will it just bolt up?? driveshaft modes??
Click to expand...
What #,s are on the side of the center section?The last 3 numbers will be either .741,.742 or 489.Thi s will help alot in knowing which u-joint,
 
the center section im looking to get is a 741. do you know how to tell a 7.25 from a 8.25 or the years they were used?
 
If the axle is original, its most likely the 7.25" axle. I say this because I think the 8.25" came out in 1972, as a replacement for the 8.75" If the axle is the 7.25", you'll need a ujoint with two sizes, which TRW makes. I don't know the PN offhand, but I do know I have one under my 72 Dart. I swapped from the 7.25" to the 8.75" axle. You'll also need to shorten the driveshaft.
 
if i moved the axle back enough could i just use the driveshaft and alow for more tire height??
 
My 66 Dart has a 6 and had the 7 1/4,pulled that and put in 8 3/4 .489.The driveshaft I used was from Donar car(73 Swinger 318 auto with 7 1./4)I used a 7290 u-joint in the rear and it bolted right in(no shortening)So I would say you need the 7260 u-joint.I could be wrong,if so someone will correct me!
 
Moving the axle back is a bad idea, since you'll need to modify the leaf springs, and the body. Mostly, its bad because the leaves are set up to counter wheel hop, with the axle mounted offcenter. This is supposed to cause the axle to use the leaf spring as a lever, and kills the harmonic that allows wheel hop. Long story short, moving the axle back will get rid of a lot of engineering.
 
gotcha... so how tall of a tire has been fit under stock wells? i have the XHD springs right now and a want to run 3.73 or 3.91's. so i need like a 28 or so to run around 3100 @ 70?
 
Thanks For the pic of the diffs! that was a good help cuz ive never seen a 8.25 before. so i need to run 30in tall tires to run 3.91's so its hwy freindly @ 3100...

will they fit? what has been fit?
 
805moparkid said:
gotcha... so how tall of a tire has been fit under stock wells? i have the XHD springs right now and a want to run 3.73 or 3.91's. so i need like a 28 or so to run around 3100 @ 70?
Click to expand...

27-1/2" is about as tall as you can fit without the front of the tire contacting the wheel opening. Springs don't affect that allot. I have the XHD springs on my 68 Cuda and had 28" tires on it and there was hardly 1/2" between the front of the wheel opening and the tire. I put 27" on it and it clears fine. If your running an automatic it'll slip a little so you have to figure that in the equation. I have a 3.73 gear in mine and with the 27" tires it spins 2900 at 60. It's been awhile since I took it up to 70 but I think that was about 3400 rpm IIRC.
 
so 28's with 3.73 @ 2900 should work. this is going behind my slant that should be making 300+ at the crank. its my daily driver 68 dart but a hot daily!
 
If you have an 8.25 you dont really need to swap. a gearset and a suregrip and its easily healthy enough to handle 300 horse. Spend your money on good axles
 
My suggestion, if you want to move the rear back, do it at the spring mounting brackets, not at the perches. Get a 1/2" block of aluminum and put it between the front mount bracket and frame.

Getting a 30" tire on a Dart is a chore if you don't either move the rear at least 1" or section the front wheel lip.

I put 28" on them before in the stock location. you may have to beat the front lip in a bit if sectioning isn't your thing.

Most likely a 741 case will have a 7260 u joint, the same as the 7 1/4. Even if it's the larger 7290 joint, ther is a conversion joint available. Spicer 5-527x, IIRC.
 
The case casting number doesn't really tell you which u-joint its going to have. My car has a 742 case with a dana powr lock and 3.23 gears (never been apart) and it has 7260 u-joints. It would be my guess that nearly every a-body every made had 7260 u-joints.
 
lots of info...
yea i wish i had the 8.25 but i don't. so im going to work on getting 28" tires with the 8.75...

unless somebody has an complete 8.25 for an a body near Sacramento Ca??
 
A dana, 8.75 or 8.25 won't have any bearing on whether you can put a 28" tire on the car. They all mount at the same point, the centerline of the axle from side to side.

The different rears may change what backspacing the wheel requires, not tire height.
 
You must log in or register to reply here.
-

Back
Top