8 3/4 swap question

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FlamesAreWicked

FlamesAreWicked

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I have a 68 Dart that I’m swapping from the stock 7.25 to a 8.75 from another A-body.. new leafs, shocks, shock plates, etc etc.. all the accoutrement plus some upgrades needed in such. Went to put the U bolts on the pass side and it’s a super tight fit. To the point where ya have to bang them on to over the tube. Once ya get it down to the shock plate, the ends don’t line up with the plate. They have spread enough to to not line up with the bolt holes. The driver side went together with zero issue..

Thoughts? Is the tolerance on the axle tube very that much from axle to axle to cause this problem? Suggestions on fixing this? The U bolt kit I bought was from Mancini for a 8.75/Dana 60 axle. Like I said the driver side worked as it should.

I’m stumped. As per usual, every seemingly easy project has been a struggle.. I’m totally over the idea that stuff will “just bolt together”. Thinking out loud, I could take some material off the axle tube, open the plate holes, and or the bolts where they contact the tube? Ideas are welcomed.
 
If it’s a 1/2” from going through the shock plate you can put a bar clamp or something like that and squeeze the ends closer together giving it a little “memory”. Any more, and id be looking at getting the next size up. 4x4 places online are good for that sort of thing. Get them a little long, decide that you aren’t gonna use a lowering block, and cut them off after install. The threads will fix themselves next time you take it apart.

$0.02.

Pictures will probably get you a better answer than mine.

$0.01.

If I remember correctly i got some from rough country lately when working on a 9”
 
I would put the U-bolts on top of each other, and see if they are both the same. It is possible one was made wrong or packaged wrong. The U-bolts for a 7 1/4 are smaller than for a 8 3/4. Definitely do not take material off the axle tube
 
I’m gonna get back on it tomorrow. I’ll measure the spread of the bolts. Even swap them side to side. Seems like for whatever reason the tube diameter is slightly bigger than the drivers side. I’ll also make sure they’re not slightly turned/twisted. Guess it’s possible to them to send me a box of u bolts that are miss matched :BangHead:
 
All of the original 8 3/4 u-bolts I saved were flattened and serrated at the top. You mat be able to see them in these pictures They prevent the housing from being squashed and the u-bolts stay tight. Do yours look like this in these pictures. They fit better then the after market. 440 and Hemi trac pac B-bodies had longer u-bolts for the SS springs.

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They look like that. Flat and ribbed at the top where it gets flat over the top. both the bolts and shock plates were purchased from Mancini Racing.. I’ll swap the bolts from driver side to see if they fit the passenger side.. if they don’t, then there’s an issue somewhere..
 
Oldmanmopar said:
All of the original 8 3/4 u-bolts I saved were flattened and serrated at the top. You mat be able to see them in these pictures They prevent the housing from being squashed and the u-bolts stay tight. Do yours look like this in these pictures. They fit better then the after market. 440 and Hemi trac pac B-bodies had longer u-bolts for the SS springs.

View attachment 1716375310

View attachment 1716375311

View attachment 1716375312

View attachment 1716375313
Click to expand...
This is off topic but what method did you use to clean up all that hardware?

Years ago we had a place in OKC that would vat parts all the way up to a complete car body but they have all been shut down.
 
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I'd leave the u-bolt over the axle housing, and then put a few nuts on the u-bolt (no shock plate yet) and squeeze it to the dimension you need. A vise if you have one unmounted, or a quality c-clamp. I would not modify the shock plate.
Comparing the bad one to a good one is a great idea.
 
33IMP said:
I'd leave the u-bolt over the axle housing, and then put a few nuts on the u-bolt (no shock plate yet) and squeeze it to the dimension you need. A vise if you have one unmounted, or a quality c-clamp. I would not modify the shock plate.
Comparing the bad one to a good one is a great idea.
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I’ll verify the bolts are the correct size and if I have to, I’ll give that method a try.
 
Just an update.. showed up this morning and crawled under it.. took measurements and they were the right bolts, right plates, and the diameter of the tube was just slightly bigger than the other side..

The idea I came up with was to set the bolts on it and push the plate up to the bolts while the holes still lined up.. put the nuts on the bolts, used a rubber hammer to knock them down and into place on the axle tube..

Then ran into problems putting the shocks on. At the time it didn’t dawn on me to knock the top sleeve out of the eyelet.. the mounting stud is the same size for top and bottom.. so I thought I had the wrong ones but I didn’t.. so all that’s left is to knock that sleeve out and put the shocks on..

Progress pics.. BBL complete… no more saggy rear

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IMG_0419.jpeg
 
FlamesAreWicked said:
I have a 68 Dart that I’m swapping from the stock 7.25 to a 8.75 from another A-body.. new leafs, shocks, shock plates, etc etc.. all the accoutrement plus some upgrades needed in such. Went to put the U bolts on the pass side and it’s a super tight fit. To the point where ya have to bang them on to over the tube. Once ya get it down to the shock plate, the ends don’t line up with the plate. They have spread enough to to not line up with the bolt holes. The driver side went together with zero issue..

Thoughts? Is the tolerance on the axle tube very that much from axle to axle to cause this problem? Suggestions on fixing this? The U bolt kit I bought was from Mancini for a 8.75/Dana 60 axle. Like I said the driver side worked as it should.

I’m stumped. As per usual, every seemingly easy project has been a struggle.. I’m totally over the idea that stuff will “just bolt together”. Thinking out loud, I could take some material off the axle tube, open the plate holes, and or the bolts where they contact the tube? Ideas are welcomed.
Click to expand...
no big deal bend the u bolt to make it fit .
 
I would bet the tube difference is the result of someone over tightening the u-bolts on the tube on that side - it would squish (that's a technical term) the tube and make the side bulge out in an oval shape. Measure tube width in both directions to confirm and then use a dolly and hammer to correct the out of round shape.

Get the proper u-bolt torque when you retighten them.
 
Charrlie_S said:
I would put the U-bolts on top of each other, and see if they are both the same. It is possible one was made wrong or packaged wrong. The U-bolts for a 7 1/4 are smaller than for a 8 3/4. Definitely do not take material off the axle tube
Click to expand...
Here's a second to that idea. Something somewhere is wonky. You should not have to apply force to get this stuff to install. Figure out what you have before you grab a bigger hammer.
 
Do not over torque them. They should be about 45 foot lbs.
 
Well guys and gals, u bolts and shocks aren’t my biggest problem right now. Tried to drive it and it doesn’t move.. drive shaft spins but, the tires do not…

Guess my center section is no bueno..should have bought a new one instead of a used one. Par for the course I guess
 
FlamesAreWicked said:
Well guys and gals, u bolts and shocks aren’t my biggest problem right now. Tried to drive it and it doesn’t move.. drive shaft spins but, the tires do not…

Guess my center section is no bueno..should have bought a new one instead of a used one. Par for the course I guess
Click to expand...
Pop the axles out drop out center section see whats going on in there
 
340sFastback said:
Pop the axles out drop out center section see whats going on in there
Click to expand...
I ended up just parking it until I get some more free time to take it apart. I emailed Cass/Dr Diff and he’s is thinking the side gear splines are stripped based on the symptoms it’s giving. He suggested replacing the 1 piece side gear kit. Digging in the innards of a differential is beyond my skill level. A kick in the jewels but what can ya do right.. when I assembled the axle/housing/diff the yoke and axle shafts spun together so there was no indication at that point. It obviously wasn’t under a load in that situation either. I’m likely gonna buy another center section and may use that opportunity to go a little tamer on gear selection. This was a 3.91 gear set. It would be fun but kill ya on the highway. Maybe a 3.55 will be in my future.
 
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