8 3/4” question

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57 Fargo

57 Fargo

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Here’s what I have going on, I have an 8 3/4” in an early barracuda with a sure grip and 4.56s in a 489 case, while fun, we are taking the car on a road trip and I have a 657 case out of a ‘59 dodge that is an open differential with 3.55s Can I swap center sections with out any problems? I read something about the thrust block and axle lengths but can’t seem to find a definitive clear answer. It still has the tapered adjustable bearings. Thanks
 
57 Fargo said:
Here’s what I have going on, I have an 8 3/4” in an early barracuda with a sure grip and 4.56s in a 489 case, while fun, we are taking the car on a road trip and I have a 657 case out of a ‘59 dodge that is an open differential with 3.55s Can I swap center sections with out any problems? I read something about the thrust block and axle lengths but can’t seem to find a definitive clear answer. It still has the tapered adjustable bearings. Thanks
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The swamp should be a go ... Obviously you might have to replace gaskets and seals.... Also check out if your 489 has a large or small yoke and then confirm that the 355 has the same size of yolk... If not it's a no big deal but you may have to get a different type of u-joint or yolk to fit whatever on the end of your drive shaft... I'm assuming you're running stock axles... So a thrust pin I don't think we'll be an issue.. I did just buy a set of axles from Doctor diff and my 391 currently has its thrust pins in I never had to remove them or had any fitment issues...
 
Andrew vanman87 said:
The swamp should be a go ... Obviously you might have to replace gaskets and seals.... Also check out if your 489 has a large or small yoke and then confirm that the 355 has the same size of yolk... If not it's a no big deal but you may have to get a different type of u-joint or yolk to fit whatever on the end of your drive shaft... I'm assuming you're running stock axles... So a thrust pin I don't think we'll be an issue.. I did just buy a set of axles from Doctor diff and my 391 currently has its thrust pins in I never had to remove them or had any fitment issues...
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Stock axles, I’m not worried about the yoke, that’s easy.
 
Yes the thrust block is different.

1.5" 1965 and newer and all sure grips.
1.25" in 1964 and older open differentials.
 
413 said:
Yes the thrust block is different.

1.5" 1965 and newer and all sure grips.
1.25" in 1964 and older open differentials.
Click to expand...
So the thrust block is actually shorter, I’m assuming there isn’t 1/4” of adjustment?
 
Hang on fella; 413 said
413 said:
Yes the thrust block is different.

1.5" 1965 and newer and all sure grips.
1.25" in 1964 and older open differentials.
Click to expand...
65 and newer AND ALL SURE-GRIPS, use the 1.5 T-bloc.
So all you need to do, is swap into the old open diff, is a later bloc, or just install a second Sure-grip.
Or do what I did, just weld a pair of hardened washers onto your skinny block until it gets close enough to work with your adjuster. Unfortunately, the whole thing has got to come apart to get the block out, IIRC.

Hey I just noticed that you are in Grimshaw. Is that Grimshaw Alberta? you are only 18 hours from me, and in the same country. I got an extra refurbished cone-type SG here ....... with a 1.5" block already installed. And I have some spare chunks here from 2.76 to 3.23s that I could install it into................ but no spare long T-blocs
 
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AJ/FormS said:
Hang on fella; 413 said

65 and newer AND ALL SURE-GRIPS, use the 1.5 T-bloc.
So all you need to do, is swap into the old open diff, is a later bloc, or just install a second Sure-grip.
Or do what I did, just weld a pair of hardened washers onto your skinny block until it gets close enough to work with your adjuster. Unfortunately, the whole thing has got to come apart to get the block out, IIRC.

Hey I just noticed that you are in Grimshaw. Is that Grimshaw Alberta? you are only 18 hours from me, and in the same country. I got an extra refurbished cone-type SG here ....... with a 1.5" block already installed. And I have some spare chunks here from 2.76 to 3.23s that I could install it into................ but no spare long T-blocs
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Ok. That makes sense
 
Doubt you can swap the blocks. Need to swap carrier for a SG or a 1965 and newer open.

Top is 1965 and up, round shafts intersect

Bottom is 1964 and older, big rectangle block fills up the space between spiders and side gears.

image.jpg


image.jpg
 
AJ/FormS said:
Hang on fella; 413 said

65 and newer AND ALL SURE-GRIPS, use the 1.5 T-bloc.
So all you need to do, is swap into the old open diff, is a later bloc, or just install a second Sure-grip.
Or do what I did, just weld a pair of hardened washers onto your skinny block until it gets close enough to work with your adjuster. Unfortunately, the whole thing has got to come apart to get the block out, IIRC.

Hey I just noticed that you are in Grimshaw. Is that Grimshaw Alberta? you are only 18 hours from me, and in the same country. I got an extra refurbished cone-type SG here ....... with a 1.5" block already installed. And I have some spare chunks here from 2.76 to 3.23s that I could install it into................ but no spare long T-blocs
Click to expand...
Yeah Grimshaw Alberta. I have other newer center sections with tall gears, the car has an 833 overdrive in it so was wanting to use at least 3.55s and I had this one, can swap them into a newer center section if need be.
 
413 said:
Doubt you can swap the blocks. Need to swap carrier for a SG or a 1965 and newer open.

Top is 1965 and up, round shafts intersect

Bottom is 1964 and older, big rectangle block fills up the space between spiders and side gears.

View attachment 1716271610

View attachment 1716271611
Click to expand...
I wondered about swapping pin and block, I’ll pull the center section out of a 66 Windsor parts car I have and figure it out!
 
413 said:
Ok let us know if it works or not.
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Just follow up on this, I messaged Cass, Doctor Diff, he confirmed I would have to swap the thrust block for the newer style, however for convenience I just swapped the entire carrier rather than dissembling both carriers. Thanks for everyone’s input
 
That's how I leaned this stuff, DR Diff. Use him and buy parts from his mopar business.
 
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