Diff Replacement swap?

[a6t9vette]

Im looking at the posibility of swaping out my stock 3.23 non-sure-grip rear (8 3/4) with a sure-grip unit with 3.55 or 3.91. I guess my questions is are there any issues with doing the swap, or is it just as easy as pulling out the axles and swaping out the center section. Is there anything I need to keep my eye out for when buying a used center section to make sure it will fit my RR?

To those that have 3.55 or a 3.91 (mine is an Auto 727) how were either ratio for normal street use?

 

[droptop]

There were 3 different types of 8.75 diff. 741, 742 and 489 case. The pinion size is different. All will fit your housing, but the yokes are different on them. The 741 and 742 have the small yoke, and the 489 has the big yoke. You should have the big yoke.

I can't believe I beat A12 to this one. :banana: 51 mins...your slipping Ray. :lmao:

 

[Big John]

Overall you may be happier with the 3.55 gear set, but the 3.91 isn't a bad choice either.

I happened to find this on the Ebay guide section. It looks like a pretty good reference for the 8 3/4 rear.

http://reviews.ebay.com/Guide-to-the-Chrysler-8-3-4-rearend_W0QQugidZ10000000004412847

 

[mcmopar]

If you don't have the Green bearings on the rear axles you may need to check end play (the shop manual explains how to do this - or check the link Big referenced) so you get everything back in to spec. Other than that its a fairly easy swap. Make sure to have a big pan ready (and a floor jack as well) under the pumpkin when you pop it because all the axle is going to come draining out. The floor jack will help carry the weight of the pumpkin. These things be a bit heavy.

 

[ACME A12]

There were 3 different types of 8.75 diff. 741, 742 and 489 case. The pinion size is different. All will fit your housing, but the yokes are different on them. The 741 and 742 have the small yoke, and the 489 has the big yoke. You should have the big yoke.

I can't believe I beat A12 to this one. :banana: 51 mins...your slipping Ray. :lmao:

Harold...well, you're making me laugh out loud...


Bob - just a couple of things that I would add to what has been offered to you already:

The guide that Big John posted alludes to this but falls short of actually stating it - the cone type SG units weren't intended to be rebuilt (although they can be by someone that knows how to cut and shim the cones) - so the clutch type SG units are the ones that you should look for.

All three are good units (I've successfully run a 741 behind a moderately built 340 for years - but wouldn't advocate doing so behind a healthy big block) but I'd look for a 742 if I were you (more likely to have the clutch type SG unit) unless you have a buddy that is experienced at rebuilding the un-rebuildable cone type SG units. :cents:

:jester:
ACME

 

[Basketcase]

my first ;69 had a 440/727 with 3.91sg. Lotta fun, but sounded like it was wound out on the highway, but not real bad. I had a '68 Charger R/T,440/ 4 spped and 3.23sg. Great out on the road,liked to cruise at 70, and I could still bark the tires. The car I lost in the fire had the same 440 from the Charger,4 spped with 3.55sg. Nice all around gears. Still liked to cruise at 70, decent on the gas, and good on takeoff.

 

[Big John]

You can interchange the sure grip units if you want to also. Like putting an early style clutch style in a later center section.

 

[mcmopar]

Jerry (moparmoose3) and Jim both know how to rebuild the cone type units.

 

[ACME A12]

Jerry (moparmoose3) and Jim both know how to rebuild the cone type units.

Jim and I actually had that conversation on Saturday night. The Swinger has a cone-type unit that has been rebuilt and we were comparing notes... I'd like to check out his Challenger at some point...maybe we could plan a trip to the track...?

:jester:

 

[a6t9vette]

How do I confirm if the case is a 489? Im assuming its the original rear as it still has the 3.23 tag on it, and all the other drive train components are original....

 

[Basketcase]

don't remeber off hand, but on one side of the punkin, there will be raised cast numbers. You'll see part of the numbers as 742,489,etc. That tells you which center housing you have.

 

[mcmopar]

Jerry (moparmoose3) and Jim both know how to rebuild the cone type units.

Jim and I actually had that conversation on Saturday night. The Swinger has a cone-type unit that has been rebuilt and we were comparing notes... I'd like to check out his Challenger at some point...maybe we could plan a trip to the track...?

:jester:

Here's a pic of Jim's Challenger:
[attachment=0:1urgku3n]Jim's Challenger.jpg[/attachment:1urgku3n]

You know you are making some power when you can dead lift that 440-6 Pack up off the ground like that!

 

[ACME A12]

don't remeber off hand, but on one side of the punkin, there will be raised cast numbers. You'll see part of the numbers as 742,489,etc. That tells you which center housing you have.

Yep. Grab a drop light and a small wire brush and 30 seconds later you'll know...may get lucky and not need the wire brush...

 

[Hoosier Bird]

Here's a pic of Jim's Challenger:
[attachment=0:3jtf5jdq]Jim's Challenger.jpg[/attachment:3jtf5jdq]

You know you are making some power when you can dead lift that 440-6 Pack up off the ground like that!

Nice.......I like it..........

 

[a6t9vette]

Thanks. Just verified it to be a 489. Now I just need to find a 3.55 Sure Grip unit to make the swap...

 

[a6t9vette]

One more question. Since finding a 489 might be hard, as another option if I do find a 742 do I have to do anything else other then swap the yoke, are they interchangable?

 

[ACME A12]

Just buy a complete 3rd member with the CORRECT (as in the same as on your car now - should be the large one) yoke. Whether you end up getting another 489 or a 742 you don't want to have to pop the yoke off of the 489 as the pinion crush sleeve is one of the "less desirable" elements (strictly from the interchange standpoint, assuming you have some reason to go back and forth with both large and small yokes - like having A-Bodies and B-Bodies) that the 489 brings. If you get the correct yoke then you don't have to worry about yoke interchange or any of that. You'll also be able to swap back and forth in about 45 - 60 mins once you get used to doing it. It used to take me just as long to get the car jacked up and take the wheels off and reverse the procedure as it did to yank the axles, swap banjos, and put the axles back in the car back in the eighties when I was doing that stuff frequently with my Duster. I used to go from 5.13 or 4.86 to 3.91 or 3.23 in less than an hour... I still have complete 3.23, 3.55, 3.91, 4.30, & 4.86 units in my inventory...man, that makes it nice...


:jester:
ACME

 

[a6t9vette]

Thanks, as this is my first Mopar (was a Chevy guy) theres a lot to learn. Now I just have to convince you to sell me your 3.55 or 3.91 thats just laying around.... :cool:

 

[ACME A12]

Thanks, as this is my first Mopar (was a Chevy guy) theres a lot to learn. Now I just have to convince you to sell me your 3.55 or 3.91 thats just laying around.... :cool:

The 3.55s are in use under the gold '74 Duster and the 3.91s are the factory original unit that goes in my FE5 '70 Duster 340...so I'll never say never, but good luck...

:jester: