I pulled the 489 center section out of the T/A yesterday and learned to my displeasure that it has an open 3:23 chunk in it. Can someone point me to a tech article or other source that can get me smart before I start my hunt for a replacement?

Thanks!!

I'm dealing with a friend who just tore up his $500 Detroit locker if that will help. I'm trying to dig up enough parts to put him together an OEM 68 down clutch type. They are rebuildable with replaceable clutches. The style that would have come in your car is a cup and cone type that is not rebuildable per say. When they start to slip, you can have the housing machined off a little and they work again. Good used parts are what I would look for. Back in the day when mopar was dumping all their spare parts for nothing, I bought 4 NOS cup and cones for 25 each! Saving the last one for my Son's R/T.Check the differential section here on Moparts.

if you want factory,,, get a clutch style unit from a 741 or 742 diff. if you want something better that that get ahold of Dr Diff here on the board.

Thanks to both of you. I'll check with Dr. Diff. A local salvage yard has several SG chunks in their warehouse. I wanted to see what style to look for before I check them out. The clutch-style has the small coiled springs visible in the SG unit right?

No the clutch type has no visible springs

Okay, I think I have it figured out

clutch type

cone

open

Yes you got it , do yourself a huge favor and avoid the cone .

Your TA would have come with the 489 case with the cone style sure grip. I would get a new or used power loc (clutch type) and correct gear ratio for your car (could only be 3.55 or 3.91 and only listed on the BS) and then use the 489 case you already have. If the 489 case you have is '72 or '73-up, it probably won't be machined for 3.91 gears if that is what you need. But, you can grind the clearance needed with a little effort.

I've read that the MP aluminum chunk needed to be machined in the pinion area for gears taller than 3.55. I've never heard of an iron case needing work to fit gears.

It wasn't all of them, but many were like that. I first read about it in a Mopar Action article years ago ( Rick E)and then experienced it first hand several years ago. Actually, HPMike is the one that set that chunk up for me. Maybe he'll chime in and share his experience.

I read the M/A article too. I'm sure that the housing that had trouble was the aluminum unit. Aluminum ANYTHING needs to be thicker than steel or iron to have equal strength.

Thanks for all the replies. the quest has begun.