Mopar rear end #'s, were are they?

[gettingreasy]

I was scrapping all the old grease/mud combo off my rear today so I could see if it was a 741 or 742 case but I am unable to find the cast on case # and the stamped ratio. Were are they located? I found "3 3" with an "8" below them on the very bottom rib(the six o' clock position)and a cast on # that doesn't match either the of the 2 #'s it could have been(at about the four o' clock). This rear is out of a '64 Fury. Thanks.
-Jesse

[four-thirteen]

bottom left side of the pinion. you are right, it should be a 741 or 742 case, if it's a 64. the 741/742 is the last 3 numbers of the 8 or so digit casting number. so it will be like XXXXX742.

if it's a sure grip, it'll have a tag under one of the bolts that says use sure grip lube.

That rear end will have tapered axles like an old ford rear end. not a big deal at all, but it's kind of a pain to swap gears in that type of rear end, and do other maintence things. David

[50dodge4x4]

The #s on the center of an 8 3/4 Mopar center are located on the driver side of the pinoin nose, just to the rear of the front seal. The #s are raised from the body and were cast as the housing was cast. I can get you a picture tomorrow if you need it. BTW there are more center section #s then the 3 usually listed in the books, so if there is something odd, don't be suprised.

Gear ratios can be found on the ring gear, next to where it bolts to the carrier. There are several #s on the ring gear in a seriies, including the date of the ring gear and the gear set part #S. The ratio # is the last three digets in the series, and will show up as 3:23 or what ever. I've not seen anything indicating gear ratio on the housing, other then to little tag on one of the studs around the center section/axle housing. Gene

[swazzie]

HAHA! Keep scrapin. I had to dig a ton of grease off of my case to find numbers.the fellas are right of course about the location.64 though? I think it should be a 741 .hope not . 742 is much nicer .good luck. swaZZie

[gettingreasy]

Over at www.moparts.com (http://www.moparts.com) there are a few tech articles about the early 8.75" and it shows all the pinions laid out and the pinion on the 741 case is actually beefier than a 9", Doctor Diff is the guys name and seems to know what he's talkin about. It said thar before '65 there was the ratio(with an "S" stamped after if it was a sure grip)stamped right after the cast on Case #. The cast on Number was 600524-14 if I remember corectly. I'll look again, thanks guys.
-Jesse

[plmczy]

I was told that a 488 is also the same as a 489 case. They were found in 69 plymouth fury's. I had one before, whole rear end that is, but got rid of it before I learned of this so I don't know if it is true. later plmczy

[Brad54]

The 741 case will have a large "X" also cast into the case. It's like the factory was telling us "Don't use this diff for a performance application."
The 741 is the weakest of the three--the pinion stem is small, and the splines for the yoke aren't desireable (I'd have to re-read an article I wrote to find out more specifics).
The 742 and 489 cases are great rear ends, and in a stock vs. stock application, either is stronger than a Ford 9-inch.
Rebuild parts for the 741 are hard to come by, but Randy's Ring and Pinion sells all the stuff for them. He talks them up a lot, but he's also got a lot invested in them.

I just remembered that the differential itself will bolt into any 8 3/4 rear end, so if the limited slip isn't shot, it would go into the 742 or 489 case. The ring and pinion gears, bearings and yoke are all different, though.
-Brad