Other than possibly the stub axles, is there any physical or metallurgical difference between an early C-3 differential and one from 79 or so? Were the big block diffs beefier or did they just have beefier IRS parts than the smallblock stuff? Ford's 9" N cases come to mind as being stronger to stand up behind higher torque engines.

 

only difference between SB and BB differentials were the half shaft caps that were used on BB's. SB did not come with the caps.

 

I happen to have gotten a '63 differential housing (pumpkin) and compared it with my '75 housing, also compared with the diff housings I got from GM Parts Dept when they were still avail. It's apparent that there were quite a few improvements in the casting to beef it up in the later years. most noticably where the cover attaches to the housing, the areas where the bolts thread into the diff hsg are much beefier, reinforced. at the front, where the front bracket attaches to the diff hsg, the later model is beefier also. The differences are significant enough that I wouldn't want to use the early model housing in any serious performance application, like a big-block.

 

Thanks for the info! The one I've been looking at is from a 77 with an auto, so I also know it hasn't been beat on with a big engine or suffered thru some high-rpm clutch dumps.

 

The 63-64 diff's used a Dana posi and the internal distance between the bearing caps is tighter( not as good for 12 bolt conversions) The Eaton posi will fit these and I'm betting most were already swapped inthe 63-64 by now.
The 65-70 Eaton used the better solid steel clutches and weaker 10-18 spiders. The 71-79 eaton posi's used the much better 10-17 spiders but junk snowflake clutches. The early posi carriers had a small rear window and were more prone to cracking then the later posi's with the large tear drop window. They all used 17 spline side yokes so you can use the standard or HD yokes on any of these. There were 2 size pinion yokes used depending on the year and transmission.
The later units, 76-79 used flangedhead bolts instead of a lockwasher and bolt on the ring gears and a lot of these failed in use. I never use these bolts in a diff I rebuild. Look for signs of a rign gear bolt hitting the inner case or where the bolts are in the carrier.
The early bearing caps used a weaker bolt and the cap doesn't have a cast in tab. The later units used the caps with a tab and gr 8 bolts. I toss these bolts out too and use socket head cap screws which are stronger. For the guys that want a HD unit I'll fit a steel left bearing cap and tap it for 1/2-13 bolts. Also have a billet pinion yoke and caps.
I tap all units for a drain hole too.
Well that's about what I know on these from working on them, maybe there's more info out there too?
Gary

 

GTR1999, thanks for all the info! That answered most of my questions, but I have a few more.
When these diffs/posi's fail, is there a common failed part? Does the carrier cliimb the ring gear and break the caps/bolts? Why a steel cap only on the left side (I assume that's the side that the ring gear is on)? Could you use studs instead of bolts and get a better torque/clamp?
Thanks again for all the help!

 

Typical wear/ fail areas are:

Worn spiders, ring & pininon
side yokes
bearings
posi carriers
Cases if the yokes were left in when worn and they hit the case and ground down the seal boss.

The posi pin hole wears on these and can be either bushed or bored for a larger pin and side gears. This will add strength. Most times it is more cost effective to replace the carrier though.

The ring gear will back out against the left cap as you stated. This is under extreme conditions like HD drag racing. I have never used a stud setup for this so couldn't say.

I haven't gotten around to fab up a 12 bolt set up like Tom does yet and most of the time the cost is very high to do such a job for a street car. Tom's 12 bolt setup is the top of the line but for most street cars my setups hold up great- but everything will break if pushed hard enough so keep things in proper perspective when thinking through a job.

Good luck

 

My 79 iron rear end failed before i even had 50,000 miles on it. the junk soft end yokes got eaten away. When the yoke snap rings got fed through - it was the death of it.

I didn't know alot back then. But I called midamerica vette parts and they sold complete rearends for about $1200. So through them I found out that their remanufacturer supplier was actually out of Houston TX. So I called the Texas place and had them build my rearend with richmond 4.11 gears....................... Including the custom Hardened yokes which were an additional $250 each.

As my power levels went up and the use of slicks and racing the next failure point was the posi units. I was elongating the case cross pin holes and it would finally wedge and break the posi housing case. This was like every year almost. I'd have my foot on the floor going around a turn and I'd hear the death rattle. I had a shop install the Eaton conical and it might have lasted two years. That's when i first heard about www.tomsdifferentials.com

I am proud to say, The $700 posi unit is now in it's 5th year with about 5 different motor combinations in front of it. That is including a 600 hp 427 ci that i broke the crank shaft.

The 4.11 gears and custom yokes still look nice after all these years