Differential identification
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Differential identification
I picked up a cast iron differential for a swap into my '81. The casting number is the same as a '77 I already own and the casting is J 11 8. It has big block style yokes and a posi. The small hole in the carrier is definitely wider at one end than the other, I hope this is the right (teardrop rather than square) one? How do I know if it's a '68 or '78? Gears look to be stock, 3.08. I read a couple of threads on setting these up and it looks like the shafts still have the bevel on the end with no wear on the pin and the gears look great with no signs of wear. The case is rusted pretty bad with some pitting but I got it for the shafts and posi unit. I understand that I need to toss the factory clutches and replace them, but with what???
I plan to completely deburr everything and set it up with help from an experienced mechanic who's done 'em before.
Thanks in advance for your help!
Once I get the guts out of it, it'll be free to whoever wants to pay shipping, I'll clean it up enough to get a good look at it.
I plan to completely deburr everything and set it up with help from an experienced mechanic who's done 'em before.
Thanks in advance for your help!
Once I get the guts out of it, it'll be free to whoever wants to pay shipping, I'll clean it up enough to get a good look at it.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 121
From: Millington Illinois
St. Jude Donor '08-'09
I picked up a cast iron differential for a swap into my '81. The casting number is the same as a '77 I already own and the casting is J 11 8. It has big block style yokes and a posi. The small hole in the carrier is definitely wider at one end than the other, I hope this is the right (teardrop rather than square) one? How do I know if it's a '68 or '78? Gears look to be stock, 3.08. I read a couple of threads on setting these up and it looks like the shafts still have the bevel on the end with no wear on the pin and the gears look great with no signs of wear. The case is rusted pretty bad with some pitting but I got it for the shafts and posi unit. I understand that I need to toss the factory clutches and replace them, but with what???
I plan to completely deburr everything and set it up with help from an experienced mechanic who's done 'em before.
Thanks in advance for your help!
Once I get the guts out of it, it'll be free to whoever wants to pay shipping, I'll clean it up enough to get a good look at it.
I plan to completely deburr everything and set it up with help from an experienced mechanic who's done 'em before.
Thanks in advance for your help!
Once I get the guts out of it, it'll be free to whoever wants to pay shipping, I'll clean it up enough to get a good look at it.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
As best I can make it out, it's 3899143 on both cases. The good, clean one is marked that it's a '77. Hope this is the good one.
One other thing - I've read about identifying the weaker posi carriers and it seems that the one with the square backside hole is weaker and teardrop is stronger. If anyone could post pics of these, it would be very much appreciated. If I had to make a call without seeing any others, I'd guess it's more teardrop shaped, definitely wider on one end than the other.
One other thing - I've read about identifying the weaker posi carriers and it seems that the one with the square backside hole is weaker and teardrop is stronger. If anyone could post pics of these, it would be very much appreciated. If I had to make a call without seeing any others, I'd guess it's more teardrop shaped, definitely wider on one end than the other.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 121
From: Millington Illinois
St. Jude Donor '08-'09
According to my Corvette by the Numbers book the 3899143 center section housing was used from 1967 through 1975. What are the stamped numbers on the bottom pad? Sounds like the older unit to me.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
It looks like it was taken off of a car that sat with flats - it's pretty badly rusted on the bottom. I'll have to get after it with a wire wheel or steel brush to get 'er figured out. Is the casting number the only difference appearance-wise?
Tech Contributor
Joined: Aug 1999
Posts: 15,114
Likes: 3,909
From: Connecticut, USA
The 68 case would have the small sq window in it, the hex head brg cap bolts may have 5 lines instead of 6, the brg caps would may not have the tabs cast in, the pinion yoke may be the smaller one but that could have been changed. Regardless the tear drop case tells me it's a 78, f the ring gear bolts are flanged head instead of hex with lockwashers then it's a 78. Both are good to rebuild and with the proper mods will be better then any new eaton posi or stock rebuilt one.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
GTR1999, thanks for stepping in. I appreciate your help.
The clean bare case I have is actually harder to read the stamped numbers on. It looks like Q(O?)A168, then on the other side of the casting line is W7E(F?)1. The rusty one looks like AWW300 on one side, then E1 on the other. Am I missing letters? With any luck, I'll have the carrier, axles and gears out and will send/post pics of my findings. By the way, the clean case had the stamping area cleaned, then the previous owner wrote "77 3.08" on it with a blue paint pen. Both have 6 marks on the cap bolts and the complete one has shoulder-less bolts with lock washers holding the ring gear onto the carrier.
Thanks to both of you for your help.
The clean bare case I have is actually harder to read the stamped numbers on. It looks like Q(O?)A168, then on the other side of the casting line is W7E(F?)1. The rusty one looks like AWW300 on one side, then E1 on the other. Am I missing letters? With any luck, I'll have the carrier, axles and gears out and will send/post pics of my findings. By the way, the clean case had the stamping area cleaned, then the previous owner wrote "77 3.08" on it with a blue paint pen. Both have 6 marks on the cap bolts and the complete one has shoulder-less bolts with lock washers holding the ring gear onto the carrier.
Thanks to both of you for your help.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski1982, 2000, 77, big, block, c3, carriercase, casting, corvette, differential, differentials, id, identification, input, location, marks, yoke
