1971 Differentials

[Wirenut48]

Hey Guys,
I am new at this so bear with me. I am putting a modified 1971 Corvette frame and differential under a 1948 Bentley. When I bought the frame, etc I was told the rear was a Dana 60. Now in talking with other 'vette owner's I have my doubts. I pulled the following numbers off the rear end housing. 8889143 or maybe 8888143, J249 Axle 1, 3871375, E149. Can anyone tell me just what I really have. Supposedly the car had a 427 Big Block originally.
Thanks

 

[JohnZ]

3899143 is the diff housing used from '67-'79, and J 24 9 would be October 24, 1969 (1979 production ended in September). 3871375 is the rear cover used from late '65-'79, and E 14 9 would be May 14, 1969.

The '63-'79 Corvette never had a Dana 60 (or 44, for that matter); the Corvette diff is completely unique, and its small ring & pinion design wasn't used on any other car line - all were made at Chevrolet-Warren, using Eaton Posi units. The only difference between small-block and big-block Corvette diffs was the U-joint retention configuration of the output yokes - small-blocks used U-bolts and nuts, and big-blocks used steel caps and bolts; the housing and internals are identical.

 

[Wirenut48]

71 Differential

Thanks for the fast response. This project has more surprises all the time, some not so good. If I could ask one more favor. Would you know what the gear ratio would have been.
Thanks again

 

[JohnZ]

Thanks for the fast response. This project has more surprises all the time, some not so good. If I could ask one more favor. Would you know what the gear ratio would have been.
Thanks again

There were about 18 different axles for '70 - the ratio code and assembly date are stamped on the bottom flange of the diff housing; it's not a machined surface, will take some cleaning to see it.

See how many turns of the pinion flange it takes to turn the output shafts one revolution, and that will tell you the ratio that's in it now; 3 = 3.08, 3-1/3 = 3.36, 3-1/2 = 3.55, 3-3/4 = 3.70, etc.

 

[Wirenut48]

I got it. Thanks. I will check this weekend.

 

[fine69]

There were about 18 different axles for '70 - the ratio code and assembly date are stamped on the bottom flange of the diff housing; it's not a machined surface, will take some cleaning to see it.

See how many turns of the pinion flange it takes to turn the output shafts one revolution, and that will tell you the ratio that's in it now; 3 = 3.08, 3-1/3 = 3.36, 3-1/2 = 3.55, 3-3/4 = 3.70, etc.

John,

Could one use the method you described by observing and comparing the tire rotation to the rotation of the drive shaft?

Ralph

 

[GTR1999]

John is correct. Since this is a used vette diff of probably unknown history, I would remove the cover and take a look at it.
If you have GM gears they will be stamped on the side of the ring gear Gm along with the date and teeth on them, ie: 37 10 = 3:70 ratio.
Look at the posi case, as the 69-79 cases are better then the earlier ones. The clue is the size of the little window. If it's square then it's a early case if it's tear dropped then it's the better later model.