1961 Rear End Numbers

[Richard P.]

I need to verify 1961 rear end numbers. I have a build date of Dec. 7, 1960. The numbers I see are 3725899, K290, and AC1.
Thanks

[Dennis C.]

1961 Rear End Numbers

Richard, Things seem to look OK, however the AC1 is probably part of a longer stamping. AC should equate to 3.36 non posi, 3 speed. The rest of the stamping following that should be the asy date of the pumpkin. I'd keep at it with the wire brush, etc. I might guess you are chasing a 11/?? stamping. Often they are quite hard to read as they were hand hit into a rough casting. Regards, Dennis

[Richard P.]

Re: 1961 Rear End Numbers

Richard,
The 3725599 indicates an open(non-Posi) rear end from 1957-1962.
The K290 indicates Nov.29, 1960. The AC indicates a 3.36:1 gear ratio with a 3-speed transmission. This information is from "Corvette by the Numbers"

[Richard P.]

Re: 1961 Rear End Numbers

Oops I meant 3725899.

[Richard P.]

Re: 1961 Rear End Numbers

My VIN indicates a 4 speed. Is it possible someone just changed out the rear end?

[Richard P.]

Re: 1961 Rear End Numbers

I looked at my copy of Corvette by the Number (page 44) and I don't see AC anywhere. AE, H, N, P, Q, S and T. But no C. My car has a 4 speed, so I am confused.

[Richard P.]

Re: 1961 Rear End Numbers

Richard,
I don't think the VIN has a character to indicate transmission. I am restoring a 61 and am constantly amazed to find things that are not original. After all, in 47 years a car has had time to cycle from new/pristine to junk and back several times. I would think its possible that the rear end has been changed but far more likely that somebody changed the transmission to a 4-speed because thats what we all had to have back then. Is the transmission a T 10?
Cheers,
Richard

[Richard P.]

Re: 1961 Rear End Numbers

The numbers I referred to are actually the ones stamped on the block. They end in CQ, which I believe means standard 283/230 with 3-speed. Is this correct?

[Richard P.]

Re: 1961 Rear End Numbers

Richard,
CQ suffix is for a 283/230 manual transmission. This covers years 1958-1961 and could be for a 3- or 4-speed.

[Mike B.]

Re: 1961 Rear End Numbers

You might want to check the gear ratio which could lend a bit more light if it was original and/or the insides were messed with. Since it is non posi, simply jack one wheel off the ground but please be sure to use jackstands for safety. Then put the car in neutral.

Crawl under and put an index mark on the wheel and one near the rear end pinion yoke (the collar where it exits the front is a good spot) using paint or tape. Then turn the wheel counting how many times the drive shaft/yoke rotates to complete one wheel revolution. That number, say 3.36:1 is your installed gear ratio. You'll have to approximate a bit on the last revolution.

If you can't turn the wheel with only one off the ground, that is a sign that it is a posi rear. It was not uncommon for rear carrier "pumpkins" to be modified to accept a posi clutch unit. To test, raise both wheels spinning one - the other should turn in the same direction. You can then test the ratio as above.