66 Diff Ring Gear ID

[Dave B.]

Recently went into the differential and upon checking the ring gear numbers on the outside of the gear I found the following...3735390 11-39 GM 2 66 2. References say that 11-39 is a 3.55 rear (39 divided by 11). I always thought I had a 3.36-1 ratio rear end because the diff assembly info is AM 2 28 66 which agrees with the POP. Checking the archives, I came away with the impression that 3735390 ring gears were 3.36-1 rears.
But the diff didn't look like it had been opened. I figured the 11-39 to be a 3.55 ring gear in a 3.36 case...until I counted the teeth.
There were 37 teeth

So, does anyone know why a ring gear labeled 11-39 would have 37 teeth?

Also...does the 2 66 2 mean a date of Feb 1966, and if so, what is the last 2 for? This is a Mar 4 1966 built car.

Thanks...Dave

[Joe L.]

Re: 66 Diff Ring Gear ID

Recently went into the differential and upon checking the ring gear numbers on the outside of the gear I found the following...3735390 11-39 GM 2 66 2. References say that 11-39 is a 3.55 rear (39 divided by 11). I always thought I had a 3.36-1 ratio rear end because the diff assembly info is AM 2 28 66 which agrees with the POP. Checking the archives, I came away with the impression that 3735390 ring gears were 3.36-1 rears.
But the diff didn't look like it had been opened. I figured the 11-39 to be a 3.55 ring gear in a 3.36 case...until I counted the teeth.
There were 37 teeth

So, does anyone know why a ring gear labeled 11-39 would have 37 teeth?

Also...does the 2 66 2 mean a date of Feb 1966, and if so, what is the last 2 for? This is a Mar 4 1966 built car.

Thanks...Dave

Dave---


GM #3735390 is a ring gear for a 3.36:1 gear set. It's SUPPOSED to have 37 teeth which is, apparently, what it does have. If it's stamped 39 teeth, it must be an incorrect stamping.

It should mate with a pinion gear of GM #3885942 and of 11 teeth.

The 3.55:1 gearset used a ring and pinion of 32 and 9 teeth, respectively.

2 66 2 decodes to February, 1966. I don't recall if the other 2 refers to day of the month or shift.

[Dave B.]

Re: 66 Diff Ring Gear ID

Thanks Joe...Figured it could be a stamping error.
Dave

[Wayne M.]

Re: 66 Diff Ring Gear ID

Thanks Joe...Figured it could be a stamping error. ...

I'll second that. What about your pinion gear ? It probably is end-stamped 3885942 with a 10 - 37 and a similar date.

Here's a probable mis-stamp of the year (May '64 on the ring gear) on my July '65 3.70 ratio car. Pinion end is 3864615, 6_65_1, and the ring is 3737957, 10-37 GM 5_64_1. Now that same ring # applied to the 3.70 ratio of '63-64 series of diffs, but I doubt the ring was replaced after mid-'65 with one dated May '64. The carrier was assembled FA_7_15_65.

As to the numeral after the month - year, I've only seen either 1 or 2 in the half dozen that I've examined. This one has the "1" (extreme right).

[Dave B.]

Re: 66 Diff Ring Gear ID

Wayne,
Yep, looked at the pinion today and it is indeed stamped with that part number, the correct 11-37 and the same date as the ring. Also has eleven teeth.
Interesting study of Corvette differentials and their gears and markings.
Regards,
Dave