'57 Differential Question...

[Patrick T.]

Does anyone know how many teeth are in a '57 3:55 positraction ring gear? I've looked just about everywhere with no luck. Thanks in advance. PT

[Joe L.]

Re: '57 Differential Question...

Does anyone know how many teeth are in a '57 3:55 positraction ring gear? I've looked just about everywhere with no luck. Thanks in advance. PT

Patrick------


32 teeth. It should be stamped 3731618.

[Gary C.]

Re: '57 Differential Question...

Patrick,

FWIW, there was not a 3:55 rear gear option for 1957 Corvettes.

Gary
....

[Patrick T.]

Re: '57 Differential Question...

Thanks for the information Joe.

Gary, right now there is a 4:11 positraction rear in the car and I can't deal with the way the car drives. Going to try a 3:55 to smooth the ride out.

[Joe L.]

Re: '57 Differential Question...

Patrick,

FWIW, there was not a 3:55 rear gear option for 1957 Corvettes.

Gary
....

Gary------


Well, not an RPO, per se. However, if the car was equipped with Powerglide, 3.55:1 was what you got. Nothing else available with Powerglide.

[Gary C.]

Re: '57 Differential Question...

Joe,

Correct. Didn't make my post clear as was referencing there was no RPO Positrac 3:55 for 1957.

Patrick,

Is the carrier (pumpkin) a "4 series" or "3 series" unit?

Tom Parson can best explain the difference.

Gary
....

[Patrick T.]

Re: '57 Differential Question...

Patrick,

Is the carrier (pumpkin) a "4 series" or "3 series" unit? Gary....

Gary, I honestly don't know. Can you tell by this picture below? It's the carrier assembly that's in the car now and it works fine. Thanks

[Gary C.]

Re: '57 Differential Question...

Patrick,

Tom Parsons is the man on rear ends. Hopefully, Tom will see your thread and respond.

What are the stamped rear end ratio and part number on the face of the housing?

Gary
....

[Patrick T.]

Re: '57 Differential Question...

Patrick,

Tom Parsons is the man on rear ends. Hopefully, Tom will see your thread and respond.

What are the stamped rear end ratio and part number on the face of the housing? Gary....

Gary, I'll have to get down on the garage floor and take a look tomorrow for the #'s because I'm all clean now!

[Tom P.]

Re: '57 Differential Question...

Pat,
Your picture is on the wrong side for me to tell.
BUT, here is a VERY quick way to tell if it is 3- or 4-series.
If the edge of the ring gear flange is beveled, it is a 3-series.
If the edge of the ring gear flange is squared off, it is a 4-series. As shown below.









Furthermore,
The pockets for the ring gear bolts on a 4-series are deeper than the bolt pockets for a 3-series, as below.

4-series bolt pockets



3-series bolt pockets





Now, with all of that said, you can use a 3-series ring gear on ANY 3-series posi unit, BUT, you CANNOT use a 4-series ring gear on a 3-series posi unit.
You can use a 4-series ring gear on a 3-series posi unit by using a ring gear spacer between the ring gear and the ring gear flange---------------------------ALTHOUGH, that is less than desirable.

[Patrick T.]

Re: '57 Differential Question...

Thanks again Tom, LOVE those pictures. I printed them out for reference. A picture is worth a thousand words. PT

[Tom P.]

Re: '57 Differential Question...

Now, with all of that said, you can use a 3-series ring gear on ANY 3-series posi unit, BUT, you CANNOT use a 4-series ring gear on a 3-series posi unit.
You can use a 4-series ring gear on a 3-series posi unit by using a ring gear spacer between the ring gear and the ring gear flange---------------------------ALTHOUGH, that is less than desirable.

WHOOOOOOOOOOOOOOOOOOPS, I stated that wrong, and it's too late to edit it. So, here is the correction:
You can use a 3-series ring gear on ANY 3-series posi unit.
You CANNOT use a 3-series ring gear on a 4-series posi (the ring gear flange of a 4-series posi is closer to the center line and does not allow enough room for the ring gear because a 3-series pinion is bigger than a 4-series pinion).
You can use a 4-series ring gear on a 3-series posi if a ring gear spacer is installed between the ring gear and ring gear flange, but that's not the best way to go, as below.



These are NON-posi units, showing the difference between the flanges of the 3-series (left) and a 4-series. The same will be for both a 3- and 4-series posi unit.
As can be seen, the ring gear flange of the 3-series (left) is farther away from the center line which allows more room for a 3-series ring gear (and a 4-series ring gear when a spacer is used).

[Patrick T.]

Re: '57 Differential Question...

Hello again, here is an update to my original question. It was mentioned above that a new OEM 3:55 ring gear should have 32 teeth. I bought a restored/remanufactured 3:55 rear end assembly with new ring and pinion gears and just got it yesterday. I was told that GM does not manufacture these gears any longer so I have an aftermarket set. While examining this rear end, I counted the # of teeth on the ring gear several times and it has 39 teeth. I don't know at the moment if this carrier assembly is a Series 3 or 4 but it is supposed to work correctly.

I called the Vendor on this issue and he told me since they were aftermarket ring and pinion gears, the # of teeth can vary. He checked with the manufacturer and was told that this particular setup has 11 teeth on the pinion gear and 39 on the ring gear, so doing the math...39 divided by 11= 3:54 ratio. Does this explanation sound Kosher to you? I can provide pictures of the assembly if necessary. Thanks for any help on this.

Patrick

[Ray K.]

Re: '57 Differential Question...

I would ask who the manufacturer of this gear set is.

Ray

[Tom P.]

Re: '57 Differential Question...

The original factory GM ring and pinion teeth numbers for the 56-62 (same for 55-64 pass car rears) 3.55 rears are 9-32. And it is correct that aftermarket ring and pinion teeth numbers may be different. The VERY EARLY Chevy rears had 11-39 teeth, which would result in a 3.54 ratio.
I can't verify it for a fact, but it would seem that with more teeth, the gears would be stronger.