C1 pinion gear ratio

[Geert W.]

[Tom D.]

Re: C1 pinion gear ratio

FOR A C2, 4.11 and 3.08 take different posi units. Can you go from 4.11 to 3.08 in a C1?

[Geert W.]

[Joe L.]

Re: C1 pinion gear ratio


Geert------


Yes, some C1's were equipped with a 3.08:1 rear gear ratio. I don't think it was too popular because 283"s did not have a lot of torque. You can install one but you will have to change the posi unit. I don't know if an adapter exists for this, or not.

[Gary C.]

Re: C1 pinion gear ratio

Geert,

1) What year is your car?
2) 57 has 2 different rear end (pumpkin) housings; a) series 3 for 3:70 and below ratios, b) series 4 for 4:11 up ratios. Not an expert and sorry can't recall, but one of the rear end pumpkin series requires a spacer to use the different gears. Hopefully, Tom Parson or some other knowledgeable NCRS member will respond.

Gary
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[Geert W.]

Re: C1 pinion gear ratio

Geert,

1) What year is your car?
2) 57 has 2 different rear end (pumpkin) housings; a) series 3 for 3:70 and below ratios, b) series 4 for 4:11 up ratios. Not an expert and sorry can't recall, but one of the rear end pumpkin series requires a spacer to use the different gears. Hopefully, Tom Parson or some other knowledgeable NCRS member will respond.

Gary
....

Gary,

The car is a 59, I think the axle(pumpkin type) is original but the pinion house seems to have been replaced over the years, it has no stamp on it indicating the pinion gear ratio, so it seems an original GM replacement part, casting number 3789812 and above that (date?) A274, indicating it should be manufactured in 64.
As far as I can see the original posi traction is inside, but I am certainly no expert.
On the large pinion gear(10 bolt) is stamped this number GM 3733908 / 9 37 (gears) 12 63

Hope indeed one of the experts here can help out

thx
Geert

[Gary C.]

Re: C1 pinion gear ratio

Geert,

12 63 = Dec 1963 manufacture date
9 37 = 4:11 gear ratio - divide 37 by 9

Search GM Parts Wiki for the part number 3733908 description http://www.gmpartswiki.com/query

Look inside the axle housing itself and see if there is a large "washer" welded about 2 inches inside each axle shaft tube. Also, if there is a "V" piece of metal welded inside the top center of the pumpkin.

Gary
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[Terry D.]

Re: C1 pinion gear ratio

I borrowed this from another forum, hope it helps!

Now, with that said, here are some additional things to be aware of. The EARLY guts (57-59) and the LATE guts (60-64) are NOT, repeat, NOT interchangeable------------------REMEMBER THIS! The cross shafts, spider gears and axle gears are unique to the 57-59 and 60-64 posi units. THE TEETH OF 57-59 AND 60-64 SPIDER AND AXLE GEARS ARE NOT THE SAME AND DO NOT MESH WITH EACH OTHER!!!!!! Ya, you CAN put 57 spider/axle gears in a 60 posi unit, but you must use ALL 6 pieces together, you CANNOT mix/match 57-59 and 60-64 spider/axle gears. If you lay a 57-59 and 60-64 spider or axle gear side by side, you will immediately see the difference in the teeth.

A 4-series ring can be bolted onto a 3-series posi using the spacer. BUUUUUUUUUUUUUUUUUUUT, this requires longer bolts which are more prone breaking due to sheer loading. For a street driver, it would be fine to use a 4.11 ring gear/spacer on a 3-series posi---------------but bad idea for a serious performance car.
If you have a THICK 4.11, 4.56, 4.88, etc, etc ring gear for the 3-series posi, that would be the BEST way to go.
EARLY 6cyl Chevy pass cars (AVOID the 55-6 rears) with 3sp overdrive came with 4.11 rears. That would be a good choice for 4.11 gears on a 4-series posi. Those cars probably did not see significant abuse.
I thought Richmond still made 4.11, 4.56 gears for the early Chevy center sections, but maybe not, you need to check. I no longer have any 4.11 R&P gears, or I'd just give them to you.

I have NEVER heard of welding a ring gear or spacer to the flange!!!!!!!!!!!! I'd be concerned about warpage to the ring gear flange

[Gary C.]

Re: C1 pinion gear ratio

Terry, that's Tom Parson's info. Was hoping he'd respond to Geert's question.

Gert,

Here's some more info from Tom Parsons';
- C-30743X for the series 3; and C-30751 for the series 4. Another check is the series 3 ring gear mounting flange is beveled, where the series 4 flange is square across. The numbers are stamped into the Positraction Unit itself.
- 4:11, 4:56 or lower can be used in a 3 series carrier with a spacer, but not vice-versa.
- Square edge where the ring gear bolts on and the 3 series carriers have a beveled edge on the flange - see photos Tom Parson gave me many moons ago. Top photo is a series 3 and bottom photo is a series 4 with the square edge.

Note: don't know which years these numbers apply to: C-30743X for the series 3; and C-30751 for the series 4

Gary
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3 series carrier.jpg 4 series carrier.jpg

[Patrick H.]

Re: C1 pinion gear ratio

Given that it's a stroker engine with a 4.11 gear set, I would also look at the option of swapping in a 700R4 transmission rather than the Powerglide. You'd have better cruising with the overdrive, and keep the acceleration.

http://www.superchevy.com/how-to/vemp-0201-chevy-corvette-700-r4-installation

I suspect a 3.08 with the Powerglide would make a car that is much slower off the line than you expect.

[Geert W.]

Re: C1 pinion gear ratio

All

A lot of info already, lots of thanks for that, but still struggling
I located the posi ID code 23618X 9 16 63 8
If I look it up it seems a series 4, the mounting flange is square across, so that confirms the 4 serie.
As far as I can see there are no washers or V piece welded in the pumpkin.
At this moment changing the tranny is not an option I am considering, might be if it fails on me but is working very nice now.
So the 1 million question remains if it's possible to mount a 3.08 or perhaps better then a 3.55 ring without replacing the posi?

thx
Geert

[Joe L.]

Re: C1 pinion gear ratio

Terry, that's Tom Parson's info. Was hoping he'd respond to Geert's question.

Gert,

Here's some more info from Tom Parsons';
- C-30743X for the series 3; and C-30751 for the series 4. Another check is the series 3 ring gear mounting flange is beveled, where the series 4 flange is square across. The numbers are stamped into the Positraction Unit itself.
- 4:11, 4:56 or lower can be used in a 3 series carrier with a spacer, but not vice-versa.
- Square edge where the ring gear bolts on and the 3 series carriers have a beveled edge on the flange - see photos Tom Parson gave me many moons ago. Top photo is a series 3 and bottom photo is a series 4 with the square edge.

Note: don't know which years these numbers apply to: C-30743X for the series 3; and C-30751 for the series 4

Gary
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[ATTACH=CONFIG]99782[/ATTACH] [ATTACH=CONFIG]99783[/ATTACH]

Gary------


The 3737957 ring gear (part of R&P set GM #3748438) is applicable to 1957-62 Corvettes.

[Gary C.]

Re: C1 pinion gear ratio

Geert,

From what Tom Parsons' commented in my last post was "no". You might want to send Richmond Gears Tech Support your question and see if they make a 3:XX gear set to fit a series 4 positraction carrier. https://www.richmondgear.com/technic...transmissions/

The absence of the washers in the axle housing means your car originally did not come with a positraction rear end in it. Those washers and the V drip were enhancements for hard driving to keep the rear end lubrication and oil in the pumpkin area.

Good luck. You also might want to join the NCRS Dutch Chapter. The Dutch Chapter is active and has some great resources.

Gary
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[Geert W.]

Re: C1 pinion gear ratio

Gary, thx a lot for the clarification, did not catch the 3 and 4 serie relation with the gearing... not a real mechanic after all .
I raised the question at Richmondgear, will update here if I get an answer for future questions here.
After years of membership I just recently joined the Dutch chapter(last week...) am waiting for my membership number!

Thx again
Geert

[Gary C.]

Re: C1 pinion gear ratio

Geert,

Update this thread when you get the Richmond info.

Good deal about joining the Dutch Chapter. My good friend Rob M. is one of the founders.

Gary
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