Differential Gear Ratio Question
Thread Starter
Racer
Joined: Sep 2004
Posts: 424
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Differential Gear Ratio Question
Later C3's came with gears as high as 2:73/1. When I look for gear-sets for my '68, I only seem to find 3:08/1 as the highest ratio (lowest numerically). Does anyone know if you can put a higher ratios then 3:08/1 (lower numerically) in the early C3 carrier. My purpose is that I would like like to use a Richmond 5-Spd with something higher (lower numerically) the 3:08/1.
Burning Brakes
Joined: Nov 2002
Posts: 952
Likes: 44
From: NC
from what I have been told,any 65-79 gears will work. I found a newish (used 300 miles before the person went with 3.7) set of 3.55 gears on ebay and got them for 100 bucks. 336 ratios come up maybe twice a month. I rarely see 3.70, 4.11 is pretty prevolent on ebay. Again, these are used.
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
Most reputable gear shops will stock or be able to order gear sets for your '68 differential. Somewhat unrelated since my '80 carrier is a Dana 44 but I had 3.55's installed by a reputable shop in Clearwater, FL, back around 2000. My '80 came with the 3.07 (3.08) ratio stock and that was the only ratio offered in '80 on the vette as far as I know. Therefore, you should be able to find a ratio to suite your needs.
Question: Is the 68-79 diff carrier essentially a 12-bolt housing that any 12-bolt ratio will work with? If that is the case, then you should have no problem finding a higher ratio (2.73's for example). But, new sets will probably be easier to find. Again, I'd check with a local gear shop as I would imagine they may also have some good, used gear sets.
Best of luck!
NOTE: My 68-69 NCRS guide says:
'68 - 2.72 ratio WAS offered with rear axle code 'AY' and an application of 'HD P THM 427' (Heavy Duty, Positraction, TH400 and 427 cu inch).
'69 - 2.73 ratio WAS offered with rear axle code 'CAY and an application of 'P THM 427' (positration TH400 and 427 cu inch).
But, I don't know if there was a difference in the diff housing offered on these applications vs. yours. Other more knowledgeable folks may be able to advise.
Question: Is the 68-79 diff carrier essentially a 12-bolt housing that any 12-bolt ratio will work with? If that is the case, then you should have no problem finding a higher ratio (2.73's for example). But, new sets will probably be easier to find. Again, I'd check with a local gear shop as I would imagine they may also have some good, used gear sets.
Best of luck!
NOTE: My 68-69 NCRS guide says:
'68 - 2.72 ratio WAS offered with rear axle code 'AY' and an application of 'HD P THM 427' (Heavy Duty, Positraction, TH400 and 427 cu inch).
'69 - 2.73 ratio WAS offered with rear axle code 'CAY and an application of 'P THM 427' (positration TH400 and 427 cu inch).
But, I don't know if there was a difference in the diff housing offered on these applications vs. yours. Other more knowledgeable folks may be able to advise.
Last edited by TedH; Mar 30, 2006 at 08:47 AM.
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273 's were available as an option in 1968 with the Turbo 400 and the L36 427-390. If you can find them they will work.
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
Originally Posted by jimmygmartin
Later C3's came with gears as high as 2:73/1. When I look for gear-sets for my '68, I only seem to find 3:08/1 as the highest ratio (lowest numerically). Does anyone know if you can put a higher ratios then 3:08/1 (lower numerically) in the early C3 carrier. My purpose is that I would like like to use a Richmond 5-Spd with something higher (lower numerically) the 3:08/1.
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Thread Starter
Racer
Joined: Sep 2004
Posts: 424
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Originally Posted by 63mako
Hi Jimmy, What would your objective be to go with a 5 spd which has overdrive and a real high gear. Are you looking to go 200 MPH? Or is it a fuel milage issue? In my experiance anything higher ratio than a 3.08 is real doggy on the bottom end and around town. I changed my 72 Base engine L-48 from 3:08 to 3:36 with noticable performance gains and no sacrifice in milage. In the 63 it came with an M20, a built 327 W/278 cam and 3:08 gears. It fell on it's face when trying to leave a stop sign or launch and wanted to lug between gears. I had to smoke the clutch to take off. Went to 3:55 and the car was TOTALLY different. Much easier to drive and still good for highway driving with excellent around town manners.
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by jimmygmartin
Later C3's came with gears as high as 2:73/1. When I look for gear-sets for my '68, I only seem to find 3:08/1 as the highest ratio (lowest numerically). Does anyone know if you can put a higher ratios then 3:08/1 (lower numerically) in the early C3 carrier. My purpose is that I would like like to use a Richmond 5-Spd with something higher (lower numerically) the 3:08/1.
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
Originally Posted by jimmygmartin
The Richmond 5-Spd has a very low 1st gear and a 1:1 5th gear. I've had a couple of Vettes with 3:08's and I liked them, but with a super low 1st and a 383 I thought somting like a 2:73 would be better. 200 mph?? might be fun, but realistic?? Probobly not. Does someone have a MPH calculator, I'm an engineer and can do it with a pocket calculater, but it requires a bit of work. The Richmond 5-Spds are cheaper then the tremac and are a direct fit.
Last edited by big69; Mar 30, 2006 at 08:07 PM.
Drifting
Joined: May 2003
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From: Melbourne, Victoria, Australia, the World
Originally Posted by TedH
Question: Is the 68-79 diff carrier essentially a 12-bolt housing that any 12-bolt ratio will work with? If that is the case, then you should have no problem finding a higher ratio (2.73's for example). But, new sets will probably be easier to find. Again, I'd check with a local gear shop as I would imagine they may also have some good, used gear sets.
Also, I am sure I have seen 2.78 available in the those years.
Now, even though the richmond is a cheaper box what is it going to cost you on top of the box to build a 2.78 rear end?
I think it may work out cheaper and less work to go with the Tremec.
Race Director
Joined: May 2005
Posts: 10,674
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From: Millington Illinois
St. Jude Donor '08-'09
Originally Posted by jimmygmartin
The Richmond 5-Spd has a very low 1st gear and a 1:1 5th gear. I've had a couple of Vettes with 3:08's and I liked them, but with a super low 1st and a 383 I thought somting like a 2:73 would be better. 200 mph?? might be fun, but realistic?? Probobly not. Does someone have a MPH calculator, I'm an engineer and can do it with a pocket calculater, but it requires a bit of work. The Richmond 5-Spds are cheaper then the tremac and are a direct fit.
Le Mans Master
Joined: Oct 2000
Posts: 7,831
Likes: 5
From: Austin TX
If I remember correctly you can get a 3.04 first gear for a Richmond.
I'm thinking about changing mine - it seems like a perfect match for a 3.08 rear. I like the 1-2 gear spread better too.
I'm thinking about changing mine - it seems like a perfect match for a 3.08 rear. I like the 1-2 gear spread better too.
Melting Slicks
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Last edited by shafrs3; Mar 31, 2006 at 08:40 AM.
Tech Contributor
Joined: Aug 1999
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From: Connecticut, USA
Hi Jimmy,
How's it going. You can get a Tom's 273 corvette gear to fit your car. I have used them. The last one was in a 76 w 4 spd in fact. I didn't think they would work good with only a 264 1st gear but the guy loved them. The speedo gear may be a trail and error fit if that's important.
I can get them if you want. How's the box by the way?
Gary
How's it going. You can get a Tom's 273 corvette gear to fit your car. I have used them. The last one was in a 76 w 4 spd in fact. I didn't think they would work good with only a 264 1st gear but the guy loved them. The speedo gear may be a trail and error fit if that's important.
I can get them if you want. How's the box by the way?
Gary
Thread Starter
Racer
Joined: Sep 2004
Posts: 424
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Hi Gary, by the way I love the steering box, I have absolutly no play in my steering now, and I may be sending you some new customers. My posi was rebuilt about 4000 miles ago with 3.55 gears. I had 3.08s in it before, but with a high reving 327 I needed a little help getting started. Frankly I never liked the 3.55s, not low enough to really help down low, and a pita on the highway. Now with the 383 getting started isn't a problem, but a 5spd sure would be nice.
