1970 SS 12 BOLT gear ratio's? - Chevelle Tech
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Transmission & Driveline Transmissions and Differentials

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  #1  
Old Jul 11th, 08, 11:28 PM
79scout-too 79scout-too is offline
Anthony
 
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Default 1970 SS 12 BOLT gear ratio's?

I thought it to would be easy to find information on what gear ratios came in a stock 12 bolt under a 1970 SS Chevelle or El Camino, but I guess I was wrong.

Can anyone help me out? Is there a chart that shows all the factory options?

Also,

What gears would be good for a cruiser with a 400 SBC and 4spd Muncie?
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  #2  
Old Jul 11th, 08, 11:41 PM
andrewb70 andrewb70 is offline
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Default Re: 1970 SS 12 BOLT gear ratio's?

Quote:
Originally Posted by 79scout-too View Post
I thought it to would be easy to find information on what gear ratios came in a stock 12 bolt under a 1970 SS Chevelle or El Camino, but I guess I was wrong.

Can anyone help me out? Is there a chart that shows all the factory options?

Also,

What gears would be good for a cruiser with a 400 SBC and 4spd Muncie?
How much highway driving are you going to do? How tall are your tires?

Andrew
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  #3  
Old Jul 12th, 08, 8:34 AM
SWHEATON SWHEATON is offline
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Smile Re: 1970 SS 12 BOLT gear ratio's?

331 to 342 max for all arround comprimise between decent performance when getting into it and reasonable cruise rpm with a non o/d trans,maybe even 308 if your not into the peformance end that much.

But gear like 355/373/410 etc gear is too much for reasonable street duty these days $5 gal fuel without an o/d trans and or very tall tires IMHO.

Depends on what you want,not what we prefer becausee some people think 373 gear with non o/d trans is fine on the road with 26" tires turning APPROX 3k rpms @ 60mph which can get old quickly depending on setup/how loud it is. If thats you go for 373 ,but if not go for the 342 331/331 is only avail used or nos on ebay or local swap meets but there is talk ofthe 331's being mfg's again but not yet from what i understand.

Scott
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1969 CHEVELLE SS396,ORIGINAL #'S MATCH,GOT IN 1978,(In 2001 rblt/bored original 396 .030 to 402)/M20/12BOLT/3:31'S
2006 YAMAHA 1700 ROADSTAR SILVERADO (1 owner ,GOT in 2009,4,700 miles/WK end fun)
1977 KAWASAKI KZ1000 (AM ORIGINAL OWNER ,GOT IN 1977,NOW has 29k miles/WK end fun)
2002 MAXIMA (DAILY DRIVER/1 owner,GOT 3/2013 w-44k miles)

Last edited by SWHEATON; Jul 12th, 08 at 12:05 PM.
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  #4  
Old Jul 12th, 08, 10:45 AM
70 beater 70 beater is offline
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Default Re: 1970 SS 12 BOLT gear ratio's?

If you can find an unmolested rear there may be a tag on it with the ratio.May want to try the tag team or restoration corner forum.The 12 bolt I've got had 2.73 factory gears,non SS,it has 4.56 now. I'm thinking that the 4.11:1 gears were common for the SS cars,might depend some on if the car was manual or auto,or maybe the had to be checked off,I've got a book,somewhere,maybe it will say something.
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  #5  
Old Jul 12th, 08, 11:01 AM
Doug Garland Doug Garland is offline
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Default Re: 1970 SS 12 BOLT gear ratio's?

Stock ratio was a 3.31, with posi as an option. There were a few 3.55 gears in early cars, (pre-December), and also an option for a 4.10 ratio. That was it for '70.
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Old Jul 12th, 08, 11:24 PM
79scout-too 79scout-too is offline
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Default Re: 1970 SS 12 BOLT gear ratio's?

Thanks guys. I think I will be lifting my el camino some and running 28"-30ish" tires. Not sure as of now just curious about what gears to look for as I search for a 12 bolt to swap in.
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  #7  
Old Jul 13th, 08, 8:07 PM
greasemonkey427 greasemonkey427 is offline
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Default Re: 1970 SS 12 BOLT gear ratio's?

my 12 bolt i sold had a 3:08 rear
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  #8  
Old Jul 14th, 08, 8:12 AM
DZAUTO DZAUTO is online now
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Default Re: 1970 SS 12 BOLT gear ratio's?

The 12bolt in the 70 conv is a 3.07 posi (they were 3.08 in a 10 bolt).
I have a healthy SB400 and a wide ratio Muncie (M20) also, and the combo is just right for cruisin' and Interstate driving. Admittedly, from a dead stop, it does not leave like a rocket. But the SB400 has plenty of torque to make the M20/3.07 combo work just fine.
And with today's gas prices, I'm not interested dropping to a lower gear ratio.
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Old Jul 14th, 08, 12:19 PM
SWHEATON SWHEATON is offline
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Smile Re: 1970 SS 12 BOLT gear ratio's?

Yeh Tom,i went from the stock 307's in my 12 bolt to 331s approx 5-4 yrs ago in my 69 chevelle with mild 396(approx370hp/440lbs trq) & m20 and the perf inc was decent even with small gear change.

But since fuel prices have gone nuts and i am finding myslef doing more open road/interstate crusing to new shows/cruises i am really considering re-installing the original 307's in the near future.
scott
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SCOTT
1969 CHEVELLE SS396,ORIGINAL #'S MATCH,GOT IN 1978,(In 2001 rblt/bored original 396 .030 to 402)/M20/12BOLT/3:31'S
2006 YAMAHA 1700 ROADSTAR SILVERADO (1 owner ,GOT in 2009,4,700 miles/WK end fun)
1977 KAWASAKI KZ1000 (AM ORIGINAL OWNER ,GOT IN 1977,NOW has 29k miles/WK end fun)
2002 MAXIMA (DAILY DRIVER/1 owner,GOT 3/2013 w-44k miles)
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