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ring and pinion ratio

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coryg

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Discussion starter · #1 ·
Does anyone know how to determine the gear ratio in a 12 bolt posi. When I purchased the rearend it was stated that it had 3:07 gears but i do not believe that to be true. The rear end is from a 70SS. Any help would be great.
Thanks
 
#2 ·
Take off the cover, look inside.
Count the ring teeth
Count the pinion teeth
Divide the former by the later
Some Vette gears I have 37 ring 10 pinion = 3.70 ratio
 
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#3 ·
If you're sure it's a posi, make a mark on the driveshaft or pinion yoke, Carefully turn the tire exactly one revolution and count how many revolutions the driveshaft/pinion makes. You should be able to get very close this way, and not have to take the back cover off. If it's 3.07:1 the driveshaft will turn about 25 degrees more than three full turns.

Keith :sad:
 
#4 ·
If you decide to pull the cover just to see what things look like, the ring and pinion tooth count is usually stamped on the ring gear. If you have an old car, draining the old oil and wiping all the sediment out of the bottom isn't a bad idea. It can't hurt to clean things up, if they are dirty. A magnetic plug is always good. So is new gear lube.

I hate when I do this and find a piece of a tooth in the bottom. It happens.
 
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#5 ·
kirkwoodken said:
If you decide to pull the cover just to see what things look like, the ring and pinion tooth count is usually stamped on the ring gear. If you have an old car, draining the old oil and wiping all the sediment out of the bottom isn't a bad idea. It can't hurt to clean things up, if they are dirty. A magnetic plug is always good. So is new gear lube.

I hate when I do this and find a piece of a tooth in the bottom. It happens.
Click to expand...
yup good way to find otu what you got nice clean fluid and all.
 
#6 ·
My 69 ss 396 12 bolt came with an optional 307 gear called ECONOMY GEAR but i installed 3:31's yrs later . The 331's were a much better performing gear then the 3:07 gear when you got into it while still retaining a resonable cruise rpm with m20 muncie & 25.5"-26" tires.

Scott
 
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Discussion starter · #7 ·
I was told that if you turn the yolk three revolutions mark the tire and see how far the tire revolves. I did that and when I turned it three times it did not quite make it around one time. Also when I am cruising at 45-50mph and i take my foot off the gas she decreases speed pretty quickly so I would like to figure out what I have. I currently have a t350 and I am planning on putting a 700 r4 and I just wanted to see if I needed to change the gears. with the info above can anyone fiugre what gears i do have.

THanks
 
#9 ·
Best thing to do is pull the cover and look for yourself. You can find out what it is by turning the tire but the best way is to just pull the cover. You are using someone else's rear in your car and have no idea what condition everything is in. On stock gears there will be numbers stamped on the ring gear telling you how many teeth are on the ring and pinion. Just divide the smaller number into the larger number. Or if there are no stamped numbers just count the teeth on each. All this will cost you us a little time and a gasket and some gear oil. Plus it gives you a chance to inspect everything and replace the Gear lube.

Rick
 
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