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Discussion Starter · #1 ·
Trying to figure out rear end gear ratio without takeing rear end cover off. Went on youtube and got some instructions. Couldn't remember how to do it. The video I watched showed to jack the car up and roll the rear wheel over ten times and count the number of times the driveshaft turns. In this paritcular video the drive shaft turned 48 times when the tire was rotated ten times thus being a 4.89.
I jacked my car up marked the driveshaft and the right rear wheel( both wheels of the ground) rotated the wheel ten times and the drive shaft turned 12.2 times. This comes out to a 1.21. I talked to friend of mine and he said one wheel needed to be on the ground. I let the car down and jacked up the left side. Rolled the wheel ten times and came out with the same thing. I let the car down and jacked up the right side. Rolled the wheel 10 times and came out with the same thing. I don't understand what is going on. If I roll the wheel over once the driveshaft turns over approximately one time. Can someone tell me what is going on?
 

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Brian Martin,Freelance adviser
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There is also very likely a number stamped in it or a tag with the ratio on it. Often they aren't clear, it's a "code" that you have to look up but the ratio is right there for you. What make model and rear end is it?

Brian
 

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Discussion Starter · #4 ·
ration

I think it is out of a79 or so camaro but I am not sure. Where would it be stamped or tagged on the rear end.
Like I said when I roll the wheel one complete revolution the drive shaft like 1 1/8 turn like it is almost a one to one. Any more suggestions? Thanks
 

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Brian Martin,Freelance adviser
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It will be stamped on a machined smooth spot. This is usually where the rear end cover is bolted, it will have a wide point that the cover isn't covering and the number is right there. Often it's on a machined area between the axle tube and the rear cover. If it's a drop in pumpkin like a 9" they are on the front on a machined area on the cast third member.

But on that Camaro I seem to remember a triangular tag.

Brian
 

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Brian Martin,Freelance adviser
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High Performance Rear Ends
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If you are only turning one wheel then you need to turn it twice as many times as you would if you turned both wheels together. So if you came out with 1.21 you would actually have a 2.41 gear, which was comon in the days before overdrive transmissions. Be very careful what you watch on youtube. There is a lot of completely wrong stuff on there, especially when it comes to rear ends. The Camaro rear ends have the code stamped into the right axle tube on the front side.
 

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Discussion Starter · #8 ·
rear end ratio

Thanks to all the response. I' will look for the numbers on the rear end tomorrow and see if I see anything. The last post by big gear head makes sense. I bet it is a 2.42 Thanks to all.
 

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its likely 2.56 or 2.73? What kind of car? auto or standard?
or,what is the max speed you can go in first gear? how big are the tires and what RPM are you turning at max speed?
 

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Slow but willing learner
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If you are only turning one wheel then you need to turn it twice as many times as you would if you turned both wheels together. So if you came out with 1.21 you would actually have a 2.41 gear, which was comon in the days before overdrive transmissions. Be very careful what you watch on youtube. There is a lot of completely wrong stuff on there, especially when it comes to rear ends. The Camaro rear ends have the code stamped into the right axle tube on the front side.
Big Gear is exactly right here. If you had a limited slip rear end with both wheels turning then you could turn it once. but with one wheel stationary and one wheel turning the spider gears in the differential will transfer the power in such a way that you must turn the wheel twice.
 

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Discussion Starter · #11 ·
rear end ratio

Went and did this. I have a 700r4 transmission. 28" tall rear tires. These are the rpm and seeds I got with my gps

1st at 2,000 = 20mph
1st at 3,000 =31mph

2nd at 1,000 = 20mph
2nd at 2,000 = 34mph
2nd at 3,000 = 51mph

3rd at 1,000 = 31mph
3rd at 2,000 = 60 mph
3rd at 2,500 = 70 mph

od at od lockup 1,500 = 70 mph

Any ideas on rear end ratio.
 

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2.73 rear axle ratio with 3,000 rpm on the tach,28 inch tall tires=30 in first/57 in second/92 in third

at 2,000 rpm= 20 in first// 38 in second// 61 in third

using 3.06 first gear ratio///1.62 second gear ration///third 1:1
 
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