02-15-2015, 05:09 PM | #1 |
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rear end ratio
How do I check my ratio with the driveshaft enclosed? I can`t count turns of the driveshaft.. At 60-65 it runs 3000 RPM.. 3.73 be a good guess? I am thinking about a Mitchell overdrive. Would you recommend a 26% or a 36% unit with that gear.
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02-15-2015, 05:20 PM | #2 |
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Re: rear end ratio
There are ways to check it with jacking up one wheel and counting something, but I can never remember it correctly! An easy solution would be to use one of the online calculator, you need rpm (which you know), mph (which you know), and tire diameter (you need to get). Pop in the numbers and you should have it. If you want to go to the work and have help, you could jack up the rear end, crank over the engine by hand and count the number of engine revolutions for one wheel rotation (you need to make sure the wheels turn together!).
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02-15-2015, 05:53 PM | #3 |
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Re: rear end ratio
Ok, with 6.00:16's on the back, with a 3.78 at 3000 rpm you would be doing a true 66.08 mph. With 4.11's, at the same 3000 rpm you would be doing 60.77.
If your car has a starting handle you could check it like this: Jack up one rear wheel. Turn the crank handle until it is at an easy place to start from. (12 O'Clock for example.) Mark the raised wheel and the ground so you have a datum. Now turn the crank (counting the turns) until the raised wheel has turned exactly TWO revolutions. The number of turns of the crank handle equals the rear end ratio. As we know the most likely candidates are 3.78 and 4.11, that makes it easier to judge. A bit more than 4 turns but less than 4 and a quarter means it is a 4.11. A bit past 3 and 3 quarters means it is a 3.78. If you have a reliable rev counter and can get the true speed by a sat nav device, that would be the easiest way to get an indication. Mart. |
02-15-2015, 06:13 PM | #4 |
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Re: rear end ratio
If it still has the original gears, the tooth counts should be stamped on bottom webb of the center housing. Divide the little number from the big one and you have the ratio.
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02-15-2015, 07:11 PM | #5 |
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Re: rear end ratio
9-34 would be 3.777... or 3.78.9-37 is 4.11.
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02-15-2015, 10:02 PM | #6 |
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Re: rear end ratio
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"One easier way to determine the ratio with out pulling the gear or turning wheels etc, is to count the teeth on the ring gear, put a paint pen mark on the ring gear through the drain or level plug, this will tell you the ratio, 34=3.78 37= 4.11 39= 3.54 or 4.33 40=3.63 or 4.44 41=4.55 from the green bible parts book. Lawrie" Hint: to do this you must have the rear wheels off the ground and transmission in neutral. I usually use jack stands under the small ends of each axle housing and turn the ring gear through the rear filler hole using a small screw driver.
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John "Never give up on what you really want to do. The person with big dreams is more powerful than one with all the facts". Albert Einstein Last edited by JM 35 Sedan; 02-15-2015 at 10:15 PM. |
02-15-2015, 10:08 PM | #7 | |
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Re: rear end ratio
Quote:
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04-17-2017, 11:13 AM | #8 |
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Re: rear end ratio
I can't edit my post above. I omitted to say "engage top (3rd) gear" before turning the starting handle.
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04-17-2017, 11:18 AM | #9 | |
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Re: rear end ratio
Quote:
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04-17-2017, 02:45 PM | #10 |
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Re: rear end ratio
Can't always trust stamping on housing . Once bought a rear end that said the gears were 3.54 , once in was apart ,it turned out , some one had changed gears.
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04-17-2017, 03:50 PM | #11 |
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Re: rear end ratio
Interested to hear the responses to the second question on available Mitchell OD ratios. The 36% OD is fairly steep, more than any modern car excluding those with 2 OD gears. 2nd gear OD with a 36% ratio is a duplicate of 3rd gear direct so not a good option if gear splitting is part of the plan.
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