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Old 09-17-2010, 01:02 PM   #1
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Crawl Ratio with auto Transmission

What is the Crawl Ratio with the automatic Transmission?

My axle Ratio = 3.73


It is true, Automatics can get away with a numerically lower crawl ratio? Why?

Thank

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Old 09-17-2010, 03:12 PM   #2
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No clue on the ratio, but the getting away with a lower ratio is debatable, and I think it comes from the torque converter having a little "give" to it. (think stopping at a red light uphill... in an auto, on the right angle, you can let off the gas and just sit there... in a stick, "hovering" in the same manner without the brake would let the magic smoke out of your clutch.). I'm no expert, but that's the impression I get.

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Old 09-17-2010, 03:49 PM   #3
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My '08 JKU Rubi T-CASE (NV-241) OR Rock-Trac, has a crawl ratio of 73.1/1 all other jk's have 38.9/1

The Auto's are different in the Rubi with 4.10 axle ratio

When I'm in 4lo--there is "No Slippage" or give-

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Old 09-17-2010, 04:17 PM   #4
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Quote:
Originally Posted by goldenfalcon View Post
What is the Crawl Ratio with the automatic Transmission?

My axle Ratio = 3.73


It is true, Automatics can get away with a numerically lower crawl ratio? Why?

Thank
You can figure the crawl ratio for any vehicle by multiplying the lowest gear of your transmission x the axle ratio x the transfer case ratio.

Your auto trans 1st gear ratio is 2.84
Your transfer case ratio is 2.72
Your rear axle ratio is 3.73

Your crawl ratio is 28.81 (2.84 x 2.72 x 3.73)

An auto transmission has a lot of slip, so yes, even though your actual crawl ratio is 28.81, your effective crawl ratio really is lower because of the slip in the auto transmission.
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