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12-29-2023, 04:31 PM | #1 |
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Join Date: Feb 2011
Location: Sandy, OR.
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Help with gear ratio when engine/transm. removed
I am trying to determine the differential gear ratio and need a little help. My engine and transmission are removed and I was wondering how I could calculate the ratio by watching the driveshaft turn in comparison to the rear tires. I was assuming that I could watch the shaft turn 2 complete revolutions and watch how much the rear tires rotate (like you do with the engine turning 2 complete revolutions) and I would have my answer. I was figuring that in that configuration I would be in 3rd/direct drive. Obviously I am incorrect. Any help out there? Thanks in advance
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12-29-2023, 04:56 PM | #2 |
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Re: Help with gear ratio when engine/transm. removed
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12-29-2023, 04:57 PM | #3 |
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Re: Help with gear ratio when engine/transm. removed
Lee
Almost got it Jack up both rears off the ground and mark both wheels Best to mark where you can see both together Turn driveshaft and count revolutions If 3.78 rear gears you will turn driveshaft 3 and 3/4 revolutions The reason for marking both wheels is you can recover in case a brake drags and moves differential HNY J
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12-29-2023, 08:25 PM | #4 |
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Re: Help with gear ratio when engine/transm. removed
John,
Are you saying that 3.78 turns of the driveshaft should be 1 complete revolution of the tire/s? That does make sense. So that would be equivalent to being in 3rd gear/direct drive I suppose. Thanks Last edited by Lee Mitch; 12-29-2023 at 08:26 PM. Reason: attribute |
12-29-2023, 08:29 PM | #5 |
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Re: Help with gear ratio when engine/transm. removed
Thanks JW. I examined that thread previously and couldn't find what I needed, specifically my engine and transmission being removed.
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12-30-2023, 08:08 AM | #6 | |
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Re: Help with gear ratio when engine/transm. removed
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Quote:
If you have a 3.78 rear end. The rear wheel will rotate once for every 3 3/4 rotations of the drive shaft. If you have a 4.11 rear end the rear wheel will rotate once for every 4 rotations of the drive shaft. You have to have one rear wheel on the ground and one rotating while doing this test. Last edited by jwmckenzie; 12-30-2023 at 08:13 AM. |
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12-30-2023, 08:35 AM | #7 |
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Re: Help with gear ratio when engine/transm. removed
Jack up only one rear wheel. It will turn 2 times for one turn of the ring gear. If you jack up both wheels one can, and likely will, turn more than the other and it will be difficult to keep track.
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12-30-2023, 10:24 AM | #8 | |
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Re: Help with gear ratio when engine/transm. removed
Quote:
If one wheel is held stationary, the ratio become 2 x 3.78. Or 7.56. All part of the magic of the spider/differential gears. The spider carrier ALWAYS turns at 3.78. Hold the "circular rack" of one wheel gear stationary and you get 2x the motion of the other as it is pushed by the spider gears. Joe K
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12-30-2023, 02:48 PM | #9 |
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Re: Help with gear ratio when engine/transm. removed
Joe, I will gladly trade my horse for your Model A. Come and get it.
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A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. |
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