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| Calculating a rearend ratio https://slantsix.org/forum/viewtopic.php?t=28912 |
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| Author: | wjajr [ Mon May 12, 2008 7:27 pm ] |
| Post subject: | Calculating a rearend ratio |
I want to make sure I have done this calculation correctly. I counted between 28 & 29 one quarter turns of the drive shaft by counting each time a "U" joint cap passed the floor to two full rotations of the wheel. 28/4=7 full revolutions of the drive shaft to two revolutions of the rear wheels. 7/2 turns of the wheel=3.5 which is close to 3.55:1, or 3.54:1 I discovered that the speedometer gear presently installed in my transmission is a green 34 while installing a new cable the other day. According to (here I go again) a chart in Year One I should have a white 37 tooth gear. Is this a correct assessment? |
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| Author: | SlantSixDan [ Mon May 12, 2008 8:50 pm ] |
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Are ya sure about that count of quarter-turns? Did you chalk the inboard sidewall of the tire that'll turn and block the other tire (or don't lift it up) so that it can't turn even a little bit? Here're the ¼-turn counts for common ratios; your 28-count is exactly double the 14/4 count for 3.5 rear axle ratio, so I suspect you might've had both rear wheels free to turn... 16/4 = 4 = 3.91 14/4 = 3-1/2 = 3.54 or 3.55 13/4 = 3-1/4 = 3.21 or 3.23 12/4 = 3 = 2.93 or 2.94 11/4 = 2-3/4 = 2.71 or 2.76 10/4 = 2-1/2 = 2.45 9/4 = 2-1/4 = 2.26 |
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| Author: | wjajr [ Tue May 13, 2008 4:19 am ] |
| Post subject: | |
Both wheels were free to turn. With one wheel planted on the ground, the lifted wheel would not rotate. Both wheels turn in the same direction when off the ground when rotated by hand. I had the tires off, and placed my hand on one of the lug bolts at six o'clock while slowly turning the wheel twice, and counting U caps. |
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| Author: | SlantSixDan [ Tue May 13, 2008 9:08 am ] |
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Ah, that tells us you've got a 3.5 rear axle with Sure-Grip. |
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| Author: | MoparBrit [ Tue May 13, 2008 10:45 am ] |
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Speedo gear is going to depend on what rear axle ratio you have and how tall a tyre you are using. For example: a 235/60/14 rear tyre and a 3.54 rear comes out to 36.97 or a 37 tooth gear needed. A 195/70/15 tyre calculates to 36.05 etc. Post your rear tyre size and the correct tooth gear can be calculated. Cheers |
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| Author: | SlantSixDan [ Tue May 13, 2008 11:30 am ] |
| Post subject: | |
Or use courteous, efficient self-service!
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| Author: | wjajr [ Tue May 13, 2008 11:39 am ] |
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Year One's 'Speedometer Gear Chart' indicates I need to have a 37 tooth gear with 205/70R-14 tires. Presently I have a 34 tooth gear spinning the cable. Thanks, now to relocate the site with the cheeper used gears for a lot less than Year One's... |
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| Author: | MoparBrit [ Tue May 13, 2008 12:01 pm ] |
| Post subject: | |
Looks like you're on top of it! Calculates out to 36.69 for a gear so 37. I'd heard that you can still get gears from the dealer also. Gear number might have changed a bit from what I remember from old posts I'd seen, but I think they are still available. See loads of them on eBay also. Don't remember specifics on which, but know there are quite a few listed in sort of a bulk and you choose one sort of format. Saw them when looking for my gear, but ended up getting elsewhere. Best of luck. Cheers |
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| Author: | wjajr [ Tue May 13, 2008 5:36 pm ] |
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Mopar Brit, Hummm Minnies... There was a short 18 months back around 1975 I did not have a Mopar in the stable. The transportation device was, as you guys call them across the puddle, a 1959 Frog Eye Sprite equipped with a 948 cc engine. I lugged it home in three chunks, and several cardboard boxes and had her on the road in three months. I made a deal with the devil (wife) and sold it seven years later in order to purchase the 1982 Lebaron Convertible I'm still driving. I miss that little Bug Eye, it was fun. Perhaps I pick an other one up some day. |
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| Author: | MoparBrit [ Wed May 14, 2008 8:54 am ] |
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Those frog eyes are nice. Finding a good non rusty example is tough to do now and even knackered units are going for a mint. Getting to be that way with most of them now. Just saw a Mk1 Mini with 850 and pudding stick go for £8,000. Not that long ago you could not give one away. |
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