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rear end ratio |
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tomj
AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7522 |
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somethings off here... assuming you have 25" diameter tires, common enough, your axle would have to be about 4.5:1 to do 47 mph at 3000 rpm.
do what rockAMX did, assuming you have a smartphone, get a speedo app, i use digiHUD for android, works great, no ads or crap. they're surprisingly accurate and easy to use. when things don't make sense then its time to check your assumptions and maybe some of your tools... and fix your tach, or get a cheapie to wire in for test purposes. with tire size you can calculate diameter online, that plus RPM and you can calc axle ratio close enough to pick from the list. |
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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
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ccowx
AMC Addicted Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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71 Javelin AMX OO,
If you have gone to the 23 tooth driven gear and are still out then you are tapped out for that gear set. The standard 8 tooth drive gear(the one inside the transmission, NOT the one on the end of the cable) needs a 23 tooth gear with 3.54's and 14" tires. Your 15" tires are what are making it read too high. There are no driven gears with more than 23 teeth, so you are maxxed out. What you need to do is to change the drive gear inside the transmission to a 6 or 7 tooth gear and then you can find a driven gear between 17 and 23 teeth that will make it read correctly. Thanks! Chris
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rockAMX
AMC Addicted Joined: Sep/16/2011 Location: Lethbridge AB Status: Offline Points: 983 |
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15 inch wheels would make the speedometer slower, not faster. With 15 inch wheels and 70 series tires (standard size for 1971), that would give about a 27 inch tire height (http://www.gtsparkplugs.com/TireCalculator.html). Assuming the 8 tooth drive gear is correct, that would give a driven gear of 21-22 teeth (http://www.gtsparkplugs.com/SpeedoGearCalc.html) assuming a speedo reading of 1000 RPM at 60 MPH, which is quite standard. My guess is that your transmission came off a different car and has a different number of teeth on the drive gear. Even with 60 series tires and a 26 inch tire height, that gives 23 teeth. A good place to order the parts is http://www.laspeedometergear.com |
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DWR
1968 AMX |
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7901 |
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rockAMX
AMC Addicted Joined: Sep/16/2011 Location: Lethbridge AB Status: Offline Points: 983 |
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Well he says he has 15 inch wheels, so he would need 15 tires at the rim.Doesn't matter much if 70 or 60 series.
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DWR
1968 AMX |
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7901 |
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Edited by Sonic Silver - Sep/04/2016 at 9:04am |
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one bad rambler
AMC Addicted Joined: Jan/09/2008 Location: On The Island Status: Offline Points: 2007 |
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Just go onto Richmond gear web site and use the calculator...
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68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8
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Gremlin73
AMC Apprentice Joined: Oct/28/2012 Location: United States Status: Offline Points: 41 |
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I have 28 inch tires with 4.88 rear gear,at 3000 rpm the speed is 50 mph.you have slightly lower gears than mine. Good luck not very streetable.
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7901 |
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newat58
AMC Fan Joined: Aug/30/2016 Location: missouri Status: Offline Points: 8 |
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my wheels are 14 inch spedo exact with gps. I may leave the car alone as i probably wont be on freeway much only town driving. I can be cruising along at 30 hit the gas and get pretty good scratch as it shifts into third.
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