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#1
03-24-2003, 12:48 PM
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My GTO reads a speed that is far faster then I am travelling. I am not using special or oversized tires, so does anyone know why the reading is off? I would sure like to fix this as soon as possible. Thanks for your help.
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#2
03-24-2003, 12:48 PM
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My GTO reads a speed that is far faster then I am travelling. I am not using special or oversized tires, so does anyone know why the reading is off? I would sure like to fix this as soon as possible. Thanks for your help.
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#3
03-24-2003, 12:54 PM
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take it to a speedo shop in your area,they will put the correcr gear in your trans.Tom
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#4
03-24-2003, 01:01 PM
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Most likely, the reason it is not reading correctly is because the rearend gear was changed at some point. A numerically higher gear ratio will make the speedo read faster than you are going. Do what Tom S suggested and it should be fine.
__________________
'67 GTO Conv 400 TH400 |
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#5
03-24-2003, 01:17 PM
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In an automatic. Find out what rear end ratio you have. Go to local GM dealer and get the correct plastic speedo gear for the transmission. Take the speedo cable loose. Remove the retainer clip from the housing. Remove the cover then the gear. Reverse the process. I did it. You can. Unless yours is a manual. Then well, I don't have a clue.
 http://kurtspontiac.homestead.com/DavidJones69GTO.html
__________________
 frittering and wasting the hours in an off hand way.... 1969 GTO, 455ci, 230/236 Pontiac Dude's "Butcher Special" Comp hyd roller cam with Crower HIPPO solid roller lifters, Q-jet, Edelbrock P4B-QJ, Doug's headers, ported 6X-8 (97cc) heads, TKO600, 3.73 geared Eaton Tru-Trac 8.5", hydroboost, rear disc brakes......and my greatest mechanical feat....a new heater core. 
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#6
03-25-2003, 01:14 AM
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Not all TH400 trannys have the same speedo drive gear in them. Did you change out the tranny? Bring the two letter code and year model from the ID plate (right side of tranny) to the dealer along with rear end ratio. Manual speedo gears change out the same way.
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#7
03-25-2003, 06:38 AM
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I have found that by using this site, you can usually narrow down what is the culprit. Of course benchmarking your speed against a newer vehicle also helps.
http://www.prestage.com/carmath/calc_Gears.asp - Jim Doran -Some Pics of my 65
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-Jim Doran- 1965 389 Tripower; 4 speed; convertible 2019 Tesla Model 3 Performance 2016 Chevy SS; Sold 2001 Toyota Tacoma 4x4 2008 Infiniti G35x |
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#8
03-25-2003, 10:56 AM
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Thanks for the suggestions. The guy I bought the car from said the transmission is original, but has been rebuilt so I can assume they may have used the wrong gear. At least I know what direction to take.
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#9
09-02-2004, 10:20 PM
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www.novaresource.org/speedo
good tips in how to determine the different gears driven and drive. I did.
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White pearl firebird -71 |
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#10
09-03-2004, 04:14 AM
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I believe you can order drive and driven gears from either year1 or NPD.
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#11
09-05-2004, 03:55 AM
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If the speedo reads a speed that is higher than the actual car speed, & it is because of tyre size, then it would be because the tyres are undersize [ smaller diameter ], not oversize.
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