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02-23-2018, 07:20 PM
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#1 |
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Registered User
Join Date: Sep 2014
Location: White Sulphur Springs,WV
Posts: 6
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Speedometer gear for TH400 transmission
My truck's speedometer shows about 75mph when I think I am going about 45 to 50 mph. Can anyone tell me how many mph one tooth on the driven gear will change the speedometer? The driven gear that is in there now is a 40 so do I go up in teeth or down. I am thinking going up will bring the speedometer down. Any help will be great! Thanks Jim
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02-23-2018, 07:39 PM
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#2 |
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Registered User
Join Date: Nov 2014
Location: Lincoln City DE
Posts: 1,292
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Re: Speedometer gear for TH400 transmission
correct !! you need to confirm actual speed and one tooth = 5% of speed.... do da math....
__________________
Stan 67 swb BLU MULE posted via flip-fone |
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02-23-2018, 07:48 PM
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#3 |
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Registered User
Join Date: Sep 2014
Location: White Sulphur Springs,WV
Posts: 6
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Re: Speedometer gear for TH400 transmission
Stan, Does that 5% mean about 5mph?
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02-23-2018, 08:09 PM
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#4 |
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Registered User
Join Date: Nov 2014
Location: Lincoln City DE
Posts: 1,292
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Re: Speedometer gear for TH400 transmission
depends on actual subtracted from gauge
__________________
Stan 67 swb BLU MULE posted via flip-fone |
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02-23-2018, 11:06 PM
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#5 | |
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Post Whore
 
Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,393
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Re: Speedometer gear for TH400 transmission
Quote:
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help.  RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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02-24-2018, 01:26 PM
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#6 |
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Registered User
Join Date: Sep 2014
Location: White Sulphur Springs,WV
Posts: 6
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Re: Speedometer gear for TH400 transmission
Thanks Bob for the input, I will try a higher gear to see if that will lower the speedometer.
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02-24-2018, 01:31 PM
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#7 |
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Registered User
Join Date: Sep 2014
Location: White Sulphur Springs,WV
Posts: 6
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Re: Speedometer gear for TH400 transmission
One more question, Does it make a difference if the drive gear is 15 or 16 tooth?
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02-24-2018, 05:25 PM
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#8 |
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Post Whore
Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,393
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Re: Speedometer gear for TH400 transmission
Yes it does make a difference on the driven gear. You want to go up in size on the driven gear or down in size on the drive gear to get a lower indicated speed. Here are some links that may help you.
Good luck http://www.wallaceracing.com/speedo-calculator.php http://www.tciauto.com/tc/speedometer-gear-calculator/ http://www.gtsparkplugs.com/SpeedoGearCalc.html
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 Last edited by HO455; 02-24-2018 at 05:36 PM. |
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02-25-2018, 01:38 AM
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#9 |
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Registered User
Join Date: Jul 2013
Location: Southern Wisconsin
Posts: 126
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Re: Speedometer gear for TH400 transmission
What is your rear gear ratio and tire height?
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02-25-2018, 02:26 PM
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#10 |
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Registered User
Join Date: Sep 2014
Location: White Sulphur Springs,WV
Posts: 6
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Re: Speedometer gear for TH400 transmission
My rear axle is 3.73 and tire height is 27 inches
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