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speedometer % error -rear gear swap-speedo gear swap #1307535 09/20/12 02:40 PM 09/20/12 02:40 PM
Joined: Oct 2008 Posts: 282 USA I ignoble OP enthusiast
ignoble OP enthusiast I Joined: Oct 2008 Posts: 282 USA	2 questions - I have a car that had 2.71 gears originally [8 1/4],and put in a set of 3.55 gears instead. I do have on order a 35 tooth speedometer gear[and seal kit] thru A+A Transmission, which shows to be correct per the site calculator. [245/60/15 tires] Any trick to swapping the speedometer gear ? Is it just unscrew the cable,pull the housing on the trans, swap the seals, insert the new 35 tooth gear, bolt back in ? In the meantime the Speedo seems to be reading 15-20 mph high at what i think is 40mph down the road [ reads 55mph]. IS there a certain fixed percentage error i should expect, if so , how to figure it ? 72 B-body with factory rally 150 mph gage, i think it came with F70x14 tires from factory. Thanks.

Re: speedometer % error -rear gear swap-speedo gear swap [Re: ignoble] #1307536 09/20/12 02:45 PM 09/20/12 02:45 PM
Joined: Jan 2003 Posts: 25,910 Rio Linda, CA John_Kunkel Too Many Posts
John_Kunkel Too Many Posts Joined: Jan 2003 Posts: 25,910 Rio Linda, CA	35-tooth is the correct pinion for your gear/tire combo. Indexing the adapter is explained in the archive link below: http://www.moparts.org/Tech/Archive/auto/21.html The INTERNET, the MISinformation superhighway

Re: speedometer % error -rear gear swap-speedo gear swap [Re: ignoble] #1307537 09/20/12 04:09 PM 09/20/12 04:09 PM
Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska	Quote: Is it just unscrew the cable,pull the housing on the trans, swap the seals, insert the new 35 tooth gear, bolt back in ? IS there a certain fixed percentage error i should expect, Jack up the pass side of the car as high as you can to minimize the fluid loss. Wouldn't hurt to put a few drops of ATF on the new speedo gear teeth & not absolutely neccessary to change the seals. Should be little/no error. Get the right pinion in there to make the odo read correct checked at the interstate mile markers which are pretty accurate & go 5 miles. With the odo correct check the speedo at a roadside digital MPH sign (or GPS). The speedo is triggered from the odo and can be recalibrated if off but the odo must be dead on first and that is strickly a function of having the right tooth pinion gear in the trans. EDIT meant to say jack up the DRIVERS side of the car Last edited by RapidRobert; 09/20/12 04:22 PM. live every 24 hour block of time like it's your last day on earth

Re: speedometer % error -rear gear swap-speedo gear swap [Re: ignoble] #1307538 09/20/12 05:27 PM 09/20/12 05:27 PM
Joined: Oct 2008 Posts: 282 USA I ignoble OP enthusiast
ignoble OP enthusiast I Joined: Oct 2008 Posts: 282 USA	Thank You gentlemen ! I'll put this info to use on the weekend, assuming the gear shows up today or tommorow

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