Correcting speedometer

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I had read a post were someone stated that you can change your speedometer to read correctly after installing 285's by replacing the speedometer gear in the transfer case? Is this the VSS? Also that it is one tooth per 4% change in speed. When going 57-58 mph on the speedometer is actually 60 mph is that a 4% differance and if so which way would I go to correct the reading, more or less teeth? Does anybody know the number of teeth for the original size tires and 3. 54 gears or would it be best to remove the gear and count the teeth.
Thanks for any and all help as I know 2-3 mph differance isn't bad but if I can get the speedometer to read correctly I would like to.

Paul

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'96 2500 ext. cab, LB, 4x4, 5 speed, 3. 54, TST 280 cam plate, AFC spring kit ,pyro and boost gauges mounted on A-Pillar, tinted windows, 16x8 Eagle alloys series 1219, 285/75R16 Durango A/T's

 

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I changed the gears (they say pinion on the package) in the little (hall effect sensor ?) that goes in the transfer case. I believe I went smaller, 2 teeth for the 255's put me right-on.
John Holmes had this on his 96, he had an article in TDR that had the numbers. I saw someone else post this on this board once, but I believe they were off by one tooth.
I lost my original one (somewhere), and I think I forgot to write down the tooth numbers.
I can tell you that when you changfe the "pinion", the little dealy it goes in to has different marks with the number of teeth on it, it needs to be lined up correctly or it won't work. Go figure.

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"Roadrunner"-96 4X4 club cab-12v-auto-3. 54 gears-Amsoil bypass filter - all Amsoil fluids-trans filter-britebox-shelfit-DeeZee boards-Rhino liner-Rancho 5 speed shocks-Hellwig rear antisway & overload springs-Warn 12000 lb. winch-dual redtop optimas-combo gauge and trans. temp gauge in pillar mount-255/85R16 Kelly MSR tires-custom pinstriping- Walker muffler-Cummins mudflaps-Tuff Country control arms-2" coil spacers

 

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The OEM speedometer gear for 3. 54 rear gears & OE tires is a 31 tooth pinion. The # of teeth is stamped on the gear. The dealer has other speedo gears down to 28 teeth I believe. This is for a 33" approx tall tire. They have nothing lower than a 28 tooth. Can not help with you with anything taller than 33". I have 36" tires W/ the 28 tooth pinion. Speedometer & Ododmeter still off Approx 8-10 %. Go to your dealer W/ the size of the tires and he will hook you up with the correct pinion gear.

The Abbott ERPA may be the best way to accurately calibrate this mess.

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Bill R
94 2500 SLT,4X4,5 Speed,3. 54 LSD... . Still looks brand new... .



[This message has been edited by HEMI®Dart (edited 06-16-2000). ]

 

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Got the speedometer gear in today and it reads correctly now and I did have the 31 tooth gear and picked up a 30 tooth gear at the dealership. took all of 20 minutes to remove and reinstall.
Thanks for the reply's,

Paul

 

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I'm going to move this over to the "chassis" forum, since the SUBJECT (though not particularly this instance) is of interest to everyone. It comes up a lot, and having it over there would be most helpful.