Speedometer reads fast

[tateinca]

My 93 has a problem in that the speedometer reads

5 to 10 MPH faster than actual speed. I had a problem with the voltmeter, oil pressure, and temperature guages reading high also. That turned out to be a bad body ground. Tires and wheels are stock. Does anyone have the troubleshooting charts for this? Has anyone had a similar problem? If so, what did you do to correct it?



Thanks,



Hugh.

 

[bkokotovic]

hmmm...

I have the same problem now. It's accurate up to about 30 mph. From then it gets about 5-10 mph fast.



I calibrated this using two separate GPS receivers. Still haven't found the root cause.



Let me know what you find.



B

 

[Robin]

My '97 3500 read about 4 mph high from 35 to 65. At 75 it was about 3 mph. This was based on a GPS comparison. Changed the speedometer gear from a 36 tooth to a 38. Now the speedometer is right on the money at 55, 2 mph fast at 35 and 1 mph slow at 70. Tires are half worn, so when they are replaced this will change some.



The gear was about $11 at Dodge garage. I think the same gears have been used in Chrysler products for at least 30 years.



Be careful. My truck is a 4WD, so the speedometer gear is in the transfer case tailshaft. I twisted off the 5/16th bolt that holds the speedometer sender assembly in the tailshaft. It had corroded at the steel/aluminum interface. Had to use an angle drill to drill the bolt out, replaced it with stainless steel.



Bob

 

[Philip]

My 93 was reading 5 mph slow at 60. I checked into changing out the speedo drive pinion. But the other ones they had listed would have went to about the same only fast instead of slow. I ended up changing out my tires. I didn't like the 205's Dodge put on these trucks. I put a set of 235's on it with American racing Aluminum rims. (I had them left over from the 72 C30 I had been driving). Speed0 fell right on the money then.