The Stovebolt Site Forums The Shop Area The Electrical Bay 64-66 speedometer reads 100 mph when 70 mph

Its a 65 chevy truck street rod, has original gauges, but has 350-350 turbo, and aftermarket tach that reads 41 rpm x 1000 when I am going about 70 mph. and the speedometer goes wild bouncing around up to 100 mph. the original rear I think is 4:11, what to with the rear end and the speedometer?

What radius tires are you running on the rear end? when the diameter is different than the origional tires, it can change the "actual" speed by a few miles. I would have your speedo checked at a shop that specializes in speedo calibration. good luck

Is your speedo original? if not, you will need to get a different gear for the end of your speedo cable that goesinto the Tranny, take your tire diameter and rear gear ratio info to a chevy dealer and they can get you the correct gear. I did some rough calculations, and if you had some 3.something gears in the rear, the speedo would be right, so I think you just need a different gear.


Rob

[ 11-16-2001: Message edited by: Rob Arends ]

Try taking the truck out on the interstate where you have mile markers, drive 10 miles according to the markers and see if that compares to the odometer, if the odometer reads 7 miles it's the tires/rear end, if it showes 10 miles the speedo needs to be calibrated.. :rolleyes:

Rob has the idea, but it doesn't matter if the speedo is OE or not you changed tranny and I assume the speedo gear in it is the one that was in there for whatever vehicle it was in. These are calibrated for rear ratio and tire size also.

My chevelle has a similar problem. At about 50 miles an hour the speedometer reads about 100 mph. So what I do when I drive the thing is take the GPS receiver with me. It tells me when to slow down for smokey...