Thread: Chevy 350 Trany Question on incorrect speed o meter reading?

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Hey all...
I have noticed at speed that my speed o meter reads about 7 miles an hour slow from about 55 up?
Seems to be about right ( via my portable GPS ) from 0 to 25. Any help / ideas?
Red 32

you can take the differential ratio and tire size to a GM dealer and they will sell you the gear you need for your trans.

Or go on here. Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4 The big unknown may be which drive gear you have internal to the tranny, the spiral gear on the main shaft.

Those can be a pain to change

You might also ck your speedo gauge. Mine was also off going 5MPH too fast. I googled my VDO speedo and found out it was programmable. You line up at a mile marker, push the trip button a number of times, drive to the next mile marker, push some more times and now its perfect match to my GPS speed.

Thx All for the info. I do have VDO gauge's but I need to check out the thought from jdsaengine to see if mine has that feature.
Red 32

Originally Posted by Red 32

Thx All for the info. I do have VDO gauge's but I need to check out the thought from jdsaengine to see if mine has that feature.
Red 32

If you haven't calibrated the speedometer that's the first step for sure. Don't waste your time chasing other things until that's done. The VDO units seem to have some issues for some versions, but if you have the digital display model I think this may help - VDOCALIBRATION My AutoMeter unit is drop dead simple. Hope you find the same with your VDO.

This is my programmable VDO speedo, and the calibration instructions. Maybe it can help you