Vss

[possum70]

Well, Moira's speedometer doesn't work. New cable, doesn't work. Put a drill on the cable and she went @55 mph. So I'm guessing whatever is in the T-case isn't working.
But from what I read I have to buy a specific piece matched to my tire size and gear ratio. 33" and 3.73. Where can I find this part?

possum

 

[dyeager535]

Not VSS, you are looking for the drive and/or driven gears in the trans. Not sure what is still being sold, I thought this stuff was drying up, but check with TCI. I recall they also had a chart for the speedo gears.

Not sure where there is a gear calc for the speedo gears if you don't know what % you are off currently.

 

[4X4HIGH]

Is this on your 78 Blazer? If so and you have cruise control then there are two speedo cables involved, one goes from the t-case to the transducer for the cruise control and the other goes from the transducer to the speedo. It is very common to have a bad transducer causing this issue. In the even you do have cruise control remove the cable from the t-case and run it with a drill, if the speedo doesn't work then remove the cable from the transducer going to the speedo and spin it (guessing you already did this cable as you said it read 55mph).

 

[possum70]

Cruise didn't work I removed it. Then ran one straight from speedo to Tcase

 

[y5mgisi]

I dont know where you can buy new. Probably google "speedometer gear replacement" and go from there.

 

[4X4HIGH]

Cruise didn't work I removed it. Then ran one straight from speedo to Tcase

Well then, this place will have EVERYTHING you need to make the speedo work and also to make any corrections needed due to different gearing or tire size changes. http://www.transmissioncenter.org/GM_Speedometer_Gears.htm