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Drive Fast, Take Chances!!
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Discussion Starter #1
i recently put new gears in my 86 GMC k1500. now since i changed the gears my speedometer is off. i know i have to change a gear in the transfer case but going from 3.08 to 3.73. how do i change this gear and is there more than one gear that i need to change?



Also i put a whole rearend in the rear. it is a 3.73 posi out of a 1988 blazer,
i pulled the cover off and the setup is a bar across the spider gears with springs and like a little flipper thing. when ever i spin it spins one wheel then sometimes catches both wheels. is there a way i can tighten this up so they both spin right away? :cool:
 

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Remove the speedometer cable where it attaches to the transfer case (speedo adapter). Remove the bolt and bracket that hold the speedo adapter into the transfer case. The gear that is in the speedo adapter is calibrated for the 3.08 gears. You made a 21% change to the diff gears, make a 21% change to the speedo gear. Multiply the number of teeth on the speedo gear by 21%. That number represents the new number of teeth needed for the speedo gear.

The diff you installed is called a "Gov lock" posi. It is intended to run open when there is little or no wheel spin and gradually apply pressure when the centrifical force opens the "flipper thing". This diff is notorious for failing under hard driving. If you intend to do burnouts, buy a performance posi BEFORE you explode the one in the diff now.....
 

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Drive Fast, Take Chances!!
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59 Posts
Discussion Starter #3
speedo gear

Last night i went to my friends house and we pulled two transfer cases apart one for 3.08 and one for 3.73, the 3.08 was out of a rig so it was easy to get to, to get the mechanism out we had to pull the tailshaft off, which was easy. it had a blue inner gear and a black outer gear. we pulled the 3.73 one out with out pulling the tailshaft off. it had a white inner gear and an light blue outer gear.


Do I have to pull the inner gear out or are they the same for all gear ratios? I would rather not pull the tailshaft off of my transfer case even though it is an easy job
 
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