speedometer gears

[jpitte65]

i am trying to figure out my speedometer gears i need. i have 4.11 gears in the differentials, a turbo 350 trans, and 35 inch tires. not sure what transfer case.

 

[jpitte65]

i have tried looking up on the calculators and cant figure it out it is a pain in the arse

 

[Roadhazardguy]

Im not really sure either. Just call these guys and ask them http://www.transmissioncenter.net/speedometer_calibration_______va.htm they will know.

 

[4X4HIGH]

If this is for your 88 blazer and it still has the factory T-case (NP208) then you need to pull the speedo driven gear and look inside the t-case to see what color the speedo drive gear is. Once you post that info here I can help you out.

Are you sure about the trans being a TH350? The reason I ask is because the original trans for an 88 would be a 700R4.

 

[Blue85]

The short answer is that you need 1000 revolutions of the speedo cable per mile. So you can calculate the ratio of driven-to-drive gears that you need based on tire diameter and gear ratio.

The other solution is to determine the percentage you are off by now and then adjust the ratio of the speedo gears by that amount. Either way, the starting point is to identify the color of the two gears in the T-case now.

 

[jpitte65]

well i got to double check but the guy i bought the truck from said the block on the motor is a 78 and a turbo 350 trans i believe it is the stock transfer case but got to make sure