speedometer related question

[duanel]

Okay I have a 73 blazer auto. 203 transfer case full time 4wd My speedo is off about 10 percent wich would be right since I have 285 75 16 so I was looking at ratio adapters at http://www.transmissioncenter.net/speedometer_calibration_______va.htm and see what I think I want but when I looked at my transfer case there already seems to be one there a stewart warner 1.2020x 666f r9 I took it off to see what effect that might have and it seem my speedo was now off about 30 percent under. so my quesrion is did it come from gm with the adapter or did one of the previos owners add it because they changed transfer cases or speedo gears and if I was to get another ratio adapter should I add a 11 over inline or replace it with a 30 over,

 

[pvfjr]

I'd go with one ratio adapter. Keep it simple, no reason to have two. You may have had one from the factory, or it may have been added later. Can't tell you without looking at it really.

 

[RaisedK5]

I have that exact ratio adapter on my 75. 1.202x means is increases it by 20%. I'd replace it with a 30% overdrive unit and call it quits. Keep that one by the way , incase you swap tires/gears.

 

[duanel]

thanks for the answers I had assumed the 1.2 meant 20 percent but is nice to have congirmation.