Thread: speed-o help please

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lilrobo if you speedometer is reading 50 MPH at a vehicle speed of 60, change to a driven gear with 16 teeth.

It it is reading 70 at a vehicle speed of 60 change to a 22 tooth gear.

(You didn't say if it was reading fast or slow)

no the other way around my speedo in truck says 70 and i am going 60 ,, i am 10 over even at 30 as well ,,,

thanks

Originally Posted by Mike P

lilrobo if you speedometer is reading 50 MPH at a vehicle speed of 60, change to a driven gear with 16 teeth.

It it is reading 70 at a vehicle speed of 60 change to a 22 tooth gear.

(You didn't say if it was reading fast or slow)

Not saying Mike's approach is wrong in any way, but for me curiosity would drive me to measure the tire circumference, figure out the rear gear ratio, determine the drive gear in the tranny (by color if nothing else) and see what should work based on Physics. It's the engineer in me, looking at the details to a fault as opposed to finding a way to just make it work without knowing.

what i know so far is
drive gear =7 tooth ( red )
tire height = 28.5
rear end 3.08
driven gear = blue ( 19 tooth )

thanks

Originally Posted by lilrobo

what i know so far is
drive gear =7 tooth ( red )
tire height = 28.5
rear end 3.08
driven gear = blue ( 19 tooth )

thanks

Those numbers don't seem to work right. From the charts in the link that Tech sent, and that I listed again (have you opened the link and read about your TH350 specifics??) a RED drive gear could be either Ten or Seventeen teeth (ten could be Red or Purple). A Seven tooth gear should be Pink. If we assume that it's a Ten tooth Red gear and then plug in the other numbers you have the calculator shows 21.77 teeth on the driven gear which rounds to 22, matching what Mike recommended to you. If it's indeed Seven teeth on the drive gear then it says you need a 15 tooth gear, which is not available. That means you have to drop the tail shaft case to change out the drive gear.

Hope you get it sorted out. I can't add anything more here.

sorry its a 17 ,, i have alot of things going on sorry about that

i got 22 tooth on the way ,, i'll see in a day or 2 let you guys know

Originally Posted by lilrobo

sorry its a 17 ,, i have alot of things going on sorry about that

Originally Posted by lilrobo

i got 22 tooth on the way ,, i'll see in a day or 2 let you guys know

If it's truly a seventeen tooth driver you just wasted your money. Should be a 37 tooth driven gear for the rear gears and tire size you quoted.

In that link Tech posted all it takes is entering three numbers and hitting "Calculate" to get the answer.

OK, I'm REALLY done this time.....