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I picked up an 86' f350 yesterday. It's crew cab 4wd 460 4-speed. Ive got a Few questions on it. The axle code on the door is C9 which shows to be 3.55 gears. Is got 33x12.5's, at 60mph it's turning 2000rpm. That seems a little high for 3.55 gears am I correct on the axle code? Tach and temp guage work but fuel and speedo don't. We're these clusters bad about failing or is it prolly tank float and speedo cable? Also tank selector doesn't work is that generally a bad switch or bad sylenoid? Thank in advance for your help.
Fuel gauge problem is generally the sending unit but could also be the float (although I've never personally seen that be an issue).
60 MPH, 33" tires, 3.55 gears = 2168 RPM.
The speedometer and cable are not normal wear items... first place I suggest checking is the gear that connects the speedometer cable to the transfer case.
Yes, it will, but you will need to do some work on your own... the formulas I'm familiar with that include the transmission's final drive ratio seem to want the tire *circumference* as measured in feet, not the diameter as measured in inches.
So, go measure your tire diameter, then google around for the mathematical formulas and plug in your values....
Would'nt the transmission play a part? If it's a 5-speed it'll be different at 60 than the 4-speed.
Close, but not quite. Overdrive in the top gear will determine the final drive ratio. I have a 4 speed OD transmission that will provide a slower engine RPM than a 5 speed with a 1:1 final drive ratio.
Close, but not quite. Overdrive in the top gear will determine the final drive ratio. I have a 4 speed OD transmission that will provide a slower engine RPM than a 5 speed with a 1:1 final drive ratio.
That's a good point... I was assuming his 5-speed is an OD variant....
trans speedo drive gear (teeth count) x gear ratio x tire revs per mile
divided by 1000
will give speedo driven gear # to use (round up or down to nearest available gear #
point of reference for you is that with my truck(3 speed c6) at 60 mph revs at 2700 rpm
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