The car: 89RS 305 auto, completely stock original, new motor.

The facts:
Speedometer accuracy confirmed by radar
Tachometer accuracy confirmed by engine analyzer
700R4 trans with 0.70 final ratio
Differential with "6HP" code indicating 2.73 ratio
Tire radius = 13 inches

70 mph = 2200 RPM
80 mph = 2500 RPM
90 mph = 2800 RPM

The problem:
Speed should be much higher for the given RPM or RPM should be much lower for the given speed. I am certain the rear end has never been touched, but the calculations indicate an axle ratio of around 3.45, which would be a "6HL" axle. Could my axle be mismarked, or is there possibly some really bad loss somewhere?

Tom

 

I haven't seen a calculator that goes by a tires radius. It's either diameter or cicumference. Diameter is how tall the tire is and circumference would be a measure of the overall tread of the tire, like wrapping a tape measure around it.

 

Well, jack the rear of the car up (use jackstands please) and on the pass. side rear tire make a chalk mark on the tire and on the floor. Make a chalk mark on the drive shaft. Rotate the pass. side tire foward and count how many times the driveshaft rotates. If the driveshaft rotates around 3 1/2 times to one rev. of the tire you have 3.45 gears ect, ect.

Auggie

 

To Rustynutz: the calculator provided by this site uses radius but it's pretty straightforward to convert to any other unit you prefer.
pi x (D or 2r) = c

https://www.thirdgen.org/newdesign/t...ulations.shtml

To Auggie: I checked per your recommendation, first with psngr wheel lifted and then with both wheels lifted, repeated several times each in both directions, and I think there's something wrong with the test. Every full tire rotation yields approximately 1.25 driveshaft rotations. What gears is that?? Any ideas what's going on out there?

Tom

 

Well, man I don't know? The only thing that I can think of is that I forgot to tell you to put the tranny in "N". This method has always worked for me???

Auggie