Re: Help in Iowa

hemisedan said

Well yesterday, we crawled under the little guy, and found out some interesting things. One, the 3rd member housing is a 741 case. But, the good part is that it is a suregrip, and works. Now for the gear ratio, and this is the old fashioned way, it is seems that this is either, a 3:23 or a 3:55, as it is just over 3 turns on the drive shaft for one complete turn on the wheel. So, maybe the speedometer gear is set for a 2.92 or 2.73. Does that make sense?

Click to expand...

Yes and no,
IIRC you mentioned a 3000 rpm cruising speed.... which with 3.55s and 27"tires is; 65=2870rpm at zero-slip, so perhaps up to 3010 at 5% TC slip. Downhill with closing throttle could be less than 2870.
So if you your speed-O is saying 65mph simultaneously with 3000rpm, then it cannot be calibrated any closer. The next SpeedO gear in either direction will change the reading by about 3 to 4 percent which at 65 is ~2 or 3 mph.

Of course if your tach is in error.... who knows!
and then you are gonna have to make a run, timing the Mile-Markers, to prove 60mph = One mile in One minute, exactly. Then you would have at least one absolute.

The Speed-O gear for 3.55s is about 35 teeth.
The 2.94s would be ~.29,
so that is a difference of ~21%, and so your gauge should be reading 21% high, therefore; at 65actual mph, it might be showing 78mph ; fewer teeth spin faster to go with the slower-rotating driveshaft..