Anyone Know How to Calculate Driveshaft RPMs?

I’m keeping vehicle speed constant, you’re keeping engine speed constant. No contradiction, just different approaches

 

yes, different approach, different answers

And to your point he was probably asking about its affect on speed but just didnt phrase it that way.

I should have realized that without including the affect on speed the original question didn't really make sense. I replied based on what was said. You correctly replied on what was meant

 

Why are you asking this question, OP?

 

I'm was just thinking about how many RPM's is the minimum you would need to be sure your driveshaft is balanced under any circumstances. I think the standard shops go by is is between 7500 and 10,000 RPM's? With the 3rd gen, once you hit about 75MPH it goes from 6th gear to 5th gear, then the faster you go, it drops into 4th. So if the engine is turning 4,800RPM's , in 4th gear, how many RPM's is the driveshaft turning? Does anyone know the gear ratios for each gear in the 6 sp auto trans?


(FYI 325,60R20 with 4.56 gears)

 

As I said earlier. 4th gear is 1:1. Driveshaft is at 4800 if engine is at 4800 in 4th.

The transmission ratios were already posted earlier.

The picture is blurry but it appears you’re going 108 mph. That’s not even close to high for that speed. I’m at 6200 driveshaft rpm at 108 mph.

 

Yes.
Drive shaft RPM = Wheel RPM x Rear Axle Gear Ratio.
Drive shaft RPM changes with speed, not what gear you’re in, or what transmission you have.

Pop it in neutral and shut off the engine:
Drive shaft RPM = Wheel RPM x Rear Axle Gear Ratio

 

Agreed. If you know the speed you can calculate the driveshaft rpm by Wheel RPM x Rear Axle Gear Ratio and the graph is linear buts its not the only way to calculate. And in truth this is the simplest method since the only variable is really speed (unless you start playing with different tires sizes). I have used this method myself.

But both statements are true. I have a two piece driveshaft. If I remove the rear section so that's it no longer connected to the rear axle I still have the part that goes up to the center support bearing.
If I then go into drive and increase the engine RPM then the speed of that section of driveshaft is 100% a function of engine rpm and transmission ratio.

Its just a different way of calculating the same thing. In your example you put trans in neutral (disconnect engine). In my example I disconnect rear axle.