Grimace427
Well-Known Member
Driveshafts can vibrate based on resonant frequencies from specific RPM's of the shaft itself. The shaft can be perfectly balanced and still cause a vibration at a specific RPM based on its length, shaft wall thickness, and construction(AL, steel, CF). So with lower(numerical) gears you may have a perfectly smooth driveline but when you install the shorter gears(thus spinning the shaft faster for the same road speed) you may hit the resonant frequency of the driveshaft causing a vibration. You may have seen people install an aftermarket driveshaft and get a vibration at a specific speed and have to 'clock' the driveshaft in order to mitigate that frequency.Yeah.. like we all said we already knew...like 3 times. Your point?
None of that has to do with your DS being unbalanced. If its unbalanced with a 3.27 its unbalanced with a 4.56. Either way that is a separate issue NOT related to your rear gears.
My overall point is that because installing shorter gears will cause the shaft to spin faster you have a higher chance of hitting the critical frequency of the driveshaft which will cause a vibration and even reduce the life of the shaft or cause sudden failure.
No.In simple terms, the front of the driveshaft is connected to the engine (via the tranny) and the back end to the axle-gears.
The determining factor of how much the driveshaft spins is the engine. It cannot spin any faster than the engine tells it to.
The gears on the end of the driveshaft will THEN determine how fast the wheels spin.
Am I right??
Yes, this is about as simple as it can be explained. Changing the rear end gears only will not change the rpm of the driveshaft, it will only change how fast the wheels spin for any given engine rpm. You can change the rpm of the driveshaft based upon engine rpm via the gears in the transmission which will also effect how fast the wheels spin (i.e., by shifting to another gear or changing the actual gear ratios in the transmission altogether), but that's a totally different discussion than what is being discussed here.
This is also wrong.
You can completely remove the engine and transmission from the car and push the car down a hill as far as this discussion is concerned. The rear gear ratio is the relationship between the rotation of the driveshaft and the rotation of the driven wheels. With 3.73 gears for example, the driveshaft spins 3.73 times for every rotation of the rear wheels. Thus with 4.56 gears the shaft spins 4.56 times for every rotation of the wheels.
Going from 3.73 gears to 4.56 gears means you are spinning your driveshaft about 19% faster for any given road speed.
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