Theory behind single piece driveshaft vibrations and fix

[almostquick]

Not a platform specific application of the theory at hand but a good write up none the less.

https://www.motortrend.com/how-to/pinion-angle-change/

It’ll will be interesting to see the measured pinion angles of transmission and rear carrier. I’m due for an oil change soon and will see what mine are. Have an axle exchange alum driveshaft along with all of the whiteline transmission and rear carrier inserts.

[Turdinator]

I bought my carbon drive shaft used. At first I had horrible vibrations. It took me a few tries but eventually I found a driveshaft shop that both shimmed the uni joints to be centered and added balance weights and its been great ever since. I also have STi engine and gearbox mounts as well as a light flywheel so should be able to feel any new vibrations.

[almostquick]

So I just checked both pinion angles (rear diff side and trans side). Rear diff showed a +2 degrees of pinion angle while the trans side was at -5 degrees of pinion angle. This would put the trans side out of the ideal range of -3 degrees (assuming that ideal angles would be +/- 3 degrees at opposing ends.)

I have an axle exchange alum driveshaft, Perrin shifter bushing, and whiteline trans insert. Ideally I would be able to bring the trans side closer to -2degrees to match my opposing rear diff +2 however it looks like clearances are already very tight on the transmission side with the diameter of the driveshaft and it almost touching the perrin shifter mount. Any thoughts on potential ways to bring the trans side more in line? Has anyone else take taken pinion angles?

[gpvecchi]

The total ideal difference should be less than 1 degreee, and every side should be less than 3 degree. Your diff is ok, you have to correct the transmission angle.
You have to raise the gearbox, right? You should put a shim between the transmission support and its plate.
Keep in mind that rising the gearbox will change the diff angle too.

[almostquick]

Originally Posted by gpvecchi

The total ideal difference should be less than 1 degreee, and every side should be less than 3 degree. Your diff is ok, you have to correct the transmission angle.
You have to raise the gearbox, right? You should put a shim between the transmission support and its plate.
Keep in mind that rising the gearbox will change the diff angle too.

Agree on the less than 1 degree (opposing) differences. I’ve read that you don’t want to go any further than 5 degrees and that 3 degrees is the optimum.

Yes, ideally I would raise the transmission to be closer to the opposing +2 degrees on the diff end. The issue arises with the fact that I (and I assume anyone else with a alum 1-piece driveshaft) do not have the clearance on the trans side to shim the trans to raise it and get it to -2/-3 degrees, as the driveshaft is almost coming in contact with the rear shifter mount bushing.

As a shear test to see if bringing the two inline will indeed fix the vibration problems we are experiencing, I might try to shim the diff to +5 degrees to be inline with the trans. This is not optimal but at least gets to the answer as to whether pinion angle is the culprit for the driveline vibration many experience.

[FrickingReallySlow]

Originally Posted by gpvecchi

The total ideal difference should be less than 1 degreee, and every side should be less than 3 degree. Your diff is ok, you have to correct the transmission angle.
You have to raise the gearbox, right? You should put a shim between the transmission support and its plate.
Keep in mind that rising the gearbox will change the diff angle too.

So where on the diff should we use as the edge to measure the diff angle? I labelled (A,B,C) the areas where I think it could be close but there's no real guarantee that these edges are 100% parallel to the shaft inside.

I would say using the face of "A" where U-joint bolts to would be the most accurate but that requires removing the driveshaft so the face is exposed.

[gpvecchi]

Tha "A" place. I saw somebody putting a metal ruler "between" the diff face and the driveshaft and then use it as a flat surface.

[almostquick]

Location A. I had just enough surface area even with the driveshaft connected to put an angle finder on the face surface.

[FrickingReallySlow]

Measured my angles, 3.4 in the front and about 3.1 at the diff. One way I think this can be reduced is with the STI engine mounts (perhaps others too). They're used by ppl that has ACE350 headers to raise the engine slightly to clear the big ACE overpipe from subframe. Raising the engine and keeping the pivot point of the trans mount the same would reduce both angles slightly since the tail bushing would now be pointed slightly downward and also start lower in height (reducing the height difference between it and the diff). I guess here a softer trans mount that is more compressible could help (at least statically) since the pivot point would be lowered slightly

[gpvecchi]

I have the STi supports and bushings. They don't raise the position, but they will flex less. The only way to change the angles are shims and spacers.
Did you check the angle of your driveshaft too?

[FrickingReallySlow]

Originally Posted by gpvecchi

I have the STi supports and bushings. They don't raise the position, but they will flex less. The only way to change the angles are shims and spacers.
Did you check the angle of your driveshaft too?

Yeah those numbers are the angles between the engine to driveshaft and driveshaft to diff. I have an aluminum one. using my phone on these edges aren't very accurate (varies by a +/-0.2) depending on slight changes in how I hold the phone. So take it with a grain of salt.

Did you pull the trigger on your Carbon shaft purchase yet?

[gpvecchi]

No, I quitted the idea as I didn't want to spend quite a lot of money to have issues.
Your angles are not that bad, you could try to lower the gearbox support with washers and longer bolts. You need around 1.5 degrees, you shouldn't need big spacers.

[9101]

Originally Posted by Turdinator

I bought my carbon drive shaft used. At first I had horrible vibrations. It took me a few tries but eventually I found a driveshaft shop that both shimmed the uni joints to be centered and added balance weights and its been great ever since. I also have STi engine and gearbox mounts as well as a light flywheel so should be able to feel any new vibrations.

You mind sharing who you used in Melbourne? Also, what this would cost? Cheers

[Turdinator]

Originally Posted by 9101

You mind sharing who you used in Melbourne? Also, what this would cost? Cheers

Indrotech in Hallam. They didn't have the means to attach the balance weights to the shaft so they taped them in place and I had to then glue them on. I got Loctite involved and used their recommendation which worked perfectly. I can't remember what it all cost me though I am sorry.