Driveline vibration

**ls1camino** · 10-08-2011, 12:36 PM

Long story short, I had to replace my u-joint in my stock driveshaft. This gave me a great excuse to install the ACPT Carbon Fiber Driveshaft that was sitting in my garage for over ayear. Now that I have that in, I have a vibration like the driveshaft isn't balanced, but carbon fiber shafts are balanced from the factory. From ACPT's website: "The balance of the job is handled by ACPT's primary distributor, Inland Empire Drive Line Service, in Ontario, CA. Here the driveshaft is fitted with U-joints and yokes, and is balanced. The balancing act differs from that of a conventional shaft since weights can't be welded on. Instead of adding weight, material is ground off the end fittings directly opposite of where weight is needed, until the shaft is in perfect balance." A friend said I may have tightened the end caps onto the u-joint too far and I'm crushing the needle bearings. I doubt that since All I used was a 13mm wrench and an allen key, and I am not THAT strong.

I might also mention that I messed with the rear suspension as well. I did the heater hose mod (removed the rubber disc from the top of the rear springs and replaced it with heater hose wrapped around the top of the spring. I then centered the rear wheels using my adjustable LCAs and PHB. I checked the pinion angle of the torque arm when I was done and adjusted that back to 3* (where it was before the adjustments and the adjustments put it at 1*).

I'm completely lost as to what is going on here.

**pajeff02** · 10-08-2011, 04:43 PM

The stock driveshaft runs a damper -- could be that the vibration had been there all along but was not as noticeable. How bad is it?

**pajeff02** · 10-08-2011, 04:44 PM

You went 3* negative (nose pointing down), right?

**Knight** · 10-08-2011, 06:23 PM

You're running a 9" aren't you, Jeremy? Is the CF driveshaft set for the stock length? I know when I swapped to the 9", it was mentioned that a few people experienced a vibration issue which was resolved by going to a longer driveshaft. I have the same driveshaft, and swapped u-joints for the 9". I don't have a vibration issue, but I'm just wondering if that might be the issue for you.....

**ls1camino** · 10-08-2011, 08:47 PM

Originally Posted by pajeff02

You went 3* negative (nose pointing down), right?

Err...no...3* nose up. I looked it up and I thought it said 3* up angle. Are you sure about that?

Originally Posted by Knight

You're running a 9" aren't you, Jeremy? Is the CF driveshaft set for the stock length? I know when I swapped to the 9", it was mentioned that a few people experienced a vibration issue which was resolved by going to a longer driveshaft. I have the same driveshaft, and swapped u-joints for the 9". I don't have a vibration issue, but I'm just wondering if that might be the issue for you.....

9" has been in for over 2 years. Yes it's a stock length.

As an update, the vibration is gone. I think some driving around worked out whatever it was. Did a 50-140 pull and it was smooth all the way.

**Knight** · 10-09-2011, 04:15 AM

Jeff is correct. You should have the pinion angle set to around -2°. The pinion should be pointing slightly down from the driveshaft.

**pajeff02** · 10-09-2011, 06:36 AM

J -- picture your car taking off from the driver side. The back wheel is rotating counterclockwise and the force of the wheel against the pavement is trying to rotate your axle in the opposite direction -- clockwise -- thereby lifting the nose of your driveshaft. That means that you need a negative angle on the pinion and it should point down.

**ls1camino** · 10-09-2011, 08:25 AM

Originally Posted by pajeff02

J -- picture your car taking off from the driver side. The back wheel is rotating counterclockwise and the force of the wheel against the pavement is trying to rotate your axle in the opposite direction -- clockwise -- thereby lifting the nose of your driveshaft. That means that you need a negative angle on the pinion and it should point down.

Ok, I'll have to fix that then...good thing it's an easy adjustment.