Driveline vibration
 

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 a year. 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. 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.

Lowering it slightly by replacing the cushions with heater hose means you need to re-measure driveline angles and re-establish correct pinion angle.

I did, I adjusted it back to between 2* and 3*.

Where is your vibration occuring? Does it get worse with speed? If it's at one particular speed/gear...then you need to re-look your driveshaft. If it gets worse with speed, especially above 70mph...then look at your rear tires. An out-of-balance (or bent) rim will create havoc at speed. I know, I had a warped rear rim. Couldn't see it, but it showed up on the balancer. The car was stable to 80mph. By 120mph it was unbearable. I ended out replacing the wheel to fix the problem.

It was fine yesterday before I did this work, so I'm fairly sure it's not that. Thanks for the response though.

I'm going to call around on Monday and see if there are any places around me that can balance a DS.

Won't be the same ideal angle after lowering.

You changed two things. Vibration started.

Put the old driveshaft in and if the vibration is still there, refer to post #2.

Did you check the angle of the tail shaft to the driveshaft. I had a vibration that would occur when I would back off of the gas. Played with the shims on the transmission and zero'd out the tail shaft to drive shaft angle and got rid of most of it.

A Suggestion
 

Hello Everyone,
This thread popped up and I would like to offer a suggestion. I am President of Inland Empire Drive Line Service and so am concerned about this situation. It has been a very long tiime since we have heard about a carbon fiber shaft vibrating.

If this unit is held to the pinion yoke by u-bolts, the propper (17 foot pounds) torque on the nuts is equal to a flatened lock washer plus 1/8 turn beyond. One does not have to be Tarzan to over do that.

If putting the original shaft back in the car solves the problem (assuming the u-bolt torque did not) please don't knock yourself out hunting up someone to re-balance it. Just call Robert or Jeff at 800-800-0109 (Pacific Time) and tell them your story. We will be happy to check the balance and return the shaft to you.

Also, look at the fit of the carbon shaft at the transmission slip yoke and output seal before you remove it. Then look at the OEM shaft fit. This could tell us all a lot.

Greg

Thanks for stepping up with that, Greg.