This past week I installed a pair of 2" Belltech drop shackles on the back of my 2001 SCrew. Love the look of the lowered rear and leveled truck. Here's my problem though. After the installation, I drove the truck on the interstate and immediately noted a harmonic vibration when the truck exceeded 50 mph. Under 50 it was fine. The issue concerned me so much that I later removed the drop shackles and re-tested the truck over 50 mph on the interstate. With the shackles removed, I no longer had the noise.

How do I get rid of the harmonic vibration with the drop shackles installed so I can keep the improved look of the lowered rear?

 

I have a 2001 myself and had 2" shackles on my truck before I droped it even more. I did not have any problems with the harmonics at any speed. I have also put 2" shackles on a number of Ext. Cab F-150 and Supercrews and have not experienced any problems on those either. Have you Checked your U-joints? or loose bolts? 2" should not make enough of a difference on the pinion to affect the pinion but if you can't solve your problem...then maybe you should go with a set of pinion spacers to readjust you pinion angle...sorry for your luck

 

BigDeal, check the post below for some helpful info on your problem.

HiO


https://www.f150online.com/forums/sh...threadid=86469

 

We had the same problem on our 2001 Supercrew. Installed a set of 3 degree shims and took the problem away.

 

BigDeal,

Had same experience as you, 2002 SuperCab looked great w/
2 inch rear drop but vibration was quite noticeable. Shims no
help, removed shackles. Stock ride much better.

 

Most people use 2 Degree shims. This is what Belltech recommends as well. Some have just reversed the factory shims.

 

2 degree shims didn't work for us. Could still feel some vibration. So we went to 3 degree shims and vibration all gone. There is no fixed answer for each truck. Some don't seem to need them. Some use 2's and some need 3's. And some people just let it go untill the u-joints seem to settle in to the new angle. We didn't want to take a chance with ruining new u-joint and driveline.


good luck

 

Norm... Actually, when I contacted Belltech's tech support group, they had no recommendation for me as to a shim solution. His suggestion was for me to go measure my angles, order what I thought would resolve the issue and give it a try. I chose not to perform the trial and error approach and have since returned the shackles. Guess you can't have everything.

 

I guess it depends on who you talk to at Belltech. They told me 2 degrees. They even gave me the part number for the shim #4975.

 

Put the shackles back on, and drive it for two weeks!

I put Bell Tech shackles on my screw when it was less then a week old. I noticed the harmonic vibration the next day, but I said, Hell it's under warranty, if it breaks, they fix it.

Within a week of driving daily, the universal joint wore in at the new angle and the noise went away.

Put the drops backon, there's nothing uglier then a Pick em up truck, with the back end stickin up in the air.