I lowered the truck with the Roush kit and started to get a driveline vibration around 60-65. I searched the forums and the consensus was a bad pinion angle. I finally got around to measuring it and here is what I got:

Angle on pinion (flange) :93.5 degrees

Angle on driveshaft: 91 degrees

So if my reading was correct on the procedure, I am at positive 2.5 degrees!

Now the delimma. I measured a couple of other F-150's and they ALL came in at zero degrees. I know that the preferred pinion angle is -2 to -3 so with that said, if I install a 4 degree shim I will be at -1.5 which is close to -2 but better than zero or I can install a 6 degree shim and get -3.5 which is more than suggested.

So which would you all recommend, -1.5 degrees or -3.5 degrees? I don't plan on using shackles afterall in the back to bring it down one more inch at this time but if I do remove the spare and trailer hitch, the back will come up some more and I may want to add shackles.

Thanks for any advice.

 

just one more question. I am looking at the pinion shims and I put them against my old springs and the head of the bolt sits flush with the shim. This means that the head of the bolt will no longer sit in the mount on the differential. Will this be a problem? I got some longer bolts with the 6" shim kit from Belltech but the head of the bolt is still the same length so I would still have that same problem.

Thanks

 

Just cut some bolts you need to length. The bolts that came w/ some shim's i bought were longer, so i just swapped them out and cut them to lenght. It was either the shims came with the bolts, or the roush leaf's did, i can't remember. Anyhow, i have the roush drop on an 01, w/ 2inch shackles installed in the rear. My pinion angle was looking right at about 0, so i added a 2.5 degree shim. The driveshaft looks at a much better angle than it was before. So using your measurements, plus the shackles i have, i would guesstimate my angle to be at -1.5 or -2. I didnt have an angle finder available, so i pretty much played it by ear. Not exactly how you should do it, but oh well. Let me know what you find.

 

thanks for the reply Derek. It seems as though the bolt that holds the spring in the middle is longer than my factory one so it had enough to hold the spring still even with the spacer. I went with the 4 degree shim and the vibration is gone. The ride is smooth as ever and I also relocated the rear sway bar links (up). That made a HUGE difference in the way the truck handles.

Just thought I would post my results so people doing searches in the future can get some help and not have to go into it blind like I did.

 

could of been the rear sway bar endlinks the whole time

 

well I added some 2" drop shackles to even out the truck and the vibration came back but only at lower speeds. Pulled the truck up and found that my pinion angle was now at -6 degrees from the previous -1.5 degrees. I simply removed the shims to bring me back to -2 degrees.

The sway bar links had nothing to do with the vibration.