View Full Version : Help, what causes...

03-25-2007, 08:34 PM
Hey All,

What typically causes excess wheel lash?

I'm making a very uneducated guess that my ring and pinion need to be re-shimmed. Whatever it is, it seems to be getting worse. I don't feel any slop in the universals but you can rotate the drive shaft by hand several degrees in either direction.

I'm afraid that I'm going to tear out the rear end one day.

Any help will be greatly appreciated.

03-30-2007, 09:30 AM
There are two things that I would check.

First, be sure that the pinion nut is tight. I had the pinion nut come loose on my old F150 and it caused the issue that you speak of. I would not necessarily think that the pinion nut is your problem, though, as I have never heard of anyone else having that same problem. If the nut is loose it needs to be tightened until the pinion can be rotated with a certain amount of torque. I can't remember the actual number, but if you need it, I can find it.

Second, you should check the backlash between the ring & pinion gears. This requires removing the differential cover and mounting a dial indicator (a magnetic indicator base is the easiest method) on the housing so that you can touch it off of the face of one of the ring gear teeth. Ford Racing 8.8" gears call for a backlash measurement of .008" to .012". If the backlash is wrong, you will need to remove the differential and re-shim it until the backlash is within the acceptable range. If your backlash is out of spec, the gears usually generate enough noise to indicate that something is wrong.

Hope this helps.


03-31-2007, 12:02 PM
Thanks for the input. I was thinking about taking the cobra back to the shop that installed the 4.10 gears a few years back. Now I know I will. Maybe they will float me a little discount (fingers crossed).

04-01-2007, 10:39 PM
If the job was done right, there should be no need to re-shim in order to adjust the backlash. One mistake that some people make is that they do not pre-load the carrier bearings by installing extra shims (If I remember correctly it about an extra .006" of shim). This ensures that the backlash between the ring and pinion will not change after the bearings are run for a while.

Good Luck.