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Ford 9" new gears, pattern check help


This is my first time ever doing gears.

I have a 9" out of a 79 Bronco with a new Yukon Nodular Iron Pro N-Case (3.25 bearings), Nodular iron daytona pinion support, and 5.14 gears all from quick performance.

I have 0.007-0.008 backlash, 26in lbs on the pinion, and these are my patterns.

I started with a .020 shim and got this pattern

so then I added a .015 and .010 to bring it to 0.045 and got this pattern

Then I removed the 0.10 and brought it to 0.035 and this is where I'm at now

Does this look alright or should I remove the .020 and replace with a 0.012 to bring it down to 0.028 total shim pack and run another pattern?

Bert is my name

Well-Known Member
You should check in more than one spot. With the ring gear loaded.i use a pry bar to put drag on the case. Check ring gear run out with a dial indicator too. These will affect pattern. Set pinion depth first. This is kind of a fixed measurement needs to be correct. Then set backlash. Then check pattern as described. Properly setting the bearing preload and gear set takes some specialized tools. Summit sells most of the tools. I've gotten by a few times but usually get noisy gears or bearing failures by not taking the extra steps to make it right. Pinion depth looks wrong to me.

Bert is my name

Well-Known Member
Buy the pinion depth tool from summit or one of the other diff shops. Diffs look easy but your measurements are in 3 dimensions so one change will affect the other. The fastest way to a proper setup is to know pinion depth is correct. Then you check ring gear runout.if this is excessive a new set of gears or machining may be required. Then set gear lash. Smack the housing with a hammer. This will change lash settings and bearing preload. Re check lash. Adjust as necessary then check pattern.

Bert is my name

Well-Known Member
Most dealerships and shops charge around 8 hours of labor to set up a diff. This isn't an afternoon thing for a guy who doesn't do this daily.


Well-Known Member
Your first pattern looks pretty close for a 9310 gearset. Maybe .005" more shim and reset backlash.


Well-Known Member
first one was alright, pinon looked a little bit shallow but its still not that bad. as the gear loads and deflects the pattern will move up the gear face. basically what you had originally on the drive side but centered a little bit more is ideal. run the least ammount of back lash within spec aka the tighter the better.

jon coleman

Well-Known Member
first look good.if any thing more load on heel better than toe, its a little more noise, but stronger area of r g