I rebuilt my 8.8 a few months ago and thought I would share. I'll paste my post from another forum.
Be aware there are two types of Ford gears, face hobbed and face milled. The new Ford OEM gears are all face hobbed. Adjusting the gear pattern is different depending of which gear you are using. The PDF below shows how to determine the gear type and how to adjust the pattern.
http://www2.dana.com/pdf/5717.pdf
The 8.8 IRS differential is relatively easy to rebuild. The pinion depth is adjusted using a shim that sits beneath the inner pinion bearing and the backlash is adjusted using shims that sit between the carrier bearing race and the housing. Ford uses a crush collar to set the pinion preload but I will be using a solid collar with shims. As with any differential build, the gear pattern and backlash are the key determinants of a properly installed gear set.
Before tearing the diff apart, the backlash, pinion preload, gear runout, and gear pattern were checked just to get a good baseline. Next the diff was torn apart and cleaned. I did this back in 2010 and have since lost the pictures I took.
For the rebuild, I started by fabricating a diff fixture. It allows the diff to be rotated 360 degrees and held at any point.
First, the two pinion races and carrier bearings are pressed on. Ensure the races are completely seated down otherwise you would have issues adjusting the pinion depth. Care should be taken to ensure the races are installed straight otherwise they may damage the aluminum case.
The ring gear, pinion gear, and carrier are then prepared for assembly. A file is used to remove any burrs that may be present on machined surfaces. Running your finger on the machined surface easily picks up any burrs that may be present on these surfaces. The filling is light and minimal. Finally, the surfaces are cleaned using solvent.
Before the ring gear is bolted onto the carrier, I install the carrier onto the housing and check for the diff runout. The Ford spec here is max of 0.003". Anymore runout and the housing is not usable. My run out was just shy of 0.001" which is well within spec. The carrier is installed using shims that a 0.006" thinner than the original shims. This allows the shims to slide right in without any force.
The ring gear is then installed onto the carrier and bolts torqued to 80 foot pounds. Red loctite is required on these bolts. At this point, the carrier is ready for install. Time to prep the pinion gear.
Before the pinion bearing is pressed on, a pinion shim must be installed on the pinion. I started with the original shim that came with the housing. It is a 0.028" shim. The bearing is then pressed on. I made a press tool by welding the a pipe onto the inner race from the old pinion bearing.
At this point the pinion gear is installed into the housing and the pinion nut is torqued to give 20 inch pounds of torque. The carrier is then installed. The carrier shim thickness is selected by subtracting ~0.006" to 0.007" from both the original left and right shims. This allows the shims to slide in easily. The backlash and gear pattern are then checked. The initial setup resulted in 0.015" backlash and pattern as shown below. Ford's spec for backlash is 0.008"-0.015". While this backlash of 0.015" is within spec, the pattern is not as it favors the heel. Ideally, the pattern should be centered, heel to toe, therefore I need to move the pattern towards the toe.
On face hobbed gears such as this, in order to move the pattern toward the toe, you have to decrease the backlash. I prefer a tight backlash therefore I shot for 0.008". That means I needed to decrease the backlash by 0.007". Per Ford's documents, this would require a 0.010" change in shim thickness. I chose to go with a 0.008" shim change. This means the driver side shim was increased by 0.008" and the passenger side shim was decreased by the same amount. This worked out perfect. It resulted in 0.008" backlash and a much better pattern. The pattern is centered heel to toe as well as root to top. I'm happy with this pattern.
more to come
Be aware there are two types of Ford gears, face hobbed and face milled. The new Ford OEM gears are all face hobbed. Adjusting the gear pattern is different depending of which gear you are using. The PDF below shows how to determine the gear type and how to adjust the pattern.
http://www2.dana.com/pdf/5717.pdf
The 8.8 IRS differential is relatively easy to rebuild. The pinion depth is adjusted using a shim that sits beneath the inner pinion bearing and the backlash is adjusted using shims that sit between the carrier bearing race and the housing. Ford uses a crush collar to set the pinion preload but I will be using a solid collar with shims. As with any differential build, the gear pattern and backlash are the key determinants of a properly installed gear set.
Before tearing the diff apart, the backlash, pinion preload, gear runout, and gear pattern were checked just to get a good baseline. Next the diff was torn apart and cleaned. I did this back in 2010 and have since lost the pictures I took.
For the rebuild, I started by fabricating a diff fixture. It allows the diff to be rotated 360 degrees and held at any point.
First, the two pinion races and carrier bearings are pressed on. Ensure the races are completely seated down otherwise you would have issues adjusting the pinion depth. Care should be taken to ensure the races are installed straight otherwise they may damage the aluminum case.
The ring gear, pinion gear, and carrier are then prepared for assembly. A file is used to remove any burrs that may be present on machined surfaces. Running your finger on the machined surface easily picks up any burrs that may be present on these surfaces. The filling is light and minimal. Finally, the surfaces are cleaned using solvent.
Before the ring gear is bolted onto the carrier, I install the carrier onto the housing and check for the diff runout. The Ford spec here is max of 0.003". Anymore runout and the housing is not usable. My run out was just shy of 0.001" which is well within spec. The carrier is installed using shims that a 0.006" thinner than the original shims. This allows the shims to slide right in without any force.
The ring gear is then installed onto the carrier and bolts torqued to 80 foot pounds. Red loctite is required on these bolts. At this point, the carrier is ready for install. Time to prep the pinion gear.
Before the pinion bearing is pressed on, a pinion shim must be installed on the pinion. I started with the original shim that came with the housing. It is a 0.028" shim. The bearing is then pressed on. I made a press tool by welding the a pipe onto the inner race from the old pinion bearing.
At this point the pinion gear is installed into the housing and the pinion nut is torqued to give 20 inch pounds of torque. The carrier is then installed. The carrier shim thickness is selected by subtracting ~0.006" to 0.007" from both the original left and right shims. This allows the shims to slide in easily. The backlash and gear pattern are then checked. The initial setup resulted in 0.015" backlash and pattern as shown below. Ford's spec for backlash is 0.008"-0.015". While this backlash of 0.015" is within spec, the pattern is not as it favors the heel. Ideally, the pattern should be centered, heel to toe, therefore I need to move the pattern towards the toe.
On face hobbed gears such as this, in order to move the pattern toward the toe, you have to decrease the backlash. I prefer a tight backlash therefore I shot for 0.008". That means I needed to decrease the backlash by 0.007". Per Ford's documents, this would require a 0.010" change in shim thickness. I chose to go with a 0.008" shim change. This means the driver side shim was increased by 0.008" and the passenger side shim was decreased by the same amount. This worked out perfect. It resulted in 0.008" backlash and a much better pattern. The pattern is centered heel to toe as well as root to top. I'm happy with this pattern.
more to come
Last edited:
