Tools used:
Depth micrometer with 2-3 inch rod installed
Precision ground piece of flat stock, 0.250 thick. This has holes drilled at the ends and off center for the depth mic to hit the pinion head.
Dial calipers for measuring the pinion head and shims
An inner pinion bearing that has been honed by a machine shop to be a slip fit on the pinion gear.
Note: Inner and outer pinion races have already been installed in the 8.8 housing. Also, there are a few MHD floating around on the net. By recommendation I'm using the one below (Thanks Lou!).
Variables:
FS = Precision ground flat stock = 0.250 thickness (Known and verified)
MHD = Master Housing Dimension = 4.415
PH = Pinion Head
M = Measurement
ADJ = Adjusted measurement to account for the thickness of the flat stock.
Process:
1. Using the dial calipers, I take measurements of the pinion head. This will include the 'shoulder' that the shims rest on. I measure without any shims. I took about 10 measurements from various different places on the pinion head, then added them all up and divide by 10 to get the average. For me, the average was 1.8745. So PH = 1.874.
2. I installed the slip fit pinion bearing onto the shaft of the pinion gear with no shim and installed this into the rear housing. I give it a few revolutions and a light tap with the rubber end of a hammer to make sure it's seated. I installed the flat stock using some cap screws (the stock main cap bolts are too long) and tighten it down. I made sure that the flat stock and the surface its resting on are clean and free of debris. Using the depth mic, I take a few measurements. Measure, turn the pinion head, take another measurement. I found that one measurement kept coming up. This is the measurement I will use. So M = 2.822.
Here's a pic I took of the setup:
3. Now I can do the math to find out what shim I should add. The goal is to have the result of the math equal to the MHD. For this exercise, I'm not torquing down the pinion shaft until the final install. Because of this, I will add .002 to the final shim thickness to account for everything being torqued down.
Using the variables above, the formula is:
M - FS = ADJ
ADJ + PH = Result
MHD - Result = Shim thickness
2.822 - 0.250 = 2.572
2.572 + 1.874 = 4.446
4.415 - 4.446 = - 0.031
This means I need a shim thickness of 0.031 to raise the pinion head closer to the depth micrometer. This will decrease the measurement value (M) by the shim thickness. Remember I wanted to add .002 to the final shim thickness. So really I want a shim of 0.033. I stacked a 0.021 and a 0.012 shim to make the 0.033. I also made sure the shims were clean and no debris or rust on them.
4. Same as number 2 but this time with a shim of 0.033 added between the pinion gear and slip fit bearing. Take a few measurements. I landed on M=2.789. Time to do the math again.
2.789 - 0.250 = 2.539
2.539 + 1.874 = 4.413
4.415 - 4.413 = 0.002.
This is perfect. I expect to be off by 0.002. That 0.002 will be 'squashed' by torquing everything down during the final install. The squashing will increase M by .002, and therefore the overall result by the same (4.413 + .002 = 4.415) and 4.415 = MHD.
Even with everything I've done here, the contact pattern on the gears (after the final install, add marking paint and rotate to see the contact pattern between ring and pinion) will command if any final shim adjustments are necessary. If they are, I'll be sure to update this post with whatever is needed.
I used this as a reference: M-4209-8.8 8.8 Ring and Pinion Installation INSTRUCTION SHEET
Disclaimer - Please keep in mind that this is just an exercise. This is not how ford recommends installing gears. It is how I was taught and how I've done it the past few times installing gears. If you choose to follow the steps here, you do so at your own risk!
