Ford 8.8 IRS Diff Rebuild (DIY)

• Ford 8.8 IRS Diff Rebuild (DIY) by Schitzo on 16 May, 2014 16:18
• I reuploaded the pictures here:
  http://s412.photobucket.com/user/Project_E57/library/Ford%20Diff%20Build?sort=3&page=1
  
  I rebuilt my 8.8 late last year and figured I would make a DIY out of it. This is not the only way to go about rebuilding an IRS 8.8 but just one of the many ways to go about it. I prefer Ford OEM gears over the aftermarket offering as they have a lower tendency to whine, assuming they are setup correctly. For the rebuild parts, I use Timken bearings coupled with Ford OEM seals.
  
  First off, I made a holder for the diff housing. This makes the rebuild much easier
     
  
  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 - 90 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. Time to tear everything apart and establish pinion preload.
  
  
  
• #1 by Schitzo on 16 May, 2014 17:36
• Once the desired backlash and gear pattern were obtained, I set about setting the pinion preload. The old crush sleeve dimension provides a good starting point. Mine measured 0.4460" so I setup the solid collar as close to this dimension as possible. I managed to get it to 0.4470". The collar I used is made by Yukon and is a two piece design. Shims are placed between the two pieces and this is how the desired collar thickness is achieved. The collar is installed onto the pinion which is then installed in the housing and the pinion nut is torqued to 130 foot pounds. The pinion preload is then measured using an inch pound beam type torque wrench. The carrier is off the housing while pinion preload is measured. With the collar at 0.4470", I got a pinion preload of 17.5 inch pounds. Ford's spec is 16-29 inch pounds.
  
  While 17.5 inch pounds is within spec, I wanted to get it a little tighter so the shim stack was decreased to give a total height of 0.4435". This gave a preload of 24 inch pounds which I like.
  
  
  
  
  
  Finally, I adjust the thickness of the carrier shims until I have the desired total preload. I ended up with 0.2745" and 0.2690" for the driver and passenger side shims respectively. It is recommended to spread the case in order to slide the shims into position. The passenger side shim stack is installed by hand then the driver side shim stack is installed using an aluminum drift after the case is spread. The case must be spread no more than 0.030". I spread mine to 0.025" then installed the shim stack using a rubber mallet and aluminum drift.
  
  carrier shims installed
  
  
  Next the carrier caps and side seals are installed and and final specs are checked. Backlash and the gear pattern remained unchanged and final total preload was measured at 32-33 inch pounds at the yoke. She's done!
  
  
  
  
  
  
• #2 by digitalsolo on 16 May, 2014 22:23
• Sticky'ing this one...  nice job!
• #3 by quinns on 17 May, 2014 00:50
• Great write up!
• #4 by frijolee on 17 May, 2014 03:03
• Great write up.  Clear and concise.
  
  The thing I liked most about doing this myself was just getting a better understanding of what all is going on in there and seeing how small changes affected the gear pattern.  The thing I liked least was all the custom tools required.  Like you I ended up making several tools myself (case spreader was the big one).
  
  My experience:  http://www.norotors.com/index.php?topic=1274.msg226366#msg226366   (Starts in post 286 if the direct link acts weird).
  
  Did you end up using shim stacks for the main shims or ordering specific sizes?  If the later, where did you get them?  I got lucky and my former solid shims were perfect.
  
  BTW...  What kind of red was on the menu for the first picture?  Also, I'm impressed with your tool collection (Snap-On, Starrett, etc).  You're working with some nice stuff.  Are you a professional or just serious hobbyist? 
• #5 by Schitzo on 18 May, 2014 23:13
• Joel, I assume by "main shims" you are referring to the carrier shims. If so, I used a set of stepped shims made by Yukon. They comprise two large discs between which the shims are sandwiched. This ensures the shim stack does not back out once the cap is installed. They cost the same as 1 Ford OEM shim. I highly recommend them (see the pics below)
  The drink is a Stout, Kalamazoo stout by Bells out of MI. Good stuff . 
  
  
• #6 by danny_6725 on 19 Feb, 2015 10:51
• I know its out of topic, but where do you guys usually find your 8.8 rears? junk yards?
• #7 by bikedad on 19 Feb, 2015 11:31
• Quote from: danny_6725 on 19 Feb, 2015 10:51

  I know its out of topic, but where do you guys usually find your 8.8 rears? junk yards?
  

  
  Got my 2005 Explorer diff with axles for $275 from a local "Used Parts Distributor". Kind of like a junkyard but deals mostly with late model parts.
  Most of these places are on a nationwide network of used parts distribution. The place I went to actually had the totaled Explorer sitting on their lot so I was able to look at it before buying it.
  I didn't care what the internals were as I was replacing everything with Ford Racing components anyhow. I used the carrier and axle inners. Discarded everything else.
• #8 by largeorangefont on 19 Feb, 2015 11:51
• Yes. That or craigslist or Ebay. I got mine on ebay.
• #9 by danny_6725 on 20 Feb, 2015 12:57
• Yeah I haven't had any luck on craigslist, i'll try ebay and check local junkyards!  Thanks for the response to both you guys 
• #10 by Schitzo on 28 Feb, 2015 14:30
• I use www.car-part.com to search local junk yards.  Mine was out of a Mark VIII and cost ~$60.
• #11 by largeorangefont on 28 Feb, 2015 14:57
• There are a few on eBay now for between $250 and $350 shipped.
• #12 by ebdyguy on 28 Feb, 2015 15:03
• I was going to do the rebuild myself and this would have helped greatly with that.  But after looking at all the special tools required I will probably try to find a good shop somewhere close to me.......  UNLESS you guys with the tools want to rent them to help out your fellow forum members   
• #13 by fd3sls3 on 26 May, 2015 21:51
• It's amazing to me of the amount of shops that don't use a case spreader.  I won't mention names, but it was kind of appalling.  It has forced my hand to just do my own.  Did you make your own spreader or buy?  Any info would be greatly appreciated.
• #14 by ebdyguy on 27 May, 2015 09:22
• I have found the same thing !  Many of the shops I have gone to claim to regularly work on the aluminum 8.8 case as well as other similar units and do not use a spreader.  Some of these were high end shops.  I am still looking for someone I can trust with this.  I made a spreader of my own to get the carrier out of the housing and that worked well.  But there are several other tools that I don't have so still not jumping in to try the complete rebuild myself.  Still trying to find someone local to do the rebuild for me.