How to Rebuild a Ford 9.75″ Differential

This rebuild was performed on a 2006 F150 Crew Cab 4×4 with a 9.75″ limited slip differential.  The differential was full of metal particles and burnt gear oil.  Start by lifting the rear differential off the ground and safely supporting it.  Remove both rear wheels.

IMG_0750IMG_0754Remove the brake caliper and support it.  Remove the brake rotor.
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Remove the differential cover making sure to have a drain pan underneath to catch the old gear oil.IMG_0751 IMG_0752
Remove the rear drive shaft and lay it off to the side.  Even though this is a complete rebuild, I still have the habit of measuring the remaining pinion threads as a reference and taking a sample of the old gear oil.

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IMG_0765 IMG_0766 It had gotten so hot inside that it cooked the gear oil onto the main bearing caps to the point that the gear oil peeled off like paint.IMG_0767

Remove the pinion shaft retaining bolt and the pinion shaft.  The pinion shaft is what centers the spider gears in the case.  This is after I’ve cleaned it with brake cleaner trying to minimize the metal slivers in my hands.IMG_0768 IMG_0772

Press one drive axle at a time toward the center of the differential and remove the C-clips, as shown in the picture, from the end of each drive axle (there should be a rubber o-ring underneath/beside it that helps hold it in there).  Then slide the drive axles completely out of the differential.  At this time it is wise to measure the ring and pinion gear backlash as shown in the bottom right picture.IMG_0771IMG_0774

 

 

Remove the bearing caps (total of 4 bolts and 2 caps) while keeping a hand on the differential case (never had one fall out after I’ve removed the bearing caps but it’s still a good idea).  Then use a pry bar or large screwdriver to hold the bottom of the ring gear while using an end wrench to rotate out one of the bolts holding the ring gear onto the differential case.  Once it initially breaks free you can usually pull it out by hand without further using the tools.  Make sure to not let the shims installed on the sides of the carrier bearing races fall out.  Once removed measure each shim and write down the measurements and what side it was on.

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This is a picture of the differential case with the ring gear and ABS toothed ring still attached, the carrier bearings still pressed on, and the side gears and spider gears still inside.IMG_0777

Even though we’re replacing the entire differential case, or carrier, I still thought it would be a good idea to show how easy it is to remove the carrier bearings with the Yukon bearing puller kit.IMG_0778 IMG_0779 IMG_0780

Even though we are replacing the entire carrier assembly we still needed the ABS ring which has to be transferred over to the new carrier.  The below picture shows the bolts taken out of the ring gear after I had marked the original location of each piece with a yellow paint marker (probably overkill to mark these parts as most have indicators but it’s a habit).  Remember to use high strength thread locker on ring gear bolts and make sure the threads and holes are clean before installing.  Also when installing the new ring gear tighten the bolts in a star pattern.  Sometimes installing a new ring gear requires a little persuasion.
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Next, remove the pinion nut, pinion flange (also called pinion yoke), and oil slinger (looks like a large flat washer).  These sometimes come off with a light tapping on the backside with a rubber mallet, but if not, you can use a pinion flange removal tool.
IMG_0784At this point the inside of your differential should look like this.  Even though we’re not reusing the pinion we still need to remove the pinion shims located under the pressed on pinion bearing.IMG_0785 IMG_0786In this case the Yukon tool would not remove the pinion bearing (some pinions you can use it but not on this 9.75″) so we used a bearing removal tool and then placed it in our press.  MAKE sure to remove the old pinion shim as you will reuse it when setting up the new pinion depth.  In most cases, when rebuilding a differential back to stock you can reuse the original pinion shim without having to measure for pinion depth.
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Here is the revised Ford 9.75″ pinion with the much larger crush sleeve.IMG_0789 IMG_0790

I prefer to place the old pinion shim on the new pinion, press on the new pinion bearing, and install the new crush sleeve at this time. A helpful trick to make the new bearing press on easier is to leave your pinion in the freezer for at least 30 minutes before you’re ready to press on the new bearing.

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Go ahead and remove the outer axle bearings and seals with the bearing removal tool shown in the pictures below.

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Here is a few pictures of the differential housing stripped.

IMG_0796IMG_0800 It took me over 2 hours to get the metal slivers/shavings out of this differential but it is extremely important to remove all metal particles and other contaminants before putting it back together.

Drive out the inner and outer pinion bearing races with a punch and hammer.  Install the new inner and outer pinion bearing races using a bearing race installer tool.  After installing the races, I like to go ahead and coat the races with the gear oil I’ll be using in the differential.  

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Install the pinion seal (I prefer to coat the outer edge with high temp silicone before installing it) making sure to re-install the oil slinger first.

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A couple things:  coat the inner and outer pinion bearings in gear oil and coat the inside lip of the pinion seal with Vaseline before installing the pinion and pinion flange.  Sometimes when installing a pinion yoke you’ll have to have a helper hold the pinion in place while you tap on the face of the pinion yoke with a rubber mallet or a block of wood and hammer in order to get the pinion nut started a few threads.  Once the nut is securely started on the threads, hold the pinion yoke in place using either a large pipe wrench or yoke holding tool and begin tightening the nut.  This takes quite a bit of muscle doing it by hand.  I prefer to use an impact wrench until the bearings are seated and there is no endplay. Then I will slowly continue tightening the nut, checking often with an inch-pounds torque wrench, until the proper pre-load is reached.  Guys who have been rebuilding differentials since before I was born vary in what they believe to be ideal for the pre-load, everything from 16 to 29 inch lbs., but I prefer 24 inch lbs.  Remember that when you’re measuring the amount of force it takes to rotate the pinion, initial rotation will naturally be higher so you’ll want to watch the dial while it is rotating for correct rotational force.  
IMG_0807After the pinion is installed you’re ready to install your assembled carrier remembering to lightly tap the shims into place while installing it.  Do not use a steel punch as this can sometimes crack the shims.  Shim install tools work best but a brass drift works well also.  Tighten the bearing caps to the proper torque.

 

 

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IMG_0809Before installing the axles you’ll need to check two things:  the pinion backlash using a dial indicator and the pinion to ring gear pattern.  A picture of using a dial indicator was shown early in this article and is easy to read as long as you remember your readings are in thousandths.  As for verifying the correct teeth pattern, start by applying marking compound to at least 4 consecutive teeth on both sides of each tooth.  Then, rotate the pinion yoke while applying light drag to the ring gear until the painted gears come in contact with the pinion.  If you put too much compound on the ring gear teeth (as shown in the picture) you may have to work it back and forth a few times to get a clear pattern.  One of the best indicators of a good pattern is if the pattern position is centered between the face (top of each tooth or top land) and the flank (base of each tooth or root).  Whether or not the pattern is more toward the heel or toe of each tooth is not always a good indicator to go by.
IMG_0814 Once you’ve verified your backlash and teeth patterns are good and no further shim adjustments are necessary, it is now time to re-install your axles making sure to apply Vaseline to the outer seal lips and ensure the C-clips are installed correctly before sliding in and tightening the pinion shaft.  Also, re-install the driveshaft making sure to apply Vaseline to the front yoke before installing it into the transmission.
IMG_0815By this point you’re ready to re-install the differential cover using either sealant or a gasket, and then fill the differential with the required weight, type, and amount of gear oil needed.  It is a good idea to take the initial test drive to verify there are no abnormal noises coming from the differential and to begin breaking in the new gear set.  Remember, heat is the new gears #1 enemy so it is wise not to place a heavy load on the new gears for at least 500 miles (e.g. pulling a trailer, racing, 4 wheeling, etc.).  Also, it is a good idea to replace the gear oil after the initial 500 miles break in period.  Congratulations for all your hard work, time, and energy you put in, and your willingness to try something new!

6 thoughts on “How to Rebuild a Ford 9.75″ Differential

  1. “At this time it is wise to measure the ring and pinion gear backlash as shown …”
    I’ve located the tool but am uncertain if I move the pinion gear or whay to determine backlash, and what amount is acceptable.
    Otherwise, your expose is saving my ’01. THX!!!

  2. Chainge yhe break-in oil? Glad you said that. Every time I do any rear end work and find no drain, I add one to the cover. (Don’t crush the washer, if it’s teflon.) DO remember to loctite the interior nut! And you must use 2 wrenches to remove tbe drain plug, but if you add this drain, YOU will remember and teach your heirs what they must remember. Sadly, these sometimes do not come with a magnetic plug. I dislike using the type that don’t require welding/brazing but I will use them over not adding a drain. Some say map gass will braze a drain while mapp+oxy is too hot but others say the oxy mapp is required. I prefer paper and Permatex #2 over rtv’s, being old school, but I want a drain…! ;>)

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