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Wierd road noise when decelerating

Zman302

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I have a 1998 Ford Explorer Eddie Bauer with the 5.0 and it seems around 55-60 mph, you hear what sounds exactly like road noise, but only does it when your foot is off the gas. It goes away when you hit the gas. It sounds like it’s coming from the front of the vehicle, but it’s kind of hard to tell.
 



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koda2000

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Might be a bad pinion bearing if it makes a noise on deceleration.
 






Zman302

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Yeah the yoke on the rear diff has a fair amount of play in it. I tried tightening the nut down but it’s already tight. And when you turn your head to look out the window, you can clearly hear it coming from the rear of the vehicle while driving. Can I do the pinion bearings with the diff still in the vehicle?
 






koda2000

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Yeah the yoke on the rear diff has a fair amount of play in it. I tried tightening the nut down but it’s already tight. And when you turn your head to look out the window, you can clearly hear it coming from the rear of the vehicle while driving. Can I do the pinion bearings with the diff still in the vehicle?

Technically? Yes, you'll have to empty everything out of the housing to remove the pinion gear. Are you experienced in rebuilding a diff? There's a lot involved, special skills and tools required.
 






Zman302

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It’s got the positraction rear end in it. I rebuilt a ford 9 inch at a vocational school a while ago, I have the general grasp of it, but I don’t think I ever tore apart a positraction one. What kind of tools do you need for those exactly?
 






koda2000

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It’s got the positraction rear end in it. I rebuilt a ford 9 inch at a vocational school a while ago, I have the general grasp of it, but I don’t think I ever tore apart a positraction one. What kind of tools do you need for those exactly?

A posi-traction unit isn't much different than an open diff. There are clutches and plates on each side behind the axle spider gears (no special tools needed there). There is an "S" shaped spring that must be removed and reinstalled, it keeps tension on the clutches. A pair of needle nose vise grips and a hammer is needed to compress the spring and reinstall it (nothing very special needed for that). Other than the above pieces the posi unit is pretty much the same as an open diff. One area you need to be very careful with on the Ford 8.8 is with removing and re-installing the spider gear shaft's small retaining bolt. If you have to, buy a new good fitting wrench for the job If you round-off the head on that puppy (which is not hard to do) your job will be in trouble, though there is a special extractor tool you can buy to try to get it out. I always install a new retaining bolt rather than reusing the old one to minimize causing damage to the bolt head.

The special tools are needed to remove/install the inner bearing from the pinion shaft, which requires a press. You also need a dial gauge to measure the backlash on the pinon gear to the ring gear and shims to get that correct. Getting the shims set right requires pressing the pinion bearing off/on multiple times, checking the wear pattern on the ring gear teeth. Lastly you need to install a new crush sleeve and set the rotational resistance on the pinion yoke, this requires a dial-style torque wrench.

Note: It may be that if you are only replacing the outer and inner pinion bearings you don't need to mess with the shims, just re-install the original shims on the pinion shaft - IDK. Checking the wear pattern on the ring gear teeth will tell you that. There is a special compound you can paint on the ring gear teeth to check the wear pattern, though white grease should also work. If there is any damage to the pinion gear, or its shaft, you will be in for a full diff rebuild, which is more complicated. Sometimes the outer and/or inner pinion bearings can weld themselves to the pinion shaft which can require replacing the diff case/housing. Even if you can get the pinion out of the case if it's damaged you need to replace the ring and pinion gear-set, which requires taking apart the carrier.

Be very careful to keep all parts, clutch pieces and shims in the right order and location for re-installation.

Having a specialist rebuild a diff can cost $1200-$1500. There's a lot to getting it right, but that includes messing with the carrier bearings, which you shouldn't need to mess with.

I suggest you watch a YouTube video on rebuild the Ford 8.8 posi unit to know what to expect.
 






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