High-pitched whine primarily on deceleration

#1

Hi guys, I posted this over on Wrangler Forum and NJ to see what the hives would say. Does anyone have any ideas?

My ’98 TJ (4.0L, 5-speed, Ford 8.8 has developed a high-pitched whine primarily on deceleration. I can occasionally hear it at a steady speed, but it is very faint. I cannot pin point where it is coming from even with the aid of 3 different people. KM2s don’t help here too much. The pitch is very high (and pretty loud) but is right on the edge of hearing range so it is hard to identify. I’m pretty sure it is coming from the rear-end but haven’t ruled out the transfer case. Turning left or right has no impact. It does not do it when the Jeep drivetrain is cold. After a short run down the interstate, it becomes present. It is mainly from 35mph down to 0mph just before you stop. When you apply the brakes as you are stopping, sometimes the noise will dissipate slightly – I’m thinking something is unloading.

What I’ve done (and has made no change):

  1. Replaced my known worn (CY pin was galled) rear DS with an Adam’s.
  2. Changed rear diff fluid (that still looked good and didn’t smell bad, extremely small amount of glitter present – I’d call it normal).
  3. Change TC fluid (old fluid looked OK – still had some pink to it but dark).
  4. Replaced a passenger rear brake caliper that was suspect as sticking (the dust seal was torn and loose).
  5. Front and rear pads are both acceptable thickness (this is not seemingly a brake squeal).
  6. Removed front drive shaft – the noise does not go away.
  7. Removed rear drive shaft and the noise is less prone.

I’m thinking that acceleration pressure from driving is what makes the failing item develop heat and cause the noise. From the reading I’ve done online, it would imply the pinion bearing has lost its pre-load? This is probably starting to hurt the bearings, but I’m still just guessing. I have not put a socket to the nut, but I didn’t feel anything wrong when replacing the DS. I guess that’s my next check. Of all the axle bearings I’ve replaced, they have always growled, and you could make them come and go by turning left and right. I haven’t ruled out the bearings in the TC or SYE. I would assume they growl also.

Please help me out here as this sound and it’s chase is making me crazy!

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#2

I know you think it’s coming from the rear, but let’s go outside the box for a second. Pulleys and belt are in good shape?

Back to the rear, have you checked the parking brake? Those shoes could be dragging and causing a noise. Not sure how that works on the 8.8 though.

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#3

Thanks for the input James.
Brand new belt (2 months) and alternator. Pulleys are fine and not squeaking/squealing. Also, you must be moving to have the noise.
Ford 8.8 works as you think it would. Disk pads and manual ebrake shoes inside the disk. I have removed and inspected the pads and ebrake shoes and they seem to be fine - within spec. The Ebrake play is correct also. I am/was a little leery of the caliper I rebuilt, but i think I trust it now. I did put a temperature gun on it this morning after leaving my house in Lorton, going down 95 and stopping at Wawa on Caton Hill/Minnieville road. This would be a few high-speed stops and it was making the noise at this point. The air temp was already 78d. The temp gun only read about 125d on both sides meaning they are at least equal (one isn’t sticking). The pinon area on the rear was at 122d and the SYE housing was at 120d. The axle bearing areas were at about 95d both sides.

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#4

wheel bearings?

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#5

I think I figured it out. Drivers side carrier bearing race had a funny pattern on it. Perhaps the race was not 100% seated. It was nothing you could feel, it just looked like a different sheen and was starting to leave little radial marks like when you draw sun rays in a cartoon. I replaced the races and the pinion bearings and races for good measure. Of course I had to reset backlash and pinion preload. We’ll see, it made no noise yesterday or today coming to work. It was sure hot in the driveway doing this.

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#6

Cool, hopefully you solved the problem.

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