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Ironmike, Ford Technician
Category: Ford
Satisfied Customers: 3377
Experience:  30 years ASE Master tech L1 . Ford master
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After changing the rear diff. Fluid, we hear a random noise.

Customer Question

After changing the rear diff. Fluid, we hear a random noise. Changed fluid again and added the ford modifier with same results????
JA: The mechanics have tons of experience in that area. Are those all of the "symptoms"?
Customer: Yes
JA: Anything else I can tell the Ford Mechanic before I connect you two?
Customer: Not really, it's very confusing
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Submitted: 6 months ago.
Category: Ford
Expert:  Ironmike replied 6 months ago.
greetings,could you tell me what model ford you have and if it is 4x4. could you try to describe when the noise occurs better. Like on turns, on acceleration, over bumps. is the noise a buzz, grind, chatter and are vibrations felt and where.was the noise there before the fluid was changed? what did the fluid look like?
Customer: replied 6 months ago.
99 explorer xlt awe 5.0 L, the noise is random and under acceleration. We did not have the noise prior to changing the fluid. The fluid was the original and very low because if a leaking cover
Customer: replied 6 months ago.
After eating my response, just to clarify, it's an all wheel drive
Expert:  Ironmike replied 6 months ago.
what fluid did you use and how much modifier? did the fluid show signs of metal? how is the transfer case fluid?are the tires all with 1/4inch in outside circumference? if the clutches needed new fluid and modifier to grab it could be causing the sound from somewhere else. The best method to isolate or pin point a drive line noise would be on a lift. 4x4 drive line noise even harder to locate with no lift. bear with me on the questions
Expert:  Ironmike replied 6 months ago.
sounds will travel through the drive shaft
Expert:  Ironmike replied 6 months ago.
could be chatter from the limited slip clutches. tag on the differential will have a L if it is limited slip. carrier has to come out to replace the clutches.
Customer: replied 6 months ago.
Our explorer is an automatic, our tires only have about 15,000 miles on them. I used Lucas 75 / 140 sun with 4ozs. of ford modifier. The old oil had some signs of metal, not to bad though with 200k miles. Transfer case oil is good with no signs of metal or discoloration.
Expert:  Ironmike replied 6 months ago.
does the noise change if put in 4x4 high or low?
Expert:  Ironmike replied 6 months ago.
​FORD site is down. does it have a 4x4 switch?
Customer: replied 6 months ago.
It's all wheel drive, there's no switch to change to high or low. I'm not sure about the tag containing the "L". The wife has the truck out so can't check it now. Still don't understand how a fluid change could create the issue unless your using the wrong fluid. The other Tag says to use 75/140 syn.
Expert:  Ironmike replied 6 months ago.
other tag will show gear ratio and L if limited slip. 200k, WOW. I would try to add one more modifier. could be the clutches. 200k is way to many miles to have never changed the fluid. I would be surprised if the pinion or carrier bearings are shot. you can disconnect the driver shaft at the rear differential and check the pinion for play. chake sure the wheels are chocked. you can see if there is excessive play up and down and how much back lash(turning the yoke back and forth) to see if there is too much wear between the pinion gear and ring gear.
Expert:  Ironmike replied 6 months ago.
I do not think the wrong brand fluid would do this. either the clutches or bearings if the noise is from the rear differential
Customer: replied 6 months ago.
There's no "L" on the gear ratio tag, only the type of fluid needed. I did not put the modifier in the first time the fluid was changed because the tag didn't identify the "L". The noise was present and ford said it was because no modifier was added. So I changed the fluid again with the modifier and had the same results. I did check the pinion and bearings, no sign of excessive wear. Don't know how to check the clutches, this is why I need help. Thanks
Expert:  Ironmike replied 6 months ago.
there are supposed to be 2 tags on the differential. one for fluid type and the other for gear ratio and if limited slip.clutches would be checked on turns, rear axles have to turn at different rates. That is why slip or limited slip is needed. one turns with bad clutches they chatter or if really bad no drag or slip is felt.if you have the vin number I can check if it has limited slip
Expert:  Ironmike replied 6 months ago.
still waiting on the ford site, it is down now
Expert:  Ironmike replied 6 months ago.
lets make sure it is limited slip
Customer: replied 6 months ago.
Ironmike, there is 2 tags on the diff, one has some numbers, not sure if the L is on it or not, the other is the fluid type with no L. The only time the noise is heard is under excelleration and again very random. There's no noise when making turns. Can't check the vin until the wife returns later today.
Expert:  Ironmike replied 6 months ago.
ok. let me know the vin# ***** she gets home
Customer: replied 6 months ago.
Ironmike, vin # *****
Expert:  Ironmike replied 6 months ago.
ok, you have 3.73 gear ratio. they show a long list and it is possible you have limited slip. they do not make it clear weather that is an option or you have it.if it has the tag I would try to add more modifier, in any case the bearings probably are allowing the pinion and carrier to move too much. I have seen this with vehicles with miles like you have. too much backlash.

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