Rear Axle on Work Truck


backporch

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I have a 99 4.0 4wd with the 8.8 open rear axle. I have only been driving the truck for a few hundred miles since an engine swap. Don't have any knowledge of what it was like before that and I haven't driven too many trucks. I think the rear end makes noise... not sure if its normal. The rest of the truck is surprisingly quiet.

Given its high mileage (220K miles) I would like to use it every now and then until it dies of rust in a few years. I really don't want to crack open the axle and rebuild or even look to replace unless I have to. I don't like noises, but I can ignore it.

The symptom now is a noise that is loudest when under load and it sounds to me like a low pitched grumble like a mechanical noise of a bus slowing down. it goes away on coasting or in neutral. With the back window open there is noise when slowing down in gear, but not nearly as loud. The noise under load may be reverberating in the cab a little too...

It would like to understand what the typical failure for this part is. If things are getting a little loose or out of spec and I still have a few thousand miles left in the rear end, I should be good. If it may lock up the rear wheels at any time, then I need to address it.

I did just replace the rear axle lube with 80W90 gear oil. The oil in the case didn't look out of the ordinary. The fill plug looked magnetic and there was the typical buildup of fine metallic paste. The gasket on the old cover was black RTV, not sure if recently/ever serviced.

I really haven't done any more diagnostics or had the rear end up on jackstands.

I think this truck was more of a passenger vehicle for at least the later majority of its life and does not have a tow hitch or ball, so may not have been used to haul much.
 


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Dirtman

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Sounds to me more like a transmission issue than a diff issue. There's no real reason the noise would go away in neutral if it was a problem with the differential.
 

RonD

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You should have seen some signs of wear, i.e. metal bits, in the old fluid, if the differential was the problem

The axle bearings at the wheels could be worn, drive next to a concrete wall with windows down and listen
If it sounds louder on one side then axle bearing is likely, they both won't start to fail at the same time, so if sound is the same then both are OK

If you have an extended cab then could be the start of carrier bearing going out, article here: https://therangerstation.com/tech_library/carrier_bearing.html
This tends to cause a vibration as the rubber deteriorates
 

backporch

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Yes. it is an extended cab. the link showed the carrier bearing in the pre 98 rangers.
I will look for a place to do the concrete wall test. Thanks.

I suspected the rear end because the noise seems to be behind the cab, but that could always I guess be noise coming from below the cab

Not sure if it has any bearing on this, but it is a 4x4 with the off-road decal and seems to sit higher than a standard 4x4
 

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If one piece drive shaft then there's always the slip yoke on the drive shaft, but that's usually a "clunk" noise
 

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Worn pinion bearings will usually make noise during acceleration and deceleration. They allow the pinion to move slightly. The difference in sound is because of the different force applied during drive and coast.
 

backporch

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Just took another truck owner for a ride and he verified that he once had the same noise on an F-150 and was told by a mechanic it was nothing to worry about. I will still keep investigating.
 

Dirtman

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Deaf mechanics are the worst.
 

backporch

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I wish I were deaf... problem would be gone

I think I may put the ranger rear on jackstands and search for anything strange... Maybe even start it up and look for strange things while in gear spinning the rear tires. Any suggestions on a way to diagnose the drivetrain?

Could the noises I am hearing be a result of crappy mounts near the transmission? I can't get over that the noise seems to resonate in the cab, but maybe that is normal for axle noise to travel through the frame...

I may also pickup an axle that I saw online. Donor truck had lower miles, but from a parts truck so the owner never drove the truck and doesn't know whether it has issues. Not too different than any scrap yard.... outside of me not being able to bring it back.
 


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