Ricky5

I have been reading about the whine sound coming from the rear end of these cars and was wondering if there was a way to tell if the whine was something simple or serious.

Some threads just say change the fluid and others say the rear end is shot.

How could I tell during a test drive to walk away or make an offer?

ND2RACE

Just listening to the sound you'd need to experience multiple cars to get a feel for the severity. I bought my car when it was 1 year old, I know that these cars made zero noise at some point in their lives. I also have driven or been around many of these cars. The mild whine that they all get isn't noticable over the radio at a moderate volume, this type of whine is because some of the clearances have changed in the rear causing a gear whine. Eventually the whine gets louder and this is when the bearings start to fail, this is typically amplified on accel or decel. It doesn't always progress very fast but as a technician at this point I would recommend an overhaul. Once you move past the bearings starting to fail they start to develop flat spots on the rollers or seize up and that's when you get major failure. If you can get under the car and see the pinion dripping fluid on the ground, it needs rebuilt, if you can push up and down on the pinion and get movement it needs rebuilt. If I was looking at buying one of these cars getting on a lift, checking for movement, and spinning by hand feeling for rough spots are the only real way to know anything about the condition of the rear end.

So it is true that some noise is typical, it is hard to judge even for an experienced tech without putting it in the air and looking for clues. Short of pulling the cover that's the best advise I know to give.

1 FMF

iTrader: (1)

if you have an android phone there's an app called "frequencsee"
it has a real-time graph of frequency vs amplitude.
drive the car and watch the graph,
when i had problems i could see a nice spike at 550 hz when i could hear the rear end hum from ~50mph upward.
this way you can somewhat quantify things.
here's a pic i grabbed off the web of what the app will look like on your phone... it shows a spike at 1000 hz. What i experienced was a spike like that but only to 60dB and it was at 500-600hz

usnfenix

iTrader: (11)

Interesting app, but really how does this help the OP at all in regards to his question. All its telling you is yup its making a noise.

1 FMF

iTrader: (1)

go ride in a few other rear axle cars which are considered in good condition and observe the noise pattern, then compare to the car with the problem.

when you drive the car you can watch real time the lump happen as you hear the rear whine, and it'll be a very repeatable measurement. the whine i get is around 550 hz. and the frequency does not change with speed, and it's a steady lump. this is for a 3.73 ratio. not sure if an oem 10-bolt with 3.42 or lower will be a significantly different frequency, i never measured my oem axle before i replaced it. if he's got damaged gears or something is grinding then i'd expect to not see a steady lump but a lump that fluctuates in amplitude.

the one thing he may not know unless he uses something like chassis-ears to pinpoint the source of the noise by the amplitude, is if the noise is from the ring & pinion vs axle bearing vs something else.

and with a somewhat good measurement vs seat of the pants,
if he changes axle fluid maybe add some friction modifier he might know if it quieted down the axle. there's some pretty good "frequency spectrum analyzer" apps for phones, for a free app it's better than listening with your ear and speculating, and he might feel better before he spends a grand on a rebuild.

usnfenix

iTrader: (11)

Interesting method of troubleshooting the problem, I can tell you from my job experience that the 3.42 gear ratio will most certainly produce a different frequency.