What is this noise?

[leto_knife]

I hear a strange noise coming from the rear of my 1997 FJZ80, and need help in identifying the cause.

When I drive it on the interstate and hit 70 mph, the truck produces a medium-pitch whirrrrrrrrrrrr sound, sortof like a tire whirl, but louder, like the noise from blowing into a coke bottle. It only occurs when I hit 70 mph and above, and only when I have the gas pedal depressed. The sound stops when I take my foot off of the gas, even if the truck is still traveling at greater than 70 mph.

???????

 

[Jacques Villeneuve]

Rear differential. The noise only is heard with load on the gears. The ring and pinion gear(s) are worn. Check the seals and fluid levels.

 

[leto_knife]

Thanks, man. Now that I searched on "rear differential", I see it seems to be a common issue.

 

[84CRUISER]

Check the rear pinion bearings. Does the pinion seal leak? (usually a sign of loose, worn bearings. Also a u-joint can make that noise but is usually accompanied by a vibration.

 

[IdahoDoug]

Stock truck? Miles?

DougM

 

[leto_knife]

Stock truck, 78k miles, P.O. was an old man who had it serviced at a dealership, i have all the dealership records with generic descriptions of the services performed, but without exact knowledge of what was done

 

[GXO]

Easy way to check is to give the rear driveshaft a push upward and side to side where is mates to the rear diff. If it moves AT ALL you have play in the pinion nut and need to fix it ASAP or you will have a bad day. Sounds like bearing wear, which would need a full tear down by someone that knows what they are doing.

The good news is, the bearing itself is cheap. ($40 or so max) The bad news is it will be between $350 (full service) and $150 (if you pull the third) to get it fixed.

Either way, that really isn't that bad for the $ side, just make sure to take care of it.

 

[leto_knife]

The driveshaft doesn't move at all where it mates to the rear differential. I guess I should take it to the dealership *gasp* tomorrow to make sure it's ok, since I don't really know what I'm doing. I didn't change the rear differential oil a few weeks ago when I had the truck baselined. Maybe that will help.