So my screw fx4 has been making a whining/howling sound when I am accelerating, it starts at around 50 mph and stops when I reach 58. If i let of the gas it immediately stops no matter what speed I am going. Yesterday I pulled the cover and drained the fluid, and to my surprise the ring and pinion looked and felt like new. All the edges of the gears were still sharp enough you could cut your hand on them, and there was no grooves or pitting. I have a 3.73 LS rear end and the spider gears seem to be the only thing that are worn. They look kind of rounded off but I literally found NO metal shavings anywhere in the whole pumpkin. I dug around in the bottom and there wasnt even glitter or any grey tinted fluid it was amber colored and looked very clean. My question is what could cause this noise on acceleration if the ring and pinion look good? I rotated the driveshaft with it jacked up and didnt feel any flat or rough spots when turning. I couldnt get the spider gears to rotate at all is that a problem?

 

Fill her back up...and don't forget the friction modifier...see what happens and BTW welcome to the site.

 

I filled it back up with Royal Purple 75-140 that has the friction additive already in it. Noise is still there, maybe a little bit quieter. Any ideas?

 

For reference heres the spider gears on my 2006 with 110k miles. Also a shot of the ring gear. Yours do look a bit more worn, but hard to tell. My differential is silent with no vibrations. Im not sure what to tell you, im no differential expert. I used royal purple as well in mine though.

 

thanks for the comparison shots! I look at the pinion and see the shiny marks where it meshes with the ring gear, and cant help but think there might be too much space between where the marks start and the end of the tooth. Im no expert by any means but it seems to me the pinion is sitting too far in towards the rear cover. creating a gap when the two teeth are fully meshed together making a harmonic howl. I have seen this in several small engines when gears dont mesh completely. couldnt this be fixed by adjusting the preload? does anybody know where I can get the correct torque specs for preload and maybe gear clearances?

 

Turn the radio up lol, gears will have a harmonic sound so it a nature of the beast kind of thing. My dad has a cobra kit car and the rear end was making a whining sound so he had the rear end rebuilt and it still does the same thing.

 

What about a wheel bearing? Or axle bearing? Just something to take a look at

 

id be fine with that lol but this is loud enough you cant have a conversation in the cab at 50 mph. Its loud....

 

generally a bearing would make the sound all the time instead of only on acceleration. my first thought was bearings but since theres no leaks anywhere its unlikely.

 

Oh i thought u meant like a slight hum, it might be a pinion bearing.