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Hello, I have a 93 3000GT (AWD) and I have a whine similar to a harmonic from the drive train in the rear. It is load related as when I get on the gas it will get louder from 40 to 45 then it goes away for the most part. If I let off the gas or give it a certain load it will stay relatively quiet. I have solid aluminum rear differential bushings, a 2 piece aluminum / steel hybrid drive shaft and a rebuilt transfer case (installed less than 500 miles ago). I checked the backlash on the differential about 5000 miles ago according to the FSM and all was within spec. U-joints are good and greased up and the shaft has no vibrations. scratching my head at this one. Any ideas?
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You probably have the limited-slip differential, which since its inception has always been a bit picky. The gears are usually given a bit of a angular twist, so they don’t mesh with a click but with a scissoring swish, to minimize noise. But that means that the viscosity and lubricity of the differential fluid is critical towards minimizing gear noise. In addition, the limited slip business is sometimes done with friction slip clutches, like inside an automatic transmission, only they’re carefully compressed just enough to slip but not too little or two much, or it’s done with some fancier kind of viscous or hydraulic or even electrically controlled slip or resistance. So you are in a heck of a Goldilocks situation, where you need a fluid that will work well with the gears, and have just the right amount of slip for the particular kind of limited slip technology in there.
First I would check that the gears have to cookbook amount of mesh and spacing and no burrs or scoring. Then I’d ensure, if you don’t know for sure, that the right kind of differential fluid is in there.
Yup it has a Viscous coupled LSD in the rear, and let me tell you it is LOUD when the spider gears start moving from slippage. Ill check the fluid when I get home today IIRC it is 75W90 hypoid gear oil, nothing special according to the FSM. What do you mean by cookbook I’m not familiar with the saying?
Cookbook = FSM, just my variation
If you’ve checked all the mechanical gaps and alignments and they’re okay, and you’re using the original spec goop, and it’s not a particularly fancy goop, it may be time to start playing with all the enhancers. Maybe a thickener? it’s not a science, you’ll just have to experiment.
Ah, I see. Maybe I’ll try some lucas heavy duty oil stabilizer in there. I think last time I was at Autozone there was a lucas oil product for differentials. I seem to have good luck with their products.
LSD differentials require additives or special fluids. Check the FSM to see if one is listed. Many times these noises are caused by old or incorrect fluid.
Keep us posted.
Have not been able to work on the car much recently, been too busy with a few other projects. I am 100% sure it is the rear differential however. It may be a pinion bearing going out on me, so I have my spare rear differential that I’m going to adjust the backlash and bearing preloads correctly then throw it in when I get the time. Heres the FSM fluids page [URL=http://s289.photobucket.com/user/bloodlust182/media/zzy_zps1305a19e.png.html][IMG]http://i289.photobucket.com/albums/ll203/bloodlust182/zzy_zps1305a19e.png[/IMG][/URL]
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