recently i did a major rear end overhall of my fc. fitted mmr subframe bushes, diff bushes, lower control arm bushes, dtss eliminators, re greased and re booted cv joints, mazdatrix competition front diff bush and the diff pinion snub mod recomended on this forum to reduce wheel hop. before i did all this the diff made no noise. when i fitted everything back together i changed the diff oil to penrite limslip 85w-140. whenever ive got the power down (mostly noticeable in 1st and 2nd gears) it make a whining noise, it also make a whining sound when decelerating and when cruising it makes a "shhhhhh....." noise. what do you guys think it is? and why is it doing it? im thinking somewhere along the lines of pinion gear not meshing with crown gear properly??? the diff is a series 5 lsd.

 

Now that you have all the solid bushings, you can hear the noises the diff always made through the body of the car.

Unless there is something strange about brand of oil, I've never heard of it. However I'm fairly sure the factory spec is 80W-90, so 140 is pretty thick.

 

As far as I understood, you've installed some racing parts and lubs in your car's diff.
So now the diff (and consequently the car) will behave and sound very well while in "hard-mode" racing on the track, but it will sound and behave somewhat weird while in normal everyday road cruising.
Factory spec parts and lubs will make your car behave and sound very well in normal road usage, but will make it struggle while racing on the track.
Racing spec parts and lubs will make it behave well on the track, but not in normal road usage...

I think that what I've wrote makes sense...

 

Thanks guys that is reasuring. Was afraid oil viscosity somehow fucked the lsd. Even if it does root itself eventually I'll just weld it.

 

they sell a LSD additive that got graphite in it. usually its used in LSDs that have clutch plates but it may work to calm some noise.

 

I would suggest a fluid flush and refill with some 80w90. The thicker oil could be causing a problem. Does the noise get worse as the car warms up? Or is it more prevelent after first startup in the morning. Also did you notice any metal shavings coming out when you drained the oil? Did it smell burnt? These can be signs of a worn out LSD.

 

Flushing it won't change anything....though I'm not sure that heavy viscosity is going to do any good. My bet is that it's simply the solid bushings transmitting NVH through the car. You'll also get gear noise, primarily in 1st and 2nd gear, when changing to a short shfter with a shaft that isn't isolated in rubber like OEM.

 

I bought the car about 6 months ago and I haven't done many kms in it but the old oil looked like new. No shavings, no burnt smell, clean goldy brown colour. i put the thicker oil in cause it specified it was for comercial and 4x4s so i fiqured it would be able to take a bit more punishment on the track.

 

Is your diff still together? Cause mine is doing all that and I am 90% sure that the ring and pinion might be going. Put it up on Jack's and try turning your rear wheels.

 

yea its back on the car and seams fine at the moment. i talked to this guy who use to work at rotor master and told him everything i told you guys and he said that as mentioned above its most likely just the stronger bushes transfering diff noise.

on another note i think that thicker diff oil is doing exactly as planned. i can feel the tires skipping just a little while reversing out of my driveway.

 

sounds to me like your just hearing vibrations in the cabin from your "racecar" parts

 

it seriously did sound like a whine that got higher pitch as you go faster. but only when your putting power down in 1st and 2nd. thats what worried me.