Best lube to quiet down singing rear diff ??

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When I had Synthetic Gear lube in my rear diff. and transfer case. the rear was noisy, but as soon as I went back to conventional oil it was quiet again.
 
Originally Posted By: busfreak
very interesting ! same weight ? if yes, what could be the reason for it ?



Same weight range yep. I dont know why, so I just keep the Conventional oil in there now. Oh, and it leaked with the Syn. oil too. Doesn't now.
 
Molakule, can you help ?

whats the reason of lexus114 observation ?

what lube would you recommend for my slight whining ?
 
Originally Posted By: lexus114
When I had Synthetic Gear lube in my rear diff. and transfer case. the rear was noisy, but as soon as I went back to conventional oil it was quiet again.


Which one was making the noise, the diffy or the TC?
 
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Originally Posted By: MolaKule
What vehicle and transmission?

There could be quite a few causes:

It could be your tires, or pinion/ring gear contact loading, axle bearings, etc.


We really don't know where the noise is coming from. I have had slight clearances in manual transmissions give me the same noise.

Quote:
Molakule, can you help ?

whats the reason of lexus114 observation ?

what lube would you recommend for my slight whining ?


Makes no sense to me.

For the diffy, try a weight one notch up. For example, if it specified 75W90, go up to 75W110; might be you have some increased clearances in the ring/pinion or axle bearings due to wear.
 
Last edited:
Originally Posted By: MolaKule
Originally Posted By: lexus114
When I had Synthetic Gear lube in my rear diff. and transfer case. the rear was noisy, but as soon as I went back to conventional oil it was quiet again.


Which one was making the noise, the diffy or the TC?




The rear diff, The TC was fine.
 
Originally Posted By: MolaKule
For the diffy, try a weight one notch up. For example, if it specified 75W90, go up to 75W110; might be you have some increased clearances in the ring/pinion or axle bearings due to wear.


MolaKule;

Is there any instance where going to the thicker gear oil (even 2 weights higher, i.e.; a 75W-140) could actually make for more noise??
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currently I'm using RL 80W-140 GL5;

Assuming that the slight noise could be quieted by lube, what brand, weight, type would be the best option ?
If Schaeffers is it, what # of the following would be the most reasonable ?

#167 75W-140
#209
#209A SAE80
#239S
#239 80W-90
#293 75W-90
#740 EP 80W-140 E/A
#741 Ep 75W-90 E/A
 
I recently changed my rear axle to Millers CRX 75W-140 NT gear oil, and the coast/decel whine I had is almost gone, despite most on here probably calling bee ess on this.

Maybe there really IS something to those nano-technology fullerenes?? (One most certainly DOES pay {$$$} for them though!
frown.gif
)
 
Originally Posted By: busfreak
Hi guys,

- above 80 kmph at the point of loading (acceleration) and unloading (deceleration w/o using break) there is a slight singing / whining from the rear
- the same singing is present in idler neutral gear between 80 and 100 kmph (just as additional info)

I dont know if it comes from diff or it is tramsmmitted from gearbox via power train - rear axle to car body.

What is possibly the best / most successfull diff lube to try to get rid of the slight noise ?
Who has experience ?

In car manual is recommended:

temp < -30 °C SAE 80
-30 < temp < 30°C SAE 90
temp > 30 °C SAE 140 °C

temps here are between -20°C in winter and 35°C in summer.

thanks for answer


Busfreak:

Vans/Buses are the most sensitive of any vehicle to amplifying ring and pinion whine through the body structure. American vans even specify certain ring & pinion sets to minimize vehicle owner complaints.

At very light load at highway speed, and to a lesser extent during a light coast, is when normal gear whine is most evident. If your gear whine is not increasing in volume or the range of speeds it is audible, and there is no excessive metal on the magnet in the differential housing, it is likely you have normal gear whine.

Although I have heard antedotal reports that gear oil can increase or decrease ring and pinion sound, I have never found any difference when experimenting by changing gear oils. Since the ring and pinion whine is caused by the particular ring to pinion gear contact pattern in play causing a vibration and resonance in the vehicle body, I cant see how an oil can affect this but so much. Maybe a thicker oil would give a thicker film when lightly loaded , but it is still two pieces of iron separated by a non compressible oil film. I would guess that when all the bearings are very lightly loaded as well as the gear teeth, the slack in the all the bearings as well as the gears allows these resonations to become more audible when they are at the resonant frequency of your vehicle.
 
Jeff_in_VABch: a lot of thanks for your very helpful and competent answer !
I think your diagnosis is very likely.
But what I observed is, after switching to Redline MT85 in the gearbox the whining was nearly gone. It was in early spring. Now in early summer the whining is back. Maybe the whining comes from gearbox and is transmitted via power train - diff - rear axle to body. The thinner the oils are because of higher temperature the more the resonations are. It's only a assumption, I don't know.
Maybe the gearbox is the cause. It's very difficult to find out.
If it comes from gearbox, the gear lube should be thicker, but then the speeds are hard to change in winter. Thicker oil cushions more.
 
Since you say the noise happens in warm weather then a thicker oil should help. A multi-grade synthetic such as 75w140 will work well in the summer and still be thin enough in winter.

I changed the diff fluid in my BMW from stock 75w90 to 75w140 (back speced by BMW ) and it quieted down the diff noise substantially.
 
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