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  #16  
Old 08-16-2013, 01:54 PM
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The tighter the clearances, the lower the oil viscosity required to allow sufficient lubrication and cooling at the bearing surfaces.

The higher the viscosity, the greater the power required to move the oil.

Higher viscosity oil has more resistance to "squishing out" of an area and therefore can help quiet noise from pitted bearings. Bearing noise is generally "rumbly" compared to the whine that can be caused by ring and pinion interaction.

Gear oil additives don't get depleted under normal use. Unless it has been overheated or has water or metal contamination, gear oil is generally good for hundreds of thousands of miles.

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  #17  
Old 08-16-2013, 02:16 PM
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The numbers are not always what they seem. Use the viscosity specified by MB.
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  #18  
Old 08-16-2013, 04:46 PM
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Hmmm.......

I've always heard that sawdust was the best way to make the rear differntial quieter.
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  #19  
Old 08-16-2013, 05:10 PM
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Originally Posted by SD Blue View Post
Hmmm.......

I've always heard that sawdust was the best way to make the rear differntial quieter.
Nah, bananas is where its at.
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  #20  
Old 08-16-2013, 05:14 PM
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It works, but DO NOT open the gearbox after the banana trick. Pheeeew!
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  #21  
Old 08-16-2013, 08:44 PM
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I have a 1991 300SE and I changed the differential fluid to a synthetic grade that Walmart sold as gear oil. Drives OK in city but as soon as I drove it high speeds for 40 miles there was a howling so bad I thought the rear wheel bearing was going out. This happened every time I drove it on the interstate.

So I went to the dealer and got their last liter of special Hypoid gear oil and changed it. What do you know, no more mowling and its spec. So in some cases it does pay to use MB Fluids.
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  #22  
Old 08-16-2013, 09:45 PM
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Kris, I also seem to recall a 100,000 interval. Let me go check my owner's manual.

**EDIT** My 1972 Maintenance Manual says to do the job at the "1st and 2nd maintenance jobs". Is something that old even applicable to our cars? And what are the first & second maintenance jobs?
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Last edited by Mölyapina; 08-16-2013 at 10:01 PM.
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  #23  
Old 08-16-2013, 10:15 PM
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Originally Posted by SD Blue View Post
Hmmm.......

I've always heard that sawdust was the best way to make the rear differntial quieter.
I serviced a jeep for my brother that his friend bought on a lot... it was packed SOLID with axle grease... took the rear cover off and it was like a jello mold of the rear cover...
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  #24  
Old 08-16-2013, 10:19 PM
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Originally Posted by SD Blue View Post
Hmmm.......

I've always heard that sawdust was the best way to make the rear differntial quieter.
I heard that the best way to keep the diff quiet is to not drive the car... the diff's dead quiet then.
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1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

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  #25  
Old 08-16-2013, 10:23 PM
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Originally Posted by vstech View Post
I serviced a jeep for my brother that his friend bought on a lot... it was packed SOLID with axle grease... took the rear cover off and it was like a jello mold of the rear cover...
My father used to work for a small car lot, and they would sometimes pack the diff with ...


wait for it...



um...





hamburger...



forget the banana's smell, P fricking ewwww!!!!
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"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
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1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #26  
Old 08-16-2013, 11:29 PM
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Well:
Multivis 5W40 wont gum up in the winter so bad.
Hypoid 85W90 may get quite thick in the winter.
Transmission Fluid probably too thin to provide good coverage and non-compressability is not an advantageous property.

When the gears turn, as there is no actual pump, the oil must be thick enough to adhere to the gears so that all round lubrication coverage is achieved. I don't think Tranny fluid is optimum for this application.

Just my opinion.

The oil that came out of my diff was about the viscosity of 30W oil so I put in Multivis 5W40 oil. There is enough oil mass in the diff if it is filled to overflowing at the fill port to handle most lubrication needs. No weird noises from the rear end.

Years ago, I had a Toyota transmission rebuilt. The rebuilders put hypoid in it when the manual called for 30W. The transmission ATE itself just after the warranty expired.
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Last edited by Codifex Maximus; 08-17-2013 at 12:36 AM.
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  #27  
Old 08-17-2013, 03:01 AM
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Quote:
Years ago, I had a Toyota transmission rebuilt. The rebuilders put hypoid in it when the manual called for 30W. The transmission ATE itself just after the warranty expired.
Yep. The bearings will be burned up from lack of oil. Many modern manual transmissions use ATF which is about a 10 wt base oil. 90 wt will burn those up fairly quickly.

Quote:
When the gears turn, as there is no actual pump, the oil must be thick enough to adhere to the gears so that all round lubrication coverage is achieved. I don't think Tranny fluid is optimum for this application.
ATF is missing the extreme pressure lubricant added to gear oil. A hypoid ring and pinion slides as it meshes so that ep lube is very important. ATF could allow a fair amount of wear in a ring and pinion if the vehicle is used hard.
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  #28  
Old 08-18-2013, 02:48 AM
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I remember quite a few years ago a viscosity demonstration at a repair shop.

There were two demonstrator devices.

One had lower viscosity thin oil like ATF. You'd turn the crank and watch the gears turn - I think there were three. The lower gear was about half in the oil and the two top gears were dry. No matter how fast you turned the crank, you couldn't get the top gears wet.

The other demonstrator had hypoid gear oil in it. It used standard and not hypoid gears though. When you turned the crank, the larger lower gear spun and picked up the thicker oil that adhered to the gear. When the larger gear meshed with the gear above, the oil transferred to it and on up to the highest gear till all were coated with oil.

Very effective demonstration of viscosity and lubrication method.
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  #29  
Old 08-18-2013, 05:21 PM
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Quote:
Originally Posted by ohiomike View Post
I have a 1991 300SE and I changed the differential fluid to a synthetic grade that Walmart sold as gear oil. Drives OK in city but as soon as I drove it high speeds for 40 miles there was a howling so bad I thought the rear wheel bearing was going out. This happened every time I drove it on the interstate.

So I went to the dealer and got their last liter of special Hypoid gear oil and changed it. What do you know, no more mowling and its spec. So in some cases it does pay to use MB Fluids.
Hmm I wonder if this would help my 190E's howling out...hm
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  #30  
Old 08-18-2013, 05:37 PM
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I use heavier gear oil,because I drag race,and will soon tow a trailer.Small trailer pop up 1500 pounds

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