redline synthetic what weight?
 

i plan on changing my diff. fluid to redline synthetic to help reduce the noise coming from the diff. my question is what weight should i use?

Always use gear oils with 75W-90 or 80W-98 rating for regular Mercedes cars.

Eric

Unless your differential is a limited slip variety, use 75W90 see:
http://www.redlineoil.com/pdf/5.pdf
I just got two jugs in the UPS for my '87 300D rear end
I doubt the noise will go away though, that usually is a sign of worn bearings. BTDT.

Dieseldiehard has it right. You want the 75W90 and yes it may help but won't probably make the noise go away. If you haven't used synthethic oil there before plan on changing it again after about 10,000 miles or so because that stuff really cleans out all the gunk.

how much do i need?

Around 1.1-1.2 quarts.

ERic

When I changed my axle halves several sources suggested Mobil One. Redline and Mobile are close to the same price. Both are good. It was less than 2 quarts.

The synthetic 90 wt will look almost like 30 wt motor oil. It will do the job with less friction. The problem it will probably make more noise than the regular stuff. Neither will fix a worn bearing.

MB are not known for having problem differentials. It has been said that they are trouble free if maintained.

Good ones are easy to find at the local self service junk yard. Open one up and if it looks like it's brand new it's probably good. If it looks like an American part, all black and foul smelling, pass.

If you don't want to fix it, pack the diff with sawdust and put the old oil back in. Should be good for at least 20 miles, and it will be quiet.

pack the diff with sawdust and put the old oil back in Should be good for at least 20
 

Use bananas, not sawdust, that should let you drive at least 200 miles.
kidding aside, try the synthetic but like I said it is no cure all for a noisy differential, flash123 is right it will be louder. I've proved that already :( There is however a thickener (MGF?) that comes in a tube, you add it to regular differential oil and it will quieten noisy bearings. Let me know if you want more info I still have some and know where to get it (the boys at http://www.importpartsspec.com/ sell it)

Actually, my experience has been that with no regular maintenance MB some differentials begin to whine after 200K miles or more. The best remedy is a replacement differential, hopefully a low mileage one. These are entirely too difficult to replace the bearings, properly torquing the pinion nut is very difficult even if you have all the wherewithall to do the job.
I highly suggest finding one from an '85 300SD with its lower ratio. Your car will really run better down the road with only a very slight loss of acceleration. The pre '85 ratio is 3.07 while the '85 used 2.82 and the taller gearing is easier on fuel and the engine will run more quietly at 70+ MPH.



:(

so the 85 will give me better mpg and reduce engine speed?
what about my top speed will it go up/down? where can i get that thickener you speak of?

Assuming the differential in your car is a 3.07 ratio then yes it will give you better top speed, about 8% mathematically (divide 3.07 by 2.82) One look at the lower left ear of the housing (on the back where the cover is attached) shows the ratio that it came with.
In my experience our '83 300D really is a much better highway car after such transplant (and no more WHINING!) and little downside except finding a used diff from an '85 vehicle and having it installed, and the speedometer error that comes with such a change. In my case, the reading was fast, and after the swap it came back to near perfect, I guess I lucked out on that.

As for the MGD or whatever it is called, call Andy or Rick at Import Parts Specialists in Boise 1-800-897-7278

There have been a number of posts from members that have been happy with the change to lower gears, but remember you will lose some acceleration. You are converting some torque to speed.

Yes, there will be a slight loss of acceleration but if the car is a turbo diesel with a good running engine the loss of a second or two in 0 -60 run is not a problem, trust me, our '83 is ever bit as good with the taller gears in it.
OTOH, I have resisted changing the differential (again, it came with 3.46 gears) in my '79 300TD work car. I've used it to haul 1200 lbs of ceramic tile on two occasions and almost hauled a large deep freezer last weekend, until I figured it might punch out the rear window with the hatchback resting on the top surface of the freezer. I want to keep the 3.07 gears in it because I do use that car for heavy loads. But my '85 road wagon is stock with the 2.82 and its acceleration is every bit as good even with 5 adults in it, cross country trips over mountains and so on have never been a problem in terms of acceleration. There is however the noisy back seat drivers that aggravate the driver, me :mad: