Mercedes-Benz Parts Catalog Mercedes-Benz Accessories Catalog Mercedes-Benz Technical Articles Mercedes-Benz Tech Forums
 
Follow Pelican Parts on Facebook Follow Pelican Parts on Twitter Follow Pelican Parts on Instagram Follow Pelican Parts on YouTube Follow Pelican Parts on Pinterest Follow Pelican Parts on Tumblr
  Search our site:    
View Recent Cars  |   Cart  | Project List | Order Status | Help    
 >  >
Rear Axel Differential Oil Change
 
Bookmark and Share

Pelican Technical Article:

Rear Axel Differential Oil Change

Tom Morr

Time:

1 hour1 hr

Tab:

$40

Talent:

*

Tools:

14mm hex wrench or bit, ratchet, extensions, breaker bar, torque wrench

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Gear oil

Hot Tip:

A hand pump such as Pelican's

Performance Gain:

Can eliminate gear whine, prolongs bearing life.

Complementary Modification:

Check for undercarriage leaks and inspect the differential mount bushings.

Most home mechanics know that few things extend component life more than routine maintenance. The average Mercedes-Benz owner is diligent on engine oil, but even hands-on SLK owners are less enthusiastic about changing axle oil. Gear oil is thick and stinks. Many differentials likely bathe too long in old lube because changing it isn't glamorous, and possibly due to the "lifetime lubricant" myth circulating around the time the R170s were manufactured.

Unlike some other fluids in the car, differential oil isn't filtered. As metal parts wear, particles circulate through the oil. So even if the oil itself hasn't lost lubricity, it should be changed to clean out shavings and debris.

MB didn't publish a recommended service interval for the R170's differential oil in the owner's manual. A general rule of thumb is that gear oil can remain good for about 80,000 miles, but proactive owners might want to use 50,000 for an easy-to-remember threshold.

Gear whine can indicate low differential oil level (look for spots on the ground under the axle). Changing the oil sometimes solves the problem. If not, bearings could be the cause of the sound.

Oil specs and recommendations are also a topic for a separate article. The MB owner's manual recommends 85W90 hypoid gear oil for the R170 SLK. Enthusiasts generally prefer synthetic oil, which tends to outlast mineral oil.

Basically, changing axle oil is the potentially messy job that someone has to do. It isn't difficult, but a non-standard tool is required to remove the plugs.

Tips: Plan ahead: The car's drain and fill plugs have internal 14mm hex heads. Most standard hex/Allen sets don't go this big. Pelican Parts has the tool for the job so consider ordering it along with the gear oil. Raising the car rear on jack stands or ramps makes access much easier just make sure the car is level so the fluid level is correct. Ideally, spray the plugs with penetrating lubricant ahead of time. Always start with the fill plug: it's the higher one, on the left of the differential housing toward its front. We attempted to use a 14mm-headed bolt and locking pliers while waiting for the 14mm bit to arrive. Our bolt wasn't hardened and snapped. Torque spec for both plugs is 41 ft-lb / 55 Nm. For some reason, the fill plugs tend to freeze in place. We had to use a 1/2-inch-drive breaker bar to jar our project car's plug free. The warmer the oil, the better it will evacuate out the drain plug. Plan on the oil stream going somewhere other than in the capture pan when it initially starts to drain One-quart bottles with the witch's hat spouts can be maneuvered above the axle and poured into the fill plug. The bottle can be raised so that most of its oil pours into the differential. A better fill method: use an affordable hand pump that screws onto the oil bottle. If using a hand pump, stroke slowly so that the oil doesn't splash out and give a false-full signal. Add oil until it weeps out the fill hole. Published differential capacity is 1.4 US quarts/1.3 liters.

Even after spraying penetrating lubricant on the plugs, we had to use a breaker bar on the fill plug.
Figure 1

Even after spraying penetrating lubricant on the plugs, we had to use a breaker bar on the fill plug. Luckily, we bought a 14mm 1/2-inch-drive hex bit.. Removing the fill plug first releases pressure and won't leave you stranded if the drain plug comes out but the fill plug refuses to.

The drain plug is on the right side at the rear of the differential.
Figure 2

The drain plug is on the right side at the rear of the differential. It also takes a 14mm hex wrench or bit.

Capture the old oil in a container that holds at least two quarts.
Figure 3

Capture the old oil in a container that holds at least two quarts. Put cardboard or something similar under the pan if you want to protect the ground from drips and sloshes. Dispose of the old oil in accordance with the regulations in your area. Most oil change shops will take your old oil..

Quart bottles with conical spouts can be used to fill the differential.
Figure 4

Quart bottles with conical spouts can be used to fill the differential. They won't fit vertically enough to totally empty though.

A hand pump is an inexpensive (available at Pelican parts for aound $10) and cleaner way to fill the diff.
Figure 5

A hand pump is an inexpensive (available at Pelican parts for aound $10) and cleaner way to fill the diff.

The job requires a male 14mm hex bit, wrench, or bolt to remove the plugs.
Figure 6

The job requires a male 14mm hex bit, wrench, or bolt to remove the plugs. We used a 1/2-inch drive setup. You'll also need a drain pan and, ideally, a torque wrench. Discretionary items include penetrating spray, a breaker bar, and a hand pump for filling the differential with gear oil.

Bookmark and Share
Comments and Suggestions:
mike Comments: My 1998 slk 230 rear seal has a leak how to fix rear differential seal
March 21, 2016
  Followup from the Pelican Staff: We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
Ron Comments: I need to replace the right rear side that the tire bolts to?
July 21, 2015
  Followup from the Pelican Staff: What are you trying to fix? This article is about a fluid service. - Nick at Pelican Parts  
AK Comments: Thanks for all the technical articles you guys write! Might want to correct the spelling of axle in the title.
January 24, 2015
  Followup from the Pelican Staff: Thanks for the feedback and catching the error. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 

  Search our site:    

View Cart & CheckOut | Project List | Order Status |  Help    

 

[Home] [Customer Service] [Shopping Cart] [Project/Wish List]
  [Privacy Statement]  [Contact Us] [About Us] [Shipping] [Careers]

Copyright © Pelican Parts Inc. -    DMCA Registered Agent Contact Page

Page last updated: Fri 12/9/2016 02:26:23 AM