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Transmission Fluid and Filter Change
 
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Pelican Technical Article:

Transmission Fluid and Filter Change

Kerry Jonsson

Time:

2 hours2 hrs

Tab:

$75

Talent:

**

Tools:

5mm Allen head bit or key, 13mm socket with ratchet, Phillips head screwdriver

Applicable Models:

Mercedes-Benz R129 (1990-98)

Parts Required:

Transmission oil, transmission pan gasket, transmission filter

Hot Tip:

Run the transmission through all the gears then check the oil level

Performance Gain:

Possible elimination of poor shifting, extend transmission life.

Your automatic transmission is one of the major components of your car. After your engine, it is probably the second most expensive repair you can do to your car. The job of your automatic transmission is to take the torque produced by the engine and transfer it to your driveshaft and differential. As engine speed increases the automatic  transmission changes the gear ratios automatically so you don't have to and drops the engine rpm as you go faster. The number one killer of transmissions is heat. Excessive heat makes the transmission fluid so thin it allows the clutches in the automatic transmission to slip and will eventually lead to transmission failure. A sure fire way to maintain your transmission and extend its life is to change the transmission fluid and filter. I recommend you change it every 50,000 to be safe but it really depends on how hot it is in your area and how much stop and go driving you do. Changing the transmission fluid yourself is relatively inexpensive with the cost of the pan, gasket, filter and fluid. In this tech article we will go over all the steps to replace your transmission fluid and filter.

Please note: It is necessary to drain the oil from the torque converter when changing the transmission oil for a '91 300SE.

In order to service your transmission you will need to lift and support your vehicle. We recommend you lift both front and rear axles. See our tech article on jacking up and supporting your vehicle. Drive your vehicle for about a mile to warm the fluid.

Remove the 5mm Allen head drain screw from the oil pan.
Figure 1

Remove the 5mm Allen head drain screw from the oil pan. Allow the oil to drain into a drain pan for a few minutes. I like to measure the amount of fluid drained, so when refilling I have starting point.

Remove the six 13mm fasteners that hold the oil pan onto the transmission.
Figure 2

Remove the six 13mm fasteners that hold the oil pan onto the transmission. ThisPicture illustrates that we are starting at the right rear mounting fastener.

Here are the locations of the six fasteners (green arrows) that mount the oil pan to the transmission.
Figure 3

Here are the locations of the six fasteners (green arrows) that mount the oil pan to the transmission. Pull down the oil pan and remember even through you drained the oil first there is still some fluid left in the pan. Leave one mounting bolt in the corner and loosen it by hand while your other hand supports the pan. Fully remove the pan from the transmission.

Look toward the rear of the transmission with the pan removed and locate the transmission fluid filter.
Figure 4

Look toward the rear of the transmission with the pan removed and locate the transmission fluid filter.

Remove the three Phillips head fasteners that hold the transmission fluid filter to the transmission.
Figure 5

Remove the three Phillips head fasteners that hold the transmission fluid filter to the transmission.

With the filter removed make sure the gasket sealing surfaces (green arrows) for the transmission fluid filter are clean and do not have any of the oil gasket material stuck to it.
Figure 6

With the filter removed make sure the gasket sealing surfaces (green arrows) for the transmission fluid filter are clean and do not have any of the oil gasket material stuck to it. Installation is the reverse of the removal steps. Fit the filter and tighten down the mounting screws. Position the new transmission pan gasket to the pan making sure the sealing surfaces on both the pan and the transmission are clean. You can use silicone sealant as a gasket or in addition to a gasket for proper sealing. Make sure the drain plug is tight. Fill the transmission through the dipstick tube with 3 quarts of transmission fluid (or the amount you drained from the transmission if you measured it) and check the fluid level. Remember oil will be traveling down the dipstick tube and the dipstick may pick this oil up and give a false reading. Continue to fill the transmission one quart at a time until it is up to level on the dipstick tube. Then start the engine and while your foot is on the brake run the car through all the gears including the lower gears spending about 1 minute in each gear. Check the transmission fluid level while the car is running and fill until the level is correct. You may have to wait for the oil to fully drain out of the dipstick tube so you do not get a false reading.

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Comments and Suggestions:
steve Comments: Regarding the transmission oil change which you illustrated so clearly, is it also necessary or important to drain the oil from the Torque converter when changing the transmission oil for a 91 300 SE
October 4, 2015
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
mel Comments: 1997 SL320 100,000 miles. Transmission works flawless.

should I drop pan, change filter, put in all old fluid? -or-
measure old fluid and fill with new fluid ? -or-
Drain converter, if plug is available measure and replace with new? -or-
do nothing until there is a transmission problem?
September 8, 2015
  Followup from the Pelican Staff: It's worth replacing the filter is you can. Just be sure to measure and add the same amount of fluid that comes out,. - Nick at Pelican Parts  
Jim Comments: Does anyone know where to get these two transmission plugs or covers. MB dealers don't have...help...thanks
August 14, 2014
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
 
JIA300D Comments: Great instructions, Thanks. I have a couple of questions.
I have an 87 300SDL and when I look in the The Maintenance Manual Step 2702 it says that for 6 cyl engines with 722.3 automatic xmission mine, the Full Fluid Capacity is 7.3 liters and the Fluid change is 6.2 liters.

Since the maintenance step talks about draining the Torque converter I assume that the fluid amount to replace includes the fluid in the converter.

This article and many threads recommend to measure the fluid drained when the pan is removed and replace the same amount around 3 Quarts, ~3 liters but nobody talks about draining the converter.

The replacement fluid for both the converter and the pan is poured through the stick tube.

Questions:

1- When or how often Should the converter fluid be replaced?

2- If not to be replaced, would the old fluid inside the converter mix with the new fluid in the pan during operation? If so,isn'that a problem mixing old and new fluid?

Thanks.

May 4, 2014
  Followup from the Pelican Staff: If your owner's manual suggests replacing it, I would do it at the interval it suggests. I would assume the capacity reflects the converter as well. My suggestion is to replace it when performing the auto trans service. Measure the amount drained and refill with the same amount. Then check level and top up as needed. - Nick at Pelican Parts  

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