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Automatic Transmission Fluid Flush and Filter Change
 
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Pelican Technical Article:

Automatic Transmission Fluid Flush and Filter Change

Tom Morr

Time:

3 hours3 hrs

Tab:

$200

Talent:

****

Tools:

Floor jack, 27mm socket, 5mm hex wrench, screw-extractor set, T27 Torx bit, special dipstick tool, infrared heat gun, torque wrench, ratchet and sockets, wrenches: 17mm, 19mm

Applicable Models:

Mercedes-Benz SLK230 (1998-04)

Parts Required:

Filter kit, Mercedes-Benz ATF

Hot Tip:

Get the special dipstick to simplify fluid level-checking

Performance Gain:

Fresh fluid for smoother shifting

Complementary Modification:

Check and replace the transmission mount and driveshaft flex discs if necessary to limit transmission vibration

Mercedes-Benz's "fluid for life" mantra was still ingrained when R170s were manufactured. Since the manufacturer didn't recommend changing automatic transmission fluid at the time, dipsticks weren't included on the cars.

Mercedes-Benz subsequently back-tracked and now recommends changing the ATF every four years or 40,000 miles.

Flushing the fluid is more messy than difficult. The first step is raising and securing the car on jack stands. Because ATF will likely splash off the drain pan (make sure it holds at least 10 quarts), cover the ground under the transmission pan to prevent stains. Paper towels and rags will contribute to cleanliness. The lower engine shield will need to be removed (see that article for location of the six bolts that hold it on).

If you don't have the special Mercedes-Benz dipstick tool, attempt to capture all of the old fluid. Then measure it and replace with the same amount of new Mercedes-Benz ATF. Over- or under-filling the transmission by only a few ounces will cause shifting problems. If in doubt, replace the old fluid with the same amount of new ATF and have a repair shop check the level and adjust it if necessary.

The transmission drain plug takes a 5mm male hex/Allen wrench. Consider spraying the plug and the transmission pan bolts with penetrating lubricant first. Even then, our project 2000 SLK230's drain plug stripped.

Six T27 internal Torx-head bolts (OE part number 004-990-35-12) hold the pan in place. Even when fluid stops dripping from the plug hole, a significant amount remains in the pan.

The old filter pulls out of its mount on the valve body. The filter has a retaining clip that secures it to the valve body.

Always inspect the pan for debris and clean it thoroughly. Some models have a magnet in the bottom of the pan to capture metal shavings. Consider adding one if your pan doesn't have it. The OE part number is 220-271-00-98-MBZ.

On cars that don't have a torque converter plug, a full flush requires draining the system from the cooler line with the car running. Some owners run the car until clean fluid comes out. The Mercedes-Benz manual recommends two sequences of adding and flushing three liters of fluid. This requires 14 total liters of ATF for a complete fluid change.

Torque specs: pan drain plug = 20 Nm, pan bolts = 8 Nm.

Begin by raising and securing the car and removing the lower engine cover.
Figure 1

Begin by raising and securing the car and removing the lower engine cover. SLKs manufactured before 9/22/1999 have drain plugs on their torque converters. On these cars, rotate the crankshaft clockwise with a 27mm socket until the torque converter's plug is visible in the access window.

If the torque converter has a plug, drain it, and then replace the plug, installing a new sealing washer first.
Figure 2

If the torque converter has a plug, drain it, and then replace the plug, installing a new sealing washer first. Otherwise, move to the transmission pan's plug. It takes a 5mm hex wrench. Tapping the wrench can help break the plug loose. The fluid drains better when it's warm.

Make sure to have a minimum 10-liter/10-quart drain pan.
Figure 3

Make sure to have a minimum 10-liter/10-quart drain pan. If you don't have the dipstick tool, try to capture all the ATF and measure it so you can add the same amount that came out. Allow the fluid to drain at least 15 minutes--longer if the car is cold.

Thoroughly clean the area around the transmission pan
Figure 4

Thoroughly clean the area around the transmission pan -- dirt can easily plug the transmission's hydraulic passages. Remove the six bolts with a T27 Torx bit; tap the bit into the bolts for good contact. More than two liters of ATF remain in the pan, even after its plug is removed. One trick is to leave the front right bolt (the one attached to the heat shield) halfway in to allow the pan to tilt, draining most of the trapped ATF out the hole.

Six M6x40mm bolts, each with a metal clip, hold the pan on the transmission.
Figure 5

Six M6x40mm bolts, each with a metal clip, hold the pan on the transmission. Their Torx heads often strip during pan removal. Be prepared to use locking pliers or a screw extractor and source replacement bolts. (Two of the six bolts on our project car had to be drilled out. The pan has enough clearance to accommodate head styles other than internal Torx.) Before re-use, some shops clean the threads with a wire wheel, then coat them with high-temp grease.

The old filter simply pulls out of the valve body.
Figure 6

The old filter simply pulls out of the valve body. Additional fluid will spill out of it. When installing the new filter, make sure that its locating clip seats in the transmission's slot. Clean the gasket-mating surface to help ensure a leak-free seal.

The filter attaches to the valve body at the snout and clip.
Figure 7

The filter attaches to the valve body at the snout and clip.

Thoroughly clean the pan with brake cleaner or similar solvent.
Figure 8

Thoroughly clean the pan with brake cleaner or similar solvent. Consider adding a magnet if your pan doesn't have one. The new rubber gasket gets pressed onto the pan.

The filter kit includes a new sealing washer for the drain plug.
Figure 9

The filter kit includes a new sealing washer for the drain plug. Reinstall the plug and pan, tightening the six bolts and clips in a criss-cross pattern.

Use a small screwdriver to depress the filler cap's retaining clip (red arrow), then remove the cap.
Figure 10

Use a small screwdriver to depress the filler cap's retaining clip (red arrow), then remove the cap.

Use14 liters of ATF to thoroughly flush the system on cars that don't have a drainable torque converter.
Figure 11

Use14 liters of ATF to thoroughly flush the system on cars that don't have a drainable torque converter. On these cars, the first step is to add 5 liters of ATF.

Next disconnect the cooler line at the banjo bolt on the right side of the transmission.
Figure 12

Next disconnect the cooler line at the banjo bolt on the right side of the transmission. This requires replacing the sealing washers during reinstallation. We disconnected the return line at the union near the oil pan, using 17mm (red arrow) and 19mm (blue arrow) wrenches.

If disconnecting the banjo, run a hose from it into a container.
Figure 13

If disconnecting the banjo, run a hose from it into a container. Instead, we used the exiting hose that connects to the oil cooler in the radiator. Have an assistant start the car. Run it until three liters of fluid have evacuated into the container. Then add three more liters of fresh fluid and repeat the flushing cycle.

Reconnect the return line, then top off the ATF.
Figure 14

Reconnect the return line, then top off the ATF. The WIS lists total capacity at 7.5 liters, plus/minus .5 liter. If you have a dipstick tool, use it to check the level. Also, check for any signs of leaks at the pan, plug, cooler hose, and wiring connector above the pan on the right side.

Possible stripped bolts aside; transmission servicing is fairly straightforward and can prevent a costly overhaul.
Figure 16

Possible stripped bolts aside; transmission servicing is fairly straightforward and can prevent a costly overhaul. The filter kit includes a new pan gasket and drain plug washer. You'll also want Mercedes-Benz-approved ATF. Fluid level is critical, so a dipstick tool is handy.

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Comments and Suggestions:
JJ Comments: What if my tranny drain plug is way too tight on my 1999 slk230, can I pound on the wrench or use a cheater bar to loosen it? Please advise.
June 24, 2016
  Followup from the Pelican Staff: I would suggest using a breaker bar. so it doesn't slip off like a wrench would. - Nick at Pelican Parts  
Steven Comments: Any chance you have details on how to change the transmission conductor plate on a 01 SLK320?
June 1, 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
 
beachcruiser Comments: I have 2007 SLK350 and would like to change transmission fluid however, I could not find a dipstick, where is the filling hole for this model? Thanks so much.
January 19, 2016
  Followup from the Pelican Staff: There is likely a cap doesn't come with a dipstick when new, you have to buy a dipstick. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
roy.halaby Comments: Hello, i have a slk 230 1997, my transmission is making noise between 10km/h and 20km/h and it's loosing its smoothness, i changed the fluid and filter but nothing changed . So i was thinking about buying a used transmission and replace it, do you recommend changing the whole transmission or it will cause more problems ? thanks in advance
January 8, 2016
  Followup from the Pelican Staff: If you think the noise is internal to the trans, you may need a new one. First inspect the driveline, check the driveshaft, axles and connections for play or noise. - Nick at Pelican Parts  
steve Comments: does the transmission dip stick check, need the transmission hot or cold and engine running or not?
May 3, 2015
  Followup from the Pelican Staff: What vehicle are you working on? - Nick at Pelican Parts  
keith Comments: 1998 slk 230 had transmission fluid service but gears still not sliding in properly any ideas
February 25, 2015
  Followup from the Pelican Staff:
First check the transmission fluid level to be sure it is correct. Then check the transmission ECM for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.

This could be a slip caused by low fluid or low pressure. Start by checking your fluid level. If it is OK, you may have worn parts causing a pressure drop and slip. I would have it checked before it gets much worse. - Nick at Pelican Parts
 
Bahram Comments: I have received helpful information and this is my pleasure and appreciation for your management and colleagues. Thanks.
February 9, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
bahram Comments: I need to know the procedure to drain the automatic transmission fluid completely from the gearbox.
The capacity is 7.5 liters, drain plug can drain only 4 liters, 3.5 liters cannot be drained, please advise how to drain completely before refilling 7.5 liters.
February 2, 2015
  Followup from the Pelican Staff: To completely drain, you would need to fill as you drain using a flush machine. Otherwise some fluid will remain, for example in the torque converter.- Nick at Pelican Parts  
Norman Comments: Thank you very much for the very usefull information.
July 28, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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