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1998 Pano SL500; 1993 SL500; 2005 ML270cdi
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Just for reference this is the hydraulic pump p/n 129800 0548 that supplies the fluid to the operating cylinders.
It is located in the trunk under the plastic covering that the spare wheel fits on to.
There are Max and Min fluid marker lines which are about 2.54 cms/1" apart.
The reservoir in the photo is filled to the Maximum level.
Note: entire system holds 1.25 Liters of fluid

1993 SL pump
 

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RST hydraulic system fluid flush and renew

Renewing the hydraulic system fluid every 25K miles or every 2 years should extend the life of many of the hydraulic system components. This is not a part of Mercedes prescribed maintenance, so most cars are still running around with the original fluid (plus years of accumulated contaminants).

Here is a proactive approach, which I believe will improve the longevity of the RST hydraulic system.

1) With the soft top stored and roll bar lowered remove the R129 spare tire. Under the spare tire you will find a plastic cover over the hydraulic reservoir. Remove the plastic covers three nuts with a 10 mm socket wrench.

Note: The total capacity of the system is 1.25 liters, so you should have 2.0 liters of fresh hydraulic fluid MB p/n 000989910310 or Febi-Bilstein p/n 02615 = p/n 0009899103 in order to flush the entire system. My reservoir holds 250 ml when the fluid level is between the min. and max. mark. Here is the MSDS for Febi-Bilstein 02615

3) Remove the reservoir cap and approximately 250 ml. of old fluid with a rubber bulbed battery filler then add new fluid to the reservoir so that you have about 400 ml in the reservoir. Remove the reservoir cap return line. Place the return line into a >500 ml container. Note: read below if you have a pump like the one pictured above.

4) Now have someone in the car. Turn the ignition key to the number two position. Cycle the soft top and roll bar 4-5 times and refill the reservoir to approx. 400 ml as needed between cycles. Then fill the hydraulic pump to the min/max line. Note: you will eventually see the color change to the new fluid color.

5) Replace the reservoir return line, cap, and plastic cover. Wipe up any mineral oil spillage. Return the plastic cover. Replace the spare tire and put the trunk back together in the reverse order.

I did my first fluid flush/renew on my seven year old 30K mile SL. I tested the pH of the old and new fluid. Both read the same slightly acidic pH of 5.5.
 

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3) Remove the reservoir cap and approximately 250 ml. of old fluid with a rubber bulbed battery filler then add new fluid to the reservoir so that you have about 400 ml in the reservoir. Remove the reservoir return line and place the return line into a >500 ml container.
I followed your instructions but in my 91 300 SL things have not worked out as planned. I have the pump as seen in the top picture of this thread. I unscrewed the first hydraulic line (closest to you as you bend over the trunk and the one on the left in the picture. I placed the hydraulic line in a suitable container but when the top was cycled, hydraulic fluid came shooting out of the pump not out of the line. So I figured the other hydraulic line must be the return line so I reconnected the first line and unscrewed the other hydraulic line (to the upper right of the first one in the picture) and the same thing happened. Fluid came shooting out of the pump from that outlet.

So I figured the only line left was the large black knob. I unscrewed it and placed it with it's filter into a container and I thought it was working as I cycled the top until the top began to stop working. It appears that I found an efficient way to introduce air into the entire system. It took many cycles to get things working again but I still have not determined how to flush it correctly. I have considered removing one of the pump hydraulic lines and screw a bolt into the pump and see what it does but would appreciate any advice from those that have done this job on my model year.
The above quote is from Jim Karas after he had R&R'ed all 12 cylinders with no problems yet his hydraulic fluid renew did not work as easily as my 2000.
 

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I did my 1991 last year and had no problems at all. As I remember it, the top line on the reservoir was the return line. The pump takes it's suction from inside the reservoir through the hose clamp connection, and directly into the pump. I simply placed the top line in a container, emptied the old fluid from the reservoir, filled it with new, and had my wife cycle the roll bar and soft top. As she did this I added oil to the reservoir to keep it in the operating range until clean fluid was coming back in the return line.
I think on mine that both the lines on the top of the pump are "pressure" side lines, I had assumed one going to one part of the system and the other to somewhere else (ie: one for roll bar, one for top)
I am going from memory on this, but I'll have a look in the trunk when I get home to verify unless someone else gets back to you first.

Update: O.K Lynn, I had a look at my car. My pump looks very similar, if not identical, to the one in the above picture. After having a look at mine, I'm sure I disconnected the round knurled plastic connector on the reservoir cap and placed it into the container for collecting the old oil. I left the cap off as we did this.
 

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Looks like the design and the shape of the fluid tank had changed over the years :
This is for 129.068 HYDRAULIC AND VACUUM SYSTEM with pump p/n 129800 1448
This is for 129.067 HYDRAULIC AND VACUUM SYSTEM .
The 129.066 looks same as a 129.067

But a pump is a pump, and there are 2 hydraulic lines shown going out to the RIGHT side block (The diagram may not have shown the return line ?)

From the picture in post #1 and what BenzBrat said, there are 3 hydraulic lines and looks like the one attached to the reservoir cap is the return line ?
 

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Looks like the design and the shape of the fluid tank had changed over the years :
This is for 129.068 HYDRAULIC AND VACUUM SYSTEM with pump p/n 129800 1448
This is for 129.067 HYDRAULIC AND VACUUM SYSTEM .
The 129.066 looks same as 129.067

But a pump is a pump, and there are 2 hydraulic lines shown going out to the RIGHT side block (The diagram may not have shown the return line ?)

From the picture in post #1 and what BenzBrat said, there are 3 hydraulic lines and looks like the one attached to the reservoir cap is the return line ?
Your bold statement isn't the case here. There are two different pump designs.

Take a look at the older pump at HYDRAULIC AND VACUUM SYSTEM
 

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I have not done any flushing myself as my fluid in the tank still looks clear.
But I verified it with AllData for the 129 067 :
129.066 is for 1990-1992
129.067 is for 1993-1998
129.068 is for 1999 and on to ? (my AllData does not go beyond 1999)

The larger hydraulic line #12 at the bottom (in post #1) is for the operation of the top controller.
The smaller line #10 above it is for the roll bar, so that it will get the full pressure from the pump without pressurizing everything else.
The plug #11 above that is for testing.
The return line #13 is the one to the Cap.

Seems like the filter is on the return line, which makes sense, as it will not introduce pressure drop to the supply line.
 

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I always thought there was a filter...

Anybody know the p/n for it? I'd like to replace it when I do my flush.
 

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Can't find the P/N for the filter, but it should be located at the end of the return line right at the cap (I have not verify that as I am too lazy to go out and remove my spare wheel, but seems to be a logical location, and Karas did mention a filter there).

Karas may have introduced air into the system when he cracked open the supply lines, but looks like the system is self bleeding so he should be OK after a few cycles.
 

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Can't find the P/N for the filter, but it should be located at the end of the return line right at the cap (I have not verify that as I am too lazy to go out and remove my spare wheel, but seems to be a logical location, and Karas did mention a filter there).

Karas may have introduced air into the system when he cracked open the supply lines, but looks like the system is self bleeding so he should be OK after a few cycles.
My pump p/n is 129800 0048.
Here's a picture of the filter attached to what should be the return line.
IMG_2744.JPG
 

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Chris, there you go, the P/N from Karas.
Looks like just a metal screen filter. May be you can clean yours out with compress air? You know just another blow job:D
 

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Chris, there you go, the P/N from Karas.
Looks like just a metal screen filter. May be you can clean yours out with compress air? You know just another blow job:D
Yes, but here we go again with the confusion. Chris has a 2001 and Jim Karas has a 1991.

I can tell you fer sure that my 2000 p/n 129800 1448 has nothing in the fill cap area that looks like that the OLDER pump cap.
 

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So Lynns, does your 2000 has the round cylindrical tank ? Is there a 3rd line attached to the cap ?
Is it a 129 068 or different # (069?)
Chris's 600 will have a different # 07x
 

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Chris, there you go, the P/N from Karas.
Looks like just a metal screen filter. May be you can clean yours out with compress air? You know just another blow job:D
Just for clarification. The p/n is the pump p/n not the filter p/n.
 

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I have not done any flushing myself as my fluid in the tank still looks clear.
But I verified it with AllData for the 129 067 :
129.066 is for 1990-1992
129.067 is for 1993-1998
129.068 is for 1999 and on to ? (my AllData does not go beyond 1999)
The chassis is not as important as year the car was built and the VIN.

RST hydraulic pump design and p/n

p/n 129800 0048 or 0548 (OLDER top and roll bar pump - from 1990 to 1998, boxy in shape)

p/n 129800 1948 (NEWER top and roll bar pump - from 1997 VIN 145547 to 2002, cylindrical in shape)


NOTE: using your VIN I suggest that you verify with the Elec. Parts Cat. - EPC.
 

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So the old pump has 2 feed lines plus the return line at the Cap with a filter. Flushing will be simple : just remove the cap with the line and put the whole thing in a receiving container.
The newer Pump has only 1 feed line plus a return line. Flushing will require disconnecting the return line (per your write up). Is there a filter somewhere ?
 

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My pump p/n is 129800 0048.
Here's a picture of the filter attached to what should be the return line.
Jim are you sure that your pump p/n 129800 0048 is not really p/n 129800 0548 ?

Note: this is not in any way meant to take this thread OFF TOPIC but FYI the RST electronic controller for a 1990-1993 is p/n 129820 0097 and has a seperate rollbar controller if built prior to 11/92. After 1993 the rollbar controller was incorporated into one controller unit.
 

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I always thought there was a filter...

Anybody know the p/n for it? I'd like to replace it when I do my flush.
Chris,
When I did mine it was like the one in the picture. Yours is newer so maybe different. Mine looked like it was a very fine stainless steel mesh. There was pretty much nothing in it, but I still cleaned it with a spray degreaser, and then blew it out with air (not too much pressure). I don't think you need to replace it unless the screen is damaged, but your choice.
Karas,
Yours is the same as mine. i can't remember if the filter threads off, or just a light pull, but I had it apart enough to see the inside was clean when I flushed it out.
 

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So Lynns,
does your 2000 has the round cylindrical tank ? YES
Is there a 3rd line attached to the cap ? NO
Is it a 129 068 or different # (069?) 129.068
Chris's 600 will NOT have a different chassis # than my129.068
R129.068 is a correct chassis number for a MY99-02. Engine and transmission numbers DO change throughout the 99-02 R129.068 chassis number. Example: Chris has an V12 M120.983 engine with a 722.6xx transmission and I have a V8 M113.961 engine with a 722.624 transmission. NONE of which has anything to do with the pump p/n's.
 

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My pump p/n is 129800 0048.
At this point I think we can agree that MY90-98 has a center return line, shown in the above pictures, and the return line should be placed into a >500 ml container as the top and rollbar are cycled with fresh fluid and the pump is filled with new fluid as it empties.
 
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