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.

 

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.

 

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.

 

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 ?

 

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

 

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.

 

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.

 

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.

 

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.

 

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

 

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.

 

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

 

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.

 

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 ?

 

While chassis # doesn't change from year to year (only when there are significant design changes), it (the chassis #) is also reflected as part of the VIN #, and when production switch in mid-1998 from MY-98 to MY-99 the chassis # also switch from 067 to 068. That is what I learn from AllData (of course they could be wrong). So we were talking about the same thing : chassis # is part of the VIN.

And the issue here is quite simple regardless of P/N or Chassis # or VIN # or even model year :
If you have a square tank and 3 hydraulic lines, the return line is the one attached to the cap, just unscrew it. There is also a wire mash filter attached. Blow it out with compressed air to clean if needed.
If you have a cylindrical tank and 2 hydraulic lines, then the return line is the one closest to rear of the car and needs to be disconnected with a wench (per your instruction).

After identifying the return line, the flushing instruction is simple as posted by you (Lynn) earlier, and it is the same for both pumps. I am not going to repeat it here.

 

Karas,

Appreciate that you at this point believe that "air" might have been introduced into the return line from the reservoir cap. This is a logical deduction if you ignore the way the system is plumbed. At each stroke of the hydraulic cylinders both locking and actuating, one side is pressurized and the other is connected directly to the reservoir.
If you do not see fluid coming out of this tube when the pump is running and the switch is actuated (either top or roll bar) you have an interlock preventing pressure from reaching the cylinders or some problem other than air. I urge you to try again and see if the symptoms have disappeared.

On another note: Lynns correctly provided the system description for your car which is different from the later models

"The entire electrohydraulic system consists of fifteen hydraulic cylinders, eleven
solenoid valves, five distribution and connection pieces and 45 lines. In the off
state the hydraulic system is not under pressure and all latches are locked
mechanically. A total of 17 limit switches signal the present position of the top to
the control unit in order to assure that the opening and closing operations are
completed properly."
For all readers, please note that the later models which can be identified by having only two hozes reduce the parts count by 3 solenoid valves and one hose.

It is a completely different system and therefore the two pumps cannot be interchanged without some jury rigging.

This is a difficult thread to follow because of the multiple comments but I hope this will help.

Regards,

George Anderson

 

This is a difficult thread to follow because of the multiple comments

Yes, I agree that the Thread became much more difficult than it ever needed to be.

So to summerize:

If you have a square tank and 3 hydraulic lines, the return line is the one attached to the cap, just unscrew it. There is also a wire mash filter attached. Blow it out with compressed air to clean if needed.
If you have a cylindrical tank and 2 hydraulic lines, then the return line is the one closest to rear of the car and needs to be disconnected with a wrench (per your instruction).

After identifying the return line, the flushing instruction is simple as posted by you (Lynn) earlier, and it is the same for both pumps.

 

Flushing hydraulic system - the first time.

Have followed LynnS directions of about one week back to flush my hydraulic system. A MY90, with the 'boxy' tank and three lines. Sadly, the whole car was seriously neglected before becoming mine in December - the previous owner carried a 4 litre can of some nameless hydraulic oil in the truck and just kept filling the system when it was low.....

First, tried taking out old fluid with a battery acid tester - as per your suggestion. The tip was too short to reach the bottom of the reservoir - so added a short length of rubber.
Then discovered the fluid was a mix of all the bad things that really shouldn't be there - small globules of water, several lumps of congealed matter, more like vaseline than fluid, black residue and some brown coloured fluid. The overall viscosity was so high that it was going to take for ever...

So switched systems, and (using a hand vacuum pump just purchased to begin diagnosing other problems) made a jam-jar suction set-up (see picture). This worked much faster - but still left a mess of black sludge at the bottom of the reservoir.
So - next step was to take the pump out completely (should have done this at the outset) and turned it upside down to drain into a waste-oil can. Also used correct new MB fluid to flush the reservoir several times, until all black residue was cleared away.

Next, re-install, fill with correct new fluid, and begin flushing the rest of the system into that jam-jar. One jar full of brown muck each half cycle and things were going OK, except there was a "pop" and a strange sound behind me on repeat three!

The filter (not mentioned in earlier instruction list - as later cars do not have one) had popped off and the line fallen away to leave fluid in the wheel well. So - no great problem, clean up and continue with filter removed (and draining) and cap now back into jam-jar.

Suddenly, the entire operation takes half the time - is almost "aggressive" with the new speed of operation. Conclusion is that filter is seriously blocked. A few more minutes to wash it, blow it clear and try as best to resolve. Confirming - it's become almost completely plugged (see picture of drained acetone washout).

Am trying to get a new filter, but no part number (as with other posts). Have now order the only item identified (the cap) and will learn if the filter is included (but not shown on drawing). Looks like filter is included, since price around $45 and a 6 day delivery from Europe. If any other member finds the answer - much appreciated.

Bottom line - if there is black sludge, or flushing has never been done before, recommend taking entire pump out and flushing tank.

Some pix available - now trying the uploading bit...



With best regards,

Ali Denton-Cardew.

 

- the previous owner carried a 4 litre can of some nameless hydraulic oil in the truck and just kept filling the system when it was low.....

.

You might still have a leak somewhere, should look into it as hydraulic fluid does not evaporates.

 

Thats the same as my "Filter". Its really just a steel screen. Mine was shiny and fairly clean compared to yours, but you may be able to do as I did, just sprayed it (from outside in) with an areosol spray solvent and blew it dry with air. Don't use too much pressure. Then make sure there is no damage to the fine screen.

 

I was reading about this so as to do it correctly. I think back on 11/10 iresfrank may have used power steering fluid in his soft top tank? my power steering fluid has a pale green color. iresfrank are you out their how is your soft top working? reading all of this was very funny.

 

Mercedes 0009899102 equals FeBi 02615 equals Aral Vitamol equals BMW 54340394395

I hope I'm not repeating anyone's previous post within this thread - in Europe, the alternative to FeBi 02615 is Aral Vitamol ZHM. I suspect that Aral is actually the manufacturer for all these fluids.

Sadly, BMW E46 and Porsche 996 convertible owners believe that they need to purchase Aral Vitamol in 250-ml bottles (1/4 quart) for $30 and up. (Sold as BMW part number 54340394395 or Hoerbiger HB92952-215)

Mercedes Hydraulic Fluid for Hydropneumatic Suspension (1 Liter) (MBZ Approval:343.0) 000989910310 - RM European Auto Parts

I would not hesitate to use Pentosin CHF-11S, which has very similar qualities and is oftentimes available in better car part stores (at a slightly higher price than Febi 02615).

Klaus

Top Hydraulics | Rebuilt and Upgraded Convertible Top Cylinders, Pumps, Hydraulic Lines - Top Hydraulics, Inc

 

I just flushed out mine last night with new 02615 clear, the 2 year old fluid came out looking like medium beer. I think it is working faster now. thanks for the thread I have been sick cant wait to feel better 1 week so far. pneumonia

 

I was wondering what side of the car is your holding tank on for hydro oil? In most pictures I see it seems to be on the passenger side. I also see a slot on the cover that goes over the pump on the right pass side, is that to see the oil level. The tank for my pump is on the driver side? so the view slot doesn't show the tank. thanks

 

The tank for my pump is on the driver side? so the view slot doesn't show the tank.

Please post a picture of your uncovered pump and cover, taken from the rear of the trunk facing forward, so we can see your MY97.

 

Just did this weekend on MY 2000

Just performed the procedure above on MY 2000. Freaked out for a minute when top stopped closing mid-operation - realized it was because we let the fluid "run out" - did not replace enough as we were draining the existing fluid. Works fine after filling up. Hopefully this does not cause any residual issues.

Like usafrank, also find that the top is "faster." Could just be imagining it, though.