SL/R129: Flushing hydraulic fluid in cabriolet
Thread Starter
Super Member
Joined: May 2003
Posts: 696
Likes: 4
From: Motor City
95 E320 Cabriolet, 108K
Flushing hydraulic fluid in cabriolet
I'm big on changing fluids and filters as needed on my W124 95 E320 cabriolet. The hydraulic fluid for my electro-hydraulic top mechnism is still original at 95K, and I'd like to change it out completely, just as I do with my brake fluid and power steering fluid.
I could just change the fluid in the reservoir, but I'd rather do a better complete job of getting all the old fluid out of the system.
I propose the following plan:
- remove the return line, direct it to a dump receptacle
- change the fluid in the reservoir
- operate the top through a complete cycle - up, then down. All the while keeping the reservoir topped off.
- button everything back up
- top off the fluid
I'd like the job to be thorough, but not wasteful. Has anybody done this? Is there a consensus on how to best completely exchange the fluid? I'm posting in the R129 section because there is a high volume of expertise in electro-hydraulic tops here. Comparably, W124 cabriolet owners are somewhat rare.
I could just change the fluid in the reservoir, but I'd rather do a better complete job of getting all the old fluid out of the system.
I propose the following plan:
- remove the return line, direct it to a dump receptacle
- change the fluid in the reservoir
- operate the top through a complete cycle - up, then down. All the while keeping the reservoir topped off.
- button everything back up
- top off the fluid
I'd like the job to be thorough, but not wasteful. Has anybody done this? Is there a consensus on how to best completely exchange the fluid? I'm posting in the R129 section because there is a high volume of expertise in electro-hydraulic tops here. Comparably, W124 cabriolet owners are somewhat rare.
MBWorld Fanatic!
Joined: Nov 2002
Posts: 1,028
Likes: 133
From: Massachusetts
2018 GLE350, 2014 G550, 2000 SL500, 1980 TR8, 1995 E320 Cabriolet
Kestas -
Ironically, I have both an SL and an e320 Cabriolet. The hydraulic top systems are basically the same in both cars except that the e320 does not have the release cylinders in the A-pillars. Since the e320 was a hand-built conversion, I suspect that MB raided the SL parts bin for the top components.
I did a hydraulic PM on my SL per this post: pm-top-hydraulics and the results have been excellent. I plan to do the same with my Cab.
The reason for cylinder failure has to do with the soft plastic MB used for the seals which deforms due to heat/age (MB used polycaprolactone for the seals - a material that's primary used for prototyping). Moisture in the system is not usually a cause of failure, so a total fluid change may not buy you much. An additive that helps keep the friction loads down seems like the best bet to me.
Anyway, I thought I would share my experience.
- FD
Ironically, I have both an SL and an e320 Cabriolet. The hydraulic top systems are basically the same in both cars except that the e320 does not have the release cylinders in the A-pillars. Since the e320 was a hand-built conversion, I suspect that MB raided the SL parts bin for the top components.
I did a hydraulic PM on my SL per this post: pm-top-hydraulics and the results have been excellent. I plan to do the same with my Cab.
The reason for cylinder failure has to do with the soft plastic MB used for the seals which deforms due to heat/age (MB used polycaprolactone for the seals - a material that's primary used for prototyping). Moisture in the system is not usually a cause of failure, so a total fluid change may not buy you much. An additive that helps keep the friction loads down seems like the best bet to me.
Anyway, I thought I would share my experience.
- FD
Newbie
Joined: Apr 2008
Posts: 10
Likes: 0
1998 SL500
I have done this to my SL. Your method is sound but I'm not sure you need to go to the trouble of removing the return line. Use a turkey baster or similar device to remove as much fluid as possible then top off with new ZH-M. Cycle your system (including the roll bar if you have it) until the fluid turns dark again and repeat. I needed 2 quarts of ZH-M to completely flush the system. The system is self-bleeding so don't worry about getting air in the system. It will come back through the return line. Fresh oil will be the color of canola oil and you will see the difference readily.
