Hey guys — problem I'm trying to diagnose on my 2008 SL. No problems with the roof since I bought the car and now this! Figured I'd start a separate thread.

A few days back, I closed the top and, particularly in its final stages, it moved extremely slowly.

I cannot get it open again — the trunk lid lifts slightly but won’t proceed any further:


If I keep pulling on the switch to open, the pump continues to run but I eventually start hearing a “whining” noise.

If I push down on the switch to close, it slowly closes back up.

I've attached a couple of videos -- one captures opening, the other captures closing.

I think there is some hydraulic fluid residue in my trunk. And I'm not sure, but perhaps the pump is a little low?





I would have thought it’d be the trunk lid drive cylinder but that area seems dry... I don't see any obvious leaks, and I'm having trouble tracing this liquid in the boot anywhere.

Does anyone have any idea what the "whining" noise I'm getting from the pump is after a time? Also, any guides to removing the trunk trim? Having trouble doing that.

I intend to try the diagnostic procedure I've seen on here and elsewhere (involving removing a few of the lines from the valve block), but figured I'd ask first.

Of note, my rear windows do not drop before the whole thing times out. Looking at the diagnostic aid... would seem to indicate the tubular frame cylinders or the trunk lift cylinder in the rear left corner of the trunk?

I know that internal leaks are supposed to be rare but it seems like that might be what is happening here? Or do I have a bad valve block?

(Of note, the roll bar works just fine)

A slow-moving roof is an enigma to me.

In the spring of '18 I got an '04 SL500 for just $6500 because the roof was inoperable. After repairing a broken hydraulic line and front lock cylinder with an internal leak, functionality was mostly restored. The roof was fast to open/close, but during an opening operation the tubular frame would not move to close unless assisted manually. The roll bar did not work at all.

I managed to cycle the roll bar up/down with manual assistance, and subsequently everything worked tremendously slowly. Comprehensive diagnostics revealed nothing wrong. Then suddenly for no apparent reason everything worked beautifully well.

The level of oil in the pump reservoir looks to be adequate to operate the roof, but it appears to be low. That suggests an external leak.

I'd monitor the oil level closely. You might put a piece of making tape on the side of the reservoir and mark a line with a pen which is even with the fluid. That way you can quickly and accurately gauge whether or not you are losing oil.

Meanwhile, I think checking the lock and tubular frame cylinders for internal leaks as you suggested doing is a worthwhile exercise.

Thank you! Will do.

In browsing Top Hydraulics’ site I just discovered that 2006 and later models have a different arrangement in for the trunk lifting in the form of an additional cylinder:

Any thoughts on what this would mean for checking internal leaks and whether the line numbering is any different?

I was unaware of this change. The test steps for the roof hydraulics seem to be the same for all years, and the technical documents in the the diagnostic software (DAS) seem not to reflect the added cylinder. I won't speculate how the numbering scheme for the hydraulic lines is affected.

Alright, so I finally managed to tear apart the trunk lining (not looking forward to trying to put all of that back in...) and I think my wife and I found the problem...

Consistent with my observations of a leak coming from the right side of the trunk, when we removed the right side trunk lining we found a lot of dark fluid hiding in the shelf above the battery.

At first I was puzzled because I wasn't sure what fluid of that color I could possibly find in that area of the car. But then I noticed that the fluid had caused some of the grey rubberized material in the top left of the picture (which extends down behind the BCM) to become viscous/sticky and to start degrading.

Touching the right tubular frame lock cylinder gave me another strong hint -- it was wet to the touch. And, I think I found a small piece of a black o-ring in the morass. So, pretty sure the source of the trouble is that cylinder.

Am I right that there's nothing else that could be leaking in that area? Could this be the sole cause of my issues?

Previously, the trunk was lifting up slightly and then failing to continue its cycle. Now it doesn't lift up at all. I assume it's falling short of engaging Switch 118 and so the trunk lift cylinder never kicks in as a result? As a means of testing this out, should I get the whole sequence to work if I manually unlock the tubular frame, or would the trunk lift motor still fail to engage?

The mechanic that did the PPI on my car noted that the roll bar was a bit sluggish -- I wonder if this has something to do with it and if it's been a problem for a while now, as I believe there's some pressure in these cylinders as well when it's operated? It still works...

When the pump runs and the main valve is open, the lock cylinders and the tubular frame clinder(s) are always pressurized on their "rod" sides. So an internal leak in any one of those cylinders can cause a drop in system hydraulic pressure and affect operation of the entire system, including the roll bar.

I agree with all of your assumptions in regard to what you have found. At a minimum I would send the leaking cylinder to Top Hydraulics, and unless you have reason to believe he locking cylinder on the other side has been replaced, I would likely send it too as a preventive maintenance measure.

Took another look at it and, sure enough, when I activate the roll bar the frame lock cylinder starts visibly bubbling and leaking fluid. Guess I’ll rip it out and send it off (and probably the other side too).

Thanks for the help!

So, I wound up sending both cylinders off to top hydraulics. I got them back, put everything back together... and got pretty much the same problem. I could operate the roll bar (sluggish at times) but when trying to open the roof the pump would eventually make the same “squealing” noise and time out.

I figured there was air in the lines, not enough hydraulic fluid in the pump, or a bad seal elsewhere in the system.

In the end it was probably all three. I eventually filled the reservoir enough to get the roof to open but my moment of success was ruined by a massive leak of hydraulic fluid from the front lock area immediately destroying my Alcantara headliner...

Now to figure out the best way to get this front lock cylinder replaced on a car that is my daily driver at the moment.

Just to close the loop, did a front cylinder swap with Cabriolet Hydraulics and everything works now! Still
hearing a little bit of whining from the pump but I’m thinking that could be some air in the lines.

Thanks for your help @bobterry99 !!