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 Hydraulics and pressure; how long?

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Ruud Posted - 10/17/2010 : 15:56:53
I've done some testing lately in order to try to establish how 'healty' the hydraulic parts of my W100 are - so I know when I'll have to start saving money ;-) After killing the engine I can open and close the drivers window 23 times, which I think is a pretty good score. When I start the engine after this, the system is pressurized almost immediately. Also, so far I didn't find any leaks whatsover. But here is the question; when I park the car after a drive, the hydraulic system slowly depressurizes in 3 or 4 days. I kinda don't like that, I ususally take the car out for a ride once a week but like this it is always a hassle with the trunk - unless I start the car first. So; for how long should the system stay under pressure? And, as in my situation, the pressure in the hydraulics slowly decreases, where does it go?! Where is it leaking from? It certainly doesn't spill any hydraulic fluid in the process...... Any ideas? Thanks, Ruud
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Ruud Posted - 05/29/2017 : 14:00:45
It has been a long time, but I guess one shouldn't rush fixing the hydraulics of a 600.. But finally, finally my car holds pressure for a long time. And to be honest, not so much due to my skills, but for the most part due ot the interventions of Mr. Werminghausen. Some of you may remember this old thread, that started with problem that in approximately three or four days all hydraulic oil would flow back to the reservoir - including the oil from the accumulator. So every time I would take the car for a drive, it had to repressurize. For way too long I tried to find the element(s) with an internal leak ‘downstream’ as Mr. Werminghausen calls it. That is, behind the shut-off valve. But whatever I tried (the book describes some testing procedures), it never prevented the reservoir from being filled after a while. In the end I even tried to block the return hose completely - still the same problem! Then I remembered an almost forgotten suggestion that Mr. Werminghausen made months earlier. That is, to suspect the check-valves of the pump and the accumulator. So oil would not (only) flow back from the elements, but directly from the accumulator, using the supply hose. Finally it all made sense. But by that time the reprssurizing of the system started to take longer and started to act erratic. Just when I was wondering wether to remove both the pump and the accumulator (I always get nervous shipping parts), the accumulator seemed to have broken down completely, not being able to hold any pressure. Things got from bad to really worse. I discussed the repair of both the pump and the accumulator with Mr. Werminghausen. He strongly suggested to add a hydraulic gauge in the system, that would make it possible to closely monitor the system. Fortunately I had a spare flexible hydraulic line. After Mr. Werminghausen sent a gauge, I attached it to a spare connection of the shut-off valve. In the mean time I shipped both the pump (Bermag) and the accumulator to Mr. Werminghausen, who has developed a dedicated test bench for the pump. Both items were in desperate need for some attention, and the accumulator was even clogged with big chunks of dirt that may be deteriarated rubber. The hydraulic system really needs to be clean on order to keep working. Well, my parts were in a different condition - to say the least. Mr. Werminghausen completely overhauled both the pump and the accumulator, using new designed parts and even a new piston for the accumulator. The re-fitting of the pump and the accumulator is not too complicated. After starting the engine I immediately noticed the pressure build up by the gauge, that ended at exactly 200 bar. It has been quite a long adventure, but I finally feel that I am in control of the hydraulic system, and not the other way around. Much to the credit of Mr. Werminghausen to be honest, who suggested to add a permanent hydraulic gauge. I just feels great to really see how the sytem is behaving, in real time. No more guessing and assumptions. I do not own any shares in Mr. Werminghausens company :-) so I am at liberty to really recommend him for both the air suspension and you hydraulic parts. Besides the perfect job he is doing, he is always there to answer questions or share thoughts. Anyway, here is the setup of the guage:

Ruud Posted - 11/05/2010 : 07:00:22
Hi Chris,
I've been monitoring the fluid level in the reservoir after parking the car a couple of days ago. Baselevel immediately after stopping the engine: distance fluid to top-of-reservoir = 9,5 cm. After 24 hrs: distance = 8,5 cm, which means an increase of hydraulic oil in the reservoir of 1 cm. After 48 hrs: distance = 7,8 cm, additional increase of 0,7 cm. After 36 hrs: distance = 7,3 cm, an additional 0,5 cm. Total rise in reservoir: 2,2 cm, almost an inch. I wouldn't know how much cc this, someone that is better than me in math should be able to calculate that when knowing the diameter of the reservoir. On the other hand, I don't think it is relevant for my purpose. I think it is quite interesting that the speed with which the fluid level rises decreases with time, probably due to the fact that the system depressurizes.

Next week I'll use the car for a wedding, after that I'll start blocking the feeds. I'll start with the front seats, next will be the trunk because I know the former owner worked in it and I don't really trust him to have done the best job possible.
Chris Johnson Posted - 10/31/2010 : 12:34:47
Hi Ruud,

Technically, the book is correct. However, this assumes that the shut-off valve itself is working correctly.

The only way to 100% guarantee that there will be no mess is to fully exhaust the system pressure by operating a device (window) until no pressure is left.

Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.
Ruud Posted - 10/31/2010 : 12:17:22
Hi Chris,
I defenitely will determine the magnitude of the leak before starting with the front seats. Just one question before I start to plug the feeds; the manual says that it I just have to close the shut-off valve, and open/close one of the windows only one time in order to depressurize the system (behind the valve). Is that 100% correct? Just checking - better safe than sorry - I don't want to create a hydraulic fountain in my interior......
Chris Johnson Posted - 10/30/2010 : 19:00:38
Hi Ruud,

The front seats are the easiest to do. Slide the seats forward and pull out the rear seat carpets, and the connectors are accessible at the very front of the rear footwells. You have a full emergency kit so you may as well do both seats at the same time. It will require a total of four plug pins.

If possible, I think it would be advantageous to determine the magnitude of the leak before starting. Using tape or some other material, mark the fluid level in the reservour as soon as you shut off the engine. Make successive notes on fluid level at regular intervals until you begin to get a feel for the magnitude of the leak. Continue to do this until you know how long it takes for all system pressure to be bled off. This will make it a LOT easier to determine if there is more than one leak in the system since you will be able to determine if disconnecting a section of the system has had an effect on the bleed-down rate, even if it didn't stop it completely.

You have a late car, so all your switches should have brass bodies. These are still easy to scratch, but not as easy as the early type bodies made of aluminum. However, you'll still have to be careful when removing the U pins to not bugger up the metal. Without special tools, about the best I can recommend is to find some thin but strong steel and a very small flat-blade screw driver. The screw driver can be pushed between the U clip and the body to lift the clip far enough to get hold of it with a pair of quality pliers. Something like a cut-up hose clamp will give you a piece if thin and strong steel to put against the switch body so that the screw driver doesn't actually touch the body and scratch it.

You won't be pulling clips from switch bodies in order to plug off the front seats, but the in-line connectors for the seats will give you a chance to understand better how these U clips work and practice a little before having to move on to the more delicate parts.

Note that if you do find a leak in a seat switch, you should remove the entire switch assembly from the seat and have the whole thing (all three sections) repaired. There are quite a lot of short rigid lines going to the individual switches, and I suggest not trying to remove these lines without the special pliers. The rigid lines have to be bent to remove them and great care must be exercised to avoid kinks and possible splitting of the lines.

We will have to talk again when (if) it is time to expand the search into other parts of the car. Other than the trunk latch and the parking brake release, the other parts of the system in the car have multiple switches in parallel and you have to plug off multiple feeds and returns at the same time in order to avoid being fooled.

The climate control unit is functionally straight-forward, but getting to its feed and return is a real nightmare, so it will be last to be tested.

Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.
Ruud Posted - 10/30/2010 : 18:14:13
@Chris: You must be right about this. I am not completely familiar with how the accumulator works, so I just thought it was possible that the loss of pressure could be caused by the accumulator. Anyway, I am going to test the switches now, starting with the switch of the drivers seat. Do you have any suggestions which switches I should give priority thereafter? Any known weak spots that are first suspects for the internal leak? And, if not, what feeds are most easlily blocked? If order doesn't matter, I would like to start blocking feeds that are most easy to work with.
Chris Johnson Posted - 10/30/2010 : 12:51:44
Hello Ruud,

While I think it is always important to satisfy our own concerns, do note that it is not possible for the accumulator or the lines to the shut-off valve to cause this problem. The problem must exist in a part of the system that can return fluid to the reservoir.

Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.
Ruud Posted - 10/30/2010 : 12:36:02
First test: accumulator (hydraulic oil pressure container). Just to be absolutely sure that the internal leak is caused by a switch, I decided to further test the accumulator. So I went for a ride, parked the car in the garage and immediately closed the hydraulic shut-off valve (btw, I have nr 2361, a pretty late car). Though I already knew that the accumulator could accumulate enough pressure, it still might be possible that it would loose pressure over time. So after a week I checked the car, turned on the shut-off valve and checked the pressure. I found out all pressure was still there, so nothing wrong with the accumulator or any lines that can be found before the shut-off valve. I guess this means I have to start checking the swithces one-by-one now...
Art Love Posted - 10/24/2010 : 02:09:58
Well, I've had front seat creep for 20 years, but never window creep.
Chris Johnson Posted - 10/23/2010 : 20:49:36
Hello Ruud,

Note that hydraulic fluid is non-compressible. Once the system pressure is gone, any minor movement of an element will completely eliminate any pressure behind it instantly. The windows (or seats) will have no pressure on either end of the element and no longer move.

Truthfully though, if your 600 doesn't have creeping windows, you have one of the precious few.

Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.
Ruud Posted - 10/21/2010 : 05:52:59
Reading the post of FrikRoux makes me wonder; my car looses hydraulic pressure, but the windows never drop, nor any other system that I know of... appearently when the feed is no longer under pressure, the line beween the switch and the working element keeps its pressure, isn't it? Hmmm intriguing..........
FrikRoux Posted - 10/20/2010 : 14:31:57
Thank you for informative reading gents! I've just noticed that my car's left front window goes down somewhat whet it stands for more than a day.

Ruud Posted - 10/19/2010 : 18:18:05
Hi Chris, Thanks again for the time and effort you took to help me diagnose the internal leak. Indeed, I will start with the seat, because it is at least clear the something is wrong with it. Let's hope that plugging the feed (just found out I own a repair set :-) ) wil stop the loss of pressure.... I will try this first and then wait a couple of days, and compare the increase of oil with the 'point zero' measure.

I must say I am not looking forward to a situation where I still see an increase of the oil level..... In that case the leak can be just about anywhere!! That is going to be a matter of trial and error...

I will keep you updated, but won't do things in a hurry. Let's just hope this is not going to be a very long thread.....

Thanks again!

Ruud Posted - 10/19/2010 : 18:03:01
Hi Art,
Just did some pulling, and was pleasently surprised by what I found... It looks like this set was never ever used, some items are still packed in plastic.... No for long I guess...

Chris Johnson Posted - 10/18/2010 : 22:30:49
Hi Ruud,

I think you have the situation well understood.

Indeed if the seal between the two sections of the actuator leaks, then the actuator will extend out. However, regardless of the service manual's comments, actuator leaks occur much less frequently than switch leaks. I won't deny the possibility though.

And there still has to be a defective switch somewhere in the system. I took a good look at the schematic this afternoon, and there are a couple of locations in the car where a switch is always operated in one direction, or the other. All of the user operated switches return to the center position where neither valve should be open, and any problem associated with any of these switches would require two leaks to totally bleed off pressure. But there are a total of eight switches that are not directly operated by the user. The four door latches each have one switch (assuming your car has these, what is the VIN of your car?), the trunk latch has two switches, the climate control unit has two switches, and the parking brake release has one switch.

Each of these eight switches is driven to a default position (one side or the other), usually by fairly heavy springs. Another device drive the switch to the other side under certain conditions. The point is that one valve on these switches is always operated when in their default position. In these cases, if the other valve in the respective switch was leaking there would be a complete path that would leak off pressure. I include this just to show that there are a few cases where a single fault could cause your problem, however, it doesn't change the troubleshooting process.

I think it is still appropriate (as a starting point) to plug off the feed and return lines to the seat. Whether a faulty switch or a combination of switch and actuator, if the problem is in the seat assembly then this will stop the slow loss of pressure.

My hope, of course, is that there aren't multiple minute leaks in the system. If there are this could make for a most aggravating exercise. To help identify this situation, I suggest selecting a default position for all hydraulicly operated items in the car and marking the fluid level in the reservoir immediately after shutting off the engine. Default positions would be, for example, all windows up and all seats forward (and "up" for the front seats) and sunroof closed, etc. At some preselected time (which may have to be determined emperically), make a note how much higher the fluid level has moved. This would be good to do even before plugging the seat lines.

Let's say that the fluid level increased by an inch in two hours. Now you plug the seat lines, recharge the system pressure, and reset your reference mark on the reservoir. Now lets say that the fluid level doesn't rise at all in two hours. Well, we know that something in the seat assembly has a problem and continue chasing it furthur.

But let's say that the fluid level rose a half-inch in two hours after plugging the seat lines. This would give us reason to believe that there is a problem in the seat, but also indicate that there is a leak elsewhere in the system as well.

You will have to sort of figure this out as you go. The actual time over which to watch the fluid level will vary widely depending on the magnitude of the leak, but you get the idea.

I hope this helps, and I wait anxiously to read what you find!

Chris Johnson
If you aren't constantly impressed with your car, then it needs fixing.

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