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 Hydraulics and pressure; how long?
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paul-NL

Netherlands
4176 Posts

Posted - 10/18/2010 :  19:32:19  Show Profile  Reply with Quote
Oeps fellows,

that was not my box, but i took a picture from my collection

but here are pictures in black/white of mine :








Edited by - paul-NL on 10/18/2010 19:33:31
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Chris Johnson

USA
3751 Posts

Posted - 10/18/2010 :  22:30:49  Show Profile  Reply with Quote
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.
100.012-12-000790
100.012-12-000867
www.300SE.org
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Ruud

Netherlands
66 Posts

Posted - 10/19/2010 :  18:03:01  Show Profile  Reply with Quote
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...

















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Ruud

Netherlands
66 Posts

Posted - 10/19/2010 :  18:18:05  Show Profile  Reply with Quote
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!



Edited by - Ruud on 10/19/2010 18:19:01
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FrikRoux

South Africa
103 Posts

Posted - 10/20/2010 :  14:31:57  Show Profile  Reply with Quote
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.

100.012-22-01214
109.018-22-004349
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Ruud

Netherlands
66 Posts

Posted - 10/21/2010 :  05:52:59  Show Profile  Reply with Quote
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..........
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Chris Johnson

USA
3751 Posts

Posted - 10/23/2010 :  20:49:36  Show Profile  Reply with Quote
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.
100.012-12-000790
100.012-12-000867
www.300SE.org
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Art Love

Australia
6101 Posts

Posted - 10/24/2010 :  02:09:58  Show Profile  Reply with Quote
Well, I've had front seat creep for 20 years, but never window creep.
Art
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Ruud

Netherlands
66 Posts

Posted - 10/30/2010 :  12:36:02  Show Profile  Reply with Quote
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...
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Chris Johnson

USA
3751 Posts

Posted - 10/30/2010 :  12:51:44  Show Profile  Reply with Quote
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.
100.012-12-000790
100.012-12-000867
www.300SE.org
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Ruud

Netherlands
66 Posts

Posted - 10/30/2010 :  18:14:13  Show Profile  Reply with Quote
@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.
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Chris Johnson

USA
3751 Posts

Posted - 10/30/2010 :  19:00:38  Show Profile  Reply with Quote
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.
100.012-12-000790
100.012-12-000867
www.300SE.org
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Ruud

Netherlands
66 Posts

Posted - 10/31/2010 :  12:17:22  Show Profile  Reply with Quote
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......
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Chris Johnson

USA
3751 Posts

Posted - 10/31/2010 :  12:34:47  Show Profile  Reply with Quote
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.
100.012-12-000790
100.012-12-000867
www.300SE.org
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Ruud

Netherlands
66 Posts

Posted - 11/05/2010 :  07:00:22  Show Profile  Reply with Quote
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.

Edited by - Ruud on 11/05/2010 12:14:19
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