A new roof problem - Mercedes Benz SLK Forum

SLK R170 General Discussion SLK 200, SLK 230K, SLK 320, SLK32 AMG

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  • 1 Post By efair
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#1 Old 03-18-2017
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A new roof problem

Well this is something new.
I've already posted that the top is not working again. I would try to retract the roof and nothing would happen except that the red light would flash rapidly. The windows would not lower, the pump would not run, etc. Nothing.
If you put the button in the raise position the pump would run and you could see the top flinch a bit as the pressure in the cylinders built up. Then the pump would stop.
I figured that it had to be micro-switches again. I started with the trunk/boot. I unscrewed the pressure release on the pump. I pulled the cords so I could raise the lid. I listened for the click on the switches and could hear each of them operating as I pulled or pushed each side of the lid the little bit necessary. The switches all tested good electrically with my VOM. I installed a jumper in the connectors and still the top would not work.
So it now has to be a switch outside of the trunk. I put the trunk all back together. Just for the record I thought I would try to open the top again.
This time the windows lowered and the pump started running.
Here is the 'something new'.
Nothing else happened other than you could see the roof relax a bit as closing pressure released. The pump will continue to run as long as the switch is held in the open position. The trunk/boot lid does not open and neither does the top.
The cylinders are not leaking and the oil level in the reservoir is right where it should be.
There is obviously no pressure being built to operate the top in the lowering cycle but pressure is built in the raise cycle.
Has anyone heard of this? I've read through the roof threads when I worked on this a couple of months ago and didn't see anything about this in the them.
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#2 Old 03-18-2017
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You need to determine the state of all the pins when it's failing, and note the physical position of all items, and report back here.

Intermittent problems are usually due to sticking switches or wiring faults in the flex point.

https://www.slkworld.com/slk-r170-gen...ere-start.html

If you've previously fixed it with some success, please let us know what you did.
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#3 Old 03-19-2017
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Try removing the headliner and watching if the mechanism works fine there..another "common" fault on the roof opening is the cables from the roof latch switches that run down the US passenger side, break in the area of the joint between the roof and rear windscreen sections, due to the continuous folding action of the roof.
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#4 Old 03-19-2017
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Let me restate the problem.
The pump runs and continues to run but nothing else happens when attempting to lower the roof. Something has to happen to cause the cables to operate. Nothing is happening other than the pump runs and will continue to run as long as I hold the button. Pressure should build up to the point of stopping the pump. But it does not.

efair, my previous fix was replacing leaking cylinders.
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#5 Old 03-20-2017
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The roof is a very detailed system and therefore diagnosis is very detailed.

The pump will only stop if it overheats - IDK how long that might take. The self-bleeding design allows the pump to run continuously without developing over-pressure.

With 1) the roof closed and the boot lid down, 2) the switch pulled back, 3) the pump running, 4) the light on solid: at the very least you should see motion from the rotary latch turning and then the boot lid raising.

Did you remove the round plug from the headliner to confirm the rotary latch is moving?
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#6 Old 03-20-2017
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If the pump is running and the top doesn't move, it sounds like one of two things:
1.) You have a hidden hydraulic leak that is causing all of the pump outlet to be dumped out the leak. (and the leak is hidden, so it hasn't shown up yet)
2.) The pump is bad and isn't producing any pressure

If you run the pump for awhile, if its 1.) above, hydraulic fluid will start appearing somewhere and the fluid level in the reservoir will go down. If not, it sounds like you have a bad pump.

Quote:
Originally Posted by dedgar View Post
Let me restate the problem.
The pump runs and continues to run but nothing else happens when attempting to lower the roof. Something has to happen to cause the cables to operate. Nothing is happening other than the pump runs and will continue to run as long as I hold the button. Pressure should build up to the point of stopping the pump. But it does not.

efair, my previous fix was replacing leaking cylinders.
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#7 Old 03-20-2017
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Originally Posted by twright View Post
1.) You have a hidden hydraulic leak that is causing all of the pump outlet to be dumped out the leak. (and the leak is hidden, so it hasn't shown up yet)
There is no leak. With the amount of time I have run the pump trying to get the top to move, there would be no fluid left in the reservoir. But the level is right where it should be at about half.


Quote:
Originally Posted by twright View Post
2.) The pump is bad and isn't producing any pressure.
The pump will produce pressure if I operate the system in the closing direction. The pump will even shut off after the pressure is built up.
However, if I try opening the roof, the pump runs, will continue to run as long as I hold the control switch that way, but nothing else happens.
Why is the pump producing pressure in one direction but not the other?
The micro-switches all have to be in the correct orientation or the pump would not run at all. As witnessed by having one stuck that I found and corrected thus allowing me to find this new problem.
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#8 Old 03-21-2017
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I agree that my two suggestions don't seem like likely issues. How about another one?

Is it possible that some of the hydraulic lines are hooked up incorrectly? Have the lines been off since the top and pump worked correctly?

Quote:
Originally Posted by dedgar View Post
There is no leak. With the amount of time I have run the pump trying to get the top to move, there would be no fluid left in the reservoir. But the level is right where it should be at about half.




The pump will produce pressure if I operate the system in the closing direction. The pump will even shut off after the pressure is built up.
However, if I try opening the roof, the pump runs, will continue to run as long as I hold the control switch that way, but nothing else happens.
Why is the pump producing pressure in one direction but not the other?
The micro-switches all have to be in the correct orientation or the pump would not run at all. As witnessed by having one stuck that I found and corrected thus allowing me to find this new problem.
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#9 Old 03-21-2017
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twright, the lines have not been removed. Even if they had been, something would become pressurized. That isn't happening and the pump continues to run.
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#10 Old 03-21-2017
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The logic and switches used during opening vs. closing are separate. I don't think it's safe to assume that all switches are OK just because the pump activates in one direction.

What does the red light do now when you pull the switch back? Still flashing fast?
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#11 Old 03-22-2017
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If the vent windows go down when you are trying to lower the top, I would confirm that the roof latch at the windshield frame is releasing. Try to manually unlock the latch by turning the latch release clockwise. Then pull back the convertible top switch again and see what happens..
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#12 Old 03-25-2017
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Quote:
Originally Posted by SLKKID View Post
I would confirm that the roof latch at the windshield frame is releasing.
You have to have some pressurized oil routed to the cylinder to make it operate. There is no pressure being generated.
No pressure = nothing moving
However, I found the problem with the hydraulic unit. One of the solenoid controlled directional control valves stopped working.
If you look under the motor end of the unit you will see two small 'cans' attached to that end. Those are the solenoids. Attached to them, inside the main block, are the directional control valves. They port the oil to the correct lines for all the cylinders to operate in the direction needed.
I had replaced the whole hydraulic unit last year during the rebuilding of the car. I had not recycled that unit. I took the solenoid valves off that one and put them on the one currently installed (but taken out to swap the solenoid valves). After reinstalling the assembly into the car, the roof now operates again.
With the solenoid valve now allowing oil to go to the correct places, pressure is built and things operate.

Now on to other niggling bits.
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#13 Old 03-25-2017
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Excellent - so a faulty solenoid was preventing the pump from running?
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#14 Old 03-25-2017
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Quote:
Originally Posted by efair View Post
Excellent - so a faulty solenoid was preventing the pump from running?
No. The pump would run but the oil was just recirculating. The solenoid for RAISE or LOWER has to activate to change the position of the directional control valve.
Only one of the solenoids was working, the one for the RAISE side of the system. The LOWER side was not working so the directional control valve stayed in the neutral position.
The pump merely took the oil out of the reservoir only to pump it right back to the reservoir through the body of the main valve.
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#15 Old 03-26-2017
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dedgar,
I've been collecting details on the R170 roof for a while, and the biggest mystery to me is the aluminum block, the relief valves inside it, and the two solenoids. Your findings are of particular interest to me, and much appreciated.

If you could, please let us know which solenoid failed, and what specific symptom resulted. Also, do you know if your solenoid fail electrically? Or mechanically?

The job of the solenoids, as I see it, is to switch hydraulic pressure to the appropriate lines at the appropriate times. So a failed solenoid would (might?) result in unexpected pressure (high and low) developing at unexpected places and times. We're you able to discern where and when?
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#16 Old 03-26-2017
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I do not know which one failed. Which ever one it was had failed mechanically and you cannot see the internals without destroying it. And in destroying it you would destroy any evidence to point out the reason for failure.
I did a continuity test on the coils to see if one of them had developed an open in the circuit. But they were both good.
The valve itself is a fixed sleeve with ports drilled in it with a poppet inside that the solenoid moves when energized. The clearance between the poppet and the sleeve is minute. It has to be or the oil would just bypass the poppet and go right to the return port.
The clearances are so tight that, if you handled the poppet with your bare hands, the acids in your sweat would eventually etch the surfaces and destroy the valve.
I believe some tiny bit of grit or something is preventing the poppet from moving.
I was ready to buy a complete unit from ebay if my parts swapping did not work. Luckily for me it did work.
As an 'Oh By The Way', I'm a retired industrial machinery mechanic. Both with the US Navy and later with Boeing Commercial Aircraft Co. I've worked with hydraulics as part of my job for over 40 years. So I know how these things work.
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