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I just rebuilt all hydraulic cylinders on my wife's 2001 SLK320. Cylinders were leaking for more than a year (my wife is patient:) and the Vario Roof worked but leaked.

After I was done with the job I went to test. The top would not operate with full pressure, pump ran but top would not operate. I thought at first it was air in the system since I removed all lines. I kept pump running until the overheat shut down was active, after cool down, still no top movement.

I plugged in my SDS and checked for faults, no faults found. Looked at Live Data. All seemed good.

I talked to a couple techs who told me that the pump was bad... "seen it a dozen times" they said. I did not accept that result (pump was $$$ my cost) since the top worked great before I fixed the cylinders.

So I looked into it with my thinking cap on. The pump ran but not enough pressure. The pump has a pressure regulator and a pressure relief screw valve. I took apart and cleaned the regulator, no go but found bits of what seemed to be an 'O' ring. Then I took out the pressure relief screw and found an 'O' ring was cracked and broken. NOTE: Take note of a small spring at the end of the screw.

Refer to photos (pic1 - screw location, pic2 - missing 'O' ring)

My guess is; similar to a sink/toilet shut off valve, works great until you turn it. Same here, I had to release the pressure to operate the top manually and I believe that cracked the 'O' ring. So I looked thru my tool box and found 'O' rings that would work -- BAM, top works great.

Everyone told me it was a pump, glad I don't listen to people:)
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Premium Member 2005 SLK55 AMG; 2005 SLK350
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This is a great find - I wonder how many pumps have been replaced due to this.

I have a question though. Are you talking about the relief valve that you have to unscrew for emergency/manual closing of the roof? If yes, how do you get to this o-ring? I didn't think you could fully remove this screw - it seems to have limits how far it can be unscrewed.

https://drive.google.com/folderview?id=0B7bz5FHsVan-Tno0a3p1TmtwdkU
 

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efair, yes the pressure relief valve will come out all the way.

If you look at the first picture I attached (vario_roof-pump.jpg) you will see the brass screw valve, where I circled, and an aluminum screw valve next to the brass screw valve. The aluminum valve blocks the brass relief from being removed all the way. So remove the aluminum valve (5mm allen) carefully and put a rag to catch oil. NOTE: Be sure to clean and check the copper seal for the aluminum valve, for it can leak. Then the brass relief screw valve can be removed all the way. Be careful because at the end of the brass relief valve there is a spring and a small steel ball.

The next picture I attached is the brass relief valve removed all the way.

When you put them back in... DON'T OVER TIGHTEN! I would imagine they would break easily.
 

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Thank you for your post. Just fixed mine with
the same problem. Shop said needed new pump but your fix worked! Saved big $$$ Thanks again!
 

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Thanks for this very useful and money saving post! I'd appreciate more details about how to clean the pressure regulator. I'm not sure which part it is.
 

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Great Find and thanks so much for posting, this solved my problem to and the roof works faster than ever! Best 15 cents I ever spent *lol
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Dont' know you but THANKS MATE!!!

Exactly the same prob with my old man...you just saved me a few hundred bucks.
Cheers
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I just did mine too. Here's the O-rings I used and it works great: The chrome bolt is a 11/32" x 7/32" x 1/16" . The brass relief bolt uses 2. The rear one (towards the head of the bolt) is a 9/32" x 5/32" x 1/16". The front one (the one nearest the spring, and the one you show missing in the photo) is a 1/4" x 1/8" x 1/16". They do fit a little snug, so be sure to put some fresh oil on them prior to inserting. Top cycles fast now!
Thanks
 

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Great posting and it shows one more time that the policy of the professional mechanics is making more money with replacing rather than repairing.
That is 5 cents versus 500 $.
When I had my cylinders repaired by a mobile mechanic he messed up the cylinder and replaced the oring he broke with a too large one.
Result was the there was no pressure build up because the oil could nicely flow around. Needles to say that mechanic lost a customer for life.
So back to the cylinder, examining what happened and replaced the oring with a correct size one and the roof worked again.

Your posting shows another spot to look for ! Great find.
 

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Discussion Starter #13
Yes you must remove the aluminum first.


Why can't you remove the aluminum valve?

-- 5mm allen stripped? If so use an "easyout" or apply valve grinding compound to your 5mm allen wrench.
-- Aluminum valve comes loose but does not want to come out all the way? If so, I believe the 'O' rings might be preventing it, carefully wiggle to get it out.
-- Other? Write back and let me know with pictures.
 

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O-Ring Info for the pressure relief valve

I just rebuilt all hydraulic cylinders on my wife's 2001 SLK320. Cylinders were leaking for more than a year (my wife is patient:) and the Vario Roof worked but leaked.

After I was done with the job I went to test. The top would not operate with full pressure, pump ran but top would not operate. I thought at first it was air in the system since I removed all lines. I kept pump running until the overheat shut down was active, after cool down, still no top movement.

I plugged in my SDS and checked for faults, no faults found. Looked at Live Data. All seemed good.

I talked to a couple techs who told me that the pump was bad... "seen it a dozen times" they said. I did not accept that result (pump was $$$ my cost) since the top worked great before I fixed the cylinders.

So I looked into it with my thinking cap on. The pump ran but not enough pressure. The pump has a pressure regulator and a pressure relief screw valve. I took apart and cleaned the regulator, no go but found bits of what seemed to be an 'O' ring. Then I took out the pressure relief screw and found an 'O' ring was cracked and broken. NOTE: Take note of a small spring at the end of the screw.

Refer to photos (pic1 - screw location, pic2 - missing 'O' ring)

My guess is; similar to a sink/toilet shut off valve, works great until you turn it. Same here, I had to release the pressure to operate the top manually and I believe that cracked the 'O' ring. So I looked thru my tool box and found 'O' rings that would work -- BAM, top works great.

Everyone told me it was a pump, glad I don't listen to people:)
Thanks for this valuable information about the "missing o-ring" on the relief valve of the hydraulic pump (R170). For curiosity sake, I remove the relief valve to check the condition of the o-ring, and I discovered that there is no o-ring anymore It appears to have crumbled into pieces. I took the required measurement of the o-ring groove and determined the metric size needed. I found a suitable material and o-ring size at McMaster Carr website. In case anyone is interested, this is what I ordered: Material is Chemical-Resistant Viton® Fluoroelastomer O-Ring, Super-Resilient, 1.5 mm Wide, 3 mm ID
McMaster Carr Part number 1295N149.
Price is $4.28 plus Tax and Shipping.

I can't wait to try it. I hope it will fix my hydraulic pump too! I will give an update after I've tried it!:smile:
 
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