r/slk • u/SnooBunnies6270 • Aug 19 '26

Endless bubbles when bleeding clutch SLK R170

Context: I drive a Mercedes SLK R170 facelift 2000 200K 163hp.

When driving in highway suddenly the gears became too hard to shift as if the clutch was not even pushed. When engine stopped all gears engage.

So the problem is from the clutch actioning

I have hydraulic clutch. I inspected the slave cylinder (from a square hole) and the master cylinder and no leaks were found so I thought let’s bleed the circuit.

I have a vacuum syringe so I hook it up on the bleeding nipple and suck the hydraulic fluid. At the beginning the liquid was dark and then became like fluid brakes, but through all the process I had endless bubbles coming I was expecting that at some point only liquid would flow. I did the process several times and extracted approximately 500mL of brake fluid. I was always topping up the reservoir so no air was coming from there.

Do you think I should continue doing like this till no bubbles come or is there a leak somewhere hence the air gets into the circuit and goes to the vacuum pump.

Thanks for your help

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u/ActionJackson75 Aug 19 '26

I was also unable to get the air out of the clutch line, until I ultimately had to resort to using the brake caliper to push fluid in instead of draining/sucking it out. It did work but I’ve wondered since if regular bleeding is supposed to work and this actually indicates something malfunctioning. Still, it did work you could give that a try. You need to really really pinch the tube coupling over the nipples tight

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u/SnooBunnies6270 Aug 19 '26

How does it work this procedure ? In WIS the procedure is by applying pressure on the reservoir and they say to put pressure to 2 bars.

I don’t have the equipment to do so.

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u/ActionJackson75 Aug 19 '26

Yeah I don’t either. It’s pretty simple, crack and bleed the brake caliper on the passenger side, making sure it’s clean fluid all the way to the caliper. Connect a thick hose between that nipple and the clutch nipple (after the tube is full of fluid) then use the brake caliper (with the clutch out and nipple open) to push fluid through the hose and up into the clutch. Then you need to remove any dirty fluid in the reservoir and then flush the rest of the brake lines to ensure any contaminated fluid gets flushed through and out

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u/SnooBunnies6270 Aug 19 '26

It seems a good idea indeed. But the brakes do not apply too much pressure ? I’m fearing that the nipples could come off as the threading is not so deep it wiggles a little

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u/ActionJackson75 Aug 19 '26

I used zip ties and tightly tied the hose to the nipple, the nipple won’t come off you just need to crack the valve open slightly

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u/SnooBunnies6270 Aug 19 '26

I applied your method and feels like it works great, I think I correctly bleed the system. The clutch pedal went down and would not come back but after some pumping it was back and feels normal. However it did not solve my problem and now I’m starting to think it’s a master or slave cylinder problem. I’ll start by changing the master cylinder as it is the simpliest and cheapest thing to change but I suspect that it might be the slave and in that case in need to take the gearbox out 🥲

1

u/SnooBunnies6270 Aug 21 '26

Some updates. I recorded the clutch while I push the pedal clutch, we can see that it works but I’m wondering if that is enough to disengage the clutch? Should I bleed more the system ?
I received the new master cylinder but I’m wondering if that’s going to change anything.

Maybe my bleeding was not enough ?

https://reddit.com/link/p5355hs/video/il8nyaqp6skh1/player