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Registered 2007 SLK350
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656 Posts
Discussion Starter #1
Recently i hve replaced all four brake hoses, rear brake lines, and fitted new four pot calipers to the front.

I bled the brakes thoroughly, no air bubbles at any brake bleed screw, yet the brake peddle is awful. (feels OK untill the servo is on, and the peddle goes nearly to the floor.)

Since the last air bubble I have put through nearly 2l of fluid, with no change!

There is some air in their somewhere, but how do i get it out?

I suspect ABS unit.

Any tips or advice how to get it cleared?

I am using a pressure bleeder, at about 25psi into the master cylinder, and get a slow but steady flow from each bleed nipple, but no air is comming out!

Brakes have no bite, and are just soft for about 60% of the movement. Emergency braking is non existant!

Thinking of finding a garage to do it, but before admitting defeat hopefully someone has some advice.

Note this is not the same as replenishing the brake fluid, I am starting from an empty state!

Thanks
 

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Registered 2012 SLK250 CDI
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231 Posts
I am no expert on this but the only time I have done the same on an old MGTF (new calipers and lines) the workshop manual said that it must be done in a set sequence to avoid air in the lines and the ABS system.
Someone here will look it up for you on WIS I am sure!
 

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Super Moderator UK SLK 55 AMG 2007
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27,311 Posts
NEver done it, but have read what David said in one of our docs/diys.
There is a set sequence of what to do.

I'll try and find it for you Peter.
 

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Super Moderator UK SLK 55 AMG 2007
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27,311 Posts

Attachment in post 1
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,969 Posts
WIS calls for 30 PSI (2.0 bar) pressure. for US cars the order is right-rear, left-rear, right-front, and finally left-front.
 

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Premium Member 2013 SLK250
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2,385 Posts
Get a brake fluid of a different color and do a brake fluid change, yes brake fluid does come in colors. Use the order above and when the new color shows up stop and go to the next brake.
 

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Registered 2007 SLK350
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656 Posts
Discussion Starter #7
Thanks for the responses.

I read WIS before starting, as thought there may be a way of activating the ABS during bleeding. But only found the sequence, and the bleeding pressure.

I followed the sequence (three times now :mad: ) and am getting no air bubbles out of the nipples, and a good stream of fluid. I took it for a drive, and "exercised" the brakes vigourously, to try and get the ABS to kick in, but couldnt. Really need to find a loose surface, but non around here. Even bleeding after that produced no bubbles!

I have put through about 1.5l of fluid so far, so I am sure all the old fluid is out.

My only thought is that I need more pressure, but my Eezee Bleed is only rated at 20psi, and I am at 25psi already, so not far from 30psi (2bar).

Replacing brake fluid is easy, as you do not bring any air into the system, but getting air out is being a right pain!
 

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Super Moderator UK SLK 55 AMG 2007
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27,311 Posts
Left field thought. Really left field.
Disconnect battery for 30 mins.

Probably won't do it, but easy to try and you never know.
 

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Registered 2007 SLK350
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656 Posts
Discussion Starter #9
Left field thought. Really left field.
Disconnect battery for 30 mins.

Probably won't do it, but easy to try and you never know.
I did a scan on DAS, and that didnt work either :D

Battery is off now, but ....

Trying to find a garage who can bleed it at a higher pressure, and have a lot more experience than i do.
 

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Premium Member 2013 SLK250
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2,385 Posts
Question have you drove the car. I had new pads put on the front and the pedal was soft and much travel for the first miles and a day of driving. The next day the pedal was firm and travel was much less. Guess the new pads needed to seat.
 

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Registered 2012 SLK250 CDI
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231 Posts
I know this may not be the recommended method but you could try using a vacuum at the bleed end to pull the air through? That could be a more efficient route to remove air bubbles.
If air has got into the ABS unit that could be a lot more difficult to remove, I am not experienced in MB ABS units but other makes would need to be plugged in to diagnostic systems to open up ABS valves etc to remove trapped air bubbles.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,969 Posts
@DavidD I don't believe there is any such option to "open up ABS valves" in SDS or any other scanner I've seen (although I do know many brands require this, e.g. Ford). I have been under the impression that applying the requisite 2.0 bars of pressure is sufficient to bleed the ABS unit (although - honestly - I've never had anybody explain exactly how; it wouldn't be the first time I've labored under false notions). I guess someone would have to know how the ABS unit is constructed to speak definitively here?
 

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Registered 2012 SLK350
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205 Posts
I know this may not be the recommended method but you could try using a vacuum at the bleed end to pull the air through? That could be a more efficient route to remove air bubbles.
If air has got into the ABS unit that could be a lot more difficult to remove, I am not experienced in MB ABS units but other makes would need to be plugged in to diagnostic systems to open up ABS valves etc to remove trapped air bubbles.
David,
Vacuum is the only way I bleed all my Vehicle brakes. If the wife is available I some times will do the two man power bleed with Vacuum. I have never had an Issues our 2012 and it gets done every two years or when every there is any work on the brake system.
 

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Registered 2007 SLK350
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656 Posts
Discussion Starter #14
I have not driven the car, as it doesnt feel safe, but I might take it out for a few miles tomorrow to see if things get better. I fitted new front calipers (re-sealed and re-painted old ones :) ) along with Jurid White Ceramic pads (dont want to get my nice shiny calipers dirty!).

Its worth a try. Had something similar with my MG TF on the clutch. Bled it, it again was soft for a few days, but then had to park it on a slope (front up) over night. Next day clutch was firm, best it had ever been. Think some air found its way out parked like that!

I would like to do a round of conventional bleeding, as will generate a lot more pressure in the brake lines, but no one to assist.

If all that fails then its to a garage early next week.
 

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Registered 2007 SLK350
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656 Posts
Discussion Starter #15
Found a lot of tests in DAS in Developer mode, as well as in Vediamo, for "excercising" the ABS unit. Not sure what they all did (well one closed all the valves, as the peddle went absolutely solid!), and another seemed to activate all the solenoids. Ofter one of the tests the peddle went totaly soft, so bled it again. NO bubbles!!!! BUT there was a significant improvement after re-setting everything again, so will see if it beds down once the new pads adjust to the old disks.

Also never realised the car has Emergency brake activation....Found the test for that too...Wow you would know when that activated :)
 
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