Pedal still soft after bleeding
Discussion
Ok, some of you may have seen my other thread. I dismantled my front two calipers on a w204 Mercedes 2013, refurbished them and put them back together with new rotors and pads.
All fits great but now having trouble bleeding.
I bled all 4 corners starting from the furthers away from the cylinder. I used the two person method, foot on the pedal, open valve, close valve, foot off.
All 4 corners bled fine, clear fluid come through, no air.
When I start the car the pedal still goes all the way to the floor. If i pump it i get some tension which is then lost as soon as I stop.
I have checked...
Both calipers are defiantly on the right sides and the right way up!
The master cylinder never was left to get too empty.
I gravity bled the two empty calipers before normal bleeding.
There are no leeks anywhere.
All hoses are in good new condition.
All nipples are clear and work fine.
Brakes worked fine before dismantling.
Unsure what to try next? Is it possible the pistons are stuck? Could I have wound them back to far?
Considering buying a pressure bleeder to see if there is more air in the system somewhere?
All fits great but now having trouble bleeding.
I bled all 4 corners starting from the furthers away from the cylinder. I used the two person method, foot on the pedal, open valve, close valve, foot off.
All 4 corners bled fine, clear fluid come through, no air.
When I start the car the pedal still goes all the way to the floor. If i pump it i get some tension which is then lost as soon as I stop.
I have checked...
Both calipers are defiantly on the right sides and the right way up!
The master cylinder never was left to get too empty.
I gravity bled the two empty calipers before normal bleeding.
There are no leeks anywhere.
All hoses are in good new condition.
All nipples are clear and work fine.
Brakes worked fine before dismantling.
Unsure what to try next? Is it possible the pistons are stuck? Could I have wound them back to far?
Considering buying a pressure bleeder to see if there is more air in the system somewhere?
Easternlight said:
If the pedal is soft then you still have air in there. Pressure or vacuum bleeder will help but some systems can be a pain, just keep going and don't be tempted to re use any fluid that comes out clear.
OK thanks, Think I will go get one of them tomorrow. Any preference over pressure or vacuum? Edited by Easternlight on Tuesday 7th April 20:20
I also read someone with a similar problem actually unmounted the caliper and moved it around slightly to get air out?
littleredrooster said:
Is it not just that the pads have not yet bedded into the discs and flattened themselves out? New pads + discs almost always = springiness in the pedal. A couple of miles on a quiet road with some left-foot braking usually cures it.
The pedal is going all the way to the floor. I hate to sound like the alarmist Helen Lovejoy type but your advice to simply take it for a spin could actually be quite dangerous. When bleeding braking systems in the past I've had a similar problem occur.
It usually is ,as already posted ,a matter of bleeding and sometimes can be an absolute pain.
On a couple of vehicles it turned out to be the master cylinder .
When the pedal is pressed right down to the floor during bleeding the piston travel is outside its normal operating range ,if there is a corrosion ring in this area then the m/c seals can be damaged ,this gave similar problems as per OP description.
New m/c cured the fault in both cases for me .
HTH
It usually is ,as already posted ,a matter of bleeding and sometimes can be an absolute pain.
On a couple of vehicles it turned out to be the master cylinder .
When the pedal is pressed right down to the floor during bleeding the piston travel is outside its normal operating range ,if there is a corrosion ring in this area then the m/c seals can be damaged ,this gave similar problems as per OP description.
New m/c cured the fault in both cases for me .
HTH
Hi OP
I have had the same issue many years ago and spent many hours and fluid trying to bleed manually with no success.
Got a pressure bleed kit and happy time a flow of bubbles came out and the pedal feel came back to normal
I cannot explain how the bubbles didn't come out using the pedal method, but it was sorted in minutes with the pressure bleed kit
Good luck, just make sure you don't remove to much fluid and drain the reservoir too low
I have had the same issue many years ago and spent many hours and fluid trying to bleed manually with no success.
Got a pressure bleed kit and happy time a flow of bubbles came out and the pedal feel came back to normal
I cannot explain how the bubbles didn't come out using the pedal method, but it was sorted in minutes with the pressure bleed kit
Good luck, just make sure you don't remove to much fluid and drain the reservoir too low
Order66 said:
itcaptainslow said:
There’s air trapped in the system somewhere, probably in the ABS pump. It can be moved by taking the car (if driveable at all) to a quiet piece of road, getting up to a reasonable speed and braking hard so as to activate the ABS.
f
k me that;s some stupid adviceSome vehicles need diagnostic gear to open the valves in the ABS block to bleed them-case in point being my Rover 75. There's an option on the PScan diag software to do this-might be worth investigation to see if there's similar aftermarket Mercedes software available.
I had exactly the same issue with my W204 after I removed all of the calipers to paint them, my brake hose clamps weren't man enough and all the fluid had drained out of the system by the time I went to re-fit the calipers.
I, like you, tried loads of things, pressure bleeders etc with no success.
It turned out I had air trapped in the master cylinder.
I unbolted it from the servo, theres a few things to come off but it's easy enough.
Luckily there are braided hoses from the master cylinder down to the hard piping, don't disconnect these.
Once unbolted you will see that there is a M10 blanking grub screw on the side of the cylinder towards in middle of the car.
It's a bit tricky but if you make sure the reservoir is full and the lid is on, hold the cylinder so that this grub screw is at the highest point, slacken it then push the cylinder rod in with your hand. Re-tighten when it's pushed in and repeat a few times, I got a load of air out this way.
A better way would be to replace the grub screw with a bleed nipple, and bleed it again using the pedal once the cylinder is re-installed.
If you were being really thorough you could go for a full bleed from all corners again after this.
This did the trick for me, however I did still notice that the pedal would fall slightly if you held the pressure on and I couldn't remember if it did this previously. Googling does suggest that a lot of Mercs do have this issue but it appears that's just the way they are.
I now have exaclty the same issue with a Volvo C70 but can't get to the bottom of it this time.
I, like you, tried loads of things, pressure bleeders etc with no success.
It turned out I had air trapped in the master cylinder.
I unbolted it from the servo, theres a few things to come off but it's easy enough.
Luckily there are braided hoses from the master cylinder down to the hard piping, don't disconnect these.
Once unbolted you will see that there is a M10 blanking grub screw on the side of the cylinder towards in middle of the car.
It's a bit tricky but if you make sure the reservoir is full and the lid is on, hold the cylinder so that this grub screw is at the highest point, slacken it then push the cylinder rod in with your hand. Re-tighten when it's pushed in and repeat a few times, I got a load of air out this way.
A better way would be to replace the grub screw with a bleed nipple, and bleed it again using the pedal once the cylinder is re-installed.
If you were being really thorough you could go for a full bleed from all corners again after this.
This did the trick for me, however I did still notice that the pedal would fall slightly if you held the pressure on and I couldn't remember if it did this previously. Googling does suggest that a lot of Mercs do have this issue but it appears that's just the way they are.
I now have exaclty the same issue with a Volvo C70 but can't get to the bottom of it this time.
itcaptainslow said:
Order66 said:
itcaptainslow said:
There’s air trapped in the system somewhere, probably in the ABS pump. It can be moved by taking the car (if driveable at all) to a quiet piece of road, getting up to a reasonable speed and braking hard so as to activate the ABS.
fk me that;s some stupid advice.
itcaptainslow said:
Order66 said:
itcaptainslow said:
There’s air trapped in the system somewhere, probably in the ABS pump. It can be moved by taking the car (if driveable at all) to a quiet piece of road, getting up to a reasonable speed and braking hard so as to activate the ABS.
fk me that;s some stupid adviceSome vehicles need diagnostic gear to open the valves in the ABS block to bleed them-case in point being my Rover 75. There's an option on the PScan diag software to do this-might be worth investigation to see if there's similar aftermarket Mercedes software available.
k-all to do with cycling the ABS pump.Edited by lids.mod on Saturday 11th April 15:03
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