M-Class (W163) Produced 1998-2005: ML 230, ML 320, ML 350, ML 400 CDI, ML 430, ML 500, ML 270 CDI

Brake Pedal Requires Pumping to Stop

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Old 01-18-2020, 05:13 PM
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W163 - ML320 - 1999
Question Brake Pedal Requires Pumping to Stop

Hey Everyone!

Quick thing, I recently went ahead and replaced my calipers due to them seizing. I went ahead and bled each line after installing the new ones as well. However, now the brake pedal requires multiple presses in order to attain full braking authority. Anyone have any tips? No lines were opened from the Master Cylinder to the ABS unit throughout this whole process either.....perhaps I need to rebleed the calipers again? Any help is appreciated!

Car is a 98' ML320, which I have heard have some funny business with brakes.....
Old 01-18-2020, 06:03 PM
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Originally Posted by Michael Vanegas
Hey Everyone!

Quick thing, I recently went ahead and replaced my calipers due to them seizing. I went ahead and bled each line after installing the new ones as well. However, now the brake pedal requires multiple presses in order to attain full braking authority. Anyone have any tips? No lines were opened from the Master Cylinder to the ABS unit throughout this whole process either.....perhaps I need to rebleed the calipers again? Any help is appreciated!

Car is a 98' ML320, which I have heard have some funny business with brakes.....
And what funny business have you heard?
What procedure did you follow to bleed your brakes?
Did you follow this sequence?




Old 01-18-2020, 07:19 PM
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I have heard that by nature brakes on the ML's tend to be a little on the softer side. So sometimes people tend to misdiagnose them due to that haha.

I bled the vehicle by cracking the drain hole on the calipers and siphoning it into a bottle with brake fluid in it. I did get air out of the system overall!
And yes! I did bleed them in that exact order!

However, the car requires multiple pumping to come to a full stop. Almost as if there is no pressure building up in it unless I continue pressing it repeatedly.
Old 01-18-2020, 08:12 PM
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Originally Posted by Michael Vanegas
I have heard that by nature brakes on the ML's tend to be a little on the softer side. So sometimes people tend to misdiagnose them due to that haha.

I bled the vehicle by cracking the drain hole on the calipers and siphoning it into a bottle with brake fluid in it. I did get air out of the system overall!
And yes! I did bleed them in that exact order!

However, the car requires multiple pumping to come to a full stop. Almost as if there is no pressure building up in it unless I continue pressing it repeatedly.
Soft brakes comments has always been a complaint from owners. We have 2 w163s - 99 & 02 - however, no soft brake issues. But we also flush out the BF every 2 years.
Yes, to one suv, with the brake hiss problem and resolved with a patch solution.
Check your brake lines for any expansion issues. Also check vacuum lines for any cracks, etc. going to the brake booster.

There's been a rash of similar soft pedal issue posts recently on this forum I think and the other. I recall reading thru them - do a search to see what possible resolution was posted on those.

here's one of many
Old 05-17-2022, 05:02 PM
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opps, wrong thread

Last edited by 91stealthes; 05-17-2022 at 05:03 PM. Reason: wrong thread
Old 05-19-2022, 09:07 AM
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Originally Posted by Michael Vanegas

However, the car requires multiple pumping to come to a full stop. Almost as if there is no pressure building up in it unless I continue pressing it repeatedly.
When you have this problem, it indicates that you still have air in the brake system
Old 09-11-2022, 05:45 PM
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Originally Posted by Maj. Dundee
When you have this problem, it indicates that you still have air in the brake system
I have this same issue. bled the brakes, everything felt fine when I was finished. Pedal was firm. When I put the truck in reverse it stops immediately. When I put it in drive it takes 2 full presses for the car to stop.

If not the system, can it be the calipers?
Old 09-11-2022, 06:32 PM
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Originally Posted by SBundlez
I have this same issue. bled the brakes, everything felt fine when I was finished. Pedal was firm. When I put the truck in reverse it stops immediately. When I put it in drive it takes 2 full presses for the car to stop.

If not the system, can it be the calipers?
Also I should add that the hiss went away when bleeding but when I began to drive it came back. And the hiss comes when I press the pedal down and not releasing.
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