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  #1  
Old 01-11-2011, 10:59 AM
JamesDean's Avatar
Electrical Engineer
 
Join Date: Apr 2005
Location: NE Ohio
Posts: 5,021
Brake Pedal Responsiveness w201

Morning everyone,

I have the following setup on my 190E:
400E Front Brakes (Textar pads / ATE Rotors)
500E Rear Brakes (Textar pads, ATE Rotors)
420SEL Booster (same as 500E)
500E Master Cylinder
Stainless Steel Braided Soft Lines

I started noticing this a few days ago, the responsiveness of my brake pedal has been diminishing. I had the fluid flushed a few weeks ago and the pedal felt great. Brakes engaged and stopped high in the pedal travel.

Now the pedal is softer, and the brakes engage lightly high in the pedal travel and when the pedal is 1/2 way down it feels firmer and by the time I stop the car, the pedal is nearly to the floor (I can put my foot between the pedal and the floor)

My brakes should be much more responsive and the car should be stopped well higher up in the travel, shouldn't it?

Does it seem like this might be indicative of a bad master cylinder? or something else?

Thanks,

Kris
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82 300SD 265k
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  #2  
Old 01-11-2011, 05:09 PM
rick @ rick's autowerkes
 
Join Date: Jan 2011
Location: seacoast New Hampshire
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fading brakes

check for leaks first. check for brake fluid in the brake booster.after that i would suspect the master cylinder.
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  #3  
Old 01-11-2011, 05:21 PM
Rebe
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Have you checked the level of the fluid in the master cylinder?
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  #4  
Old 01-12-2011, 10:38 AM
JamesDean's Avatar
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The reservoir is full to the max mark on the side of it.

I think I'm going to replace the soft lines and bleed the system and see where that gets me.
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Check here for compatibility, diagnostics, and availability!

82 300SD 145k
82 300SD 265k
87 420SEL 230k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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  #5  
Old 01-12-2011, 11:19 AM
Rebe
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Whoever did the bleed may have let it get too low in one of the cavities. When you do the re-bleed it is important to follow the sequence on the location for the starting location to the finish, and not to let the cylinder get too low.
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  #6  
Old 01-12-2011, 12:54 PM
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Location: Southeastern PA
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Kris, I guess you are aware that the master cylinder has a front & rear chamber. It's necessary to keep both full when bleeding the braking system calipers in sequence: RR, LR, RF, LF. Also, it's best to use a pressure bleeder rather than pumping the brake pedal.
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  #7  
Old 01-12-2011, 01:01 PM
JamesDean's Avatar
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Join Date: Apr 2005
Location: NE Ohio
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Yes I'm aware of all that. I have one of those Motive Products Pressure Bleeders. When I replace the soft lines (currently stainless steel braided) I'll rebleed the system (obviously) and see if that fixes anything. If not...it might be time for a new master. I mean this one did sit on my shelf for a year or so..

For some reason I replied to the email that notified me of the new posts...WEIRD
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Check here for compatibility, diagnostics, and availability!

82 300SD 145k
82 300SD 265k
87 420SEL 230k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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  #8  
Old 01-12-2011, 01:13 PM
Craig
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FWIW, I've replaced both my W123 master cylinders due to similar problems within the last couple of years. The pedal started feeling soft and would travel near the floor before getting hard. Apparently one of the brake circuits had failed.
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  #9  
Old 01-12-2011, 01:16 PM
JamesDean's Avatar
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Location: NE Ohio
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Craig, thanks for your input. Did you have a lot of leaks? I mean if the circuit failed wouldn't there be leaks or no fluid coming out of a bleeder during a bleed?
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Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

82 300SD 145k
82 300SD 265k
87 420SEL 230k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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  #10  
Old 01-12-2011, 01:23 PM
pawoSD's Avatar
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Location: Grand Rapids, MI
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Very likely a bad master cylinder. Though, we recently experienced similar pedal response issues and found it was a stuck piston on one of the front calipers. Swapping it out with a good one resolved the issue. (Master cylinder also replaced with a good German one)
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  #11  
Old 01-12-2011, 01:28 PM
JamesDean's Avatar
Electrical Engineer
 
Join Date: Apr 2005
Location: NE Ohio
Posts: 5,021
I've contemplated replacing the front calipers...

They're around $90/each rebuilt..
A new ATE master is like $150

I too suspect the master...
__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

82 300SD 145k
82 300SD 265k
87 420SEL 230k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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  #12  
Old 01-12-2011, 01:30 PM
Craig
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Quote:
Originally Posted by JamesDean View Post
Craig, thanks for your input. Did you have a lot of leaks? I mean if the circuit failed wouldn't there be leaks or no fluid coming out of a bleeder during a bleed?
It didn't have external leaks, I think it was just bypassing internally. I didn't even try to bleed it because I hadn't done anything to introduce any air. Honestly, I just took it my indy and said, "fix this thing." A new master cylinder cured the issue.
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