w210 brakes- help please

320430

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My e430 has suddenly developed a VERY long brake pedal travel. I know new pads must be needed very soon so I plan to fit some tomorrow. However Im not conviced this is the real problem. New fluid was added by main dealer 3 months ago and the resevoir is still at max. Could it be air in the system?
Thanks for looking. All replies gratefully received.
Gary
 

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This will be a master cylinder failure where one of the piston rubbers has failed, and a new master cylinder should solve it
 
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Thanks for prompt reply. I have no experiance of this. Would this not result in lost fluid. Will the failed part be obvious?
Gary
 

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Thanks for prompt reply. I have no experiance of this. Would this not result in lost fluid. Will the failed part be obvious?
Gary

The seals are internal so no there would be no lost fluid as its retained in the system. The part is obvious to a mechanic. Not sure I'd list a master cylinder as a DIY job if you're not familiar as getting it wrong could be disasterous.
 

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As Jberks above, the fluid goes past the piston and stays with the master cylinder.. you car has a tandem cylinder, that is one part for the front and the other for the rear,,it is often the rears that fail letting the pedal go down to the floor
 

Number_Cruncher

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>>My e430 has suddenly developed a VERY long brake pedal travel.

Don't drive the car - at least not at anything above walking speed - until you've fixed this potentially dangerous fault.

I wouldn't rush to fit a master cylinder until I was sure that the master cylinder was indeed faulty.

To check it, I would temporarily replace the output pipes with bleed nipples, and bleed the air out, then, see if the pedal becomes solid - if you get a solid pedal, the fault is elsewhere, wheras if the pedal remains soggy, the fault is in the pedal / master cylinder area.
 
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Thanks for all your help and advice. Armed with this knowledge I have spoken to a local mechanic who has confirmed master cylinder seal failure. He has ordered part (£50) and will fit asap.
Gary
 

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on a related theme, my mates car (not MB but we all make mistakes) is losing brake fluid, has long pedal travel, but no sign of any leaks. i thought about master cylinder leaking into the servo. anyone got any thoughts on this? (car is a w reg 316 sport compact if it helps)
 

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As Jberks above, the fluid goes past the piston and stays with the master cylinder.. you car has a tandem cylinder, that is one part for the front and the other for the rear,,it is often the rears that fail letting the pedal go down to the floor

they used to be split diagonally so that you didnt lose to much braking efficiency or vehicle control. not sure if thats still the case though
 

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they used to be split diagonally so that you didnt lose to much braking efficiency or vehicle control. not sure if thats still the case though

No way that would be so dangerous,,always front and rear
 

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on a related theme, my mates car (not MB but we all make mistakes) is losing brake fluid, has long pedal travel, but no sign of any leaks. i thought about master cylinder leaking into the servo. anyone got any thoughts on this? (car is a w reg 316 sport compact if it helps)

Yes I have known the fluid to leak into a servo before now, my V70r did this some 8 years ago,,I used to keep it mint, and it upset me when the fluid took all of the paint off it
 

turbopete

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No way that would be so dangerous,,always front and rear

i thought that, but when i was in college we were told they were split diagonally! obviously we were given duff info, as mates car brakes dead straight and not that great!
 

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Yes I have known the fluid to leak into a servo before now, my V70r did this some 8 years ago,,I used to keep it mint, and it upset me when the fluid took all of the paint off it

the servo itself looks fine so i may have to look inside the servo. the fluid is obviously going somewhere and as there are no visible leaks that i can see (without taking wheels off) i reckon its leaking into the servo. it puts the fluid warning light on from brim full in about 3 weeks
 

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the servo itself looks fine so i may have to look inside the servo. the fluid is obviously going somewhere and as there are no visible leaks that i can see (without taking wheels off) i reckon its leaking into the servo. it puts the fluid warning light on from brim full in about 3 weeks

Just pull out the vacuum pipe and use a piece of curtain wire as a dip stick,, it should measure nothing up the dip stick :rolleyes::rolleyes:
 

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but he wont fit in the hole! (the driver is a dipstick! runs with low levels on everything. beyond me how its still going!):rolleyes::rolleyes::rolleyes:
 

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Hi,
You are correct in the fact that some BMW's were split diagonally, Master cylinder had two fluid outlets on it both going to individual servos, then each servo would feed 1 front and the diagonally opposed rear, this was definetly the case in the BMW E28 528i & M535i, possibly others.
 

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Yes, lots of cars have diagonal split braking systems - there's nothing inherently unsafe about them.

The item which determines how the split is designed is the steering offset - if unbalance across the front axle would produce significant steering torque at the steering wheel, then, it's more likely that a front / rear split would be chosen.

Another thing which pushes the decision towards a diagonal split is if the rear brakes do very little work - say, in the case of tall, short, front wheel drive cars, then a rear only braking system would be positively dangerous in the case of front circuit failure, so, such cars will almost always be diagonal split.
 

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