Hi all and wish Happy New Year 2009!Recently im repairing a W140 S420. The brake pedal was sinking whenever car goes downhill and have to wait for approx. 30 mins then only back to normal.the following jobs that i had done as below:3 times barke fluid bleeding;overhaul both front brake calipers;brand new original front brake pads;all brake lines replaced.i really have no more ideal what should i replace. Is there any posibilities brake booster and ABS/ASR pump.[/align]

 

you are using the correct fluid right?

Of course a few things can cause sinking brake pedal. Such as the most common, air bubble(s) in the fluid, a leak in a line or connector.

A bad brake booster usually causes a hard pedal feel. In a large car like that, can feel like pressing on a brick when that booster goes bad. But you should take a look at the master cylinder for leaks and such as a leak in the master cylinder can cause what you described especially after the work you already did.

 

BlackWolf, thank you for your reply!

ya...used mercedes benz brake fluid DOT 4
im using the pressure bleeder to carried out bleeding for 3 times, no air bubbles persist and all lines had already been checked for proper tighten.

im afraid as whathad you mentioned of master cylinder...perhaps internal leaks due to the rubber worn out...is it possible???

 

Could be.

 

it should be since you have replaced the other possiblilty...

 

Nope...this is the complaint indeed!