Serious fault on brakes.

[john orentas]

Has anyone experienced this problem before!

Model C180, year 1996. I've owned the car for 6 years, trouble free for all that time it now has 120,000 miles on the clock. 10 months ago it developed a nasty very intermittent fault.

Driving along I was aware of the familiar acrid smell of burning brakes, I stopped within 200 yards by which time both rear discs were 'hard on' and could be seen to be 'Bright orange hot'.

I left them an hour to cool off by which time they had cooled and loosened off, I carefully drove the car home. The following day my garage chap could find nothing wrong apart from the inevitable heat damage, he replaced the pads and discs. For 6 months everything was OK until one evening, getting to the end of my road .......

No brakes at all until I pumped them a few times, then everything was OK again, 2 months later the same thing happened again, everything was OK until yesterday when the original 'locking on' fault occurred.

Has anyone any ideas ? it may seem irresponsible to continue using the car but I know that if if I took it back to my garage or any other for that matter they would simply resume the process of 'throwing' new parts at it. It has had much of the hydraulics including the master cylinder assembly replaced so the exercise seems pointless to me.

A friend who has some experience with Mercs suggested that there is some form of balance valve fitted in the rear brake circuit which could possibly give the faults described.

Sorry to drone on but I am rather stuck.

John O

 

[horgantrevor]

i have the the same fault but left frount chainging the the parts as mine is the piston sticking as it is 14 years old the seals can go letting in water and rusting the parts so they stick but as you say you have changed most of the parts it sounds like this valve may be it

the man to ask is malcom or better known as televison

 

[wireman]

You do not have a ballance valve.
It may be that the new master cylinder was incorrectly fitted (my first guess) or the pistons in the rear calipers are rusted and can stick thereby holding the pads in contact with the disk, this would tend to only occur on one wheel.

You "No brakes at all" would have me removing and checking the fitting of the master cylinder to the servo body, or the linkage to the servo from the pedal since both of these could be holding the pistons in the master cylinder slightly forward of their proper rest position. It may be that a slightly different master cylinder was used as the replacement.

There are two small holes in the side wall of the master cylinder which allow fluid (from the reservoir) to top up the system at the rest position, if these holes are obscured by the pistons they will not be functioning correctly and can/will hold pressure on the brakes. In addition this fault can prevent the system being topped up and leave you with no brakes or very airy need bleeding brakes which wont stop you untill some pumping has been done.

Some Merc models have an adjustment in the linkage between pedal and servo.

Please let us know the outcome of your investigations.

Has the flexi hose at the rear subframe been replaced?