strange braking on w126 300se

[FizzyFarmer]

hi i have the strange thing happening with my w126 300se. The brakes work fine exept occasionally for no apparent reason the braking changes and the i loose the top end of the braking. What i mean is that when pressing the pedal, the brakes engage from pretty well the first point of pressing the pedal. Then suddenly when i press the pedal there is no braking until my foot is nearly on the floor. I presume this is to do with some sort of brake assist. If i stop the car turn off the engine and start it up again all is fine again. It seems quite random .... any thoughts?
thanks

 

[GEORGEROV]

Sounds to me as if the problem is not with the power assistance but the seals of the master cylinder occasionally giving way.

 

[jayeastanglia]

as said above master cylinder seals.

 

[wireman]

I will second the master cylinder as being most likely culprit, I have known 2 instances where this failiure has directly led to severe injuries to inocent pedestrians, in both cases the pedal felt normal after the incident.

In these days of dual circuit braking systems this is an often forgoten but (obviously) essential part of the car, it should be replaced at ten year intervals and the fluid must be changed at 2 year if not 1 year intervals, failing to do this results in master cylinder, ABS and wheel cylinder seals failing in an undetermined and intermittent fashion. This applies to all hydraulicaly braked vehicles not just MB.

If you persist in driving the car how long will it be before both circuits fail simulaneously? I like all the others on this planet do not know, but we can all guess at how messy the outcome will be when it does fail totaly.

If its an older car with the simple system expect to pay about £100 for the parts and maybe 1 hour to fit.

Please get it sorted before you drive the car again.

 

[FizzyFarmer]

thank you for the replies. I have booked the car in already for something else for it is a new purchase and wanted to get it checked over for its an 18yr old car. I will get this looked at straight away and sorted out, thank you for the response

will