Not on a Merc but anyway

[rallen]

When I depress the pedal is kind of soft and has a long travel, if I pull my foot and depress a second or third time it progressively gets harder and travel distance shortens.

To me that indicates worn seals on the Master Cylinder, but I am no expert.

Any ideas?

 

[996jimbo]

Could be seals but sounds more as if you are pumping up the system due to an air lock. Try bleeding the brake lines - pressure bleed is the easiest way to do it (runs off the spare wheel; does away with assistant "push, hold it, OK release ... push, hold it etc).

 

[rallen]

I do have the tool, I will give it a go. I hope the airlock is not somewhere else in the system and cannot be removed from the calipers.

 

[996jimbo]

If you aim to replace all the brake fluid in the process you should be able to dislodge air locks wherever they are.

Having said that I still shudder when I remember the problems I had with a hydraulic clutch system some years ago...

 

[rallen]

How about the ABS system? I read that at the shop they use software to force ABS valves to open...

 

[996jimbo]

Hmmmmmmmmm... dunno.

Not sure whether ABS affects the procedure. I know what ABS does but not where in the system it operates and therefore whether the ABS system can hold back fluid / air locks.

I guess you have two options - 1. Wait for someone to post a definitive answer, 2. Give it a go anyway. Ultimately if you are unsuccessful and it does require the dealer to do something to the ABS your only loss is the cost of the brake fluid.

 

[nicky]

How about the ABS system? I read that at the shop they use software to force ABS valves to open...

If you use a pressure bleed system it should bleed ok...

 

[rallen]

If you use a pressure bleed system it should bleed ok...

OK I have the spare tyre system, will give it a go.

 

[paulcallender]

The symptoms for airlock in brakes, and failed primary (but ok secondary) seals in the master cylinder are the same. So, to resolve this one, you'd eliminate one from your enquiries. Obviously, bleeding the brakes is cheaper than replacing the master cylinder!