Brake pedal spongy- air in system?

[Chazchuzzlewitt]

Just replaced the front brake pads on my 116 and when I went to pump the pedal to push the pistons against the new pads I wasn't feeling much resitance- then realised I'd left the cap for the master cylinder slightly open- now the pedal is spongy- does this sound like air in the system? And will I need to bleed the whole system?
When I reversed out of my parking bay I had to use the handbrake to stop the car as I had hardly any power- then I took it for a short road test and it slowly started to feel more normal, but still not great.

 

[tom7035]

What method did you use when retracting the pistons in the caliper, e.g. clamp the hose and allow fluid to flow out the bleed nipple or simply push the pistons back in? If the former, then it sounds as though the hose wasn't tightly enough clamped. The reservoir cap has no bearing on air getting into the system, which appears to be what has happened.

 

[Chazchuzzlewitt]

actually just pushed the pistons back in- didn't clamp the line + bleed.
The discs are quite worn and need to be replaced soon so maybe I'll try a longer test drive as the pads felt like they were bedding in a bit better the more I drove.

 

[television]

Tom is an expert on these things, the only thing that I would add is to give a few hard presses on the brake pedal.

Air in the system shows up when the brake pedal has not been pushed for a while and it sinks to the floor, but can be pumped up, the brake master cyinder is a tandem, one half can fail causing a long pedal movement, but you should not have this problem.

malcolm

 

[oigle]

This isn't unusual with badly grooved discs. As the pads wear in to the shape of the disc, the pedal will firm up. A few hundred miles with numerous brake applications will see it become a lot better. From your description of how you replaced your pads, I doubt you have allowed air into the system.

 

[KOMPRESSIT]

Hello, CAN someone help please? My car E320 2006 (facelift no SBS) failed its MOT today for spongy brake pedal and brake pedal 'creeps'. Brake pedal only creeps when the car is running and stationary with excessive force applied to the pedal. The amount of force would be far more than is required to lock the brakes. I read on the internet that brake pedal 'creep' is common in some diesels. See the link below:

http://www.brakesint.co.uk.html#techNote202

The pedal does not creep during normal operation even under emergency stop situation or when the engine is not run in. This confirms the master cylinder is OK ? (Car has done 70,000 careful miles) .

The MOT guy stated these cars need a computer to bleed them and his computer would sort the problem. He supplied an estimate for £100 then went very quiet when one of the mechanics stated that the computer wouldn't do an EClass.

So now I have a problem - car failed and garage cant fix it. I think I have two options: get the brakes bled somewhere else then take back for a retest . Or just take it to another garage for a complete MOT. Any advice would be appreciated. Thanks.

 

[Cole@MBS]

Take it somewhere ease, all mercs pedals will go to the floor if you sit and push the pedal......

 

[television]

Hello and welcome. on all cars with standard brakes that you have you can press the pedal down till it will go no more, you start up and the pedal will sink further down once the servo has kicked in, but from that point on it should never sink further. with any system you should not be able to pump the pedal to get it higher.

For all it cost these days, get the fluid changed and put it down to the 2 year fluid change period.

You could ask another MOT station for their advice, it only takes seconds to feel the pedal.

 

[KOMPRESSIT]

http://www.vwt4forum.co.uk/archive/index.php/t-178355.html


There are a lot of discussions on the internet about brake pedal creep on diesels. (See the link above).

The brake fluid was changed less than a year ago. Good suggestion about asking another MOT station to check it, I think I might try that. Thanks Television.