spongy brakes but catching fine??

[rufman]

folks

Got my pads, front and rear done today. Bled the system, one caliper at a time but now my brakes are very soft and 'spongy' going almost to the floor. However, they do catch immediately and the stopping power is fine. Just doesn't feel right.

I know this may have been posted before and ive done a search on various forums but the confusing point is that the brakes work excellent and catch very early but are just very spongy.

Im hoping to go away for a few days but dare not with family if there may be a problem with the braking system.

Any thoughts?

 

[Dieselman]

Firstly drive round the block with your foot on the brake pedal, this will seat the pads to the disks.
If still spongy re bleed the brakes but if not using a pressure bleeder have an assistant press the brake pedal BEFORE cracking the bleed nipple free. This will guarentee a good bleed.

 

[television]

If you can pump the pedal and it comes up, and sinks when just touching the pedal, you have air in the system.

If this is a tandem system on your car, with separate front/back the if the rear section has failed, then the brake pedal will work, but it will go a long way down before it stops the car.

 

[bolide]

As per Dieselman: if you've put new pads on old discs with any sizeable wear lip at the edge then the pads will only be touching the lip till they wear to conform to the discs

Assuming the calipers are moving freely if they're sliding, or assuming all the pistons are moving freely if they're not, then I'd check the pad and disc mating surface to see if that's the problem

Nick Froome
www.w124.co.uk

 

[rufman]

thanks to all for the replies.

One point is interesting..the rear discs are quite worn and there is quite a substantial 'lip' on both discs. However, as this car has turned in to a never end of pit of money, I plan to change them in a few thousand miles. This may be the problem.

key point is they catch immediately and stop perfectly but just seem to go down a little more than id expect. There is also a 'pumping' or 'pressure' sound when braking.

after the ignition is turned off, they are normal as id expect, quite hard and little play. is this a clue?

Im just a little scared of the words 'brake master cylinder' or 'servo'.

thanks again

 

[television]

As per Dieselman: if you've put new pads on old discs with any sizeable wear lip at the edge then the pads will only be touching the lip till they wear to conform to the discs



Nick Froome
www.w124.co.uk

Its doubtful if the ridge is causing the problem as the pads do not go that far out to the edge of the disc,that is why a ridge is formed on the disc, this ridge is also a quick visual indication of the thickness of the disc.

Malcolm

 

[television]

thanks to all for the replies.

One point is interesting..the rear discs are quite worn and there is quite a substantial 'lip' on both discs. However, as this car has turned in to a never end of pit of money, I plan to change them in a few thousand miles. This may be the problem.

key point is they catch immediately and stop perfectly but just seem to go down a little more than id expect. There is also a 'pumping' or 'pressure' sound when braking.

after the ignition is turned off, they are normal as id expect, quite hard and little play. is this a clue?

Im just a little scared of the words 'brake master cylinder' or 'servo'.

thanks again

If the pedal travel is more than normal,you will possibly hear the servo hence the hiss. I doubt very much if there is anything wrong with the servo as this only effects the preasure and has nothing to do with the pedal travel.

The Master cylinder is a simple and not expensive job to do, if there is anything wrong with that.

malcolm

 

[rufman]

Thanks malcolm

I actually prefer the feel of the brakes now to what it was before, a little abrupt and stiff.

Will get them checked out by my local specialist just in case.

 

[miro]

I would say on balance that as the new pads get thin on the old rotor that they will get even more spongy.

I replaced all my rotors. pads and calipers with AMG spec (think of it as buying callipers given that the other items are on your shopping list or already installed).

The braking was back to being agressive and sharp.

As the travel distance increases the feel gets markedly soft.

 

[kth286]

Rufman

Re E55 brakes.

I think you will find that with cars featuring traction control the brake bleeding is more complicated than normal as you have to get involved with the ABS unit.

So, do the further caliper first and end doing the shorter run caliper, then turn your attention to the ABS unit bleed function.

For the ABS bleed function the engine has to be started and there is a strict sequence.

You need to have instruction notes applicable to your car which I do not have.

Only take car to a Merc dealer/specialist that is familiar with your car.