Brake Creep / Soft Pedal After Pad Change

[jim_tdi]

Hi all, pads were low so changed the backs first a few weeks ago, all good, then the fronts this weekend. I swapped them out as I have done many times, just eased the piston back into the calliper and put the new pads in etc. After doing this (forced a little fluid out of the master cylinder), I have a soft pedal that needs pumping once to get a pedal and then it creeps down if compressed. I suspected air but can't see how it could have got into the lines.

After researching, it seems that I should have un-done the bleeder whilst pushing back the piston, but again, I haven't had an issue before. So I have bled the brakes, and quite a bit of air came out. However, I still have the soft pedal. I suspect there is still air in the lines, and am hoping that I haven't screwed the master cylinder....

Any thoughts appreciated.

[mikeybutch]

How did you take fluid out of the m/ cylinder?I have usually remove any excess from the res

[jim_tdi]

I didn't - I didn't notice and a bit spilled over the top - forced out of cap. Not too much so easy to wipe down the top of the MC.

[Danny-boy]

That's the way I do it on all my cars, although with the cap removed so as not to over-pressurise.

[jim_tdi]

Yes, I've not had this problem before - I can't see how air has got into the lines, and so am worried that the MC seals maybe damaged - maybe as I forced the piston back in this way?

[Danny-boy]

If I'm honest, I have forgotten to remove the cap a few times in the past and not caused any problems.

Can't be sure if the fluid was 100% full though, so there may have been some slack there.

I don't understand where your air has come from either. Maybe a problem with the piston seals?

[audia4qts]

is it diesel or petrol?

When you say pedal creep. Do the pads bite and then if you keep the pedal pressed hard the pedal will creep slowly to the floor?

I've never bothered to remove the cap and never had any issues before.

[Alan02]

If this is the pedal having further travel/soft feel when driving, it would be best to bed the pads in then see if it improves. A slight lip on the discs will cause this `soft pedal` feel.

[Danny-boy]

Very good point Alan.

Although OP noted his brakes bled a fair bit of air out after the work, so unless it was already in there it's a little strange.

[jim_tdi]

This is a diesel 130 TDi on an 04.

[touranasurus]

Hi, Its nomal for the footbrake to feel "spongy" when a new set of brakes have been fitted, there have to be "run-in". at first brake firmly but lightly, then medium braking, and then heavy firm braking - this "runs" the pads in over a few miles. you will find they get better the more you use them.
make shaw the pads are free in the caliper, I always use a light file on the ends of the pads to remove the paint and put some copper slip grease on, good luck.

[jim_tdi]

Hi, Its nomal for the footbrake to feel "spongy" when a new set of brakes have been fitted, there have to be "run-in". at first brake firmly but lightly, then medium braking, and then heavy firm braking - this "runs" the pads in over a few miles. you will find they get better the more you use them.
make shaw the pads are free in the caliper, I always use a light file on the ends of the pads to remove the paint and put some copper slip grease on, good luck.

I've changed pads on many cars and not had this issue. Have just use a pressure pump to bleed again and no air. I wonder if there is air trapped in MC and needs a long bleed. Alternative - new MC. I still think air is the issue.

It's not just a bed in issue - the brakes sink to the floor - without air or master cyl failure - that wouldn't happen.

[zollaf]

is there a bleed nipple on the mc ?

[touranasurus]

HI, If you push the brake pedal to the floor, then jam it down with a piece of wood cut to length and leave overnight, if there is air in the master cylinder should release itself. have been successful in the past doing it this way.:beerchug:

[niall campbell]

I too have had the spongy feel with new pads as you describe like touransurus points out. I don't know how air got in. I just wonder if you pushed them in too far or too hard. You could try bleeding them in reverse ?

[nevo]

If the pedal's hitting the floor there's air inside no doubt! do a full bleed again starting at the mc nipple if there's one also check you've not twisted a flexi when you've had the caliper off.I would recommend using a vac pump to draw it out rather than pressure bleed.

[jim_tdi]

still can't fig how air got in there.....