Hi all,

 

Just fitted new brake discs /pads, and rebuilt my calipers. now pedal travels about half way down, but doesn't go to the floor before resistance is felt. I have pressure bled the brakes twice but no difference.

 

So my question is:

 

1) Is it normal for the pedal on new discs/pads as it beds in? 

 2) Do I still have air trapped in the system, and if I do what are the signs for example my pedal don't feel spongy but does feel  softer than before.

 

 

If you have rebuilt your callipers, they are most likely needing less pressure to operate. Discs and pads will need a bit of bedding in until they reach optimum performance so brake gently for a hundred miles or so. On bleeding, I think you bleed in a certain sequence, then apply brakes and pump a little. Turn off. Pump again to allow them to go hard. Stat up again and pump again. Take the car for gentle test drive to assess brakes work ok, dissipate any residue from the surfaces, allow callipers to set and all to operate as is meant to. Then try again after leaving a day or overnight. Softer, though, could be a good thing, once you are used to it. Remember, the system is hydraulic, so braking will take place as soon as you start to depress the pedal, not when you feel the resistance.

With the engine off and handbrake on, after a press to dispell any vacuum is the pedal then hard at the top and no sinking under sustained pressure ? If not does one or two quick pumps make it hard at the top, but if then released for say 20 seconds make the pedal go down again ?

If pedal is hard at top all the time but sinks right down when the engine is started then is there any chance you got air in the abs unit ? The pedal should sink a bit on starting the engine but only a bit, not too far down.

1 hour ago, mrgf said:

If you have rebuilt your callipers, they are most likely needing less pressure to operate. Discs and pads will need a bit of bedding in until they reach optimum performance so brake gently for a hundred miles or so. 

 

Thanks.

Just trying to figure out, if the the pedal feel is more to do with the bedding in or air still in the system.

52 minutes ago, aubrey said:

With the engine off and handbrake on, after a press to dispell any vacuum is the pedal then hard at the top and no sinking under sustained pressure ? If not does one or two quick pumps make it hard at the top, but if then released for say 20 seconds make the pedal go down again ?

If pedal is hard at top all the time but sinks right down when the engine is started then is there any chance you got air in the abs unit ? The pedal should sink a bit on starting the engine but only a bit, not too far down.

 

The pedal remains hard after several pumps with engine off.

 

The pedal  when holding the depression, sinks about half way with engine started. It never sinks to the floor. 

Sounds about right...

 

Yes, that sounds totally normal.

Ok that's a bit reassuring, thanks.

 

So does this rule out air in the system?

I can't say 100% certain but it does sound normal.  If you're still unsure, bleed again, if thats not bleeding obvious!

As you said with engine off and handbrake on, after killing off any residue vacuum you have a permanently hard pedal right at the top then there's no air. Air would give you a bit of movement first before the air was compressed. In reality there is about 2cm movement max in the pedal and no sinking with sustained pressure. It should feel like the pedal is hitting a hard stop with the engine off. If there was air then pumping the pedal would of caused the hard point to rise on the pedal because you compressed the air gap. Then leaving the pedal loose for 20 seconds would of lost that compression and the extra air gap would return. So if you have a sustained hard stop and no change in height when pressed once or pumped and pressed then again that's good.

Start the engine and that sustained pressure causes the pedal to drop about half way.

That is totally normal. If that didn't occur then your vacuum booster would of been an issue.

If when the engine is started the pedal as good as drops to the floor then that is often air in the abs unit and an abs bleed with VCDS is needed to purge the abs of air.

You said yours dropped half way, that's normal.

Another thing you will find which proves no air is with the engine running and the car on a very slight slope, just enough to make the car roll. Then the slightest little press on the brake stops the rolling. Again if there was air you would be compressing the air before the hydraulic pressure moves the pads. It should really be the slightest of press stops the rolling.