Brakes.. Is there a known air trap in the system?

Ducklakeview said:
Any more thoughts peeps?

Mike
Click to expand...

New pads can be a bit spongy where it looks like you have to press deeper. With the first presses when you load up the pistons and put pressure on the pads it looks like it then is very hard, but when braking again, in the meantime the pressure was off the pistons and pads, so you get that spongy feeling again.
Brake pads are porous and in time that will be filled with brakedust and it will glaze up and get hard.
At least that's what I experienced with my bbk's. At first I thought I maybe had to fit a larger master brake cylinder (because I thought that I had more travel because of maybe more pots/volume in the large calipers, but that feeling went away in a week or so.

You did put the correct caliper at each side? so that the bleed nipple is at the top, not at the bottom? (otherwise you cant bleed properly of course)
 
GuidoK said:
Ducklakeview said:
Any more thoughts peeps?

Mike
Click to expand...

New pads can be a bit spongy where it looks like you have to press deeper. With the first presses when you load up the pistons and put pressure on the pads it looks like it then is very hard, but when braking again, in the meantime the pressure was off the pistons and pads, so you get that spongy feeling again.
Brake pads are porous and in time that will be filled with brakedust and it will glaze up and get hard.
At least that's what I experienced with my bbk's. At first I thought I maybe had to fit a larger master brake cylinder (because I thought that I had more travel because of maybe more pots/volume in the large calipers, but that feeling went away in a week or so.

You did put the correct caliper at each side? so that the bleed nipple is at the top, not at the bottom? (otherwise you cant bleed properly of course)
Click to expand...


Lol, I do have many years experience working on cars. The pads are fully bedded in, having covered probably 6-700 miles now. I am going to bench bleed the master cyl at the weekend, as I'm thinking trapped air between the two pistons..

Mike
 
If you bled the brakes thoroughly with the 2man method, the master cylinder should be air free (as the piston moves).
Half the air is bled back into the reservoir and the other half to the lines into the ABS.
Did you activate the ABS relais with software to purge them from trapped air? (there is a special protocol for that, its in that TIS link, there they describe it with DIS but it can also be done with ISTA-D and maybe with INPA (not sure), and generic professional diagnostic stuff like maxidas probably can do that too).
If air has come in/through your master cylinder, its also in your ABS relais.


For the caliper furthest away from the master cylinder, bleeding 250ml (the amount you did with the pressure bleeder) may be too little to regard that as a full flush. For the first caliper that is (so that is caliper plus master cylinder plus ABS relais). For the other calipers its ok (as the master cylinder and abs are then already bled and giving air free fluid if all went well). When I used ATE racing blue (when that was still available) you could really easily see (with 100% confirmation) when the line was fully flushed but I didnt take exact measurements on how much ml was needed for the first caliper. But it was a lot (compared to the other ones, and total minimum flush amount is about 800ml I guess)

So all in all if you first did the 2 man bleed (thus purging the master cylinder from air imo) and some air went into the system if there was any, but you flushed (with pressure bleeder) enough/equal amount to the volume of the lines/pistons etc, my guess is that air is trapped in the ABS.
 
GuidoK said:
If you bled the brakes thoroughly with the 2man method, the master cylinder should be air free (as the piston moves).
Half the air is bled back into the reservoir and the other half to the lines into the ABS.
Did you activate the ABS relais with software to purge them from trapped air? (there is a special protocol for that, its in that TIS link, there they describe it with DIS but it can also be done with ISTA-D and maybe with INPA (not sure), and generic professional diagnostic stuff like maxidas probably can do that too).
If air has come in/through your master cylinder, its also in your ABS relais.


For the caliper furthest away from the master cylinder, bleeding 250ml (the amount you did with the pressure bleeder) may be too little to regard that as a full flush. For the first caliper that is (so that is caliper plus master cylinder plus ABS relais). For the other calipers its ok (as the master cylinder and abs are then already bled and giving air free fluid if all went well). When I used ATE racing blue (when that was still available) you could really easily see (with 100% confirmation) when the line was fully flushed but I didnt take exact measurements on how much ml was needed for the first caliper. But it was a lot (compared to the other ones, and total minimum flush amount is about 800ml I guess)

So all in all if you first did the 2 man bleed (thus purging the master cylinder from air imo) and some air went into the system if there was any, but you flushed (with pressure bleeder) enough/equal amount to the volume of the lines/pistons etc, my guess is that air is trapped in the ABS.
Click to expand...

Correct, the ABS / TIS procedure was suggested nearly 2 weeks ago, certainly needs to be done before doing anything else as it's a standard BMW tech' requirement.
 
Ewazix said:
GuidoK said:
If you bled the brakes thoroughly with the 2man method, the master cylinder should be air free (as the piston moves).
Half the air is bled back into the reservoir and the other half to the lines into the ABS.
Did you activate the ABS relais with software to purge them from trapped air? (there is a special protocol for that, its in that TIS link, there they describe it with DIS but it can also be done with ISTA-D and maybe with INPA (not sure), and generic professional diagnostic stuff like maxidas probably can do that too).
If air has come in/through your master cylinder, its also in your ABS relais.


For the caliper furthest away from the master cylinder, bleeding 250ml (the amount you did with the pressure bleeder) may be too little to regard that as a full flush. For the first caliper that is (so that is caliper plus master cylinder plus ABS relais). For the other calipers its ok (as the master cylinder and abs are then already bled and giving air free fluid if all went well). When I used ATE racing blue (when that was still available) you could really easily see (with 100% confirmation) when the line was fully flushed but I didnt take exact measurements on how much ml was needed for the first caliper. But it was a lot (compared to the other ones, and total minimum flush amount is about 800ml I guess)

So all in all if you first did the 2 man bleed (thus purging the master cylinder from air imo) and some air went into the system if there was any, but you flushed (with pressure bleeder) enough/equal amount to the volume of the lines/pistons etc, my guess is that air is trapped in the ABS.
Click to expand...

Correct, the ABS / TIS procedure was suggested nearly 2 weeks ago, certainly needs to be done before doing anything else as it's a standard BMW tech' requirement.
Click to expand...

Borrowing the neighbour's Snap On Modis Ultra on Thursday to do it..

Mike
 
Ducklakeview said:
Ewazix said:
GuidoK said:
If you bled the brakes thoroughly with the 2man method, the master cylinder should be air free (as the piston moves).
Half the air is bled back into the reservoir and the other half to the lines into the ABS.
Did you activate the ABS relais with software to purge them from trapped air? (there is a special protocol for that, its in that TIS link, there they describe it with DIS but it can also be done with ISTA-D and maybe with INPA (not sure), and generic professional diagnostic stuff like maxidas probably can do that too).
If air has come in/through your master cylinder, its also in your ABS relais.


For the caliper furthest away from the master cylinder, bleeding 250ml (the amount you did with the pressure bleeder) may be too little to regard that as a full flush. For the first caliper that is (so that is caliper plus master cylinder plus ABS relais). For the other calipers its ok (as the master cylinder and abs are then already bled and giving air free fluid if all went well). When I used ATE racing blue (when that was still available) you could really easily see (with 100% confirmation) when the line was fully flushed but I didnt take exact measurements on how much ml was needed for the first caliper. But it was a lot (compared to the other ones, and total minimum flush amount is about 800ml I guess)

So all in all if you first did the 2 man bleed (thus purging the master cylinder from air imo) and some air went into the system if there was any, but you flushed (with pressure bleeder) enough/equal amount to the volume of the lines/pistons etc, my guess is that air is trapped in the ABS.
Click to expand...

Correct, the ABS / TIS procedure was suggested nearly 2 weeks ago, certainly needs to be done before doing anything else as it's a standard BMW tech' requirement.
Click to expand...

Borrowing the neighbour's Snap On Modis Ultra on Thursday to do it..

Mike
Click to expand...

Lets hope that sorts it for you, it's a shame special kit is needed just to trigger the ABS pump.
 
Ewazix said:
Lets hope that sorts it for you, it's a shame special kit is needed just to trigger the ABS pump.
Click to expand...

I have actually tried by triggering the ABS in the (rare ;) ) rain that we have had, but suppose it physically needs to "pump" for a few seconds.

Mike
 
Ok, so did the "proper" brake fluid change & bleed procedure yesterday using the Modis Ultra Limited Edition (WHAT a piece of kit, glad it's my neighbour that's paid for it though!)

Procedure was;

Connect pressure bleeder, max 2 bar
Open rear right nipple, click ok and ABS pump "did it's thing" for 40 seconds, close nipple and move onto next.

Interestingly, the sequence was OSR, NSR, OSF, NSF which I thought was for a LHD car, but nope, apparently that's the correct sequence for RHD.

And?

It's STILL the bloody same :x

Mike
 
I did an upgrade on my friends Z, same problem turned out to be the pipe from the inlet manifold to the servo had crushed.
it worked with the oem brakes but wasn't pulling enough vacuum to work the servo for the bigger calipers.
might not be your problem but worth a check ?
 
Have you got to the bottom of this problem yet?

I have just upgraded my fronts to 330I spec and have a similar problem, the calipers were totally rebuilt with new slider bushes etc yet it seems to me the issue lies with the amount of movement in the caliper before the pads really bite, these calipers seem to have a lot of flex in the slider arrangement?
 
It won't be the sliders. If it was then it wouldn't happen at walking pace, and the discs would need to be warped enough to physically push the pistons back. Also at high speed you wouldn't be able to pump them up because as soon as you lift off, again the discs would push the pistons back virtually instantaneously.

I've checked run out with a dti and mine are well within spec as I would expect from new discs. I've a feeling it could actually be run out on the rears causing my problem, so I will be checking those on Saturday.

Mike
 
Be interested to see what the resolution to this is. Just about to do this upgrade myself and it would be good to have all the answers before getting into it.
 
What I believe is happening is the calliper is flexing a considerable amount before the pads are being squeezed.

I base this on studying the calliper movement when the pedal is pressed, I asked my son to tell me when the pedal was being moved and when he felt the pedal firm up, I could see just how much movement the calliper was taking to square up to the pads, it was not a coincidence that as the calliper squared so the pedal firmed up.

pressing the pedal immediately after the first application meant the calliper and pads had not relaxed back off the disc before the next application of brake so you had a firm pedal for the second application.

The first thing I am looking at is the spring clips that hold the pad in the piston on the Ferodo pads were causing the pad to tilt very slightly off the piston, so I am going to re shape these clips to locate the pads correctly, next job is to turn up a set of brass bushes to replace the rubber ones which allow the calliper to float to an excessive amount, you can literally move the calliper by hand, if the brass bushes eliminate this excessive pedal movement then we will know the problem is definatly there.
 
Quick update on this issue,
Having seen the amount of flex in the calliper with the replacement rubber bushes I did a little digging regarding possible replacements.

I found a set of brass bushes online but having taken a look at the items in the photograph decided I could make my own to a better spec, the online bushes were just long enough to clear the bore in the calliper, this left a large proportion of the sliding pin exposed to dirt and dust, I decided to make up a set the same length as the rubber bushes to support the pin over the full length and allow me to fit a rubber cap to prevent the ingress of dust and dirt from the rear.

I then bored a 0.5mm deep by 2mm width slot in the bore of the bush 2mm in from the calliper and , and another 10mm down the bore, these serve as grease reservoirs and the front one also doubles up as a dust trap.

before installing the brass bushes the pedal was quite long on first application and then firmed up on the second press of the pedal.

with the brass bushes fitted I have roughly 20mm of pedal travel followed by a firm and consistent feel press after press.

It's obvious now the rubber bushes were allowing too much flex which required piston movement to take up before the pads bit, obviously this is not a problem with the factory calliper so I am assuming the aftermarket rubber bushes are softer than the factory ones.

So problem solved and a very happy Z4 owner with brakes that give confidence, unlike the standard ones!
 
Make more of these up, I have the standard set and thought they could do with improvement. A lot cheaper than getting from the US too.
 
How are the brass bushes holding up if you don't mind me asking? Resurrecting my Z4 currently. Did the brass bushes ever get stuck and cause the brakes to bind?
 
You must log in or register to reply here.
Back
Top Bottom