BBK install - stumped!

[MrPT]

I decided to take the plunge and buy the Vagbremtechnic M3/Z4M big brake kit. This works with the standard rotors, using Brembo 4-pot front calipers and pads from the DB9 (also the same as the previous gen TTRS/RS3). Now, everything about this kit, quality-wise, is outstanding - will post pics etc in due course.

But for now I'm stuck because everything is installed and bled but my brake pedal is going to the floor! I can pump it once or twice, and with either the engine off or on I eventually get a superbly firm pedal. With the engine on, if I wait a few seconds it will go to the floor again.

I actually went for a very short test drive like this and I can already tell that the brakes have improved feel compared to stock, but that's only after a couple of pumps. Great for that 1950s-racer vibe, but otherwise quite hairy. Here's what I've done/checked:

* Depressed pedal 80% before changing brake lines and calipers
* Checked calipers are the right way round (valves on top, small piston before large)
* Pressure bled everything twice with a one way bleed valve
* Checked that fluid actually flows freely from all four corners
* Given the calipers a decent thump with a rubber mallet while bleeding
* Bled inner and outer valves
* Checked for brake fluid leaks in every visible part of the braking system
* Checked fluid level - went to minimum once but never below
* INPA ABS bleed procedure, >3 times per corner, LR/RR/LF/RF
* Checked E46 M3 master cylinder is the same size as the Z4M
* Checked pads are contacting disc when idle
* Checked that pads move freely on the pins
* Checked that I can stomp on the pedal (when firm) and it doesn't sink to the floor slowly

Any ideas? Fairly sick of bleeding now, but I'm open to the idea that it might just take a few hundred more bleeds.

[Stu Boy]

if the brakes were fine before you fitted the calipers then surely you must have introduced air into the system
As you know I've not long changed my calipers too, mine had slightly more pedal travel ( but never went to the floor) initially but after a hundred miles or so and a rebleed all is well.
Have you been using the bleed pipe with the one way valve? Might be worth a go with a pressurised bleed kit? If these have been tried looks like it's a trip to your nearest dealer?
Good luck

[Smartbear]

Have you checked the replacement brake pipe fittings for leaks? Did you install new copper washers each side of the fitting?
Rob

[MrPT]

if the brakes were fine before you fitted the calipers then surely you must have introduced air into the system

Exactly. I think, despite everything, that is still the most likely cause. Everybody has done this crazy dance at some point.

Have you been using the bleed pipe with the one way valve? Might be worth a go with a pressurised bleed kit?

Yes, I'm using a one-man bleed hose on the caliper valve and a Sealey pressure bleeder on the reservoir. Flushed half a new bottle of dot 5.1 through so far.

Have you checked the replacement brake pipe fittings for leaks? Did you install new copper washers each side of the fitting?
Rob

I think the whole system is pretty tight because it will hold pressure or a firm pedal push for a long time. It did cross my mind that various valves etc would be cutting sections off, so I will check the fittings, thanks. Pretty sure they don't have washers though, since they aren't banjo bolts. I need to work today but will also try removing the calipers and manipulating them a bit.

Urgh, so close. Cheers team.

[hopz121]

Is the pedal spongy or solid?

It could be a case that they just are not working properly yet, I remember when I changed the disc's and pads and calipers on my 3.0i, took it for a drive pressed the brake and not much happened a pretty scary moment! Could it be that the system needs to bed in?

Do you have nay pictures OP so we can take a look and see if its something obvious?

What pads are you using?

Ash

[MrPT]

Cheers Ash. Pedal was spongey until pumped, then firm, before going spongey again after not braking for a couple of seconds. Pads are OEM Pagids for the RS3.

It's sorted now - of course it was a bleed issue!

I took both calipers off and manipulated them to try and free bubbles. Then I put them back the carriers, and I did a four corner pressure bleed, plus the ABS INPA bleed procedure. Front right had bubbles on the inner valve. Come to think of it, I might only have bled that valve using INPA since installing that caliper upside down initially (on the other side!), so it's my fault for being a muppet. The ABS bleed probably pushed bubbles out of the pump into that caliper and then I didn't flush them through properly. When I did it was only 4-5 small bubbles but I can't think of anything else that might have caused it. I guess the bubbles look small in the bleed hose, relative to how "long" they are in the braking system.

Lesson learned - at least I got some bleeding practice in, and the pedal feels mighty now.

[john-e89]

Cheers Ash. Pedal was spongey until pumped, then firm, before going spongey again after not braking for a couple of seconds. Pads are OEM Pagids for the RS3.

It's sorted now - of course it was a bleed issue!

I took both calipers off and manipulated them to try and free bubbles. Then I put them back the carriers, and I did a four corner pressure bleed, plus the ABS INPA bleed procedure. Front right had bubbles on the inner valve. Come to think of it, I might only have bled that valve using INPA since installing that caliper upside down initially (on the other side!), so it's my fault for being a muppet. The ABS bleed probably pushed bubbles out of the pump into that caliper and then I didn't flush them through properly. When I did it was only 4-5 small bubbles but I can't think of anything else that might have caused it. I guess the bubbles look small in the bleed hose, relative to how "long" they are in the braking system.

Lesson learned - at least I got some bleeding practice in, and the pedal feels mighty now.

This looks a great kit Mr PT, where did you source your calipers from?

[cj10jeeper]

Don't beat your self up about it. Stuff like this happens all the time and the more you do it the more frustrated it becomes and easier to miss the obvious and start looking for complex issues. Glad its fixed and you can enjoy

Also while the bubbles may sound small they compress in a linear manner, so 10x pressure take /10 the volume. That makes a bubble minuscule at 1200psi and then consider that the amount of fluid moved is tiny so your air bubbles represent a relatively large volume of what a pedal press moves

[MrPT]

This looks a great kit Mr PT, where did you source your calipers from?

VBT buy calipers in bulk from Aston, so it actually worked out cheaper to go down that route than buy second hand calipers or source from Aston direct.

Don't beat your self up about it. Stuff like this happens all the time and the more you do it the more frustrated it becomes and easier to miss the obvious and start looking for complex issues. Glad its fixed and you can enjoy

Thanks. Exactly that - got frustrated trying to dream up what else it might be, and actually what was needed was a decent night's sleep and more attention on the obvious stuff.

[Machine monkey]

Did you fill the new calipers before fitting? As that might be the issue keep bleeding them. I am sure they will come good.

Sorry if already fixed I just read the first few posts.

[john-e89]

This looks a great kit Mr PT, where did you source your calipers from?

VBT buy calipers in bulk from Aston, so it actually worked out cheaper to go down that route than buy second hand calipers or source from Aston

Great cheers.

[Stu Boy]

Glad it's sorted
You muppet

[hopz121]

Easy mistake glad you sorted it though

Now lets see some pictures

[MrPT]

Glad it's sorted
You muppet

It's your fault I'm doing this. And 'dawg's.

[bmwaddict]

Pics or it didn't happen! I'd like a bbk at some point, it's at the bottom of a long list of mods and jobs though.