Brake Woes

[faithsmummy]

Hi

My A8 (4.2 98) has been having brake problems. I originally changed the OSF driveshaft gaitor and in the process, squeezed the pads (pistons) back, so I could get the caliper off.

After I'd done the gaitor, I noticed that I didn't have much of a brake pedal- it sunk halfway to the floor before doing anything. After unsuccessfully bleeding the brakes a couple of times, I tried a new master cylinder (and a new servo since I managed to break it), but it's still the same.

Do you think the problem could be with the caliper? I wondered if it was either sucking in air, or maybe sticking a bit, so that it sits too far away from the pads when not braking? I can't help thinking 'caliper' since the brakes were fine until I touched it. I did notice that the outer boot was torn.

If not this, then does anyone have any thoughts where I should look next?

Any and all help appreciated.

Regards, Nick.

[kenney]

I tend to agree with your thoughts Get someone to brake while you observe the travel on the brake pads,(on the side you replaced the gaitor)

[faithsmummy]

Yep, I'll try that. Would you go for a caliper rebuild kit, even if you didn't see anything when doing what you said?

[kenney]

I don't think so,because if the pistons were easy enough to push back,then there is nothing wrong with them.

[faithsmummy]

Any thoughts as to what it might be then?

[kenney]

Not really,but i would compare,it with the other side and it might throw some light on the problem

[Micha_elD]

It sounds like it might need bleeding, that is the most common problem when you press the pistons in it can push fluid out of the master cylinder, then when you put the brakes on, there isn't enough fluid so air gets drawn in.

You've already sunk the cost of a master cylinder and servo on some speculative diagnosis, it might be time to get the brakes bled by a pro and then see what happens. Would be good to replace that split gaiter first, that won't have caused your current problem, but might cause some in the future

[faithsmummy]

I have changed the gaitor- that's when the problems started. I've now bled the brakes 4 times and gone through 3 litres of fluid. What would a professional mechanic do differently?

I've fitted a pressure bleeder and started with the furthest wheel from the master cylinder and moved towards it. I bled each wheel twice and waited about 20 seconds after seeing the last air bubbles before closing the nipple. What else can I do to bleed it better? :1zhelp:

[Micha_elD]

OK, that sounds like you're doing it right. Do you know if the pads are moving onto the disc OK?

[faithsmummy]

Hi all, just to let you know,I sorted out the brake problem. I did the caliper rebuild which actually made things worse. Long story short, I removed the OSF brake pipe and blew it through. It had sludge in it. Refitted, bled system and now it's all hunky dorey.

Thanks for your input. Much appreciated.

[Micha_elD]

Good to hear you got it sorted OK