Brake Question - The Unofficial BMW M5 Messageboard (m5board.com)

LeatherMan · 25th December 2004, 06:20

I replaced my front rotors, pads, sensor, and added SS brake lines all around tonight. A friend and I bled the brakes until the brake fluid came out clean. My problem is that I seem to have to apply more length before the brakes grab. Before it seemed that the brakes came on as soon as I hit the pedal. Now, I have to push the pedal at least 2" before they start to grab. It doesn't feel mushy when they do grab, it just seems like I have to push the pedal further then before. Do I need to bleed the brakes more? What would cause this?

jhowton · 25th December 2004, 07:25

You're not getting all of the air out of the lines. I have had the same problem with my 95 M3 and 2002 330i. What has helped me is to:

1. Install speedbleeders www.speedbleeder.com
2. Use a pressure bleeder
3. Bleed Right rear, Left Rear, Right Front, Left Front
4. Repeatedly tap the brake caliper with a hammer while bleeding to dislodge any trapped airbubbles.
5. Pump the brake pedal in the conventional manner while doing all of the above.
6. Put the wheels back on and go and do some hard stops making sure that the ABS activates.
7. Repeat 2-5 above.

Sometimes I get it the first time, sometimes it takes several tries to get a firm, high pedal.

Good luck.

DZeckhausen · 25th December 2004, 07:28

Quote:

Originally Posted by LeatherMan

I replaced my front rotors, pads, sensor, and added SS brake lines all around tonight. A friend and I bled the brakes until the brake fluid came out clean. My problem is that I seem to have to apply more length before the brakes grab. Before it seemed that the brakes came on as soon as I hit the pedal. Now, I have to push the pedal at least 2" before they start to grab. It doesn't feel mushy when they do grab, it just seems like I have to push the pedal further then before. Do I need to bleed the brakes more? What would cause this?

There are a couple things it could be. When you first install new pads and rotors, the brakes feel terrible. After a few stops, the pads and rotors begin to mate and you get better pedal feel and more grip. But they don't really come into their own until you bed them, following the process described here: http://zeckhausen.com/bedding_in_brakes.htm.

If the brakes still require extra pedal travel after they've cooled following your bedding run, then the odds are good you need to rebleed. There's probably one last pesky bubble trapped in there somewhere. I've written up a "best practices" page on bleeding brakes. I suggest you review it first, then do a second bleed. See: http://zeckhausen.com/bleeding_brakes.htm

Even if you think you're an expert bleeder, take a good look at the article. Tapping the calipers with a rubber mallet really makes a big difference in terms of knocking loose that last bit of trapped air.

LeatherMan · 25th December 2004, 08:38

Thank you both for the information. I should probably clarify a few things:

1. I am not expert brake bleeder, but I did bleed them according to the Jhowton strategy for the most part. I don't have the speedbleeders though... I just used the old fashioned way of pumping the pedal and then releasing fluid.

2. The brakes are more than strong enough to activate the abs.

3. I did find the brake bedding page on the zeckhousen webpage and followed it to the "t" as far as I could tell.

That said I think both of you are right about me still having air in the lines. I will bleed them again tomorrow. Will I need to rebed the pads considering that they may not have been compressed against the rotors with full pressure?

Thanks,
Eric

gsfent · 25th December 2004, 14:20

Quote:

Originally Posted by LeatherMan

Will I need to rebed the pads considering that they may not have been compressed against the rotors with full pressure?

Thanks,
Eric

If the pads are bedded, you are fine. A few air bubbles won't stop you from getting enough pressure to bed the brakes; for street driving it just affects how soon you get the pads to contact the rotors when you first hit the pedal.
Regards,
Jerry

jhowton · 25th December 2004, 14:38

Quote:

Originally Posted by gsfent

... for street driving it just affects how soon you get the pads to contact the rotors when you first hit the pedal.

The reasons that I like my brake pedal to engage at the top of it's range of motion are twofold:

Some miniscule amount of time is lost for the pedal to travel that extra inch or two before the brakes engage, sometimes this seems like an eternity.
Brake pedal position in relation to accelerator pedal position is critical for heel-toe downshifts which I do all of the time. If the brake pedal falls too far and engages at too low of a point it is next to impossible to avoid applying pressure to the accelerator when you don't want to.

Anyway, just my rationale for wanting the brakes to work as they do from the factory.

Regards

gsfent · 25th December 2004, 16:38

Quote:

Originally Posted by jhowton

The reasons that I like my brake pedal to engage at the top of it's range of motion are twofold:

Some miniscule amount of time is lost for the pedal to travel that extra inch or two before the brakes engage, sometimes this seems like an eternity.
Brake pedal position in relation to accelerator pedal position is critical for heel-toe downshifts which I do all of the time. If the brake pedal falls too far and engages at too low of a point it is next to impossible to avoid applying pressure to the accelerator when you don't want to.

Anyway, just my rationale for wanting the brakes to work as they do from the factory.

Regards

I agree! It very much improves the driving experience. But in context, the question was only would air bubbles prevent bedding of the pads, the answer to that is no.

Regards,
Jerry