mushy/soft pedal after Brembo rebuild

[P5Boy]

Hey Everyone,

So I rebuilt my Brembos with new piston seals and piston dust boots. I bled the brakes 2-3 times. I can take the pedal all the way to the floor before I get ABS kicking in. This isn't how the pedal felt before. This is the first time I've replaced the boots and seals. Normally, I just swap in new ST-43 pads and/or rotors, bleed and I'm good to go. This time, not so much.

Any ideas?

/allen

 

[JAJ]

Which Brembo's do you have? I don't recall hearing that Raybestos made an ST43 for the factory 15" six-piston setup.

Did your master cylinder reservoir drain down while you had the calipers off? That can allow air to get into the ABS/Advancetrac pump, and that requires a dealer bleed to clear it because they have to cycle the ABS valves and pump.

 

[Derek@Lethal]

Which Brembo's do you have? I don't recall hearing that Raybestos made an ST43 for the factory 15" six-piston setup.

Did your master cylinder reservoir drain down while you had the calipers off? That can allow air to get into the ABS/Advancetrac pump, and that requires a dealer bleed to clear it because they have to cycle the ABS valves and pump.

This right here. You can first just try bleeding the master cylinder if you do not think air made it's way down into the ABS unit, but if you did get air in there, a dealer bleed would be the best way to get it back to normal, unless you have the computer equipment at your disposal to cycle the ABS and such.

 

[P5Boy]

I have the stock Brembos. Porterfield takes a set of ST-43s made for some other application and modifies them (trims about 1/2" off each end) to fit 13/14 GT500s. I get them from Van.

My master cylinder did not drain down. There was still fluid in the master cylinder when I put the Motive pressure bleeder cap on it. To replace the seals and boots didn't take that long. A couple of hours for each side.

How do you bleed the master cylinder?

 

[JAJ]

Interesting. I've been running ST42's in my Brembo Racing kit and they're great pads but more than a little noisy until they're hot.

As for your soft pedal, there's got to be air in there somewhere. Have you bled the rears too? These brakes are brain-dead simple devices, so there's not a lot that can go wrong mechanically, but the hydraulics can be full of surprises. Did you open the system at the hard line or at the banjo joint?

The other possibility is that air is getting into the brake fluid and the pressure bleeder is pushing the bubbles through the system, but it seems far-fetched to me.

Maybe this is the moment to get a friend to run the pedals and do a more traditional pressure-bleed.

 

[LEXiiON]

Did you bleed them on both nipples per caliper? Inside first and then outside? If you only do outside, then there is still air in the caliper, which results in a very soft pedal.

LEXiiON

 

[P5Boy]

i'm late but i've got a good excuse: NASA VIR.

thanks for all the suggestions and help. there was air in the system. i finally used a human -)) to help and that what did it. i got the car working late Friday and headed to VIR.

/allen

 

[JAJ]

Get rid of your pressure bleeder and get a set of these (http://www.stahlbus-us.com/bleeding...n-bleeder-valve/conical-sealing-standardtype/) in M10x1.0x16. They're every bit as good as a human, they're always available and they never complain. I had to do an "urgent" brake fluid flush on my car this summer (my racing fluid was causing leaks) and pumped about 2 gallons of brake fluid through the system (with four different caliper sets) over the course of three weeks. These things were perfect - never a glitch.

 

[Cman01]

My car's going in this weekend to the dealer for this issue, back story:

Powdercoated my calipers last fall, did my best to plug up the open connections while they were out getting done but all the fluid drained out. Once installed bled them like crazy but still felt that the pedal didn't feel really firm so I'm hoping the dealer with the device to activate the ABS valves will remove what trapped air that's in there to give me back my firm pedal.