Double pumping brakes after new fluid and pads

Hi guys,

I feel like I have a puzzle in my hands. I asked several people at the race track and came out with different answers. I drive a 16 GT with PP (manual). I went to a road course for the first time yesterday (The FIRM). I have done AutoX before but not track days. I decided to upgrade my brakes, and changed:

1) Brake fluid to Motul RBF600
2) Pads to Power Stop "Track Day"

I bleed the system from farthest tire from master to the closest. Went through 1.75 bootles of Motul. After that I, went out to do the Bedding process per the box instructions into the same OEM disc.

Problem:
The brakes perform really good cold or hot. However, the first time I press on the brakes it brakes lower than the factory making it too long of a travel for racing. I noticed that if I do a double pump I can get the pedal to firm up higher (less travel) than with the first press. During the whole day they never faded or failed. The pedal never went to the floor either.

Has anyone had this problem before? I can really use some help, I will like to regain that short travel that even the worn OEM pads had.

I appreciate any help you can provide.

You've got air in there!

That's what I thought. But, is that a normal behavior for air in the lines? I was told at the track that I would feel the pedal slowly sinking to the floor, and that did not happen.
I also would expect for it to behave that way every time but then why does it "firms up" on the second push of the pedal?

Sorry to answer you with more questions, but I really want to learn more about what is going on.

not totally familiar with the Mustang ABS module but you dont have to command, scan tool, the module to open while bleeding?

melwff said:

not totally familiar with the Mustang ABS module but you dont have to command, scan tool, the module to open while bleeding?

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Ohhh!!! I definitely did not do that. I did not see any post that said I had to, but I could have missed it.

Do anyone know more about the double pumping of the pedal or if I need to mess with the ABS to bleed properly?

Thanks!

I have the same issue at the track/autox. So far, no amount of bleeding will fix it. I have not tried the abs procedure. I tried to talk my dealership into doing that and the looked at me like I was a speaking gibberish. I really wish they had a clue.

My current theories are:
1) need to bleed the abs module with that procedure
Or 2) its a high RPM vacuum thing, maybe a problem with the booster or maybe not?
3) pad setback with the fixed calipers (except my pads arent low)
4) my rotors are too worn?

Its pretty annoying, and sometimes downright dangerous. I'd love to hear from someone who has had this issue and fixed it.

If you're not driving the car on a track or autox, you havent seen it. My car behaves normally on the street and fluid had been flushed countless times.

Mine is weird in that it has a small bit of spongy/soft pedal initially and then is nice and firm, can't really move it. Other cars I've had with air in the system are just spongy pedal fully.

BmacIL said:

Mine is weird in that it has a small bit of spongy/soft pedal initially and then is nice and firm, can't really move it. Other cars I've had with air in the system are just spongy pedal fully.

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X2

Ohh man! I kind of feel good that I am not going crazy! Someone has felt the same behavior. Although I feel bad that we have this problem.
[MENTION=19933]NightmareMoon[/MENTION] I agree with you. It feels dangerous. I was pushing 125+ on the straight and it was taking my brain a LOT of guts to trust my brakes.

There might be something in the process of bleeding this cars that could hold the answer to this problem. I wonder if having the car "ON" or "Running" would make a difference based on ABS servos position or vacuum levels.

I wonder if we should ask on the Road Course/AutoX/HPDE forum section...

sunfigt said:

Ohh man! I kind of feel good that I am not going crazy! Someone has felt the same behavior. Although I feel bad that we have this problem.
[MENTION=19933]NightmareMoon[/MENTION] I agree with you. It feels dangerous. I was pushing 125+ on the straight and it was taking my brain a LOT of guts to trust my brakes.

There might be something in the process of bleeding this cars that could hold the answer to this problem. I wonder if having the car "ON" or "Running" would make a difference based on ABS servos position or vacuum levels.

I wonder if we should ask on the Road Course/AutoX/HPDE forum section...

Click to expand...

I made sure that the car was keyed to run/accessory when I was doing it. Maybe it needs to be on on.

It does not sound like common sense to me for the engine to be "Running" but knowing you already tried "ACC ON" at this point I might try with the engine running later this week.

I really enjoyed racing this weekend and will like to keep doing it. But with the brakes like this I will not feel safe and will just get mad and disappointed with the car...

sunfigt said:

It does not sound like common sense to me for the engine to be "Running" but knowing you already tried "ACC ON" at this point I might try with the engine running later this week.

I really enjoyed racing this weekend and will like to keep doing it. But with the brakes like this I will not feel safe and will just get mad and disappointed with the car...

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The biggest thing that's different is that the vacuum booster is running. It shouldn't do anything but I'm up for trying anything to get it to feel better.

Serious opcorn:

sub'd, i had same issue last time i was at the track. bleed brakes while the car was off last weekend and did nothing, even though alot of air came out of the front left side caliper. will try to bleed again with with car on. i also have a replacement master cylinder on the way.

I realize the behavior of the pedal looks like the master cylinder is going bad. But, Why? Why would the Master cylinder be bad? All I did was changed the fluid and pads.