I've noticed over the years my brake pedal seems a little bit firmer. Not so much firm in terms of a good pedal, but firm in terms of a pedal that take more effort than it did when it was new. Aside from air in the lines (which I doubt is a problem because it feel solid and has been bleed recently) what other issues can you see with the system. I have checked the brake booster with the manufacter's test procedures and found nothing wrong. The brakes are still plenty strong but I'm just trying to put my finger on what is slightly off.

 

Bump, old problem that still exists. Recently, I power-bled the brakes and didn't see much of a change. I just feels as though the booster has lost power. I have begun using the Nismo R pads and they do have less initial bite but I would still imagine the pedal feel would be close to what it was. One last thing, I do remember a time when the pedal and arm assembly seems to be sqeaking, not sure if this was a sign the booster was having a problem.

 

Probably air, unless you have a shop with a "great" power bleeder you won't get all past the ABS/TCS pumps. The Motive bleeder does well, but its not as good as what the shops use.

It can also be that over time brake fluid likes to swell the rubber O rings, the tighter the fit, the more pressure needed.

Going back and forth between my 2 Z's and all the G/Z side work i do, all these cars are different. So far, the touchiest brakes ( non race) seem to be the stock pads on my 05 followed by my moms 04 G, both cars completely stock.

 

I can keep pushig fluid through, how much fliud do you normally push through each line? I didn't see any air in the lines and ended up pushing about half a regular sized water bottle capacity through each line.

 

Air in the line would make the pedal spongy, and you say it's firm, but it requires more pressure (not more travel) than it used to.

You may have something amiss with the brake booster. Look in section BR of the service manual for your year, and then look under Brake Booster for the procedure to check it out.

Here's info on how the brake booster works in case you're not familiar with it.
http://auto.howstuffworks.com/auto-p...wer-brake1.htm

 

Thanks winchman, I've been studying that section and found the car passed all of the on car tests. Have you ever dealt with the part directly, I'm trying to understand the function of the booster and possibly determine if I'm barking up the wrong tree.

 

The booster is used to amplify the pressure you apply to the pedal with your foot. The amount of boost is proportional to the pressure you apply.

If there's some leakage or blockage in the booster assembly, you'll have to press harder to get the boost needed to stop the car.

If the booster passes the tests OK, the problem is with some other part of the braking system. You could have glazed pads that don't have same friction as when they were newer. It could also be a stuck piston, but that would probably cause the car to pull to one side when the brakes are applied. If the pads are significantly worn, they'll get hot more quickly. That'll increase the pressure needed to stop the car, too.

 

Pad-wise, I've noticed this over the past 3 pad sets (2 Nismo R, and set of regular Raybestos and two different sets of rotors) Most recently, about a year ago, the problem was still noticable after new pads and rotors at the same time. They were well bed'ed and strong otherwise so I've ruled out hardware (minus the calipers).

Also, thanks for the heads up on the booster but that's pretty much the understanding that I already had. I'm just trying to get a mechanical understanding of it so I can rule it out.

 

Waiting to get my car back from the body shop and re-bleed the brakes but I rented a G37 and it is even more pronounce how off the pedal feels. I want to say about double the pedal effort is required in my car. As well mines seems to have a ton of mechanical friction at the pedal compared to what I remember when it was new and what the G has. This leads me to believe its more than air in the lines and that's not good, the brake booster is an expensive piece.