The solution may be simply turning your car on every morning and waiting til the engine is at normal running temperature before moving. This allows brake fluid to properly circulate to brakes and lubricate parts.

 

Brake fluid doesn't circulate.

A sticking one way valve could be the culprit.

 

I can tell you that the Brake Booster may not be the problem(about 90%sure).

Even though my original Brake Booster looked almost new, I had it replaced with a new one anyway and a few days later, I still had the brake issue. Kinda pissed because I spent about $900 for that. That could've gone to other mods like rims or HID's...

I will have the one way valve checked on the vacuum system as this may be the culprit. I'm running out of solutions here as I've checked everything else. At this point I'm thinking there is an issue in the vacuum system/lines, either a relief valve or check valve.


This does not work either. And as someone said, the brakes dont work that way.

Every time I get into my car, I start it up and usually wait at least a minute to let it warm up to temps before moving. I even sit there and pump the brakes to ensure they are working properly. Last week when I had the brake issue, I remember sitting in my car and letting it warm up for a good minute but that did nothing to solve the issue.

It could be a number of other things, but I can tell you its not the Master Cylinder, Brake Booster, or ABS module (at least not for me). I had all those checked my the shop (Midas) already, and even flushed/bled my brakes and I continue to have the issue. My brake pads and rotors are also good so that is not the problem.

 

 

Seems this is an old thread...and i've learned a few things about G35 brakes since it was started.

I've had this issue a few times with my car where the pedal would improve after a few pumps. After pulling my hair out, i discovered the issue was the rear calipers.

When driving in snow/salt, the rear slide pin on the caliper would be prone to seizing in the bore, or getting very difficult to move. I would relube the pin, but the issue would reappear sometime later. I've actually replaced both rear calipers at some point ($40 plus core at rock auto.com)

It a common issue, and at 153K miles, i've had to redo my rear brakes at least 3-4 times already (not including when i swapped the caliper) due to the pedal getting soft and spongy. As i sit here and write this, i have to repear the process again as I'm definitely feeling "slack" in the pedal again.

I drive my car in snow all the time. In fact, i enjoy it and purposely go out in snow to "play" so i'm sure the problem is exaggerated on my car, but i'm sure any northern car may see the same issue.

The prob isn't the caliper itseld but the damn pins sticking or seizing. If the bottom pin can't move, the caliper tends to only press the inner pad against the rotor. As the pad wears, the gap between pad and rotor grows requiring that extra press to get a firm pedal. If you let your pads wear waaaaay down, you will notice a huge mismatch in pad sizes.

So my recommendation, if you can, is to pull the rear brakes apart and verify that the pins are freely moving and the caliper can slide side to side freely.

On a rarer note, i've also discovered a possible issue with the front calipers. The 05+ version use a rubber sleeve on one of the slide pins. If you accidentally use petroleum based grease to lube the pins (oops..all i had), it causes the rubber to swell up and the pin to be harder to move. So you can also run into the same issue with the front calipers. So definitely use the correct caliper grease, and inspect for proper movement of the floating calipers.

This may not be your issue at all, but if anyone searching for brake probs has a similar issue, this might give them some ideas to check.