I have a serious problem with my 2006 G35 coupe. First thing in the morning, my car won’t stop until I am part way into the intersection, scary stuff.

I live in Canada, so it is somewhat cold here in the mornings. Here is what happens:
• I park my car in the driveway on an uphill slope
• I start to back my car out of the driveway, hit the brakes (just fine)
• Put the car in drive and drive down the block
• I approach the busy intersection and attempt to hit the brakes, however the pedal is as stiff/hard as can be, so the car won’t necessarily stop in time
• Eventually the pedal will go down, then operate normally for the remainder of the day

The pedal feels like pressure has built up, as it would when you pump the brakes while the car is off.

This has happened a few times in the previous few weeks (I have only owned the car for about a month or so). I am not quite sure how to figure out the problem, or go about fixing it. I have read a few threads where people have had a similar issue, but I did not find a solution.

I am guessing it could be the brake booster, but I have also heard that it could be a vacuum issue. If it is a vacuum issue, I am not sure how I would go about troubleshooting it.

I did feel around a rubber hose that is connected to the master cylinder or brake booster (can’t rem which one), and there is a small section of the hose that is hard. I am not sure if this is normal or not for a G35.

Sorry for the long post, any help or insight would be great.

 

Found these for you.

http://www.ehow.com/way_5777092_brak...eshooting.html

http://www.dummies.com/how-to/conten...-problems.html

Hope it helps!

 

I'm in no means a mancanic but I do know vacuum is what helps you with the pedal if not it would be as hard as a rock to push. If your not losing brake fluid into the booster or you don't see any around the booster then chance are the booster is fine. I would start with that one way vacuum line something might be happening there.

 

Thanks for the replies. I did some trouble shooting and Vacuum hose seems to be fine.

One thing I am not sure is if there is 1 one way valve or 2. There is a one way valve on the passenger side by the battery, I tested that by taking the hose off and blowing in it, works as it should. I am not sure if the hose connected to the booster on the driver side is also supposed to have a one way valve, it feels like there is something in the rubber hose, but if there is supposed to be a one way valve there, then it is not functioning properly.

Master cylinder does not seem to be leaking, that was one of the first things I looked for, so not sure what it could be. It is odd because it only happens once a day (not every day), then it is fine from that point forward.

 

Not sure what else to tell you, try blowing it first thing in the mourning maybe its freezing shut or getting stuck at first. Reason it works at first is maybe it still has vacuum from when you parked the car the day before.

 

I tried to pump the brakes a few times today as I backed out of my driveway, and it did it on the third time I pressed the brake. Almost as if the car had vacuum from the night before when it was started, then once that was used up, it lost vacuum?

I will try blowing in the line first thing in the morning. Does anyone know if there is also a one way valve in the rubber hose that is connected to the brake booster?

 

Yes, there is a check valve in the vacuum hose shaped like a "U". It is marked by an arrow on the hose itself that says "ENG". You'll likely need a vacuum pump to test it though. Here are the inspection instructions:

"CHECK VALVE INSPECTION
Airtightness Inspection

Use a hand-held vacuum pump to check.

When connected to booster side (1):
Vacuum decrease should be within 1.3 kPa
(10 mmHg, 0.39 inHg) for 15 seconds under
a vacuum of -66.7 kPa (-500 mmHg, -19.69
inHg)

When connected to engine side (2):
No vacuum will be applied"


Probably best just to replace that hose assembly and see if it helps. Can't be that expensive.

BTW, here are the Brake Booster check procedures:

"BRAKE BOOSTER PFP:47200

On-Vehicle Service AFS0012D
OPERATING CHECK

With the engine stopped, change the vacuum to the atmospheric pressure by depressing brake pedal several times. Then with brake pedal fully depressed, start engine and when the vacuum pressure reaches the standard, check that the clearance between brake pedal and floor panel decreases.
CAUTION:
Depressing pedal interval is approximately 5 seconds.

AIRTIGHT CHECK
Run engine at idle for approximately 1 minute, and stop it after applying vacuum to booster. Depress brake pedal normally to change the vacuum to the atmospheric pressure. Check that distance between brake pedal and floor panel gradually increases.
Depress brake pedal while engine is running, and stop engine with pedal depressed. The pedal stroke should not change after holding pedal down for 30 seconds.
CAUTION:
Depressing pedal interval is approximately 5 seconds."

 

i would say more than likely the calipers have to be serviced. i get a lot of these issues at my garage. brakes should be serviced at least twice a year to keep all the sliders free and so the pads dont stick in the brackets. try that.

 

Thanks for all the suggestions and input.

I paid a little more attention to notice when the issue happens, and is actually on the 2nd or the 3rd time I press the brake when the pedal gets stiff. So it is like the car has vacuum from the night before, then once that is used up, the pedal gets stiff.

I called the dealership today, and apparently there is only 1 one way check valve. If this is true, then my check valve is fine on the passenger side of the motor.

The “U” shaped hose connected to the booster itself apparently does not have a one way valve, according to the dealership. However, when squeezing the hose, it does feel like something is in there (so I'm not sure what that is about). We did do a few tests with a hand held vacuum pump that I use for the brakes, and all seems fine, at least with the 1 one way check valve on the passenger side. I also did the booster check and airtight check, both seemed to operate as they should.

I asked to order the hose connected to the booster but was told it is $40 and about 3 – 4 weeks away, as there aren’t any in Canada. So I did not order one for now.

What does servicing the calipers involve? I wouldn’t think that the pads are sticking to the brackets in this situation, since the brakes do work the first few pumps and then get stiff, then after is fine for the remainder of the day. But this is definitely worth a shot, as I am running out of ideas as to what it could be.

 

Yes, there is only 1 check valve, but it is in the larger U-shaped hose (which I assume is what you mean by passenger-side hose). If that checks out OK, then that must not be the source of the problem, but it can't be much more than $50 either so may be worth trying a new one. You don't need the smaller u-shaped hose that attaches directly to the booster as that has no valve in it. Here is the 2006 Field Service Manual showing the hoses. The hose I've circled in red is the one that you need to test (which it sounds like you might have already). It's on page BR-19 in the FSM.

 

Before you concern yourself with brake boosters did you check the brake fluid level? If that's really low you'll have trouble stopping especially in cold weather. You're better off finding a independent brake/alignment shop in your area rather than the dealership.
Gary

 

Thanks for this, I did check the larger "U" shaped hose, and it is indeed OK. From the diagram, the smaller "U" shaped hose is hard when squeezing the hose in the exact area where it says "orifice marker", indicated by #7. This is what made me question whether there was 1 or 2 one way check valves.

What is and orifice marker? Sorry if this is a stupid question, google didn't help me much, it keeps referring to A/C lines. Is this something that can be clogged, or a potential problem source.

Brake fluid was the first thing I checked, it looks clean and full.

This is such an odd problem, and have never come across it or even heard of it before.

 

Hmm...if the smaller u-shaped hose is stiff/blocked then that could be a problem, as there is no valve in there. Maybe remove it and blow air through it. I think the orifice marker is just where it connects to the booster opening or plenum opening (I'm not exactly sure).

 

I've run into this issue before and the cause was the pads being so worn thin that the wear warning nubs were hitting before the pads came in contact with the rotors. Thus the inablility to stop the car. Is this possible here?
Gary

 

I have tested that hose, and it was free flowing when blowing air through it and trying to suck air through it, on both ends. Which is why I wanted to know if there was a one way valve in there, because that would indicate that the valve is not working. I think I touched on this in an earlier post (post 4). I guess it might be worth trying again. Also, the hose is only stiff in about a half inch to one inch section, exactly where the diagram states "orifice marker", the rest of the hose feels as it should.

I don't think that is the issue here, the brakes still have a significant amount of meat on them. If the pads were thin, then they would likely make a squealing sound, and the car could be difficult to stop throughout the day. This is just a stiff pedal, on the 2nd or 3rd pump, in the beginning of the day, then fine thereafter.

If this problem was continuous and persisted throughout the day every time I got into the car, the issue would likely be a lot easier to diagnose. But this seems to be a one-off unique problem (for the most part). I have read other G35's having similar issues, but did not find a resolution.