04 G35 Coupé automatic 120k miles. Ok so my car was working and braking fine not sure what's going on but my brake pedal is really hard the car barley slows down I have to apply a lot of pressure on the brake pedal. And what's weird that it seems to happen in the cold mornings, in the afternoon it seems to be working better but not perfect like it's supposed to. Anyways I bought a used oem brake booster and its seems to have got a little better but it's still hard. What would be the chances of that one not working? I have bled the brakes mutltiple times and still no success. I'm tired of this already, I'm ready to give up and just take it to a mechanic. Is thier anything you guys recommend me doing that might fix this problem? Can it be the brake master cylinder? I heard when brake boosters go bad you'll hear some sort of airleak but I don't hear anything on mine so I'm just lost. Someone had told me to bleed the abs pump but how do I work that? Any help would be appreciated thank you!

 

Hey bud.. There is a vacuum line that goes to the booster. Follow that and make sure it's not disconnected some where...

 

That would be my first guess also, you either lost the line from the manifold to the Brake Booster or the diaphragm in the brake booster split.

You might be able to hear the hissing from the leak, listen closely by the brake booster.

 

Try this to determine if the booster is storing vacuum.

With the car off, pump the pedal a few times to vent air into the booster. Pedal should be hard as a rock. With light pressure on the pedal, start the car. The pedal should sink slightly and should be softer now.

If it isn't, check the 1 way valve and the vac line heading to the booster.

Hard pedal could also be caused by a seized caliper piston. With the piston frozen in place, the pedal may be slightly harder. You may want to go around ot each caliper and remove and press the piston in with a C-clamp to determine if they are frozen in place.

 

I've had this same problem on my car, which seemed to happen mostly when the weather is chilly. I had my brakes bled, my break booster replaced with a new one, and multiple inspections at a brake shop that could not figure out the source of the issue. After all that, the hard pedal issue still happend to me a few of times.

I concluded that it could be a problem with the vacuum line. There is a Check Valve in the line that may be faulty, or the Vacuum line may also be dirty inside, which will interrupt the vacuum suction to your booster. I Seafoamed my car though the vacuum line that goes to the brake booster. This seemed to relieved the issue for my car and I haven't had the hard pedal issue since then (this was last week).

Try using Seafoam (there are a couple of threads here on how to do it). Its available in most Auto stores for around $12 per bottle-- I bought mine at Autozone. Follow the Seafoam procedure and see if that solves your issue.

If that doesn't help, then you could look into your Brake Master Cylinder, and finally inspect the calipers/pads to make sure they are not freezing up.

Good luck man.

 

Vac leak....

 

Ok so I think I found a solution but then I think I didn't lol. Ok check it out...I went to a junk yard and bought 3 vacuum hoes with check valves inside from random cars. Then I removed my oem hoes from my brake booster and tired one of the hoes that I bought and surprisingly my brake pedal isn't hard anymore but I feel like it can and has to brake better, it doesn't feel like if it's working 100%. So I went to a Nissan dealer bought a new oem vacuum hoes and put that one on and then my brake pedal gets stiff again! And yes it had a check valve inside. The hose that I bought at the junk yard seem to has air flow from the brake booster to the intake manifold and the check valve stops the air from returning back, which it did. I would blow on the side of the hoes with would go to the brake booster and air would come out from the side of the the hose that goes to the intake manifold. Then i tried blowing from the side of the intake manifold and air would not flow out, which I'm thinking that's how it should be? But the oem Nissan vacuum hose had air flow on both directions I could blow air on both side and air would come out on whichever side I tried it.

So my problem here is...?

It can't be the master cylinder right? If that goes bad I believe the brake pedal sinks down...

My brake booster isn't leaking any air...or at least I don't think it is. I haven't heard any air leak.

Vacuum hoes maybe was damaged? That's how my old oem was too air flowing both directions.

Anyways I'm ready to give up lol take it to the dealer. How does your oem vacuum hoes work? I'll try seafoam I guess. It's my daily driver so i need to get this fixed it's working like 75% but not 100% and I plan on selling the car and I'm sure no one is gonna want to buy it like that ;( thanks if anyone has anymore info.

 

Another possibility would be that there is contamination in the master cylinder, such as a metal shaving or spec of dirt that causes the master cylinder piston to bind.

 

The 1 way check valve is just that...a check valve. The engine should be able to pull a vacuum from the brake booster through the valve towards the direction of the intake manifold. The check valve should stop air from flowing back into the brake booster from the engine when engine vacuum is reduced.

So the check valve should only allow air to flow AWAY from the brake booster. You should not be able to blow INTO the brake booster.

Sounds like you have check valve issues.

I'd just swap that junkyard part on and call it a day unless you can just swap the check valve over to the new hose.

BTW that hose is just standard vacuum line. Hopefully you didn't pay a lot at the dealer. The check valve can even be sourced through parts stores as well

 

That's a lot of hoes.

 

Yeah I paid 35 bucks for the oem hose but returned it. Anyways I have the old junkyard hoes works good but not 100% so I guess I'll leave it like that or maybe take it to the dealer sometime in the future. I think I'm done with this brake system...stuff it's complicated lol

 

You replaced the brake booster? Did you buy a new 15 dollar o ring and seal it properly? If you reused it than its probably trashed now. How does the car sound at idle? Does it rev up or anything? My brake booster o ring went out that's why I'm asking. It caused a huge vac leak and weak brakes. The check valve should only blow air one way as well.

 

I bought a used oem brake booster what's the chances of that one being bad? My old one looked in good condition. Anyways my car idles fine...and the o ring? I didn't replace no oring I was thinking about buying a aftermarket booster but it's a pain to remove and install it lol

 

Simple way to test. Turn the car off. Wait, maybe 30 seconds ot a minute or so, and then press on the brakes. Do you still have a few pumps before the booster loses vacuum and the pedal firms up?

 

Depends on where you bought it from really, but I don't really hear of those going bad often. You should really replace that O-ring it goes between the booster and firewall. It also comes with a packet of grease. It creates a huge vacuum leak and problems like you're mentioning when braking. That was the problem in my case at least, but YMMV.