Driving to lunch this morning, I noticed my brake pedal was abnormally stiff. Caught me off guard, as if I only had 50% of my available braking power. I read the FSM which lead me to doing the suggested brake booster trouble shooting test. With the engine off, the pedal does not get incrementally harder to depress. It is stiff from the first pump. With the engine running, the pedal feels the same as with the engine off. Also, pressing the pedal with almost all my might (which I have to do to keep the car from rolling in car at a stop) at idle, the engine sputters and almost dies. This definitely leads me to think it is a vacuum leak.

I took a look at the vacuum line(s) that run from the intake manifold to the brake booster. The line that runs from the manifold to the intermediate metal tube on the firewall looked to be very brittle and possibly cracked at the end where it connects to the intake manifold. Upon removal, it was indeed cracked. I'm not sure it was it cracked before I took it off as it took some muscle to remove it. Either way, that line has to be replaced.

Where do I find this line? I can't find it on any Infiniti parts stores. This line has a built in check valve. Can I temporarily install a vacuum line that does not have this check valve until I can locate an OEM line?

Thanks for any help in advance!

-Seth

No, you must have that check valve for safe operation!

Did you call IoS? www.infinitipartsusa.com

Ditto on Infiniti of Scottsdale. Do you hvae enough slack in that hose to cut the cracked part off and stretch the hose in place as a temporary fix until you get the replacement part? As Brian said, the check valve is very important... without it you'd loose vacuum at certain RPMs and you would also be pushing a blast of unmetered air into the intake evey time you pressed your brake pedal - causing engine performance (choke down) issues.

Heath

I just got off the phone with infinitpartsusa (Infiniti of Scottsdale). They don't have the parts in stock, but can get them in a couple days. $19.90 a piece.

I did not have enough hose to cut and stretch to fit. The hose was extremely brittle for the first 4-5".

and a short piece of fresh hose.

I might have to hold the order and give the DIY a try instead. I did see that you can add in your own check valve. Make it cheaper to fix if this happens again.

Quick update.

While I wait for my new vacuum lines, I used a 3/8" line I had lying around from a past project. With no check valve, the brake pedal feel did not improve with this new line. Interestingly enough, at idle with the pedal firmly pressed, the motor surges really bad. It feels as if the engine is under load and wants to stall. I am almost certain my brake booster is bad. It must have a leak, causing the engine to see a vacuum leak and wanting to stall out.

I will be buying a new brake booster and hopefully installing it next week. Will update once that is completed.

Hook up a vacuum gauge to it and see if it holds vacuum and also press the pedal.

lamsv wrote:Quick update.

While I wait for my new vacuum lines, I used a 3/8" line I had lying around from a past project. With no check valve, the brake pedal feel did not improve with this new line. Interestingly enough, at idle with the pedal firmly pressed, the motor surges really bad. It feels as if the engine is under load and wants to stall. I am almost certain my brake booster is bad. It must have a leak, causing the engine to see a vacuum leak and wanting to stall out.

I will be buying a new brake booster and hopefully installing it next week. Will update once that is completed.

Did this engine condition happen after you replaced the hose and deleted the check valve? If so, that's what I was talking about in my earlier post. Your booster is pushing air back into the engine when you press the brake... since that air isn't metered by the air flow sensor, the car doesn't know to compensate for it...

There is a check valve in the system. $2 from the True Value.

What is the condition of the brake fluid? Maintenance history?

Fluid looks great. I replaced it when I got the car a year ago. Checked all calipers and none are sticking. The hard pedal feel is more than likely resulting from no assist from the booster.

Did the engine issue start after you swapped the hose?

Booster failure is very rare...

Engine issue started the morning when I realized the pedal was super stiff. I recently had a coil go bad that I haven't replaced. I thought the surging idle was related to the coil. But, after swapping in the new coil, the surging idle still persisted with a new hose and check valve.

Yes. Booster failure is rare, but not unheard off. At this point, if it isn't the booster, what else could it be? Brakes work perfectly fine, just takes a strong leg to get them to work. But, just driving around my block, car stops just fine.

Surging could be a combination of contaminated IAC valve and failed coilpack(s).

I am throwing no CEL's after swapping the coil pack. Could bet he IAC, but it hasn't thrown a code. I will check that though.

But, with the nipple on the intake manifold for the brake booster plugged, my idle is perfect.

It is a bit late, as I've ordered a booster.... but is there an o-ring between the brake master cylinder and the brake booster? I don't know why I didn't think of it, but I had an o-ring fail on my old Tahoe between the booster and M/S. It caused these same symptoms.

lamsv wrote:Yes. Booster failure is rare, but not unheard off.

Nearly unheard of though... I think in 15 years of very active internet activity I've heard of one failure on a Q - or any Nissan product for that matter. Doesn't mean it can't happen though... I've had one of the few brake pedal switch failures that I've heard of too.

I would install the new OEM hose and checkvalve first, and see if that fixes it in the hopes that you can return that brake booster.

I don't think there's an o-ring on the master cylinder that could fail and cause this... there's a test in the FSM for the booster that involves checking the piston length coming out of the brake booster. Shows some diagrams of the master cylinder as well...

http://www.nicoclub.com/FSM/

Good luck!

Heath

I took a look at the test in the FSM. I am going to give it a whirl if the OEM lines don't fix the problem.

Thanks for the help! Hopefully, I don't become the lone Q45 owner with a bad brake booster. It would just be m luck.

-Seth

I also only remember one failure of the brake booster. Cannot recall if it was a G50 or FGY33.

Another update small update. Was able to throw on the OEM vacuum lines this afternoon. It did fix the surging of the engine at idle with the brake pedal depressed. It did not fix the stiff brake pedal.

Next, will replace the brake booster. Will update when that is done.

3 hours, beat up hands, and more cuss words than I care to admit too... the end result being a replaced brake booster. Which, did fix the problem. Looks like I had that 1 in a million chance of a brake booster going bad.

End result: new brake booster, brake power and feel back to normal.

I'm glad you got it fixed! I bet that is a bear of a swap...



Heath

Bear of a swap is right! Doable by a shade tree mechanic, as long as you have extreme, and I mean EXTREME, patience.

I just lost my booster as well; 238k miles... Guess that's a long enough lifespan for a car part. Went through everything else first to narrow the problem, but it's definately the booster. Bought a new MC to compliment the new booster. Now I get to spend the upcoming weekend bustin' knuckles.

I wish I could give you some hints... but I can't. Just lots of patience.

Definately bad booster; running fine again, but not a fun repair, too much upside down. Already blew my back out earlier in the week...

Glad you got it fixed! Back pain is no fun. I have a herniated disc that's bad enough the doctor said "wow... have you seen your MRI!?" on my first visit...

Heath

Yeah, I know the feeling, mine keeps slipping, pinching the nerve. Just slipped it out again last night cleaning out the dust from my blower motor, intermittent functioning; cleaned it out and works fine, but my back reminded me it's still not healed from the booster.

I used to come here YEARS ago...like early 2000's when I ran NWMaxima.com. My account was gone, so I re-registered so I could say thanks for this thread. I had this exact problem with my 2002 Q45 (sputtering engine, hard brake pedal) tonight. The brake booster vacuum hose was crystalized and snapped off the inlet on the manifold. I pulled the broken bit off and put the line back on. Works again! Now I just got to order a proper replacement.

Thanks again! Yay Internet!

I'm glad we could help!

back to NICO and don't be a stranger!

Heath