Stiff Brake Pedal 2000 Q45 (Failed Brake Booster)

A Q45 forum / Cima forum for the President of Infiniti's lineup. Brought to you by Infiniti Parts USA, your OEM source for Q45 parts!
dan b
Posts: 18
Joined: Wed Jul 04, 2007 4:40 pm
Car: 1994 infiniti q45

Post

I am experiencing the same problem hard pedal. When you first start the car cold hardly any brakes. If you stomp on the brake the car stalls. After the car warms up there is no problem. Well its 10 degrees out side i guess i will start the procedure and geter done. Love the car 191.000 miles still ticking. Without this site and people who are not afraide to do the work a q45 is the a wonderfull car to own. Everybody please leave feedback when you find the problem and complete the process of a succesful repair so we can keep these cars on the road. We need to get people back to repairing them rather than junking them thanks to all the posters on this site.


reddog1
Posts: 1
Joined: Sun Jul 03, 2016 3:14 pm
Car: 2000 Q45 Annaversaryedition

Post

I was driving home today and brake pedal went hard. I to have a bad back. That is big reason I bought the car. It is only car I can driving for hours it comes with huge bonus, I enjoy the drive too. I have only been beaten in a race once by a GR-R ( I did not realize when I challenged him). I hit 135 and was like I was in park. LOL Best part was after talking to the guy, he was more shocked by the fact I gave him the best race ever. Where as I never saw a street car take off that fast.
I wish and hope someday I can rebuild it to make it like new. The little things add up all over the car. I love it. Only 15 MPG but it is a great 15 miles. Thank you all for your input. I did get a P0101 code once and it started driving like s*** about 3 weeks. Was thinking bad coilpack or clogged injector because right side was showing rich and raw fuel at O2.

Datsun B210
79 280zx
81 280ZX
81 280zx (with T-tops)
93 pathfinder
00 Q45

my12by60
Posts: 273
Joined: Sun Nov 22, 2015 10:32 pm
Location: Fountain Hills, AZ

Post

I just finished reading this thread. My son is driving our 2000 Q and he reported a hissing sound under the dash when the engine is running at idle and the brake pedal is depressed. I went out the other night to hear the sound for myself. Thus far, he is not reporting any unusual problems with brake pedal feel or with the idle or running smoothness of the engine.

I was hoping that possibly the check valve and or vacuum hose(s) was beginning to fail. I looked and could not see any check valve, but now I read here that the valve is likely inside the vacuum lines.

Which of the two pieces of vacuum line contains the check valve? The piece that goes into the plenum or the piece that goes into the booster?

How do I go about determining if either the vacuum hoses or the check valve have failed?

User avatar
VStar650CL
Technical Expert
Posts: 8294
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

If you can hear it under the dash but the car runs reasonably well, it's more likely you have a pinhole in the booster diaphragm. To test, pull the check valve from the booster and put a hand vacuum pump on the booster. If it won't hold vacuum then the diaphragm is damaged.

User avatar
VStar650CL
Technical Expert
Posts: 8294
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

PS - You can also check it using a scanner that will stream AF-alpha or fuel trim. Take a reading with the car warmed and idling, then pop and plug the booster hose. When the idle re-stabilizes, if the AF reading goes significantly leaner once the booster is disconnected, the booster is leaky.

my12by60
Posts: 273
Joined: Sun Nov 22, 2015 10:32 pm
Location: Fountain Hills, AZ

Post

--If you can hear it under the dash but the car runs reasonably well, it's more likely you have a pinhole in the booster diaphragm. To test, pull the check valve from the booster and put a hand vacuum pump on the booster. If it won't hold vacuum then the diaphragm is damaged.---

How do I pull the check valve from the booster? I think on the year Q that I own, the check valve is in one of the vacuum lines. So I should just pull the vacuum line that goes into the booster?

I have this kit for checking cooling systems:https://smile.amazon.com/Mityvac-MV4560 ... 220&sr=8-2

To vacuum check the booster, do I just need to adapt the tubing to fit the nipple on the booster from where I removed the vacuum line? What pressure should I inflate to on the gauge and how long does pressure need to hold to confirm that the booster is good?

User avatar
VStar650CL
Technical Expert
Posts: 8294
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

my12by60 wrote:
Thu Jan 14, 2021 2:12 pm
How do I pull the check valve from the booster? I think on the year Q that I own, the check valve is in one of the vacuum lines. So I should just pull the vacuum line that goes into the booster?

I have this kit for checking cooling systems:https://smile.amazon.com/Mityvac-MV4560 ... 220&sr=8-2

To vacuum check the booster, do I just need to adapt the tubing to fit the nipple on the booster from where I removed the vacuum line? What pressure should I inflate to on the gauge and how long does pressure need to hold to confirm that the booster is good?
Yes, just pull the vacuum line if the check valve is an inline type. If your seal is good on the tester attachment, it should hold vacuum for a long time with the pedal left untouched. Pull as much vacuum as you please, the test isn't how much you can pull but how long it will hold it.

my12by60
Posts: 273
Joined: Sun Nov 22, 2015 10:32 pm
Location: Fountain Hills, AZ

Post

Thanks for the reply. I have doing some more tests and reading on the web. I pulled the vacuum line segment that does not contain the check valve. I hear plenty of hiss from the open line and the engine idle lugs. When I cover the open line with my thumb, the idle returns to normal. So engine vacuum seems good.

Then I did the various tests that check the booster by starting and stopping the car and doing various things with the brake pedal. The booster passed all of those tests and seems to be operating normally. Current air temp in Phoenix as I do these tests is about 70 degrees.

In talking further with my son, he noted that the problem with the hissing only takes place in cold weather and then typically goes away when the car warms. Reading on the web, others have reported a dirty and/or sticking check valve that acts up in cold weather. The problem was solved by spraying some carb cleaner or other spray type cleaner through the in-line check valve. That is what I am going to try next.

User avatar
VStar650CL
Technical Expert
Posts: 8294
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

my12by60 wrote:
Thu Jan 14, 2021 3:19 pm
Reading on the web, others have reported a dirty and/or sticking check valve that acts up in cold weather. The problem was solved by spraying some carb cleaner or other spray type cleaner through the in-line check valve.
You're most welcome. Check valves can stick, but they won't usually cause audible noise inside the car and generally there will be symptoms in the brake pedal (loss of boost after WOT or steep uphills if it sticks open, insufficent or no boost if it sticks shut). If it only happens in cold weather, the booster housing may have an issue and not the diaphragm, something welded or crimped may be separating when the temperature drops.

my12by60
Posts: 273
Joined: Sun Nov 22, 2015 10:32 pm
Location: Fountain Hills, AZ

Post

Ok. I will do the check valve cleaning because it is quick and cheap. Then I will advise my son to be attentive to report any future hissing while noting the temperature if and when he hears the hissing again.


Return to “Q45 Forum / Cima Forum”