Have an 2001 infiniti i30. My brakes get hard and my car slows down after driving for a couple of miles.

One of the mechanics said that the calipers are siezed and bad, I changed all 4 calipers. ( a mechanic changed them and bled the brakes). The problem still remains. Here is what I have done so far.

1. Tested the brake in idle position. When I pump the brakes while the engine is not running, after pumping a few times the brakes get hard. Works like as it is expected to.
2. Started the engine and then I am able to pump the brake pedal all the way down. I turn the engine off while the pedal is still pressed and release the pedal. The pedal comes back. I assume the Brake booster is working fine.
3. I drove the car in the neighborhood for about a mile and a half after frequent braking. The brakes behaved normally for the first mile. Then the brakes started getting tighter. I was able to get back to the house and park in the drive way.
4. While the car is on the driveway, I started the engine back and pumped the brakes, now the brake pedal is hard to push.
There is a slight leak where the master cylinder is in contact with the brake booster. It is not a dripping leak but very slight one.

What else should I be looking for. On other forums the advice has been a) Master cylinder is bad. b) bad hoses. Since the mechanic was able to bleed the brake system are the hoses bad? If the Master cylinder is bad how can I confirm that it is the cause without having to pay a couple of $100s to diagnose and replace?

It sounds like the master is leaking out the back seal and building up pressure behind the piston after the brakes are worked a bit. You'll need to check the booster as well as replacing the master, it may be full of brake fluid and that will eventually soften and destroy the rubber diaphragm if it isn't cleaned out.

@Vstar650L Thank you.

Does this also cause the compensating port to get blocked? Is it possible to replace just the seals or do I have to replace whole master cylinder?

Yah, that's exactly the problem, if the cylinder doesn't return all the way because of pressure in the wrong place then there's no compensation. You can replace the seals if the cylinder walls are in good shape, but Nissan/Infiniti masters are pretty much all aluminum alloy with a coating. They can't be honed-out like old cast iron cylinders if there are bands of corrosion.

This is my first time I am doing, So experts please bear with me.

I was able to remove the master cylinder and emptied all the brake fluid. I removed the end cover. When I hit lightly at the other end the primary piston was able to fall out. The secondary piston seemed stuck. I was able to put a screw drive and was able to push the piston but however hard I tried the secondary piston did not fall out. I wanted to check if the seal was damaged. Is it worth trying to somehow extract the secondary piston, not sure how though?

Or buy another master cylinder and replacing the whole thing. Is it Ok to buy from carparts or parts geek ( costs about $50) Would you recommend it? Or suggest any other ?

Thanks,

When a piston is stuck it's almost certain there's a ring of corrosion that's holding it. Time for a new MC. Generally aftermarket MC's are just fine and not problematic.

I replaced the master cylinder. But the problem of the brakes siezing after driving a couple of miles is still there. What I havent done:
a) Flush the system
b) replace the brake booster.

What should I check next?

Thanks,

Your Booster is bad , it's SLOWLY sucking , and applying more and More and MORE force to the m/cyl - until it is like "Locked" - as if you (after several minutes of driving it) as if you are 'standing' on your brake pedal .
Could this be happening ? Like the engine vacuum slowly ,inside booster is ALWAYS "applying" ??

Experiment #1) Next morn. car cold , 1st start with the Booster vacuum hose OFF ! Be very , very careful - for you will have to utilize much more forces on the brake pedal . What you are looking for is DOES THE CAR STILL LOCK BRAKES ?? Or can you drive (be safe) and drive extensive time that you DO NOT SEE THE PROBLEM ???

If you don't ever figure it out , maybe you and Balkins can sell as a " two-for " BOTH your I 's to the same " collector " ...........
Not necessarily the Garbage collector either

I ruled out the brake booster because I tested per what was suggested by some folks.
a) Pressed the brakes with the engine off a couple of times - Brake pedal get hard
b) Started the engine - The pedal goes down.
c) Turn the engine off with the pedal down, and release the pedal, the pedal comes back up.

Does the above not rule out a bad booster?

All I'm saying is - remove vacuum (plugging the engine vacuum of course) removing vacuum from booster (which should began - " pumped out " & hard ) , and drive the car kinda like "manual brakes ",ya know , drive it as long as your problem would have exhibited itself .
And , with due respect , you have'nt said so far you've tried this specifically , forgive me if I'm wrong , and missed something , though.

@macgiver. No I haven't tried it yet. Will try in the morning.

One more thing , you may want to also do this with the "Booster check valve" removed , lest the front bellows may tend to 'hold-in" towards the m/cyl , thus developing non-releasing force to the m/cyl .
You basically want the Booster to be as "removed" from the equation as possible , completely transparent if you will.You want NO INFLUENCE on the inner/outer bellows ,gotta be free as a feather !
Good luck , come back with results of this experiment

On the Infiniti where is the booster check valve?

https://forums.turbobricks.com/showthread.php?t=268140 -

If the bleeding is not done properly could it be a problem. See the post above. I did it with a Vacuum pump, and may not have fully removed the air. The thread also says the hose.

Booster check valves are universally located right at the hole in the front side of booster , takes up like 1" ,and then there's the hose going into the manifold vacuum nipple - in that order. Now I only mention eliminating this check valve - remeber I said " it may tend to hold in the force into the m/cyl ". In otherwords your many brake applications, WITH the check valve still attached, may not FULLY take the Booster out of the equation - for you want , again , a virtually MANUAL/un-assisted brake application which the goal is to see if m/cyl AND ANY downstream proportioning valve , ABS , lines , AND calipers have anything to do with your problem .
I hope your check valve is situated as such , and this 'test' should be SO SIMPLE , EASY , and most of all CHEAP ...... Jeez you don't have to buy anything here , no expensive f 'n 'shotgun approach ' .
I mean you should'nt spend any money unless you break something - not likely , just if vac hose is brittle, give a little 1/4" axial cut to remove easily , then trim-off another 1/4" off of end to clean up for re-assembly ,ya know .
Persistence AFTER this experiment , I would suspect maybe if the ABS is messing up , like if the car, like it's prev. owners, whomever , neglected mucked up fluid throughout , or simply an electronics glitch/ failure in ABS ckt board which gradually builds some weird pressure during your drives ? Which you may try removing the ABS "motor-fuses" , usually 40A fuses ...........I dunno .ALL calipers you said replaced,right ??? And proportioning valves , all GUMMED -UP in the past ,have springs and check valves too that could present weird SH!#/TT ??

BUT DO this #1) experiment ABOVE first ,do it today , do it NOW.

macgiver wrote: ↑

Sat Sep 18, 2021 11:36 pm

Booster check valves are universally located right at the hole in the front side of booster

Actually, a lot of Nissans and Infinitis have the check valve integrated into the hose assembly and not conveniently plugged into the booster. Heaven knows why, because it makes "checking the check" a complete PITA and replacing it an equally stupid and expensive exercise.

I disconnected the vacuum hose ( and plugged with a wooden dowel, and was able to drive the car. Wow, the brake pedal was HARD!! But I drove very carefully and slowly in the neighborhood, pressing on the brakes often and hard to come to a full stop. Drove for about 3 miles. The brakes did not seize. Once I parked back in my drive way, I checked on the wheels. Three of the wheels were not hot to touch. The Drivers side front wheel was hot to touch but there was no smoke smell. Previously all the 4 wheels were hot to touch.

Did not find the booster check valve anywhere close to the booster.

So may be the booster is bad?

Why is the DS Front wheel hot to touch?

mmanem wrote: ↑

Sun Sep 19, 2021 9:34 am

Did not find the booster check valve anywhere close to the booster.

It's probably embedded in the vacuum line somewhere. Like I said, that's common on a lot of N/I models. Generally a check valve that's blocked or obstructed will cause high pedal effort constantly or effort which increases when the pedal is pressed multiple times. One that's stuck open will cause high effort right after the car has run at wide-open throttle. Leaky boosters will usually cause problems similar to a stuck-open check valve, but will also usually cause a high idle and erratic misfire because it amounts to a hidden vacuum leak.

mmanem wrote: ↑

Sun Sep 19, 2021 9:34 am

Why is the DS Front wheel hot to touch?

One hot wheel generally means a stuck piston or slider on that particular wheel. The only thing that causes the pads to back off from the rotor when the pedal is released is the square-cut shape of the o-ring on the piston, it distorts when the piston is pressurized and rolls back to its square shape when the pressure is relieved. That doesn't provide a whole lot of retraction force, so it doesn't take much "stickiness" in a slider pin or scored piston to prevent the pads from backing off.

So is it a checkvalve problem or a booster problem? or both?

All 4 wheels have new calipers, so you think the front DS caliper is getting stuck due to a bad caliper piston?

Something is sticking it if it's getting hotter than the others, they don't heat up unevenly for no reason. But with new calipers and a new MC, there isn't much left. If you're sure your pedal is adjusted correctly, then maybe something is sticking mechanically inside the booster. That's rare but not impossible. I very much doubt it's the check valve, everything that goes wrong with those causes some sort of high effort and not sticking.

After all said & done , my opinion - get a 'quality' Booster , Booster warranty's will state " warranty void if check valve not replaced with a NEW ONE " . A thorough install on the Booster , RE-BLEED all wheels AGAIN .
See.......
When doing this TEST , ya gonna get hot wheels maybe , cause your not caring about HARD OVERBRAKING!!! And so IF the other 3 wheels with respect to DS wheel are not copascetically bled EVEN and THOROUGH , maybe the reason for one hotter wheel rim , ya know.

Thank you all. Will get a new Booster and replace. Doesn't look like a difficult thing to do. Again since I am a first timer it may take me a while. Bleeding with a Vacuum took me over 2 hours.

One more thing , I like pedal bleeding , just me , cause my wife and daughter have become EXPERTS at precise timing while I'm at the 'screw" , AND they know not to OVERTRAVEL when they depress - they NEVER HIT BOTTOM I just like the control with positive " pedal - pushing -the -fluid " action.

Never tried gravity nor the vacuum method - just looking at those procedures , I conclude pedal bleeding for me , just me . When the pedal is brick-like , super responsive and applications are RIGHT THERE , I simply have'nt delved into any other ways , ya know. But that's me.

p.s. Some Boosters MAY come with new chk. valve "in the box" - if not , having at least the receit for one IF you have to take it back is good . So , what ya do is copy a check valve receit , see if just the Booster works 100% ????? You then make a judgement call to return chk valve within store policy by using the copy first . And I would only do this IF valve is $$$$$$$$$$ , AND FULLY satisfied with brakes for like the couple week store return policy , and you would retain this chk valve receit for the LLT warranties we see . They wanna see ya bought that chk valve ya know !!!

Booster probly RE-Man ...... REBUILT...... by $ 0.75/hr labor ....... HAVE A RECEIT !!!
Gotta be SLICKER THAN SH1!TT With this

p.s. Now that you've seen the difference of NO POWER ASSIST , even IF you 'feel' Booster unnecessary ,your twenty year old car will have that ASSURANCE . My Booster on a J-30 went out on busy f-way and I never imagined that just to reduce speed I had to put 5 times the pedal force .
When they ' go-out' ......you and passengers MAY DIE . You would'nt be able to react fast enough nor compensate , likely involving a very bad accident.

Replacing the Brake booster worked. Not sure if spending all that money on Changing the calipers was worth it. Anyway, I have a new brake system!!!

Like I said ............................................................................. LOL
Oh ........................................... your welcome ................LOL
I know , probly booster all along , I been there , everybody else here been there done that sort too !!!!!!!!!!!!