Brake Issue... Please help!

[BOHICA]

Afternoon all!

First and foremost I want to thank you guys as I am new to the the QX4 lineup and have been poking around for the last couple of weeks getting pointed in the right direction if not finding the exact solution. So thank you and it as been much appreciated. But I have an issue that I can not figure out for the life of me so I turn to everyone for some thoughts and or solution.

Background on my QX is that I purchased in cause it was garaged kept by an older couple who can not drive anymore. It is a 1998 with 87,834 miles on it. I recently replaced all the fluids, tune up and some head gaskets as they had a little leak and might as well do it all at the same time. She runs smooth, shifts better and can not beat the price of 750 bucks. They took care of her and she shows that she has plenty left in her.

The problem I am facing is that the brakes are WAY to soft. Pads and rotors have at least another 10k left on them, but may be replacing earlier just for the piece of mind. I thought that the master cylinder was dead so I swapped out it out with a Pep Boys reconditioned one. Bench bled then proceeded to bleed each tire as per this site and Infiniti guidelines. Brakes remain very spongy and even sometimes having to go to the floor and pump to get the car to stop. I even brought it to a brake shop to bleed thinking that I was missing something. Each time I bleed it seems fine for for a half day or so but then returns back to previous issues.

I have done both the RR, RL FR, FL and RL,RR,FR,RL combination of bleeding as well as redoing the master cylinder itself. Can not for the life of me figure out with the issue is but not only is it not the safest thing considering I drive a lot but also a mind F***k.

Any help or ideas would be greatly appreciated. Kinda stuck on it all and I am going insane trying to figure it out.


Thank you in advance.

[yeldogt]

Throwing parts at a car is not the proper way to go about fixing something -- and getting those parts from PepBoys is not a good idea unless you know what you are getting .. and it's good .. not just cheap.
So now you most likely spent money to install an inferior master cylinder?

It's only wise to replace parts when you have a reasonably good idea of the problem and the part is a known failure point.

And ,,,,,,, actually the brakes are IMO a weak point on these vehicles if everything is not perfect.

The brakes on the Pathfinder are on the soft spongy side. Especially -- Dependent on the pads and rotors installed-- this could be adding to your issues. Lots of people use aftermarket pads/ shoes -- the OE are very high quality and not overly expensive. The lack of 4w disk is an issue. I have installed Zimmermann rotors vs OE as they are every bit as good as the OE and cheaper -- but I always use the Nissan pads/hardware/shoes .. I have also had to replace both my front hoses as well as the rear cylinders on all three of my pathfinders. When I picked up my last 02 with low miles -- I immediately replaced the front rotors and pads as well as the rear shoes and cylinders plus all the drum hardware. The drums are normally fine unless abused. Wth all new hardware and cylinders -- the rear drums actually worked... many times the rear's are out of adjustment and not down much.

[Hawairish]

The problem I am facing is that the brakes are WAY to soft. Pads and rotors have at least another 10k left on them...

1. What is the basis of "too soft"? Spongy pedal, truck slow to stop, delay in stopping? Some/none/all of the above? It also helps to know what vehicle you're used to driving.

2. How was 10K remaining life determined? Somewhat a rhetorical question, since it's based on numerous factors: part composition, how long they've been on the vehicle, how the rest of the braking system is, braking style, tow loads, actual component measurements...as such, very subjective. To me, 10K remaining means "worn."

Agreeing with yeldogt, it doesn't usually make sense to throw parts at a problem...except in some general maintenance areas (like brakes). Pads are a consumable item, of course, and also the cheapest and easiest items to replace if braking feels compromised. As they wear down, they may need maintenance, from something simple (topping off fluids), or slightly more complex (adjusting springs, checking brake cylinders, checking caliper pins). Sometimes better to err on the side of caution, replace the maintenance items first (a master cylinder isn't generally one of them), and then see if the problem persists.

For the QX4 and many other vehicles, the brake bias is towards the front, so it's best to ensure that the rotors and pads are within spec and show even, consistent wear. For the drums, sometimes the adjusters between the shoes don't automatically adjust as they should, leaving a slight gap between shoe and drum that requires a little more brake pedal to fully engage. These may need to be adjusted as the parts wear. Conversely, if the brake shoe is dragging and causing excess heat, it will also have reduced performance.

Lastly, the rear brakes on the R50/QX4 tend to need several more pumps even after you think you've bled them completely. The pumps may come out clear for a bit after some bubbles, but give it more (at least 10 per side) to be sure.

[yeldogt]

I will add ... I'm not one to waste money just replacing stuff ... but sometimes it's better to just fix a whole system vs doing in over the next 10k miles.

A few years ago an older Lexus I used as an extra car was in need of rear pads -- when I looked over the car it was going to need more in the next year or 10k. Since I was planning on keeping the car for another 30k -- I replaced all 4 rotors and pads and put new tires on it -- cleaned and lubed everything up. That way I got the use of all the new parts -- sold it with reasonable life reaming.

[04pathse]

maybe give this a try...
https://www.youtube.com/watch?v=KIQIBLGoZJ4

[atraudes]

A couple of things come to mind that may be worth looking into/food for thought:

- Check the flexible brake lines. If they're cracked or otherwise suspect-looking, replace them. You should have two in the front and one in the back connected roughly to the middle of the axle. If they're bulging at all, that could easily explain your pedal going to the floor. Bulging is also tremendously dangerous.
- Check for leaks. Any wetness where brake lines connect is a bad sign. Check each end of the flexible lines, inside the drums, and even along the steel lines.
- Get your drums adjusted. It's a good idea anyway and will reduce pedal travel, possibly by a lot.
- What type of brake fluid are you using? I've heard people say (this was my experience as well), that after switching to DOT 4, their brakes got a lot spongier. Switching back to a quality DOT 3 remedied that.
- Use a Mityvac-type, pressure, or two-person bleeding system. I'm not sure which technique you're using but if you're using gravity bleeding I would try something else. I've never completely trusted gravity bleeding.

Let us know what you find!

[centralcoaster33]

You can try using a vacuum bleeder to assist. That with a nice clear hose helps you get to the new brake fluid and remove all air bubbles. The order is starting from the furthest caliper and working towards the closest caliper (closest and furthest from the master cylinder). Are you using the two person method? Wipe off the caliper at the bleeder screw and hose connection. Drive a bit or pump hard in your work spot and see if fluid is escaping anywhere. The calipers could be leaking at the piston seal area as well, not only loosing fluid and pressure, but also getting fluid on the rotor/ pads. Pumping the pedal and hitting the floor seem bad to me. Checking for bulging flex lines is a good idea. You have a brake shop helping with bleeding and they're probably doing that and only that. Perhaps you could have them inspect the entire system for not too much $$. After installing the new Master Cylinder, did you adjust the brake pedal? If your OEM MC was fine, I'd consider putting it back on the car. Those aftermarket ones are hit and miss.

[barnaclebob]

I never understand why people think worn pads are a cause for spongy brakes. The only thing that happens as the pads wear is that the piston extends out further but brake pistons don't retract more than the rotor pushes on the pads. The cylinder is not going to expand from the brake pressure so the pedal feel really shouldn't change as the pad wears. If i'm missing something please let me know, that's just me talking with my general knowledge of hydraulic systems.

OP, is it possible you have a damaged brake hose thats expanding as you pump the brakes? Are you getting bubbles when you bleed?

[BOHICA]

Thanks for the responses guys. To answer the your questions.

10k left is based on my experiences. Yes everything is wearing normally and nothing noted of concern. Brake lines look like new with no bulging or leaking found.

As far as spongy.. Initial press goes right to the floor then gets stiffer next press so I kinda have to pump for breaking. Not always the case though.

As far as the MC, it's literally a Nissan part that's reconditioned. Bench tested and all. It could still be the issue but have tried two with same results. Although I'm still a newb I went based on a mechanic's advice.

No bubbles what so ever, or air. I will deff try the an adjustment this weekend but if I'm going to do that I'll just replace all the way around. It was in the plans anyways I'll just do it sooner. It will need it at some point soon. I also had my local brake shop bleed in case I was messing up the two man and vacuum methods and inspect the whole system and came with same result.

Using DOT 3 fluid.

Was previously driving a 04 Trailblazer with 200k on the dash.

Again thank you for the advice and help. Hate not being able to figure this out.

[Hawairish]

Excellent response! (Seriously, thanks for answering everyone's questions.)

I missed your mention of the double-pump to apply the brakes in your first post, so now I understand why the MC seemed suspect. Is this during a gradual stop, or something more panic-inducing? Did you also perform any of the diagnostic checks for the brake booster, as described in the FSM?

Is everything for the load sensing valve intact? There should be a large spring coming from the top of the rear diff that connects to a valve, which proportions rear braking power for loads. But at the same time, "lift" from the rear (like what might occur during hard braking), would alter the proportion. There's a spec value for the spring length, which is adjusted by the hanger bolted to the diff. There's also an adjusting bolt that limits valve deflection. Surely not the cause for a double-pump on the brake, but something to be aware of (keeping in mind, too, that saggy springs also allow the vehicle to pitch more during braking).

[Hawairish]

I will add ... I'm not one to waste money just replacing stuff ... but sometimes it's better to just fix a whole system vs doing in over the next 10k miles.

Agreed! Especially on older vehicles. Sometimes, it's great to think "ain't broke, don't fix", but then sometimes, it's a "while I'm at it..."

I never understand why people think worn pads are a cause for spongy brakes. The only thing that happens as the pads wear is that the piston extends out further but brake pistons don't retract more than the rotor pushes on the pads. The cylinder is not going to expand from the brake pressure so the pedal feel really shouldn't change as the pad wears. If i'm missing something please let me know, that's just me talking with my general knowledge of hydraulic systems.

You're correct. In a properly-functioning system, the braking pressure (but not necessarily the braking performance) should remain consistent throughout component wear.

Sometimes it's just a mindset that only brake pads and shoes can wear down, but in reality, it's a collective effort by the system. A small leak, a pinched line, degrading soft lines, low brake fluid, the adjuster springs on drums...all have some impact, and easy to forget about because they don't wear down regularly.

That's usually why I ask for the driver to describe what "spongy" really means. It's just a subjective description, but I usually attribute it to the pedal feeling soft and accompanied by degraded braking. Some just talk about that initial pedal feel when it travels a little bit, but then braking kicks in fine, making it seem like there's a slight delay. In this case, I would agree that the OP does have a spongy pedal if he's having to build additional pressure by re-pumping.

[Buzzman]

Not sure where it is or how to bleed it, but I've seen other posts in the past mention the Load Sensing Valve.
Also, I've read (in the past) that the Nissan FSM says to bleed them in the following order:
rear Load Sensing Valve
left rear drum
right rear drum
left front caliper
right front caliper

[Hawairish]

Not sure where it is or how to bleed it, but I've seen other posts in the past mention the Load Sensing Valve.
Also, I've read (in the past) that the Nissan FSM says to bleed them in the following order:
rear Load Sensing Valve
left rear drum
right rear drum
left front caliper
right front caliper

Correct. There is a bleeder valve on the valve body, and it gets bled in the same manner.

[yeldogt]

We have never had any problems bleeding the brakes.

FYI: When I started driving in the late 70's (I started rebuilding triumphs before I could drive) .... getting rebuilt parts was the norm. Manufacturing was expensive/ parts had a shorter life vs today --- the norm was to find a rebuilt part. "Rebuilt" was normally "remanufactured" ....... this is not the case today. One has to be very careful buying rebuilt parts today as much of what is available is junk. Being a rebuilt Nissan part .. rebuilt by someone else ??? it's not a Nissan part. Same with alternator and starters -- most of what you get are Asian rebuilds of OE parts -- they are junk. We have had them dead out of the box -- and this was 110 years ago when we stopped buying them. It's worse today. Pepboys and the like give a lifetime warranty - not on the labor ... the car theses parts go on are old and not in the owners hands long enough. It's the next owner that has to figure out why all these parts are failing. When you buy a rebuilt part from a dealer or a rebuilt part from the actually OE maker -- that's a quality part. When my 02 LE needed an alternator -- I searched out the best price on a Hitachi alternator rebuilt by Hitachi (in a Hitachi box) --- I found one place selling the proper alternator (except the dealer). The dealers sell both new and Hitachi rebuilt. So all the other alternators sold are actually rebuilt by by someone else. In the end it's so much easier to get the correct part and fix it once -- especially if a DIY situation.

I think something is up with the Master -- or they have not properly bleed the ABS ... my gut tells me the Booster or master is not correct.

[centralcoaster33]

Check vacuum line to brake booster for leaks. Check brake booster vacuum, pump if necessary, hold in pedal, cut power to engine, wait 30 seconds. Pedal should hold firm.

[atraudes]

I wondered about vacuum to the brake booster too, but if vacuum were a problem at all, he would have a hard brake pedal, right? The fact it takes more than one pump of the pedal sort of hints at a problem with the fluid between the MC and calipers.

[centralcoaster33]

Tough to say without being there. Hard to push in but soft with actual brake application maybe? I don't know. He's got weird result per his descriptions. Has help from a brake shop even. Might as well let them check everything.

Ya know, I haven't even thought about diagnosing the ABS system until just now. I don't have ABS and don't think about it all the time. I wonder if that's acting up. I'll have to check the FSM I guess.

[BOHICA]

Evening,

Just wanted to update everything. Started to look at every component from the MC to calipers. Front completed without any issues. Thursday going to go from MC to rear calipers. Still have not ruled out the MC as a whole but before replacing anything trying to find if there are any other issues first.

New pads n rotors, shoes and drum going on over the weekend if no other issues are found.

Still will get pedal right to the floor randomly and others pretty close to normal. Weird at best. Will post more when I investigate more.

Thank you again for all your suggestions. Mitch appreciated!!!

[centralcoaster33]

Well, there's all the stuff you'll need for brakes in this chapter:
http://www.nicoclub.com/service-manual? ... 998_QX4/br
You've got ABS I think, load sensing valve to look at, brake booster inspection... lot's of stuff. You could spend some time just reading through this chapter, then go to the vehicle and start some diagnoses.