Hello everyone!

I thoroughly enjoyed my first trip with the introduction group on Friday- such brilliant fun and amazing people!
I can't wait to get out on more trips and meet even more of you!

However, I have noticed an issue with my car ('03 Pathfinder) since the trip, and it may have been co-incidence that it's become apparent in conjunction with going into the desert, but I'm guessing I perhaps damaged something whilst out in the sand!

On occasions, when I start the engine I hear a 'hissing' sound coming from somewhere in the front of the car.
This also happens when I brake, though the hissing stops once the pedal reaches the floor!

A mixture of having called my mechanic to explain the problem, and researching on the internet has led me to believe that I could have a vacuum leak in the brake booster (I believe they are related, from what I read). I gather that this could either be something to do with the pipes, diaphragm, or the master cylinder- does this sound right?

I'm having no problems braking (I'm pretty sure it feels as responsive and powerful as it ever was, and I'm not aware of having to push harder to achieve the same result), and the engine does not stall. So the problem doesn't seem to be serious (yet) and my mechanic said to just remain aware of it and of the braking performance, and if it changes (I'm guessing from other forums that I'm looking out for the braking feeling heavier or unresponsive?) then I should take it in.

I also read something about a test that one do to see how the vacuum is working, which I'm not sure entirely that I understood it but I'll explain what I did which may aid some sort of diagnosis:

With the engine off, I pumped the brake around 10 times to supposedly clear the vacuum of air, and then with my foot still on the brake, I turned the engine on and felt the brake pedal lower. Then I think I was meant to push the brake around 3 times with the engine running around 5 seconds apart, and feel the pedal go lower each time, though to be honest I'm not sure I felt much difference between each.

However, bearing in mind I'm using the car for these trips- is this something that can just be left until I notice something different, as my mechanic says, or should it be sorted asap?

Your thoughts would be much appreciated!

Thanks, Joe

Drive down and have Edgar look into this for some peace of mind.

Cant figure out what it might be just by reading this

Check monster garage

To be honest, most older cars' brake boosters his when you press the pedal. It's the sound of the vacuum actuator letting the air out. Like when you compress the handle on a bicycle pump. The air is simply being forced through the closure that typically keeps it in.

My old Grand Cherokee used to make this sound (among other sounds......) and it was never an issue in 4 years of owning it, even with much bigger tires and other additional weight.

The thing that concerned me is that you said the pedal reaches the floor. Do you mean actually touches the carpet or just gets close, but is hard to push all the way down?

Does it feel spongy or loose?

Have you checked the brake fluid level?

After a little reading, apparently there is a diaphram inside the brake booster which is prone to fail on early xterra models. You can almost guarantee that the xterra and pathy models of similar years would use the same components throughout as they are pretty much the same vehicle with minor variations.

Check the fluid level before and after conducting th test you said above and let us know the results.

Hey!
Thanks for your replies!

Tintin-

Sorry my description was misleading! I actually just meant 'towards' the floor, at its lowest point.
With what you suggested in mind, asking with a few other tests I saw mentioned elsewhere, I'll try to write in a little more detail about it...

Throughout everything I kept checking the brake fluid level, which seemed to remain constant (close to the 'max' level!) to my eye from start to finish.

As I'm not sure what 'spongy' brakes feel like exactly I can't be certain whether I should describe them as such!

It's definitely no real effort for me to press on them until the pedal reaches its lowest point, which is I'm guessing around 3 inches from the start point, and around 3 inches away from the carpet.
It also doesn't feel really loose as far as I can tell.
When driving the brakes seem perfectly responsive, and require what I believe to be a normal amount of pressure-also when driving the hiss sound isn't apparent as I don't need to depress the pedal that much in order to achieve the required amount of braking. The hiss sound only seems to happen within around half an inch to an inch or so of the pedal's movement (and if I keep it in that position it is constant)- namely when the pedal is nearer to its lowest point (though if I depress the pedal a little further to its actual lowest point the noise stops).
So that means I usually hear it at the lights, when my foot rests on the pedal, or when I'm changing gear (it's automatic).
Actually while I mention that, when in parking or neutral gear I also sometimes hear a click from the gear lever when I both depress and release the brake pedal, something I also don't remember noticing before. Though I'm guessing this is just from the brake pedal enabling me to change the gear lever's position.

So with one test I did which I believe is meant to determine whether the master cylinder is dodgy (I could be wrong, the description wasn't great), I did the following:

With the engine off, I slowly lowered my foot on the pedal until it reached its lowest point, and then pumped the brakes around 6 times. With the first slow depression the pedal went as low as described previously, with the subsequent pumps feeling too hard to press down very far (the pedal goes down to around half that of usual instead before there is significant resistance).
Then, I held my foot down hard for 30 seconds to see if I felt it lower at all (I could not feel it do so), which I believe is what would indicate a problem with the master cylinder.
After that I started the engine and I felt the pedal lower as I described in my previous post.

So that's about I can think of, if that helps!

Thanks again!

I agree it's probably nothing, but I'll say that brakes are not to be messed with and you should have a proper and full brake system test.

It's not worth being anything than 100% sure with brakes and tyres... imagine you're doing 120+ kph and suddenly need full braking power - you'll want to be certain everything works perfectly. No cutting corners there.

So, you've done the right tests, and there's no suspicion of any faults with master brake cylinder, slave, booster or anything wrong down by the wheels (the pads or disks) - therefore:

1. drain and replace brake fluid. I change this with every new car I get anyways - it gets old, collects moisture, and it just needs replacing every 5 years or so. Problem is most owners don't, and so you might even have original fluid in there! The symptoms are usually spongy brakes, but change it anyways. You could do it at home, if you know how, but any garage can do it for you. Drain completely, and flush, and then replace with fresh fluid. Some mechanics will cheat and just drain a bit and then top up - no, completely drain, and completely flush, and completely fresh can of sealed brake fluid to match the DOT specs for your model. Stand and watch while they do it.

2. Engine vacuum hoses leak test. Basically, there are rubber hoses that run around your engine bay that do not directly impact the running of the engine, and so a little leak can remain undetected for years sometimes. Basically, the test involves disconnecting these hoses and seeing if there is a sucking sound and if you can feel it when you cover the hose end with your thumb. Real easy test. Actually, for you, since you already have the hissing noise, perhaps you could start by identifying where that sound is coming from exactly (but still do the full test of all vacuum hoses). Any that are cracked, just degrease and wrap with duct tape, you don't even need to replace them.

3. While you're there, have them pop off the wheels and have a good look at the brake pads, brake disks, and the brake hoses (pneumatic lines that carry the brake fluid, going to each caliper - sometimes the 'mechanics' let them hang when they replace the pads, while they should keep the weight off them). If required, replace any of them that need it.

Just from your description, I'll bet you'll find a cracked or leaky vacuum hose, leading to the brake system.

In some models these vacuum hoses are really important and often the cause of badly running systems (which is great when you're buying as you can knock the price down, knowing they're a free fix, usually!) For instance, on the Wrangler YJ, the vacuum hoses activate the 4WD system. There's a stupid hose that runs down to the front axle, and if it leaks the 4x4 doesn't engage. Normally people think of faults with the transfer case, with the differential, all kinds of expensive repairs, but it's just a rubber hose needing some duct tape LOL

I'm not sure about the Pathfinder, but the three items above are cheap and I'd say something you should do immediately - last thing you want is the leaky hose to pop off completely when you stomp on the brakes in an emergency situation! (the vacuum operates the booster, not the brakes: so they will still work, just not as well as with the booster).

1. drain and replace brake fluid. I change this with every new car I get anyways - it gets old, collects moisture, and it just needs replacing every 5 years or so. Problem is most owners don't, and so you might even have original fluid in there! The symptoms are usually spongy brakes, but change it anyways. You could do it at home, if you know how, but any garage can do it for you. Drain completely, and flush, and then replace with fresh fluid. Some mechanics will cheat and just drain a bit and then top up - no, completely drain, and completely flush, and completely fresh can of sealed brake fluid to match the DOT specs for your model. Stand and watch while they do it.

Thanks PR for the informative post. I just have a query out of curosity. You said 'Drain, Flush and completely replace' I want to understand what does 'Flush' refer h to here. Does one need to flush (and hence clean I assume) with any special liquid, or just after draining old oil one needs to put in some fresh oil and allow that to drain that as well before finally refilling.

I would appreciate clarity on that plz.

Yes, no special liquid - just fresh brake fluid.

Basically you want to make sure you don't end up mixing the old with the new (especially if they are different DOT) - so to make sure, you first drain out the old stuff, then pour in new fluid letting it run through the system and out the bottom one wheel at a time, then close the drainage and final fill up.

That way you are assured uncontaminated fresh fluid in the brake system. Also, it will help get any debris out of the brake lines. It just takes an extra 5 minutes and a small can of brake fluid.

Problem is the "mechanics" don't care and just want to finish quickly - so they sometimes don't drain fully, and then directly pour in the new, and you end up with 80-20 new vs old.

Hey PR!

Thanks for the incredibly informative advice!
I totally agree, I don't want to risk anything when it comes to brakes!
I'll take it into the garage asap to get those things sorted, however I had a go at looking at the pipes under the bonnet just now, to see if I could figure anything out.
I couldn't actually see many that looked like they had air running through them, perhaps around 5 different lines. Some of them had suction and others didn't (I tried testing both ends of course!).
The main one I was aware of checking was the pipe running from the engine in the centre to what I believe is the brake booster, sat just at the back on the driver's side.
This seemed to have perfect suction, but I took it off anyway to inspect for cracks or anything, of which I found none.
When testing with the engine running and that pipe disconnected, the brakes felt as though the vacuum had gone so I'm certain I was looking in the right area. However after replacing the pipe the hissing still persists as before with the brake pedal depressed.
What I also find confusing is that the hissing sound was different to the hiss that came from the pipe being disconnected.
With the bonnet open, I can't hear the hissing sound coming from the engine area, is loudest when inside with the door shut, and seems to come from close to (just above) the pedals. It sounds as though it's coming from somewhere nearer inside as opposed to any of the pipes I could find to check.

Are there any other pipes that lead to the braking system?
If so I can't see or reach them myself!

I also have the problem of not being able to go and listen to where the hiss is coming from- I have to be there to hold the pedal down for it to happen!

Looking forward to hearing your thoughts- thanks again!

Joe

Dear PR,

Thanks for the clarity. Well appreciated.

Cheers! Alok

PR wrote:Yes, no special liquid - just fresh brake fluid.

Basically you want to make sure you don't end up mixing the old with the new (especially if they are different DOT) - so to make sure, you first drain out the old stuff, then pour in new fluid letting it run through the system and out the bottom one wheel at a time, then close the drainage and final fill up.

That way you are assured uncontaminated fresh fluid in the brake system. Also, it will help get any debris out of the brake lines. It just takes an extra 5 minutes and a small can of brake fluid.

Problem is the "mechanics" don't care and just want to finish quickly - so they sometimes don't drain fully, and then directly pour in the new, and you end up with 80-20 new vs old.