I had my car sitting outside in -30 weather for 6 hours. I started it up, but at the first intersection I arrived at I tried to push the brake pedal, but it wouldn't budge. I turned at the intersection onto a side street and pushed the brake pedal again, and it worked properly. Every time I pushed the brake pedal, there was less and less resistance. Now when I push the break pedal, it goes all the way to the floor before engaging the brakes. But it doesn't feel spongy, the pedal comes up like everything is fine.
I checked the brake master cylinder, it's full with brake fluid, and I checked the brake lines at the master cylinder and the four wheels as far back as I could see, there were no leaks.
When I pump the brakes with the engine off, the regular amount of pressure (with the engine off) builds up. But when I pump the brakes with the engine on, there is a just a bit of pressure that builds up, a lot less pressure than there usually is.
I don't think there's air in the lines because the pedal doesn't feel spongy, so I am guessing it is either the brake booster or the master cylinder... What do you guys think?

 

not the brake booster. that would make it harder to push down. master cylinders go out a lot. i had to do mine as soon as i got the car

 

-30 is down there. If there was any moisture in the brake lines (h2O) it would have been frozen, solid, and playing havoc with the system. Condensation will occur, especially if the reservoir isn't 100% full at all times.

Outside for six hours at -30 I'd act a bit screwy, too.

 

well the reservoir is full all the way up to the filter thingy... how would I check for condensation? do I have to bleed the whole system? And is there a way to check the master cylinder to see if it's working right?

 

Bleeding the entire system, at least until you have clean, clear fluid at each caliper would be helpful, if for no other reasons than getting rid of any water, getting the heat cooked fluid out of the system, and will give you an opportunity to get up close and personal with each caliper to inspect for leaks, and proper operation.

If the master cylinder has gone bad you would have little, or no, pedal pressure. If it is partially bad, you may have a little brake action on one end of the car, but not much.

A lesson I've learned dealing with hydraulics is that if a component of the system is replaced, it isn't long until the next weakest component fails because of the additional pressure created by the new part. This process usually continues until the entire system has been replaced.

 

1.I've already taken each wheel off and inspected the calipers and brake lines around there, and there were no leaks.

2. By pedal pressure do you mean there is no resistance when you push the pedal down? Or do you mean that one you push it down, it stays down?

 

every time that a master cylinder has gone bad on me, (3 times, 3 different cars including the Z) the symptoms have been intermittent pressure loss. after loosing pressure, i could always pump the system back up with one stroke, then the brakes worked fine. that is my defiinition of a partially bad master.
my advise is to bleed the brakes (not much to loose here. maybe $10 in fluid), and see how it does. if it persists, replace the master.
i believe that there is also a trouble shooting section for brakes in the manual no?

 

I dont have the Haynes manual for the 300ZX, but I have one for an 84 Chevy, and I tried what it told me but I didn't find much out... What are the procedures in the nissan manual?

 

Z31 FSM: http://www.xenonz31.com/reference.html

 

i work in hydraulics. If you have any water in the system at -30 it is going to freeze and possibly damage the seals, u cups, in the master, I would drain the entire system add new fluid and bleed it. if that don't work change the master, $120. through black dragon. brakes are brakes and they work about the same as the ones on your chevy.

 

That's good. Bleeding them will let you be sure you've got hydraulic pressure making the trip to each caliper, and you'll notice it squeezing the rotor as the brakes are applied.

Little, or no pressure. Very little pedal resistance is a sure sign it's by-passing fluid, if there are no leaks.

Bleed them, then get back to us.

 

So after two weeks I finally got time to try and bleed the brakes, the problem is I can't get the bleeder valves to budge. After soaking them in WD-40 Wednesday night, and than a thorough soaking before I tried a 10mm box end wrench, which stripped the nut, and so I clamped on some vice-grips so tight it nearly pierced the skin on my palm (I now have a painful bruise on my palm) but that didn't work. So now I am using some cold-weld (not JB-Weld, COLDWELD, pretty well the same stuff I think) to weld a spare wrench onto the bleeder valve.

On the other caliper I tried using a 10mm socket on the valve after a thorough soaking with WD-40 AND brake cleaner, but it still stripped the nut (although the socket will only go on the nut about 2/3 or 3/4 of the way).

1. Would a deeper socket be much better than one that's on 3/4 of the way?
2. What would you try to get these off? (It doesn't matter how, since I picked up some bleeder valves)

 

WD40 = water. It's good for squeaky door hinges, not rusty bolts.

Get yourself a can of PB Blaster... spray it on, let it sit, spray on some more... then go at it. You may have to Vice Grip it now, remove it & replace it.

Lesson: WD40 SUCKS. USE PB BLASTER.

 

I'm having kind of the same problem with my car! At first I thought I had some how lost all of my fluid. I checked that then I thouhgt I had a vacume leak at the master. New hose and hose clamps. Not fixed. I'm thinking now its the master cuz it only does it after I drive the car for awhile and If I pump the brakes a couple times it works fine but If I don't it goes to the floor before I even get anything and then the tires lock up right away. The way its sounding go ahead and replace the master thats what I'm looking into for mine now!!

Which brings me to my question (sorry to thread jack) but does anyone know if you can possible put a smaller master in there! One with the same amount of pressure and everything just smaller?

 

if you really wanted to fab all that up... but its surely preferable to put the stock master in there. brakes arn't something that i would ever want to downsize on

 

So I bled the brakes, that didn't work, than I changed the master cylinder on the advice of a friend, and I still have the same problem.

There's two things though, when I went to NAPA to get the MC, they had to order it in from the Edmonton NAPA, but the douches at the Edmonton NAPA didn't bother sending the bleeder kit that is supposed to be in the box.
But the "experts" at NAPA told me I could bleed it on the car just like I would bleed the brakes, by pushing the pedal, opening the line, closing the line and than lifting the pedal, is that OK?

And when I bleed the brakes, do I open the valve just a bit so the fluid comes out slowly, or should I give it a good half-turn so the fluid rushes out? I turned it a good half-turn to let the fluid rush out.

If those two things are a-OK, than I can't see how there is a problem with the hydraulic part of the brake system... Could it be that for some reason the brake booster isn't pushing the rod deep enough? It says in the FSM that the rod doesn't need adjustment...

 

I believe you just turn it enough to let it trickle out, and then close it. I have bled my MC by myself. Of course I have 3 foot arms. lol It usually is a 2 person job. The way I did it by myself was...Pump the brake 3 or 4 times, until it is stiff. And then slowly let the fluid out, while the pedal travels to the floor. Then close it, and pump it, to see if I have pressure. If not repeat the process again. Until you get it. May take a couple times, or it may take 3 times. It all depends on how much air you have in the lines. Also always make sure you keep brake fluid in it. Or you will cause air to go back into the lines. And in turn you will be starting the process all over again. I hope I explained it right.

 

Everytime I have bled my brakes out. I have just turned it enough to get a little drip out and then when you press the pedal its should squirt out. Do it a couple times to make sure all the air is out of the lines. And if your still having the problem make sure that your getting vacume to the damn thing! there should be a little in line air filter from the intake plenum to the master. Make sure nothing is clogging that at all. other than that I'd be lost! lol I have not had a problem with mine in a couple days and I drove home (300 miles one way) this past weekend!

 

if you cracked open the bleeder and then pumped the pedal you sucked air back into the system along with pushing a small amount of fluid out of the bleeder. Get a small diameter piece of hose that fits TIGHTLY over the bleed nipple, stick the other end into a plastic bottle or cup with enough fluid in it to cover the end of the hose. Crack the bleeder open, pump the pedal, keep an eye on the resivoir on the master and keep it filled. Keep an eye on the cup so you do not make a mess on the floor. Do not reuse the fluid that goes into the cup. Close the bleeder and Keep working your way around all four wheels untill all the brown yucky water contaminated fluid is out and nice clean new fluid comes out with no bubbles. You can prime the master by loosening one of the lines at the master and pumping the pedal a few times. use a rag or something to soak up the stuff that comes out and then tighten the lines.

 

I got a 2nd MC at NAPA (1 year warranty). It had a little more resistance but it didn't feel like it would work. I put the wheels back on anyway to see if it stopped, and turns out I have brakes now, although the pedal still doesn't have much resistance. I'll see if it lasts a couple weeks, and than bleed the brakes if the MC stays the same. Thanks for the help.