94x4

I've recently started having problems with putting the brake fluid resevoir's cap back on it.
I'd bled the brakes out, capped it and took off to try them out. They worked fine, so I let it go until a week later when I decided to take a look at the resevoir to see how thiongs were and noticed that it was slightly low so I popped the cap and topped it up.
When I went to replace the cap, it would'nt seat properly and remained raised on one side, it's retainer apparently not slotting into it's guide on the inside of the resevoir's neck.
So I figure that the cap's just worn out and get a new one. Take the old one off, replace it with the new and it seats nice and evenly on the resevoir...I'm happy again.
A couple of weeks go by and I take a little 500 mile round trip only to return home and, while giving the 'Runner the once over to check for any potential problems, I discover that the cap is cocked again and not sealed on the resevoir and irregardless of many attempts on my part, I still cannot get it to properly seat.
I'm not aware of anyone's familiarity with such a condition, but the braking is greatly reduced, nonexistent even, as the system cannot manage to pull a vacuum without the cap being sealed.

Sorry about the length of the explanation, just wanted to give you guys some background but anyway, anyone know what the hell is going on? I'm stumped.

Thanks in advance for any and all help, it is appreciated.

Flamedx4

I'd bet you have a bad master cylinder.
My best guess is the pressure from your foot is finding its way to the reservior (it shouldn't) and pushing off the cap. The other clue is that you say the system doesn't work properly without the cap being tight. It should work fine with no cap at all (although the cap should be kept on to keep out moisture and 'stuff.')

94x4

I'll try that vacuum test that's posted around on here and see what I come up with.

Any other ideas....?

jmach1

Dude, this is gonna sting a little but you will see the light. I had the same problem and could not figure why the rubber cap would not stay on, I even bought a brand new cap that again would not fit after a month. I was baffled, until I spoke with my neighbor. He asked me if by chance I put power steering fluid in instead of brake fluid. What the hell, does he think I am stupid? My neighbor asked me where the brake fluid was, I pointed to the shelf, he grabbed the bottle and said "this" I said "Yeah" and guess what, it was power steering fluid. Well, yeah, pretty stupid move on my part.
I guess the power steering fluid causes rubber components to swell, dont ask me how. I ended up replacing all rubber tubing from the master cylinder as well as all the hydraulic clutch rubber components because I was almost sure I used the same bottle to top that off too.
It sucks, but thank God I am not in the medical profession, something about reading the drug labels prior to administration to a patient. Oh wait, I am a Paramedic. Dang!!
Good Luck

94x4

That is both unfortunate and funny at the same time, jmach1.

Unfortunate that you had to change out all of your lines, yet funny in the way in which you relate it, although I admit that I did go all of the way out to the garage to check before I remembered that I managed to purchase the PS and brake fluid in different shaped containers, damn the built in personal doubt reflex.

I'm certain that it was indeed the PS fluid that I had used, Valvoline SynPower Dot 3/4, to be exact..., maybe that's the reason why?

Any other ideas??Anyone???

Flamedx4

I did a similar thing to an Audi once. Cost nearly 2 grand to replace all the ruined steering components. Some lessons would be not be learned the hard way...