Truck repair question...

[missioncontrol]

My brakes will slowly go down while I'm pressing them at a stop light...

I'm thinking it's the master cylinder. how hard is that to change out???

anybody know???

[ChadTower]

Sounds like a leak in the vacuum.

[Stingray]

How's the fluid level? A leak can cause that, but usually only once the fluid has gone down enough to get air into the lines.

A master cyl. isn't super tough to change out, at least not in a big older vehicle like your Bronco, which I assume is what we're talking about. Sometimes there's a clip or a cotter pin that connects the brake pedal linkage to the master cyl, which can be way under the dash and difficult to reach. You'll need the same kind of wrench that I recomended for your transmission cooler lines to disconnect the brake lines. You'll also have to bleed your brakes after, which can be messy, and you'll need someone to pump the brakes.

-S

[missioncontrol]

Yes it is the Bronco.....

fluid level is fine........

how would I be able to tell if its a vacuum leak or the master cyl. ?

I'm only going by the symptoms my F250 gave me back when it's master cyl went out, of course that was a few years ago and I've slept a little since then.......

poor truck, its hitting the 200,000 mile mark and starting to show her age. If I keep having to replace parts with lifetime warranty parts I'll soon have to call it the "Bionic Bronco"

[Stingray]

If you don't already have one, you should pick up a copy of the Haynes manual for your Bronco. I always buy one for every car I've owned. Really comes in handy, especially when the vehicle reaches the age where it starts to break down fairly frequently.

-S

[missioncontrol]

I've got one, fortunately mine covers pick-ups and Broncos so when I replaced my 82 F250 with my 87 Bronco I didn't have to buy a new book. The only problem is I have to remember where I put it...

[Stingray]

Yeah, that's the only real flaw with those books. You have to actually pick them up and read them for them to do any good.

-S

[LPZ]

Could be air in the lines too.  Did you open the line recently, that would allow air in?  There could be a loose bleeder valve also, but you would see the fluid.  You could also have a leaky caliper or leaky wheel cylinder in the back.  I would check all the brakes first and start there.  Make sure there isn't any fluid anywhere.  Also could be a leaky brake booster too.  Start with some basic visual trobleshooting and listen for any vacuum leaks.  If you do change out the master cylinder, make sure you bench bleed the unit first, that will save you a boatload of time.  Also, if you pickup the MS at the autoparts store, get yourself a one man brake bleeder.  They are priceless.  You could bleed all you brakes by yourself, if you don't have anyone else around to help.

LPZ

[Dartful Dodger]

I agree with LPZ, bleed the breaks.

I haven't tried a one man bleeder though.

I'm not sure how the one man bleeder works, but I'd assume it's taking away the popping a zit fun in bleeding.  Plus I'd miss the yelling DOWN, and hearing the DOWN response from inside the car, and then UP ... UP, DOWN ... DOWN, UP ... UP...

[LPZ]

I agree with LPZ, bleed the breaks.

I haven't tried a one man bleeder though.

I'm not sure how the one man bleeder works, but I'd assume it's taking away the popping a zit fun in bleeding. Plus I'd miss the yelling DOWN, and hearing the DOWN response from inside the car, and then UP ... UP, DOWN ... DOWN, UP ... UP...

It's actually pretty slick.  Imagine your bleeder fitting/valve.  There is a little plastic one way valve that inserts in it.  A hose is connected to it and leads to a 8 ounce bottle that has a magnet attached to it, that lets you fasten the bottle to a fender or a close metal part.  Loosen your fitting and go in and pump your brakes.  The fluid flows to the bottle, and the one way valve doesn't leave any air back in.  After you pump your fluid through, check the bottle and tighten your fitting.  Viola, that wheel is done.  Great simple tool that helps you out alot when your all alone.

[Dartful Dodger]

What's it actually called, and what's the brand name you use?

[missioncontrol]

wow I just went to the autozone website, they have some really good information and troubleshooting tools available.