I recently filled both of the brake reseviors with brake fluid and i noticed that yesterday while putting antifreeze in the tank that the fluid for the front was full but the back is gone. where could it all have gone ?

 

You could check around the wheel cylinder. Take off the little boot on the end and it should be moist in there but not dripping.



Assuming its drum brakes on the rear

 

Your master cylinder is bypassing, you need a new one. Pick up some wheel cylinders too, they've probably not been used for awhile.

 

The only "moisture" you should ever find inside the dust boot of a properly functioning wheel cylinder is maybe a hint of assembly gease. Any other liquid points to a leaking wheel cylinder.

 

Is the master cyl. dry? I got my snap on lid crooked once and the fluid got by the rubber seal and went down the back of the resivor. I didn't see any fluid around it but noticed a spot on the garage floor. The lid even looked straight but when I pressed down on it , it snaped down. I couldn't believe it leaked that much. Might want to check the gasket on the lid too.

 

I'll throw out a guess, maybe leaking bleeder screw front/rear or whatever the equivalent would be on a drum setup for the rear (sorry I dont know drums). Fill it back up and let it sit, check under the car and the insides of the wheels (the reverse lip) for signs of a leak. Or listen to these guys if you have drums hehe.

 

Back reservoir = front brakes

Don't waste your time on the rear brakes.

Most likely, your MC is bad. One of the ways they fail, is for the piston seal to leak fluid out the back of the cyl, where it will run into the booster, and down the outside of the booster.

Look at the booster; if it looks rusted and funky below the master cyl, different from what it looks like above the MC, then you need a new MC.

If it stays like that for very long, the brake fluid will destroy the rubber in the booster. Fix it immediately to prevent bigger problems.

 

I have had wheel cylinders look slightly wet for years before needing replacement. Sometimes seals will seap a little. Like say a front or rear seal on an engine, almost any engine with over 40-50k will have some seapage at the front or rear main seal. Wheel cylinders are cheap and not that difficult for a beginner to change
but unless fluid is actually leaking and it is wet below the wheel cylinder I wouldn't waste my time but some people are real **** about these type of things and change them unnecessarily.

 

The problem isn't the rear brakes in the first place. He doesn't need to be messing around with them anyway.

He needs a master cylinder.

Hopefully he won't take a left turn down the dirt road and get lost, messing around with something that isn't related to the issue at hand.... like piddling around with the rear brakes when the front brake reservoir is leaking. That would make as much sense as taking your left front tire in to the tire store for a flat repair when your right rear tire is flat.

 

A wheel cylinder operates at much higher pressure than an engine seal, it takes more than 80 lbs of pressure to open the springs much less activate the shoes with any force. When you see small spots of brake fluid (not assembly lube) inside a dust boot the wheel cylinder has leaked at a pressure peak and has often drawn air back into the cylinder and lines. To verify this condition, bleed the rear brakes and watch for air bubbles. And yes, they are cheap and relatively easy to replace. If a master cylinder is bypassing it probably hasn't been operating the rear brakes and they will often freeze-up and need replacement anyway.

 

I still think his cap might be loose or leaking around the gasket that may be not seated right in the cap. I've had it happen to me before even though the cap looked like it was on straight and couldn't see any fluid leak from under the hood. Only after removing the cap to refill the resivor did I realize that the rubber gasket was not straight in the cap allowing fluid to get by it. It doesn't take much with the resivor being slanted and not level for fluid to get by under acceleration and the pressure from the master cylinder brake booster. I'm just saying that's the first thing I would look for. You think he would have posted results by now with all the possabilities we have given him to look for.

 

There is a lot more than 80 psi at any wheel cylinder or caliper. A small seap is NO reason to change the wheel cylinder, but hey if you like to waste time and money go for it. Drawn air back into the system through a slightly seeaping wheel cylinder, in theory maybe but never seen it happen.

 

Probably a leaking master cylinder that is leaking into the brake booster. He never said anything about spots left on the pavement from leaking calipers\wheel cylinders.

 

OK, can we PLEASE leave all the rear brake discussion behind, and concentrate on the issue at hand? I don't think talking about rear brakes is going to do this guy any good AT ALL.