Is there anywhere other than the master cylinder that there could be an internal leak in a braking system ie. sinking pedel without losing fluid? Normally, I would assume that the problem was with my master cylinder, except that I just changed pads. It would be a fairly large coincidence for the M/C to randomly crap-out the day I was working on a totally separate part of the system.

 

actually... it depends how you actually repress the calipers in.. in my brake tech class.. i was alway told to NEVER force the fluid backwards meaning just using the "c-clamp" to push the fluid back into the line your suppose to always let it bleed out.. im guessing the reason would be is a mechanical thing in the M/C that can crap out.. just like if your bleeding brakes to not press the pedal ALL the way to the floor.. just enough to give it pressure to put it down..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ShowTymers619 &raquo;</TD></TR><TR><TD CLASS="quote">actually... it depends how you actually repress the calipers in.. in my brake tech class.. i was alway told to NEVER force the fluid backwards meaning just using the "c-clamp" to push the fluid back into the line your suppose to always let it bleed out.. im guessing the reason would be is a mechanical thing in the M/C that can crap out.. just like if your bleeding brakes to not press the pedal ALL the way to the floor.. just enough to give it pressure to put it down..</TD></TR></TABLE>

EXACT same thing i learned. From what i remember, the reason for bleeding out the fluid and u press the piston inward is because u dont want to force old fluid up thru the lines, rather u want it to exit the system. I think its more of an issue with ABS equipped cars, but should be done on all cars when changing pads.

 

I don't have ABS and I bled the old fluid out anyway. I know for a fact that I didn't bleed the brakes as well as I should have after I finished, but it's not just a soft pedal, it sinks quite quickly.

Another question, how do you go about changing the M/C without spilling brake fluid all over the engine bay?

 

So u did more than just change the pads? Now u say u bled the brakes. How old is the M/C? Did u do it the common way of pumping the pedal and cracking the bleeder screw? If u did, then u most likely messed up the master cylinder. As the fluid is being pushed out (when u open the bleeder screw), your brake pedal sinks close to the floor and at that point the M/C piston seal (aka cup seal?) now goes further into the M/C bore where corrosion most likely exists. That basically destroys your M/C immediately or shortly thereafter, depending on age. About replacing the M/C, just unbolt it off the booster with the reservoir still attached. About the 2 brake lines that are left in the bay only dribble a little fluid out. Go buy a chiltons or a helms, it'll explain it all in there.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fourthgenhatchB17 &raquo;</TD></TR><TR><TD CLASS="quote">So u did more than just change the pads? Now u say u bled the brakes. How old is the M/C? Did u do it the common way of pumping the pedal and cracking the bleeder screw? If u did, then u most likely messed up the master cylinder. As the fluid is being pushed out (when u open the bleeder screw), your brake pedal sinks close to the floor and at that point the M/C piston seal (aka cup seal?) now goes further into the M/C bore where corrosion most likely exists. That basically destroys your M/C immediately or shortly thereafter, depending on age. About replacing the M/C, just unbolt it off the booster with the reservoir still attached. About the 2 brake lines that are left in the bay only dribble a little fluid out. Go buy a chiltons or a helms, it'll explain it all in there.</TD></TR></TABLE>

Yeah, I bled them as you decribed. It never occured to me that the M/C could be damaged by that process. Live and learn I guess. What's a safe way to bleed fluid? Just avoid depressing the pedal too far?

Thanks for your help.

 

Another question, are there rebuild kits for master cylinders like there are for calipers, or do they have to be replaced? I'm just thinking if I can crack it open and replace the cup seal or whatever it's called I'd rather not spend the $$ for a new M/C, but no one ever said car's were cheap.

 

I bleed my brakes with a hand vacuum pump. You basically build up vacuum, crack the bleeder open, and the fluid is drawn out. It also only requires one person, instead of two. Some people will tell u to stay away from certain rebuilt master cylinders because some are aluminum. In some cases, in order for a rebuild to be done, the bore in the M/C has to be bored out slightly so the seal can do its job (like what you do when u rebuild an engine). But on aluminum M/C's, you dont want to bore it out because you will get rid of the anodized coating or whatever thats in the bore. The coating gives it a hardened surface because aluminum is soft. So basically buy a brand new one or the rebuilt one u get may not last long.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fourthgenhatchB17 &raquo;</TD></TR><TR><TD CLASS="quote">I bleed my brakes with a hand vacuum pump. You basically build up vacuum, crack the bleeder open, and the fluid is drawn out. </TD></TR></TABLE>

Where could I find one of these vacuum pumps? I've looked at a couple products that would allow me to bleed the brakes without someone else's help, but I've never seen these. Sounds like a good method.

 

Harbor Freight sells MityVac kits, I got one there. It works, but it's not perfect. It likes to pull air bubbles IN thru the bleed screw threads. I put a big gob of grease around the threads of the bleeder, that helps some. But I still like to finish up the old-fashioned way with someone pumping the pedal.

Next I wanna try a pressure bleeder. That's probably the only true one-person method.

 

I bought the same one from harbour freight. It does tend to pull air from the threads of the bleeder screw but it still works perfectly good, as its very effective. I consider it to be a true one man operation. I have never had any problems with it.