Brake problem

[Chets-z]

I went through my brakes, put on new rotors and pads, new back brakes, wheel clylinders, stainless braided lines, cleaned out the old nasty fluid from all the lines and put in DOT 5 fluid. what happens now is that the brakes will function great, good pedal for a indeterminate amount of times and then they will go to the floor and the brake warning light comes on! Sometimes it will be one good pedal and maybe the next time it will be 6 times and they always pump up fine. I'm stumped!

[Mike B]

Did you bleed the brakes after you changed the fluid? It sounds like they weren't bled properly and still have air in the lines.

[Arne]

No, I'm betting the master cylinder has failed. This is actually fairly common - a master cylinder that works fine suddenly failing immediately after a bunch of brake service, especially a big fluid change. Blame it on corrosion and gunk inside the master cylinder bore. During normal use, the normal stroke of the piston doesn't reach the gunk, but when bleeding the system the master cylinder piston is pushed beyond its normal travel (pedal goes to the floor when the bleeder is opened), and the seals are damaged by the stuff in the bore.

I suspect you'll need to replace the master.

[Chets-z]

I bled them a couple of times, have a self bleeder. Odd though that they work and then don't work and then work again after you pump 'em up a couple of times! Strange!

[DatsunZsRule]

Did you bleed them in the correct order?

-Master Cylinder

-Right Rear Wheel

-Left Rear Wheel

-Right Front

-Left Front

[Arne]

I bled them a couple of times, have a self bleeder. Odd though that they work and then don't work and then work again after you pump 'em up a couple of times! Strange!

Yup, that's an almost certain sign of a failed master cylinder.

[Chets-z]

Ok I'll try the Master cylinder and yeah, I bled 'em the right way, furthest first! Brakes are like women, a lot of hassle, but you sure need them!

[mlc240z]

double check bleeding order.

if i'm not mistaken, seem to remember reading that driver's side rear is actually the longest line, then pass rear.

[=Enigma=]

double check bleeding order.

if i'm not mistaken, seem to remember reading that driver's side rear is actually the longest line, then pass rear.

I believe this is correct since the rear brake line from the master cylinder terminates in a T on the passenger side, with a short line to passenger side, and a longer line to the driver's side.

[Chets-z]

Thanx for all the help! Replaced the master cylinder this morning, did a bleed job and Wallah, great brakes again! had to go through 2 master cyl., got a rebuild first, was a corroded inside and wouldn't bench bleed the front cylinder. Went and ordered a new one and it bled properly and works like a new one should!