7 replies to this topic

[Tao]

help---no brakes

recently noticed my brake pedal travels a little further than normal before catching.....no sponginess, firm braking.............I just flushed the system with new brake fluid, bled everything, went to test the pedal and now it goes all the way to the floor.........it is not totally dead--there is a little resistance to it but goes to the floor...

 

the manual mentions a "check valve" that may be the cause....that is all it says....it doesn't mention if it is in the master cylinder or the front/rear deverter.

 

your thoughts

[Alberto]

Sounds like the master cylinder.  

 

Maybe it got damaged during bleeding?

[ChrisA]

Doubt it's the check valve. But for reference it is in the rubber vacuum line that goes from the booster to the intake manifold.

[steveracer]

When you bleed a master cyl with many miles on it, it's a good idea to put a 2x4 under the pedal to keep it from bottoming. Under normal street use, the piston only travels part way through the bore, sediment accumulates where the travel stops.

When you bottom it during bleeding, the seals pass over the sediment and are torn-killing the MC. You need a new Master.

Common mistake, I did it too.

[Tao]

thanks guys,

I will change the master cylinder and report back.....I did bottom the pedal rather aggressively  when I was pumping it up.

[Keith Novak]

When you flushed the system, did you first pump all the fluid out of the master cylinder?  If you did, or if you are just going to change it out anyway, you should "bench bleed" the MC.  Air bubbles that get into the MC are difficult to push out through normal bleeding.  Bench bleeding is running some tubing from the MC gozeinta and the gozeouta back into the fluid reservoir, and manually pumping the MC.  This pushes the air bubbles out of the nooks and crannies without pushing them into the brake lines where they'll give you a really squishy pedal.  There are videos and articles on-line explaining how to do the bench bleed in more detail.

[DCP]

A friend had a similar problem when he borrowed my pressure bleeder. He accidentally ran the master cylinder dry. After the pressure bleed, the pedal went much lower but did provide braking. We bled the master cylinder while it was still in the car and this fixed it. I think that air got into the master cylinder's piston area and the pressure bleeder would not remove that air.

[Tao]

in an effort to find a great one man bleeding process I used the motive pressurized system...but I didn't fill it with brake fluid..i just used it to pressurize the reservoir...it worked great....I made sure the fluid didn't get to low but im thinking air might have gotten in the the plunger cylinder.

 

just to be sure I changed the master c. with one from a donor car, bench bleed it then rebleed the whole system........love the 2 x 4 under the pedal trick! lesson learned--I will never pump up the pedal without one now.

the pedal is back to normal and im about to road test it