Brake Booster

[Mattr04]

Just replaced master cylinder, soft lines, and rebuilt all calipers. Pedal still goes to floor when car is on. Roads are pointing to dead booster. Does anyone have one? Please PM if you do! Advice welcome as well.

Matt
#1466

[DMCMW Dave]

That can't be the booster. A failed booster will make the brakes seem weak but the pedal pressure will be very hard.

There is either still air in the system (make sure you don't have the front calipers on the wrong side of the car) or a defective master. It happens, although not very often.

[Mattr04]

That can't be the booster. A failed booster will make the brakes seem weak but the pedal pressure will be very hard.

There is either still air in the system (make sure you don't have the front calipers on the wrong side of the car) or a defective master. It happens, although not very often.

Dave,

We bled the system a few times now, so I'm not so sure it's air in the line. My mechanic gave me a test to try to confirm if it is dead or not (which I will try shortly). I'm pretty sure calipers are on the correct side of the car, but will check.

I will let you know via here if it is the booster. If not, I guess the new master is bad and will need returned/exchanged.

Matt
#1466

[sdg3205]

Matt,

the outer front calliper is an odd duck - it relies on gravity to fill and bleed since the Chunnel (haha) is over the top and the hard line and bleeder share the same physical space on the opposite side (inner) of the calliper.

Try pumping, then manually forcing the outer piston back in (gently with a pry bar or screw driver) via the pad, then a quick bleed, then pump it back up to refill the outer calliper. Some air may be locked in there.

I was informed of this possibility by the good folks down at DMCNW.

[Mattr04]

Matt,

the outer front calliper is an odd duck - it relies on gravity to fill and bleed since the Chunnel (haha) is over the top and the hard line and bleeder share the same physical space on the opposite side (inner) of the calliper.

Try pumping, then manually forcing the outer piston back in (gently with a pry bar or screw driver) via the pad, then a quick bleed, then pump it back up to refill the outer calliper. Some air may be locked in there.

I was informed of this possibility by the good folks down at DMCNW.

Thanks Dave(s). I will try that too.

Matt
#1466

[DMCMW Dave]

Dave,

We bled the system a few times now, so I'm not so sure it's air in the line. My mechanic gave me a test to try to confirm if it is dead or not (which I will try shortly). I'm pretty sure calipers are on the correct side of the car, but will check.

I will let you know via here if it is the booster. If not, I guess the new master is bad and will need returned/exchanged.

Matt
#1466

The reason I mention the calipers is that they fit just fine on the wrong side of the car, and then the bleeder will be at the bottom. Unfortunately air goes up. Pretty obvious when you see them every day, but not so much if this is the first time you've done it and may have had them off the car for a while.

I'll second other-Dave's note - if you just installed new pads and rotors this should not be a problem, but if the pistons are not all the way out (deep in the bores) when you fill and bleed the system you can trap air in the outer piston.

[Mattr04]

Hi guys,

This is my driver side caliper (excuse the bad paint job. It was a failed experiment):

http://tapatalk.imageshack.com/v2/14/10/19/c7353ff32e3f8f88c456b19d8bd67309.jpg

http://tapatalk.imageshack.com/v2/14/10/19/a654398c3e79892f8eac3e628f8d134b.jpg

Looks like it's on the right side to me, correct? Trying to do what one of you suggested by forcing the one pad to push outer piston down now.

[DMCMW Dave]

That looks right, you'll also notice "LH" cast into the housing . . .

I'm guessing you got a defective master cylinder. We can talk tomorrow. It's a pretty rare failure but it can happen.

[Mattr04]

That looks right, you'll also notice "LH" cast into the housing . . .

I'm guessing you got a defective master cylinder. We can talk tomorrow. It's a pretty rare failure but it can happen.


Dave, I did notice the LH. I was pretty sure I did put them on the correct sides, but wanted to verify and put my mind at ease. I couldn't find a buddy to help try the other Dave's idea to bleed the outer half. I did notice today the pedal didn't firm up after pumping it immediately. I walked away and tried 10 minutes later and it was firm. I'm not seeing fluid anywhere either.

Lets talk tomorrow like you said. We can go from there.

Matt
#1466