Problems after replacing master cylinder
in [Technical]
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From: jim on 6 May 2010 09:03 Mark wrote: > > Tegger, Jim, > > I took the car on another test drive to check the free play of the > brake pedal before and after vibration. Before driving, I found the > free play to be there. Then after driving for ~10 minutes on the > highway, once the vibration and pulsating brake pedal kicked in, I > pulled over. Immediately, I checked the brake pedal and the free play > was as before, there was no change. But putting the car on neutral > with engine off made it difficult to push the car. Then I got in the > car, using my toe lifted the brake pedal a couple of times and now I > could push the car easily in neutral. Then, once I got on the highway > and started driving, the vibration in the steering was gone. I have > been able to replicate this behavior twice today. If the problem is > not with the master cylinder pushrod and the brake pedal free play, > then is the brake pedal simply getting stuck temporarily? I guess the rod from the brake booster to the master cylinder doesn't have clearance. I suspect you will find if you check that the brakes are dragging whenever the car is cold. To test that when you first start the car apply the brakes nd then release them and check to see if the car rolls freely. If they are sticking pulling up on the pedal will probably release them as you have discovered. To adjust the push rod that connects booster to master cylinder you will need to unbolt the master cylinder from the booster. There may be gasket between the master cylinder and booster that wasn't installed or the new MC was just a little different than the original. -jim
From: jim beam on 6 May 2010 10:52 On 05/06/2010 06:03 AM, jim wrote: > > > Mark wrote: >> >> Tegger, Jim, >> >> I took the car on another test drive to check the free play of the >> brake pedal before and after vibration. Before driving, I found the >> free play to be there. Then after driving for ~10 minutes on the >> highway, once the vibration and pulsating brake pedal kicked in, I >> pulled over. Immediately, I checked the brake pedal and the free play >> was as before, there was no change. But putting the car on neutral >> with engine off made it difficult to push the car. Then I got in the >> car, using my toe lifted the brake pedal a couple of times and now I >> could push the car easily in neutral. Then, once I got on the highway >> and started driving, the vibration in the steering was gone. I have >> been able to replicate this behavior twice today. If the problem is >> not with the master cylinder pushrod and the brake pedal free play, >> then is the brake pedal simply getting stuck temporarily? > > > I guess the rod from the brake booster to the master cylinder doesn't > have clearance. I suspect you will find if you check that the brakes are > dragging whenever the car is cold. To test that when you first start the > car apply the brakes nd then release them and check to see if the car > rolls freely. If they are sticking pulling up on the pedal will probably > release them as you have discovered. > > To adjust the push rod that connects booster to master cylinder you > will need to unbolt the master cylinder from the booster. There may be > gasket between the master cylinder and booster that wasn't installed or > the new MC was just a little different than the original. > > -jim that doesn't explain why the pedal sticks in the "down" position. i'm with tegger - i've seen pistons stuck in the cylinder of poorly machined cheapo aftermarket brake masters. -- nomina rutrum rutrum
From: jim on 6 May 2010 11:21 jim beam wrote: > > that doesn't explain why the pedal sticks in the "down" position. i'm > with tegger - i've seen pistons stuck in the cylinder of poorly machined > cheapo aftermarket brake masters. You have to be exceedingly ignorant and stupid to believe that. When you pull up on the brake pedal you are not pulling the master cylinder piston. The MC piston returns on its own - it is never pulled by the push rod. It cannot be pulled by the push rod. That is physically impossible. If the master piston was stuck and couldn't move as you believe it is then no amount of pulling on the brake pedal is going to do anything about that. You believe in stupid fairy tale superstition about after-market parts not based on fact. There is nothing in the narrative that suggests the master cylinder is misbehaving. Something is preventing the master cylinder from returning back to the position where the brake fluid pressure is released. And that something is the push rod between the booster and master cylinder. If the piston is not returning it is because the push rod is not retracting far enough to allow it to return. When he pulls on the brake pedal he removes the something that prevents the piston and push rod to return. And when he does that then the MC behaves just like an OEM MC would. The most likely cause of this problem is the push rod is not adjusted correctly. It's possible the adjustment is off because the spacer (gasket) between the MC and booster is missing. If that isn't the cause then it is inside the booster that something is sticking and not allowing the push rod to retract far enough. -jim
From: jim beam on 6 May 2010 16:00 On 05/06/2010 08:21 AM, jim wrote: > > > jim beam wrote: > >> >> that doesn't explain why the pedal sticks in the "down" position. i'm >> with tegger - i've seen pistons stuck in the cylinder of poorly machined >> cheapo aftermarket brake masters. > > You have to be exceedingly ignorant and stupid to believe that. When > you pull up on the brake pedal you are not pulling the master cylinder > piston. The MC piston returns on its own - it is never pulled by the > push rod. It cannot be pulled by the push rod. That is physically > impossible. If the master piston was stuck and couldn't move as you > believe it is then no amount of pulling on the brake pedal is going to > do anything about that. > > You believe in stupid fairy tale superstition about after-market parts > not based on fact. > > There is nothing in the narrative that suggests the master cylinder is > misbehaving. Something is preventing the master cylinder from returning > back to the position where the brake fluid pressure is released. And > that something is the push rod between the booster and master > cylinder. If the piston is not returning it is because the push rod is > not retracting far enough to allow it to return. When he pulls on the > brake pedal he removes the something that prevents the piston and push > rod to return. And when he does that then the MC behaves just like an > OEM MC would. > > The most likely cause of this problem is the push rod is not adjusted > correctly. It's possible the adjustment is off because the spacer > (gasket) between the MC and booster is missing. If that isn't the cause > then it is inside the booster that something is sticking and not > allowing the push rod to retract far enough. > > -jim why don't you read before you rant? nothing i've said is inconsistent. yes, stuck pistons stay stuck and the rod is not attached, but that's not the end of the story. and evidently unlike you, i've actually seen poor quality aftermarket master cylinders and experienced problems with stuck pistons. adjusting a push rod doesn't address this and is such a commonly mis-suggested remedy, it's just ridiculous. push rods should hardly ever be adjusted once out of factory. if a replacement master is out of spec, it should be returned. if the pedal pivot bearings have worn, they should be replaced. adjusting a push rod is NOT the solution to either problem and they are the only causes of the thing going out of spec. as for diagnosis, maybe i should be more specific for those with reading challenges - when i say "i'm with tegger on this", i agree with his statement "I think I'd start by disconnecting and plugging the vacuum line from the booster", etc. now you can go back to your tv and ice cream. -- nomina rutrum rutrum
From: jim on 7 May 2010 07:54
jim beam wrote: > > inability to discern fact from friction? so hard to decide!!! > Yup that is what it boils down to. For instance, when someone says they only use OEM parts and also claims to have vast experience with poor quality after-market parts it does make one wonder if those statements are fact or fiction. -jim |