Problems after replacing master cylinder

Just an update... after bleeding the brake system again, the problem with pedal to the floor has been resolved and now my braking is a lot more consistent. But the vibration problem still exists. To summarize, the steering wheel starts vibrating after about 10 minutes on the highway. After another 15 minutes, the vibration goes away and then the ride is smooth. During vibration, the brake pedal pulsates while braking and increases the vibration in the steering. Do you have any other suggestions? Would a road force balancing help?

Thanks a lot again for your help.

I would check your master cylinder pushrod adjustment. It may be slightly applying the brakes causing the rotors to temporarily warp. This isn't particularly good for your pads, rotors, calipers, etc.

nate

i made some suggestions and they're known to work for hondas. did you try them on the lexus? it's a common issue with modern lightweight hubs.

roblem disappears.

extremely hot. That

Yes, I will definitely check that. That might also explain why the brake is applied just by a slight touch of the brake pedal when the vibration is occuring (and the brake pedal pulsates). When there is no vibration, I have to push the brake pedal a little more.

I have a feeling it is the pushrod adjustment. While driving on the highway today, the vibration in steering started occuring after about

10 minutes. I started feeling the pulsating pedal while braking. I put my foot under the pedal and tried to lift it upwards while driving. As soon as I did that, the vibration went away and there was no pulsation while braking.

When I returned home, I felt the vibration coming back. I pulled over (as I was on local roads), turned the engine off, put the car in neutral and tried to push the car. The car wouldn't move. Then, I lifted the brake pedal slightly with the foot and tried pushing the car again in neutral. Now I was able to move the car.

That could explain that the vibration is occurring when the brake pedal remains slightly pressed. Though I don't understand why this would only occur after about 10 minutes of highway driving and go away after 15 minutes.

If this is indeed the case, should I just take the car to the mechanic and ask him to adjust the master cylinder pushrod?

Thanks again to everyone for your inputs.

Mark wrote in news: snipped-for-privacy@x40g2000yqd.googlegroups.com:

I posted this, on April 6th, one month ago:

"Do you have any freeplay at the pedal?

"Push the pedal with your fingertips, as lightly and gently as possible. You should feel the tiniest bit of very easy movement before it hits something solid and effort becomes much greater. You're looking for something like this in the first 1/16" or 1/8" or so of pedal travel."

That's a bit difficult on most Toyotas; the booster needs to be removed to adjust it. I suggest you (or your mechanic) try my month-old advice first.

snipped-for-privacy@x40g2000yqd.googlegroups.com:

I did follow your advise back then. I had checked and found there was freeplay in the pedal. But I had checked when the car was cold. It didn't occur to me to check it while the vibration was occuring.

Mark wrote in news: snipped-for-privacy@k19g2000yqm.googlegroups.com:

You can only check it with the car stopped and you out of the driver's seat.

If there truly is freeplay in the pedal, then the master cylinder is not the problem.

snipped-for-privacy@k19g2000yqm.googlegroups.com:

The couple of times I checked it, it was exactly as your described. But that was before I took the car on a drive. Here is an example of how I checked it:

much-freeplay.jpg (btw, is that your website?).

I found the freeplay to be there when I touched the pedal. There was a very small freeplay, but it was there.

However, I get the vibration after about 10 minutes of driving on the highway. When it happened today, I pulled over, turned the engine off, put the car in neutral, got out of the car and pushed it. It wouldn't move. Then I went back into the car, lifted the brake pedal with my foot, then got out of the car and pushed it. Now I could easily push the car. It meant, the brake pedal could have been stuck.

Next time the vibration occurs, I'll pull over, turn the engine off, get out of the car and test the freeplay. If there is no freeplay at that point, would that indicate a problem with pushrod?

Thanks again!

innews: snipped-for-privacy@k19g2000yqm.googlegroups.com:

> (btw, is that your website?). >

There is no reason I can think of why the free play in the brake pedal would change after 10 minutes of driving. The pedal may be binding or the return spring is broke or missing. But you should have noticed that the pedal was not returning on its own when checking the free play. There isn't any reason I can think of that 10 minutes of driving causes the brake pedal to become stuck down and then another 15 minutes it goes away.

-jim

Mark wrote in news: snipped-for-privacy@q32g2000yqb.googlegroups.com:

Yes. But it's badly outdated, and I haven't got hours to spend updating it.

Probably not. But this new information is very interesting, indeed.

If you can pull the pedal up so the brakes release, then master-cylinder ajustment is not the issue. At the moment, this sounds more like a problem with pedal-height misadjustment, or with something sticking at the pedal, or inside the master cylinder itself. Or possibly the booster applying itself.

If it were me, I think I'd start by disconnecting and plugging the vacuum line from the booster, to see if the problem goes away. Of course, this would be done in a safe place, where it didn't matter if the brakes took superhuman effort to apply...

Basically, troubleshooting here will require separating the various systems and testing them separately, to determine which one is causing this stickiness.

Is this an aftermarket master cylinder?

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?

Yes, this is an aftermarket master cylinder.

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.

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.

I don't doubt you have had all kinds bad auto repair experiences which you have blamed on various hobgoblins and demons.

BS from a babbling buffoon. There is nothing that would suggest the MC is out of spec.

And Lexus would also say you are completely full of shit. According to Lexus service instructions the push rod coming out of the booster should always be adjusted whenever the master cylinder is replaced. Lexus even sells special tools for measuring the clearance.

Maybe you should try to explain to Lexus how ridiculous their "commonly mis-suggested remedy" is.

i'm with tegger - i've seen pistons stuck in the cylinder of poorly machined cheapo aftermarket brake masters.

[End Quote]

This piston is not stuck in the master cylinder. If it were lifting up on the pedal would do nothing at all to release the brakes.

inability to discern fact from friction? so hard to decide!!!