Having a problem where my brakes will sometimes (usually when hot or after being driven a bit) will start to grab.

When this happens the pedal gets very high, as soon as you even slightly touch the pedal you can feel the brakes engaging. When its not happening the brakes feel normal and the brakes have a normal amount of travel at the pedal.

When this happens the brakes are dragging even without pressing the pedal - if I put it in neutral and allow it to coast it will come to a stop and you can feel the brakes slightly grabbing. If I turn the car off and press the pedal a couple times, restart the problem is gone. If I leave the engine running it doesn't matter how much I pump the pedal the brakes drag when released.

I am thinking either the power brake booster has something going on or possibly an intermittent blockage of the master cylinder vent port. I don't think it's a caliper problem but I'm not sure. Seems like the front drivers side brake that drags the worst but thats also the closest to the master cylinder.

Anyone have any idea or experienced anything similar?

Ive already done the following
- Bled all the brakes and ABS system
- Flushed all the fluid
- Verified the master cylinder is not over filled

 

You know what, my brakes do exactly the same thing. You have to get them pretty hot, running a canyon is the only time I ever experience it, and only ever from sustained periods where I'm depositing a ton of heat into the whole system. I never smell the brakes and I've never cooked them (I honestly can't believe how well they hold up, they've out-lasted proper sports cars before), but I've gotten them up to temperature plenty of times. This is more than just one 80-0 highway stop. I think the fluid needs to be hot too. And even then, they don't do it every time. I've only experienced this maybe 5 or 6 times ever.

The only thing my car does that it sounds like yours doesn't is, when this whole thing happens, my brakes are much more likely to squeak. Not all the time, and it depends on the condition of the pads a lot I think, but there will be a quiet\mild squeak right when stuck in "that zone" at the top of the pedal. And then sometimes it will continue squeaking during medium brake pressure, but the latter may just be noisy brakes I am not sure. Mine are otherwise completely silent.

I haven't the slightest idea what it could be, it's always just been "one of those quirks". I will be listening to see what others have to say.

What year is your car? Mine is a 98.

 

Mine is a 99. I wish there was a way for me to get it to repeat consistently but it seems to happen mostly at random. I am planning on rebuilding the front calipers but I don't have a lot of confidence that will solve it.

 

I forgot to mention but also, the pedal feel changes during that period as well. It's like there is some sticky valve or something somewhere in the system that once it warms up, it doesn't allow a smooth flow of air or fluid or something. Instead of being a smooth linear pedal, the very top of the pedal has this unusual firmness. You have to press "past" it for the brakes to work, it doesn't require much effort at all, but it makes it really hard to be smooth. Once you're past that sticky zone you're deep enough in the pedal that the brakes grab all of a sudden quite firmly that you will toss your passengers a bit.

 

Rusted caliper's pistons cause your type of problems. I'd simply check the condition of pistons as is explained here.

 

Thank you Yamae. I ordered a rebuild kit from Lexus. I will rebuild the front calipers and report back.

 

my 1995 Ls400 my problem was the rear caliper's guide pins.....lack of grease cause my drag.I used a blow torch and grease and I was good to go

 

Update: the brakes started dragging on me again today. After I entered the freeway I felt a small thud (kind of like an AC compressor engaging) and that was the brakes engaging partially. I wasn't pressing the brake pedal when it happened.

I got home and left the engine running and jacked up the front end and sure enough the front wheels were dragging/basically locked up. I clamped the vacuum line to the booster and waited a few minutes and the brakes were still locked up.

Then I loosened one of the nuts holding the master cylinder in place and the brakes immediately freed up. I re-tightened the master cylinder and the brakes remained free.

I would say the pushrod length is misadjusted but why would the brakes be free after re-tightening? It seems like something is getting jammed up between the master cylinder and the booster, but I don't know what. Any ideas? I've basically eliminated the ABS system, lines and calipers at this point.

 

I know moisture accumulates in the brake fluid, but I have no suspicion my car has had the fluid neglected. And it's been a lifetime Colorado\Nevada car, it's pretty dry here.

Even so, is it still just a potential inevitability that it can happen?

 

Another update: I pulled the master cylinder and used a tool to check the pushrod legth coming out of the brake booster. It was very far out of adjustment, about 1/8" too long. That mean the brake booster push rod was pressing the master cylinder about 1/8" with the pedal fully released.

I adjusted the pushrod to spec and will drive again for a few days and re-check. I will update here if it fixes the issue or not, I suspect it will. I think it was pushing just far enough to sometimes not allow the relief port in the master cylinder to uncover.

 

Adjusting the pushrod between the master cylinder and the power brake booster fixed my brake drag problems.

 

Is there any way to make the adjustment correctly without the tool? Can I rotate the screw\nut on the pushrod "X" number of degrees of clockwise\counterclockwise rotation to make the same adjustment on my car (maybe starting halfway at first)?

 

No you'll definitely need to use a tool like this one.
https://a.co/d/2rao0vQ

You have to transfer the measurement from the master cylinder to the brake booster which I don't see any way of doing without the tool.

Good news is you can just push the master cylinder out of the way enough without disconnecting any lines.

 

In theory I shouldn't need any measurement, since I am assuming that mine would be messed up in the same way as yours. I could just make the adjustment by shortening it ever so slightly.

The problem I see that could happen is unintended adjustments when I'm tightening the nut. Or at any part of the process really. Now you have no idea where you started or where you are. I can't check to see that it's right once I'm done. The tool is only 12 bucks, you're right it's best just to make sure it's perfect. Thanks! I'll give this a shot and see if mine are out of whack.