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Discussion Starter · #1 ·
Hello, I have a problem with my 05 Lexus IS300 where the brakes won’t engage all the way when I press the pedal to the floor. It’s like if the brakes were just dragging along and I wouldn’t be able to come to a sudden stop if I had too.

I think it might either be a seized caliper, master cylinder or brake booster. I’m in the middle of diagnosing and wonder if anyone has gone threw the same problem and how it was fixed.
 

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Brakes to the floor? Do they sink slowly to the floor? If so I have encountered this many times on my customer’s 1iS before. Every time it ended up being seized caliper slide pins. Or guide pins if people want to call them that. On two occasions I ended up just replacing the entire caliper and bracket with complete assemblies from Oreilly auto parts. Both worked well as they were reman parts so they were still Lexus parts with new guts.

The other method which I always try first is to extract the stuck guide pins from the caliper bracket and then buy new pins and boots and regrease them and that will work also.

I haven’t encountered an actual stuck caliper brake piston yet.
 

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Discussion Starter · #3 ·
No, the brakes don’t go to the floor. The brake pedal gets stuck halfway and feels like resistance is there but the brakes aren’t fully engaging. Most of the bite happens up top so I have to brake with a bit of distance.

II’ll check out my guide pins when I get a chance. Is there anything I should look for besides the pins being seized?
 

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No, the brakes don’t go to the floor. The brake pedal gets stuck halfway and feels like resistance is there but the brakes aren’t fully engaging. Most of the bite happens up top so I have to brake with a bit of distance.

II’ll check out my guide pins when I get a chance. Is there anything I should look for besides the pins being seized?
Well you could check to see if the pistons are seized. You can do this by removing the calipers one by one and having someone press on the brake pedal while you watch to see if the piston comes out. Don’t take all the caliper off at the same time otherwise you will push all the pistons out of the caliper and have a big mess. Do them one at a time.

You can check your brake booster for correct operation by pumping up pressure with the car off (KEY OFF) until it’s firm. Then while keeping steady pressure on the pedal start the car up. If the pedal sinks down some then the brake booster is working. If the brake pedal does nothing, then the booster is bad.
 

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Replace the calipers and pins. You will need fresh pads and rotors. Make sure you clean out the pin holes well and grease with new boots.
 

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Discussion Starter · #6 ·
Well you could check to see if the pistons are seized. You can do this by removing the calipers one by one and having someone press on the brake pedal while you watch to see if the piston comes out. Don’t take all the caliper off at the same time otherwise you will push all the pistons out of the caliper and have a big mess. Do them one at a time.

You can check your brake booster for correct operation by pumping up pressure with the car off (KEY OFF) until it’s firm. Then while keeping steady pressure on the pedal start the car up. If the pedal sinks down some then the brake booster is working. If the brake pedal does nothing, then the booster is bad.
I checked the booster just now like you described and the pedal does go down a bit after starting the car. I also checked underneath the brake pedal for leaks in the booster and found none. Master cylinder looks good too. I think it’s going to be my brakes.
 

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Discussion Starter · #7 ·
Replace the calipers and pins. You will need fresh pads and rotors. Make sure you clean out the pin holes well and grease with new boots.
Have you had this problem before? I’m thinking it’s going to be the calipers too. The rotors and pads were replaced not long ago but I can warranty them. I’ll have to check out the calipers when I get a chance.
 

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Have you had this problem before? I’m thinking it’s going to be the calipers too. The rotors and pads were replaced not long ago but I can warranty them. I’ll have to check out the calipers when I get a chance.
I have run across it on customers cars.
It does not matter that the pads where done recently. If the caliper or pins were stuck. It will effect them. Even the rotor. You could take your chances with the rotors. But it is usually easier to do all of it once. Then going back again.
 

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I would 2nd the pins the calipers are supposed to float on, its pretty common for them to get clogged up and seize the caliper so the brakes are trying to do all the work on just one pad. Otherwise the pistons could be rusted and seized, though i haven't seen this on a modern car for a long time.
 

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Discussion Starter · #10 ·
I have run across it on customers cars.
It does not matter that the pads where done recently. If the caliper or pins were stuck. It will effect them. Even the rotor. You could take your chances with the rotors. But it is usually easier to do all of it once. Then going back again.
The guide pins were fine. I took them out and greased them up again and had my brother step on the brakes while the caliper was off the rotors. Both pistons travel at the same time and distance on both sides. Pads are wearing out the same on both sides and the rotor still looks new.

I did notice on my test drive today that the brake pedal squeaks and it sounds like air is coming out from underneath when I pressed down on the brake with the car turned on. Possible booster leak?
 

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Discussion Starter · #11 ·
I would 2nd the pins the calipers are supposed to float on, its pretty common for them to get clogged up and seize the caliper so the brakes are trying to do all the work on just one pad. Otherwise the pistons could be rusted and seized, though i haven't seen this on a modern car for a long time.
I checked out the guide pins and they looked fine. Still had grease on them too so I cleaned and greased them back before putting them in. Both pistons are function properly with no signs of rust and the brake pads are wearing out evenly on both sides.

There is a squeaking hiss when I pressed down on the brake pedal with the car turned on. Possible booster leak maybe?
 

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Discussion Starter · #13 ·
No, not yet. I kind of figured I would need to but I thought that since the front brakes do most of the stopping power the rears would be fine. That will be my next step.
 

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Discussion Starter · #19 ·
Did you also check the back brakes? Those also need to be checked, pins and piston operation. After that then you can dive into other areas. Namely the Brake master cylinder.
I got a used brake booster off of a junk 2001 IS300 that looked like it was in pretty good shape. I just replaced it and had to mess with the push rod because the 01 booster has more threads than the one off of my 05. Problem now is that the brakes engage when I start driving. I can feel the caliper pistons engage when I start driving keeping the car from fully accelerating. Can this be because I adjusted the push rod from the 01 since it had more threads than the 05 booster?
 

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I got a used brake booster off of a junk 2001 IS300 that looked like it was in pretty good shape. I just replaced it and had to mess with the push rod because the 01 booster has more threads than the one off of my 05. Problem now is that the brakes engage when I start driving. I can feel the caliper pistons engage when I start driving keeping the car from fully accelerating. Can this be because I adjusted the push rod from the 01 since it had more threads than the 05 booster?
I've have my brake booster totally go out and you should feel the brake pedal really hard to push without slowing the car too much, after looking I noticed the line blew off, but if the booster the pedal should be extremely firm to press from the start.
When I first started having brake issues, because they were a little warped I bought new rotor and pads, carbon based and harder to warp. Get some good pads, good rotors at autozone or Other shop, I don't always go OEM like I use to, aftermarket parts out now usally have a lifetime warranty and just as good of not better. After the install I've never had a brake issue.. changed around 60,000 now I'm at 140,000. If u wanna teat the booster do this..
  1. With the engine off, pump the brakes — about five or six times is sufficient. This depletes the stored vacuum.
  2. Turn the engine on while pushing down lightly on the brake pedal. If your brake booster is working normally, the pedal will fall away a little, but then become firm.
  3. If your brake booster is not working correctly, nothing will happen, or the brake pedal will push back against your foot once the engine starts. This could be a sign of a brake booster problem or an issue with the vacuum hose.
most likely the old booster is good. My assumption is that the oem rotors and pads for that car are a little underpowered and creat issues. I also noticed lot better handling , turning and stopping with 225 tires..
Also when you brake do u have a brake pull?
If one side seems to be braking better of slowing the vehicle it's mostly caused by a sticking or seized brake caliper that has corrosion in its bore, also need to check the back just to make sure, sounds like a leak or a bad master cylinder which leads to inconsistent brakes.
Brakes that are spongy or soft have an air leak or air in the lines.

changing brake fluid won't hurt or make sure that is at normal levels but I didn't hear I complain about any burning smells which would be present with low brake fluid too. Each brake must be bled in the correct sequence. Generally, you bleed the brake most distant from the master cylinder first, but some cars require a different order..
Now the rear brakes-
Since the proportioning valve decreases the pressure sent to the rear brakes, the main symptom could be the valve is going bad.. Is the rear wheels locking up when the brakes are applied? the wheels will lock up more easily on wet surfaces. The rear brakes may feel touchy when applied even gently..
 
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