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Brakes


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I have a basic understanding of how brakes work - i am not a mechanic but just through changing pads / cleaning calipers etc i sort of know the basic principal of how they operate (i think)

I have a problem which has been mentioned in previous posts with what sounds like squeeling shims on the front brake pads. I have replaced the caliper on the drivers side where i thought the noise was coming from / have previously replaced the sliding pins / pins are free and greased (with Castrol LM hi temp grease) / pads and shims are copper slip greased. The last thing i done to get rid of this squeel was to replace the caliper as i noticed the bottom piston on the old one was not coming out uniformly with the top piston when the brake pedal was pressed. It woudl come out but only when the top piston was a good centimeter+ out.

Changing this caliper has "deaddenned" the sound quite a bit but it's still there. I haven't had a chance yet but i will be changing the passenger side caliper in a few weeks so i am hoping it cures it. There was a bit of vibration when braking also which has almost gone so i hope by replacing the other caliper that this resolves this. brembo discs were fitted last year so i would doubt they have warped already after 5k miles. Tyre pressures ok (at 35psi) and wheels balanced.

My understanding of how the brakes work is - and this is a basic understanding - press the brake pedal and this forces the fluid to the calipers - this forces the two pistons out from the caliper pressing the first pad onto the brake disc and in turn this forces the caliper to slide in causing the other pad to connect with the disc and you stop ! So the emphasis on having good slide pins is evident as if they were siezed or sticking then the second pad would not engage the disc.

So on the other hand - when taking your foot off the brake the reverse of the above should happen. My question is actually how do the brakes retract from the disc, what forces them back to their "relaxed" state - i am trying to track down the squeel and am thinking that it could actually be the pins sticking causing the pads to touch the discs slightly (although the pins are freely moving). I have noticed that when turning round a corner there is a quiet "clunk" noise and from that point the nosie happens which leads me, rightly or wrongly to think that the pins are in fact sticking as it sounds like the noise is from that area. I have also noticed that they wont squeel when the cars cold for example when getting into it first thing in the morning and driving 3 - 4 miles but then it gradually appears. Getting into the car after work to come home is the same, ok for a few miles then they start singing!! They are a bit stiff in pulling out but i think thats the grease thats causing that in creating a vacuum/seal in the guide that the pins actually slide in and out from.

When i greased these last which was last week, becasue the grease was forming a good seal when i pushed the pins into their hole they would immediately come out as if on a bit of elastic. I had to hold them into their holes while putting the calipers back on. Not with a lot of pressure but just enough to keep them in.

It may be i am using the wrong grease on the pins so when doing the other caliper i will get the Lexus approved grease from the dealer and give that a go on both sides. I have not checked the rear brakes - the pads were changed last year and thats about as much attention i have given to them. I have been told that the rears dont do a lot of work when stopping the car (around 80% braking on the front and 20% from the rear?) Discs are fine.

Anyone with any suggestions with what could be causing this would be appreciated but i will still go ahead and change the caliper and grease and re-post the results from doing that job as there does seem to be a lot of people out there with this unresolved problem or that have the problem and it turns out to be something complately different.

thanks

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it sounds like you have sticky calipers... which is a well know problem on the IS200.

Did you change your brakepads? and even more important what brand are you using,some pagid brakepads are noisy.

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Ohh you should be fine with Mintex ;) just go a head and do the other caliper. Changes are they are running dry so not that well in sliding in and out. but if that doesn't cure it you should take the caliper apart and use a revision kit ( new seals around the pistons usually solves these problems)

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That sounds about right regarding the old ones - i stripped them down / cleaned the pistons and they moved in and out spot on but after a bit of time they reverted back to being a bit tight in their bores. Thanks for the replies anyway -

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