Help With Excess Brake Pedal Travel

[wild boar]

Please help me!

I have a 1997 LS400 and I am having some really annoying problems with excess travel in the brake pedal.

I took the car for its annual roadworthiness check (MOT here in the uk), and it failed on excess brake pedal travel. The brake balance and efficiency were both ok. The mechanic who tested the car said that it could be either that the pads on the car were worn, or the master cylinder was bust.

So I took the car home and checked through the system myself, what I found confused the hell out of me. When the car is not running the brake pedal feels absoluty fine, nice and firm. If you then start the car, the pedal sinks easily to the floor.

So far I have put new pads on the front, checked the rear pads (ok), and rebuilt the master cylinder with a Lexus supplied kit (£100/$170! for the internals only). I have blead the brakes as it instructs in a workshop manual that I have. Can anyone suggest what the problem may be? All that I can think of, is that it is the brake servo (brake booster?).

[lenore]

Could be your brake vacuum booster is failing. Maybe a unhooked vucuum line or the diaphram in the booster is leaking.

[alsalih]

To test the brake booster with the car turned off press the brake pedal 3 times and each time it should get firmer and stop at a higher level from the previous push, which it sounds like yours is doing so the brake booster is OK. I would bet that you would need to bleed all 4 calipers and the ABS pump with someone helping you. Look at the master cylinder in the engine compartment and see if you notice any trace of a leak which would noramlly run against the brake booster, if so you have a bad master cylinder but again I really think you have air in your lines.

[wild boar]

The pedal is doing as you say alsalih, and the master cylinder is not leaking. I agree that it is probable that there is air in the lines,but the only thing I have not done is bleed the abs unit, how do I do this?

ps I know that the vacuum system is working ok, as I have had the pipe of the booster and it is sucking like a Monika! :D

[alsalih]

Not sure about the 97 but on my 98 the ABS pump is just under the intake pipe (after the air filter box). On mine there is a bleed plug on top. I sure hope someone is pumping the brakes for you while you open and close the plug!! Also, just because the master cylinder isn't showing signs of a leak does not rule out a possible internal problem (very small possibility but keep that in mind). Also, you should inspect you flex brake lines that go to the calipers for signs of major cracking (not just the small fine cracks) and for blisters which can be detected if someone presses the brake for you.

[latintxn54]

wildboar, I too own a '97 LS400 with 91K miles and just recently noticed the past week that while at a stop sign, unless I really press the pedal down hard, the car will move forward. And believe or not, the pedal's almost to the floor!! After inspecting all 4 wheels' pads, cylinder, hoses and found no leaks, I'm thinking it may be my Master cylinder. After reading this article, I wasn't aware one could bleed the ABS... Here's hoping you get the brakes fixed. I'll reply when I determine the culprit & solution.

[VBdenny]

Even with new pads, my brake pedal has always had what I consider to be rather long travel. The brakes on my Lexus are crappy in emergency situations even though the dealer declared them fine?

Hopefully Lexus brakes have improved greatly since 1990

[nc211]

My story....had no real reason to replace my pads and rotors other than finding the vibration. But, I can tell you with sheer honesty....I replaced my rotors and pads with cheapo's from autozone "was in a serious pinch". The pads and rotors are loud, rough and not graceful at all "but not warped". However, in the process of changing these parts, I swamped the caliper, pads and such with brake cleaner spray. I especially paid attention to the piston, and it's seal. Man, a freakin' pizza of crud came off of the piston seal. When I had the rotors off the car, I put my foot on the brake pedal to extend the pistons. Swamped the seal again with cleaner......want mushrooms with your pizzza? Ever since then, my car's brakes will stop that sucker on a dime. Might sound like a bus, but she'll stop like hell in heaven's culdisac. My brake pedal has a lot more force too, and seems to be very touchy. I did not touch the brake fluid. Go to the auto store, blow $20 on 8 cans of brake cleaner spray, jack up the car, take off the wheels and spray away. You'll be shocked. BUT if she squeeks later, you'll want to put some grease on the back of the pads.

[92LS4008888]

Is it safe to spray brake cleaner onto the caliper pistons and boots? Will it attack the rubber boots? I changed my rotors and pads with original Lexus parts. I suspect that my calipers is sticking because the rotors were warped and the pads were unevenly worn (unfortunately, I did not know to check the pads as the came off for wear so I do not know which side is giving problems). However I removed the sliding pins and greased the hell out of them.

So far brakes are excellent, quiet and actually very powerful. If you feel that you need lots of pedal effort to stop the car, one also can look at the pads. Just buy a set of original pads and the difference might surprise you.

I also have a Toyota Avalon and it took lots of effort (brake pedal travel is normal) to stop the car. I pulled the old pads, which looked brand new, and put in Toyota pads and there was a big difference.

My story....had no real reason to replace my pads and rotors other than finding the vibration. But, I can tell you with sheer honesty....I replaced my rotors and pads with cheapo's from autozone "was in a serious pinch". The pads and rotors are loud, rough and not graceful at all "but not warped". However, in the process of changing these parts, I swamped the caliper, pads and such with brake cleaner spray. I especially paid attention to the piston, and it's seal. Man, a freakin' pizza of crud came off of the piston seal. When I had the rotors off the car, I put my foot on the brake pedal to extend the pistons. Swamped the seal again with cleaner......want mushrooms with your pizzza? Ever since then, my car's brakes will stop that sucker on a dime. Might sound like a bus, but she'll stop like hell in heaven's culdisac. My brake pedal has a lot more force too, and seems to be very touchy. I did not touch the brake fluid. Go to the auto store, blow $20 on 8 cans of brake cleaner spray, jack up the car, take off the wheels and spray away. You'll be shocked. BUT if she squeeks later, you'll want to put some grease on the back of the pads.

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[kcpth]

That's a good question i would like to know too. Is spraying Brake Cleaner good for the rubber? Cause i did that too for the 93SC400. I was just changing the pad's as well for him b/c when he braked... it travelled all the way to the floor. Found out he was realli realli low on the pads in the rear n not too bad in the front for some odd reason. That helped the travel for him.

As for bleeding the brake system.... u definitely need 2 people. I know www.lexls.com tells u how u would do it for a 1st Generation LS400. I dont know about the 2nd. Let me know wut u find out. Good luck