I put new pads and rotors on all 4 wheels a couple months ago, and have now noticed that only the back brakes are actually working. The car stops like ****, the back brakes are making a horrible grinding noise when stopping and you can still see the machine marks on the face of the front rotors. What should I check?

 

Both fronts are not working? Did you use OEM or replacement parts? Maybe an electronic brake distribution sensor is malfunctioned and only sending power to rears, or a dispreportionate amount to rear. I would take it all apart and recheck the install.

 

That's correct, both fronts not working. I ordered OEM pads, rotors, shims and bolts. Greased everything and torqued the bolts to spec. Although this was my first time doing brakes on the LS, I have done dozens of brake jobs and I'm 100% confident that I assembled everything correctly. I'm leaning towards your suggestion of electronic distribution malfunction or maybe a bad master cylinder?

I think it's funny Lexus felt the need to give us a text alert on the dash when a tail lamp burns out, but not even an idiot light for something as critical as brake system failure.

 

That probably because a tail lamp failure isnt as obvious as a brake system failure.

 

So you changed the brakes 2 months ago and just now the car is only using the rear brakes? Or for the past 2 months (ever since you did the brake job), the car has only been using the rear brakes? That's a critical pc of info to know.

Either way, it sounds like you have air in the lines. Did you properly bleed the brakes after the brake job?

 

I don't think the OP changed calipers so no air should have.gotten in from just pads and rotors. He would have sucked in a lot of air for a while front to not work. I'm leaning towards EBD sensor failure, which is rare on here.

 

Still plenty of variables.

Were the piston boots cleaned prior to pushing them back into the caliper?
Were the front calipers unbolted and somehow there is a twist/kink in the brake line?
How old is the brake fluid?

Simple test would be to bleed the front calipers and verify fluid flow. If it is not bleeding out, then you'll have to trace back through the lines.

 

When I bought this car the brakes never felt that great. The pedal required an unusual amount of force just to stay stopped at a light. My guess is the front brakes have not been working since I got it and I only took notice after putting on new rotors and seeing there was no wear.

I didn't change the calipers so the bleeding wouldn't have been necessary. It may be a good idea to have them bled anyways though now that you mention it.

I did spray down the calipers and piston boots with brake cleaner and wiped them down before compressing them back into the calipers. I did notice that there was a small tear on one of the 4 piston boots on the drivers side, but I didn't see any fluid leaking and I'm not sure that would prevent both front brakes from engaging.

The age of the brake fluid is a mystery. That'd probably be a good start to change the fluid and bleed.

 

I just installed 4 new calipers, brake hoses, new parking brake shoes and hardware, rear rotors and pads (fronts were not worn at all). Bled each wheel starting with passenger rear, driver rear, passenger front, and driver front last. I first tried using one of those hand operated mighty vac vacuum bleeders, but the handle broke so I had a friend sit in the car and push the pedal down while I opened and closed the bleeder valves at each wheel. I made sure the master cylinder reservoir stayed filled above the min line. Probably opened and closed each valve 20 times until there was no more air bubbles coming out.

Test drove and to my surprise... little to no change.. It even still makes that grinding/moaning noise that appears to be coming from the rear. If anything, I'd say there is even more pedal travel now and it is still very soft. Emergency stops are not possible, even at low speed. The car bounces back and forth a few times every time you stop (probably because only the rears are doing the work?). I have noticed if I quickly press the pedal down twice, the 2nd time it doesn't go as far and is more firm. After driving a while with several stops, I confirmed that all 4 wheels were warm to touch (I should use a infrared thermometer and get the surface temps of the rotor faces).

I'm officially stumped. The only thing I haven't tried is bleeding under the hood at the valve where all the brake lines connect after they leave the master cylinder (what I'm guessing is some type of proportioning valve or ABS module). I didn't want to open it and try because I've heard that some cars require a special computer to actuate the ABS while bleeding. I am open to any and all suggestions at this point.

 

Try taking it to a Lexus dealer and get an analysis and estimate from them. The car sounds dangerous to drive.

 

So if the brakes quit do I still have brake lights?

 

I took my car to Rohrich Lexus in Pittsburgh and asked them to bleed the brakes last year after I got the car. They charged me to bleed the brakes and there was no difference, and they simply told me that's the way the LS brakes are supposed to feel. They lied, the bleeder valves on the rear calipers were never opened, they were rusted solid.

 

In that case, I think I'd try another dealer or maybe even a Toyota dealer. Any good dealer should be able to diagnose the cause of your problem and give you an estimate of what's required to fix it.

 

You badly need a pro to look at the brakes ASAP. Brakes problems can be extremely dangerous and costly.

 

Personally, I wouldn't trust a car whose brakes I worked on :^)
That's why I always get my brake related work done at a brake shop.

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