scout928

We have a 01 CL type S w/ Nav with only 30,000 miles. It is an awesome car, but we have had a ton of problems with it. The SRS/airbag light computer had to be replaced 3 times and the transmission was just replaced due to the recall.
But now it is having an intermittent brake failure problem. It gives absolutely no indication that the brakes are going bad, but then you will be driving along and need to come to a stop but when you put on the brakes there is no resistance and the pedal goes all the way to the floor. The first time it happened we had the car towed to the dealership and when it got there, the technician said the brakes were fine. The car seemed to fix itself. So the shop kept the car for 2 weeks trying to get the problem to happen again, but no luck.. They put a brand new master cylinder, new pads front and back and a new ABS modulator just to make sure that everything would be fine. We thought that it should be fixed too, but then 3 weeks later, it happened again. But within 1 hour of the car sitting idle, the brakes worked fine again. We took it to the shop and they said that there is nothing they can do because they can't find the cause of the problem and because they have never witnessed it.
Please, if anyone has heard of this or might know how the problem is being caused, let us know.
Thanks!!!

sgmotoring

It could be your brake master cylinder is going bad. It sound like vapor lock too, it is when your brakes fluid boiled and turn into vapor. Which cause the brake to have no pressure and when the brake cool it turn back to liquid and brake pressure is restored. Water contamination is usually the cause of this problem. Oh, if your brakes are dragging that could cause high heat and have the same problem. This is just my guess.

carquest

it could be a fluid problem. have all the brake fluid flushed and replaced. this should have been done when the master cylinder was installed, but maybe not. you'll probably have to pay for this. but if it fixes it - its worth the cost. no brakes isn't worth being cheap over.

it could be the proportioning valve. this is a device which directs brake pressure to each diagonal brake circuit in the car. front right/left rear and front left/right rear. its purpose is to prevent a failure in one brake circuit from causing the brakes to fail completely. but i have seen cases where this valve fails and can lead to intermittent total brake loss. it doesn't make sesnse, but it can happen. it may require special attention when the brake system is flushed to make sure it opens completely during the flush and then is reset to an operational state. have the mechanic check it or see if you can find a shop manal for the car and see if there's any info on this valve during a brake fluid flush or bleeding the brakes.

lastly it could be a vacuum failure. the brakes are vacuum boosted. i've never seen a vacuum failure cause complete brake failure. you should still have brake pedal resistance when pushing on the pedal. it just doesn't put adequate pressure on the hydraulic fluid which results in less braking force. but if you're pedal is going completely to the floor it doesn't sound vacuum related, but anything's possible.

it could also be that the new (or rebuilt?) master cylinder wasn't bled properly when it was installed. this seems the most likely. the master cylinder has to be bled before being installed in the car. failing/forgetting to bled the master cylinder is a typical brake failure condition. but i believe that it results in the brakes never working properly, not just an intermittent failure. but again, anything's possible.

carquest

just thought of one more thing. someone may have mixed brake fluid types in your car before you bought it. i think this car takes DOT-3 but i haven't checked the fluid types yet. check the owner's manual or a shop manual. there's a high performance silicone brake fluid some gear heads like to use. i'm not sure if its DOT-4 or not. but these fluids are NOT compatible. if you have DOT-3 and the silicone fluid mixed in your system it can cause all types of problems. i don't think there's anyway to test for it. you just have to flush the fluid and install the proper type. i don't know if any damage can be caused by putting DOT-3 in a silicone only system. putting silicone in a DOT-3 system shouldn't cause any damage, since its one of the performance upgrades to a DOT-3 system.