In this car I had been getting an ABS light coming on. At one service at the dealer a year or two back they mentioned a bad speed sensor on a wheel. I bought a replacement sensor but never got around to putting it on. Light doesn't come on anymore.

But...the "BRAKE" light has been coming on while driving every now and then. No rhyme or reason to it. 102,000 miles - I know I swapped out rotors and pads on the front at about 60000 pretty sure I never did the rear.

Now....I have been putting some longer highway miles in the last few weeks - about 2000 or so. I was driving home last night and while at about 45mph I get this whine noise that start coming on quiet then very strong.

Sounds just like a powersteering pump losing a bearing or starving for fluid.

When I press the brake pedal, or otherwise introduce any pressure into the brake system it quels the whine. Coming to a complete stop and the whine stops - not to return.

Driving along the highway this morning it start up quietly again. Sounds almost like it's tire noise from another vehicle running offroad tires. Then gets louder and it's definitely a pump style whine. Hydraulic in nature. Put pressure on the brake pedal and it lessens the whine - direct effect.

Come to a complete stop on the off ramp and the whine stops again...not to return.

Ideas?

 

The "Brake" warning lamp can be triggered by low brake fluid in the reservoir. Check that.

Low fluid in turn might be caused by brake pads wearing out. The noise might be the little tabs that are supposed to squeal against the rotors. I've had them make all kinds of different sounds (not always "squealing") when they were just beginning to rub.

Also a chance it could be a wheel bearing, but check out your brakes first.

 

Definitely a pump squeal. Checked the reservoir for both systems and fluid levels are fine.

Problem is when I apply pressure on the brake system it stops. When I stop the vehicle it stops. So - unless I was able to coast to a stop and get out without applying the brakes I won't have a chance to check under the hood to isolate what pump what squealing.

 

Auto or manual transmission?

When it's making the noise, try shifting to neutral & coasting (just press the clutch pedal if it's a manual). If it's the brakes, that shouldn't make any difference because you aren't touching the brake pedal. What does it do?

 

Auto. I'll try it.

 

I replaced the front pads about 2 years ago. Maybe longer. Starting to think that the rear pas combined with the front may have worn down enough to allow the fluid level to drop enough to cause the groaning.....

Not sure why the fluid level would drop enough just at high speed unless it's moving a lot of fluid across a relief valve at a speed proportional to the engine speed....putting the brake on forces enough back pressure to allow fluid to pile back up in the reservoir? Why does it stop completely as soon as the wheels stop rolling and then doesn't come back?

I'll try the coasting bit. The trans has been hesitating when changing gears at lower speeds for a long time as well.

 

The whole idea is to allow your engine to drop to idle while the car is moving. As far as the engine (& all it's rotating components) is concerned, it's exactly the same as idling when the car is not moving.

Do the coasting without touching the brakes - well, don't be stupid in traffic. That way you try to separate the effects of brake vs. car motion vs. engine rpm.

Squeal tabs on the brake shoes are on the inboard tabs. I've seen inboard pads wear differently than outboard pads. So if you look through the wheel at the outboard pads they might be OK while the inboard ones are worn down more.

I don't see how the fluid would move around at speed. But there have been problems with the float switch inside the cap in the brake-fluid reservoir. That can cause the warning light but not the noise.

How about noisy transmission?? I'll throw that one out there but I'm not much of an auto-trans guru.