ADRNLN

Hello all...

In my '87 coupe, a horrific squeal has started up on occasion, coming from behind the dashboard area, and in my naive capacity am suspecting something related to the master cylinder... after a few minutes of driving, the loud, low metallic squeal will start up - sounds like metal on metal rubbing. After taping the brakes, it instantly goes away. After a minute or two, it'll squeal again - sometimes going away on its own, sometimes after a quick brake tap.

Thoughts??

Thanks in advance,

-Steve

rberry951

you may just have a small stone under one of the pads

Peter Zimmermann

This can be pretty typical, and the noise will vary with the type of pad (jurid, Pagid, Metalmaster, etc.) that you are using.

The cause of the noise can be two things (assuming that the pads and rotors are in good condition).
1. Your brake hoses are overdue for replacement (their service life is 10 years or 100K miles, whichever comes first).
2. Your calipers are due to be resealed/reconditioned. The front calipers usually need to have this done before the rears.

There is a slight chance that your car will need both #1 and #2 done, without knowing your cars history there is no way for me to know.

srf506

Its unclear to me from your message if, a) are you rolling and applying the brakes when this happens or, b) just sitting at idle and it starts. If it's a) than Peter is probably dead-on. If it's b), I'd say you're blower motor on your AC or defroster is dying.

ADRNLN

Thanks... noise actually appears to be coming from behind the dashboard, not from a specific wheel. Happens not when sitting in idle, but when driving after a few minutes.

-Steve

BlackPearl

I'll go waaaaaayy out on a limb:

The bearing in your fresh air blower is dry/rusty/loose/bad. As you excellerate, G-force pulls the blower fan back a touch in the race; air enters the airbox ... behind the dash .... it spins the blower fan/motor ever so slightly ... and a low grunting squeel emits. When you tap the brakes, the forward g-force presses the blower fan into the bearing race a bit, stopping the fan from spinning inside the housing, and the noise goes away.

Are all the fresh air vent controls pressed all the way to the left? Mid-point? All the way to the right?

Otherwise, brake dust build-up between the front brake pad and caliper body, causing micro-vibrations that lead to "pad squeel." or ... what Peter said ....

That's my story, and I'm sticking with it.

rusnak

the squeal would be higher pitched in left hand turns as the G-forces accelerate the fan turning, and lower pitched in right handers as the fan slows down.

I gotta tell you kids everything.

Peter Zimmermann

OK, so much for the Twilight Zone, aka evaporator housing fans, and back to the real world. Actually, there is a slight possibility that the fan might be noisy, but putting it in the off position would sure diagnose that in a hurry!

One brake diagnosis that can be made is to do a little left foot braking. When the noise occurs, maintain your speed with the throttle while gently applying the brake with your left foot. Some find this tricky, so dont do it in traffic! If the noise goes away, find a stretch of Interstate where you can drive between 50-60 mph, and it is safe to do a good impression of a drunk.

While driving about 55 in 3rd gear, left foot brake the car, aggressively enough so that you have to use a fair amount of throttle to maintain speed, for about three seconds. Wait five seconds to let the rotors cool, then repeat. One more five second cool down, then a third three second application. Even with bad hoses or sticky calipers this procedure can sometimes make your noise go away for a hundred miles or more.

That said, the first thing that you should do is check your brake hoses, which are dated on their metal ends. If they are original, highly likely, replace them with o.e. hoses and flush the fluid with Castrol LMA, Ate Blue or similar fluid before you do anything. If you go under the car yourself make sure that it is properly supported with jack stands or other proper safety equipment!

ron mcatee

Make sure your footwell blowers are not the culprit. If you have the heat on, they may be sounding off.