Brake induced vibration in car.

[MOUSE]

When braking from brisk speeds I encounter slight vibration in car. it's not the kind of pulsating one gets when a rotor is warped.  Rotors are perfect, and brake pads almost new. I have made sure calipers are sliding on their pins, and the car does not pull to one side. I have noticed that car needs a lot of pedal pressure when quickly stopping. I have never gotten a brake or ABS Warning light.  car has only 39,000 miles on it. Car is a 1991 model coupe.  Any ideas? :huh:

[Ronnie]

When braking from brisk speeds I encounter slight vibration in car. it's not the kind of pulsating one gets when a rotor is warped.  Rotors are perfect, and brake pads almost new. I have made sure calipers are sliding on their pins, and the car does not pull to one side. I have noticed that car needs a lot of pedal pressure when quickly stopping. I have never gotten a brake or ABS Warning light.  car has only 39,000 miles on it. Car is a 1991 model coupe.  Any ideas? :huh:

 

The only thing that comes to mind for me is perhaps the ABS is engaging for some reason when you make a hard stop. I don't have a '91 service manual nor do I know much about the '91 brakes. If you could figure out how to temporarily disable the ABS it might give you a clue ff that is what you are feeling. If you disable the ABS and the vibration goes away you would know that is what is causing the problem. Then you would have to figure out why....

[MOUSE]

It's not the "ABS" system, I have activated it before, not the same sound. this is a low growling vibration thru the whole car. I can feel it thru the steering wheel, but the brake pedal does not pulsate at all, and the steering wheel does not shake. thanks for the reply Ronnie.

[2seater]

I do not know anything about the '91 brakes either, but I have had a previous car that under moderate to heavy braking, particularly from high speed, the rear brakes would vibrate, not so much a sound, but the whole car just felt as if it was being shaken. The only other idea I can think of is something is shifting under braking and making contact, like a motor mount or the dogbone but with low miles that would seem less likely.

[Frogware]

When you say new pads, how new? Some brake pads require a break-in period and have been known to vibrate until they are broke in.

This would also explain less ability to brake because the pads don't have full contact yet.

 

A few years ago I replaced all my rotors and pads on a High Performance vehicle (I will leave it generic to avoid stuff) and the unnamed manufacturer required a break-in period of at least 500miles & no highway speeds or for long periods of time, just as an example.