My 91 Legacy AWD wagon is behaving strangely. When driving cold the first few stops show severe pulsation on the front. Much as if the rotors are badly warped. After 4 or 5 stops the pulsation goes away and the brakes behave normally again. What's up with that? Anybody else ever get something like that?

Lorry

Did you recently;

 

1. make a 'panic stop' or otherwise heat up the brakes

 

2. change brake pads

 

3. remove and replace the rotors

 

 

Sometimes the pads can leave material on a hot rotor after an 'incident' of quick deceleration.

 

Incorrect or over torqued lug nuts might cause a problem too.

 

 

Carl

1 Lucky Texan

I replaced the pads and the rotors last winter and up until recently they were fine. About a 2 weeks ago there was some nasty grinding noises coming from my rt. front wheel. Sounded exactly like pads worn down to the metal. I pulled the wheel and I could see that the metal shims/backing plates for the outer pad had shifted/slipped out of place. They had moved forward and bent around the end of the pad, scraping on the rotor. I pulled the pads and straightened the shims and replaced. Everything worked fine until this pulsation thing started about a week ago. Most peculiar. BTW, the rotor looked fine, no scoring or significant wear (ie. no lip near the outer edge).

That's weird.

You gotta find out what would cause that.

Also, I assume when you rplaced everything you were careful about torqueing the lugnuts and stuff?

 

maybe someone else has a thought but I'd really investigate the caliper assembly and assoc. 'stuff'. Might even try swapping front rotors and throwing in new/different pads.

 

I hope someoone else responds.

 

 

Carl

1 Lucky Texan

check your caliper guide pins......if they move freely, sand down the pads and rotors slightly and then go rebed the brakes back.

 

Go make several (10) or so stops from 60-15mph with medium/heavy brake pressure. Do them pretty much back to back. After the last one, drive slowly around and don't use the brakes, allow the rotors to cool down.

JOsh, what do you mean by the caliper guide pins? Is that the square casting that the square notch in the pads fit over?

When you get the pulsing can you feel it through the steering wheel or through the brake pedal ?.

 

If through the steering wheel - then look for something "mechanical", ie - calipers, pads, steering/suspension joints - check they are all doing what they are supposed to.

 

If through the brake pedal - then look at the rotors, A.B.S if fitted.

The brakes consist of a caliper and a bracket that mounts them to the hub. There is a bolt that holds the caliper to the bracket. It is on the bottom of the caliper. There is a top pin that the caliper slides on. The combination of these two provide the "floating" caliper design. If these pins don't move "float" any more then the calipers will stick and you get problems. Some times they can be cleaned and re-greased.

 

Re, the pulsing in the pedal or steering wheel.

 

Pulsing in the steering wheel, it's most likely front brakes. If you get pulsing in the pedal, it's most likely the rear brakes.