Braking Vibrations

[tkosier]

When braking "semi-hard" from speeds over 50 mph, I feel a vibration that appears to come from the back of the car. - almost like a tire is out of balance. I do not feel any pulsing from the brake pedal and I don't feel it at all with mild braking or hard braking from lower speeds and no pulling either right or left.

Today, I noticed that if I brake fairly hard from highway speed, feel the vibration start, back off of the brake effort a little, (vibration stops) then brake hard again it feels pretty smooth.

What's going on? (new pads were installed all aound about 5K mile ago)

Thanks, tk
1988 Carrera

[Nine9six]

Dunno...Maybe rotors, maybe bearings. Tire balance. Not sure if CV's would cause any vibration under braking.
Need more exploratory info from you.
Perhaps if you did some searching on "braking vibrations"

[Laneco]

My humble opinion is that you need to have your rotors turned, one or both are very slightly warped. If you turn them, turn them both, not just one. I always replace the brake pads when I have rotors turned, but other people tell me that isn't necessary.

angela

[kimlangley7]

My experience .. my reading of various braking issues/problems is that when it's a "vibration" /pulseing> might want to check the rotors..

[Superman]

There has been a lot of talk lately about rotors. Some folks these days, and we're talking some of the most respected car guys out there, believe warped rotors are not the problem. Their belief is that improper bedding procedures were used. They believe hot rotors and hot pads have spent too much time against each other without the wheel turning, and that this creates a tempered spot on the rotors. These same people would suggest new rotors or if you're going to try to save the rotors, you would at least find someone to GRIND them. The blade of a lathe will skip over the hardened spot. Grinding is the way to go. They say.

[tkosier]

Thanks for your replies!

Would checking disk run out with a dial gage pick up the small warp or "tempered" spot?

OK, several "votes" for rotors. Let's say I replace the rear rotors (from our host ,of course!) and pads. Would this cause any imbalance with the fronts not being replaced?

[BertBeagle]

Originally Posted by tkosier

Thanks for your replies!

Would checking disk run out with a dial gage pick up the small warp or "tempered" spot?

OK, several "votes" for rotors. Let's say I replace the rear rotors (from our host ,of course!) and pads. Would this cause any imbalance with the fronts not being replaced?

The best way to check a rotor for flatness is to put it face to face with another rotor (new preferred) or put it face down on a surface plate. See if it rocks. If it doesn't rock then that is not your problem. Sounds simple and it is.

If there is something (trash, etc.) between your rotor and the hub the dial indicator will pick that up.

[9dreizig]

I read something recently that when the rotors are "warped" that actually there's material on them and the best thing to do is go out and re-seat them. Sure can't hurt,, go out and do three or four "spirited" brakings from 80-20

[beepbeep]

I just installed Audi S8 rotors/calipers on my Audi S4 car and I can tell you, warped rotors aren't myth! Checked them with dial gauge and there is surely a radial throw on one of them, not just a "hardened spot". Disc has visible "throwout" which I'm to resurface as soon as possible.

It's possible that I did this myself by improper bedding procedure (as I reused the pads and calipers have four pads each) but rotor is sure-fire warped. Luckily, it's very thick (30mm) so there is lot's of material that left.

We sometimes resurface rotors that are within tolerances regarding thickness. It often helps. If cost of new rotors is lower then resurfacing bill or thickness is out of tolerances, just buy new pads and rotors and be done with it.

This is my daily driver and I'm a cheapskate, so I'll just go another turn with a machine