Why do my brakes vibrate more AFTER I change new pads?

[jreed]

My '97 855 GLT had new OEM Volvo blue box rear brake pads and rotors at ~80K miles and they worked fine for about three weeks and then there was a thumping vibration and pulsation that grew stronger and stronger from them over time. I actually put up with it for about 5 years, but when I redid the rear brakes last year at ~140K miles with new OEM Volvo blue box parts, I also used the stainless steel shims (available at FCP and others) and haven't had any problems since then.

[instarx]

Clearly the best course is to take it back to the dealer and explain your concern. If you have been using them for all your service they should be happy to fix it with a smile. It doesn't sound like anything urgent or dangerous.

[jblackburn]

Stomp your brakes hard & activate the ABS. Same kind of sensation you're feeling in the pedal?

Since you say it doesn't feel like warped rotors, I think what you're feeling may be because your car needs shims on the rear brakes - the pads will vibrate as you come to a stop.

I hit ABS all the time - just this morning actually. People are morons at driving here, especially when they have no clue where they're going in town. I haven't seen any grooves in my rotors.

[zhenya]

No, actually, I don't. No one you'd know, anyway. I could easily be wrong and / or actual *decades* out of date, but I'd been told a couple of times by a couple of different people that making the ABS do that juddering skip it does, hard enough or more than once or twice, was enough to put ridges in the rotors. They might be subtle, but they'd possibly be enough to account for the symptom. New pads might be less acclimated to the slightly altered shape of the rotors and therefore show up the vibration a little more.

Just a thought -- one of those bits of received wisdom you don't think to question any more, but probably should. I'd still talk to the dealer.

This just isn't true - you can try it for yourself - I promise - it won't hurt! It is regular practice in training schools for track or autocross to have students brake repeatedly to the point where abs kicks in, because most drivers rarely if ever brake that hard under normal driving. The only thing you may risk damage to is your tires! In fact, with new pads and rotors, bedding in the system by doing 10+ rapid stops 60-0 at abs threshold in immediate succession is good practice - even for regular drivers. This 'beds' a consistent layer of pad material into the rotor, and will increase your brake performance, and help inhibit the uneven pad build-up that is often attributed as 'warped' rotors. Your brakes will never get hot enough under day to day driving to do this as well as a proper bed-in procedure.

[CAvolvoSD]

JBlackburn: "Since you say it doesn't feel like warped rotors, I think what you're feeling may be because your car needs shims on the rear brakes - the pads will vibrate as you come to a stop."

What are the shims on the rear brakes?
Also when I wrote my brakes vibrate more because I assume the ABS vibrates at every brake, I don't know if ABS comes on during hard brakings only. I didn't notice any particular pulsing before the pads job. I should' ve written: Why do my brake pedal vibrate after I put new pads on...

[kcodyjr]

If it vibrates on a light touch, you probably have a rotor surface problem.

If the whole front end shakes hard on heavy braking, you definitely have a rotor issue, at least.

By contrast, imagine putting your foot over someone's butt when they break wind. That's what the pedal will feel like when the ABS is actuating, and it should be just the pedal - nothing through the wheel or the seat.

[bronxnativ]

Go to the dealer and have him install rear shims on your brakes. If he tells you what my dealership told me today:" I've never heard of shims on an 850", then RRRRRRRRRRRRRRUUUUUUUUUUUUUUUUNNNNNNNNNNNNNNNNNNNNNNNN!!!!!!!!!!!!!!!!!

Dealer cost for shims is about $15-$20.00

P.S. ABBA died with the 70's

[gswede]

This is what you need, had vibrations myself. With fairly new both disks and pads..
http://www.volvoforums.org.uk/showthread.php?t=105316

[CAvolvoSD]

Brake Shim it is! Thanks for the pic, gswede!
BTW, ABBA didn't die and still going strong with Mamma Mia then the movie with same name. Their music will live on > much longer than the Volvo in the '70's (and those car were durable!). Long live ABBA!

[gswede]

Good, just remember to lube and align the shims with the arrow pointing upwards (rotation direction).