brake vibration

cynlim · Post by **cynlim** » 25 Jun 2015, 22:06

I can't get a proper diagnosis on my 850 braking problems. I took the car for a test drive with two mechanics and came back with differing feedbacks. One said the vibration is radiating from the back, the brake discs in the rear wheels need replacement or skimming. The second mechanic said its the front brake discs. And then my husband tells me it could be the wheel sensor triggering the abs to come on as one side of the caliper is sticking.

The vibration feels wavy with a kind of groaning sound coming from under my brakes before the car comes to a full stop. It is happening randomly, sometimes a very slight vibration, other times very strong and can be felt from the passenger side. Sometimes the brake pedal feels hard like it is not going down, then it will soften and work normally. My abs light is coming on and off at the dashboard. I have my tyres changed this year and alignment done, drive shaft boots replaced as well.

Sommerfeldt · Post by **Sommerfeldt** » 26 Jun 2015, 08:24

I don't know if your husband's right or not, but I would definitely be looking at the ABS system, especially if the light's coming on.
To be fair, the brake pedal should be relatively hard - if your system isn't holding pressure, the pedal goes "soft" and sinks further to the floor before you get any braking action, if you catch my drift.So a "hard" pedal isn't necessarily a bad thing.

- Get a shop to read fault codes (or do it yourself)
- Check your discs and pads, replace if worn down
- Check caliper operation, front and back
- Check e-brake parts and operation.
- Report back.

Your fault codes should tell you if it's an ABS problem of some sort.

- S

Post by **oragex** » 26 Jun 2015, 11:22

Have you had the calipers at all wheels inspected for sliding easily? As a side note, I would suggest not to rush into replacing the brakes if they don't look too worn (which is what many mechanics like to suggest because they make money on it)

Sommerfeldt · Post by **Sommerfeldt** » 26 Jun 2015, 18:20

oragex wrote:Have you had the calipers at all wheels inspected for sliding easily? As a side note, I would suggest not to rush into replacing the brakes if they don't look too worn (which is what many mechanics like to suggest because they make money on it)

+1 on that. Don't replace unless worn to a level which would justify it.

- S

Post by **rspi** » 26 Jun 2015, 20:01

Grrrr, it is my opinion that tire shops, that also do brake jobs, have a scam going on lately. They will NOT torque the wheels back on properly which will cause the rotors to warp. Every single car that I have had tires mounted on in the past 2 years have experienced this problem.

My daughter's S70 was fine for years until I got new tires installed. About 60 days later the rotors were warped so bad that I had to replace them. My niece had her tires balanced and rotated then experienced her rotors warped within 2,000 miles, had to replace them. My rotors were warped within months of having tires rotated on my car. The last issue was a car that I sold to someone, they got a vibration checked and about 2 weeks after the check a lug nut was actually missing from a wheel. When I checked the lugs, some were loose and some were super tight. My thought is that they were trying to warp the rotors.

I'm not saying that this is your issue, I will suggest that you have all of the lugs loosened and returque them.

cynlim · Post by **cynlim** » 27 Jun 2015, 02:15

wow, this is a lot to digest. The vibration seems to get louder. My husband ask me to get a third opinion, he's asking me not to buy the crap about the rotors because he's checked and didn't see any warping.

cynlim · Post by **cynlim** » 27 Jun 2015, 02:24

how do you check the calipers? My mechanic says he's checked the wheel sensors and they are fine. The brake pads are only 40 percent worn, changed two years ago, vibration and noise are felt even when the abs light is off. Trouble is I don't have a brake specialist here.

Post by **dosbricks** » 27 Jun 2015, 12:57

rspi wrote:Grrrr, it is my opinion that tire shops, that also do brake jobs, have a scam going on lately. They will NOT torque the wheels back on properly which will cause the rotors to warp.

+1 on this. I watch them from the bay door to make sure they use the blue torque stick = 80 lbs impact torque. Unfortunately it's not possible when the car is in the shop all day for mechanical work = handing it over to the torturers. The latter being the best reason for doing your own work, which I believe Robert does.

Post by **dosbricks** » 27 Jun 2015, 13:02

cynlim wrote:how do you check the calipers? My mechanic says he's checked the wheel sensors and they are fine. The brake pads are only 40 percent worn, changed two years ago, vibration and noise are felt even when the abs light is off. Trouble is I don't have a brake specialist here.

About the best way to determine if a caliper is not opening correctly and causing the pad to drag is a blue color on the surface of the rotor from it being over heated. The overheating can cause it to warp.

Sommerfeldt · Post by **Sommerfeldt** » 27 Jun 2015, 23:28

I still say follow the checklist I put in my first reply. Since your ABS light is winking at you, you may very well have some issues there. have you had your fault codes read?

If your husband's already checked the discs, and you've got 60% left before the pads need changing, then my 2 next stops would be ABS or e-brake. But get your codes read first!

- S