1997 850 Brakes thumping?

davolvo · Post by **davolvo** » 03 Dec 2014, 10:13

Hello peeps, long time, no problems until now. When I use my brakes it sounds like I have a flat tire. Any thoughts?

Thanks everyone.

Post by **rspi** » 03 Dec 2014, 10:37

My take is likely warped rotors. Most commonly caused by someone not installing the wheels correctly, i.e. after a tire rotation you notice it within a few weeks because the person that installed the wheels, failed to torque them down properly or did not tighten the bolts in a star pattern.

davolvo · Post by **davolvo** » 03 Dec 2014, 12:26

Thank you. I will check into that because I just had my tires rotated a few months ago.

huzzsaba · Post by **huzzsaba** » 03 Dec 2014, 13:49

I had the same issue on my newly purchased s70 t5m.

If you feel vibration in the steering while you hear the thumping, its likely the front rotors. If you don't feel much in the steering wheel, its very likely the rear rotors. Replace them, and make sure that there is no corrosion between the hub and the back of the rotor, as well as the back of the wheel and where it seats on the rotor. If there is corrosion, hit it with some sandpaper to get rid of it. Even a little bit of corrosion will cause the rotor or wheel to spin in a wobble. make sure that you spin the rotors after installing to ensure it is spinning with a wobble. Lastly, make sure the wheels are torqued evenly.

Post by **jreed** » 04 Dec 2014, 05:15

+1 on above. I would add that if it is the rear brakes making the thump, then you should consider installing the stainless steel shims Volvo recommends to solve this problem. I did, and it eliminated the thump. Last time I looked a month ago at brake parts I saw that FCP still carries the shims.

Post by **oragex** » 04 Dec 2014, 06:32

What do you mean by feels like a flat tire? Is there a strong impulse in the pedal? Any noise? Or simply you feel a small vibration in the pedal?

If there's only a small vibration in the pedal, most likely the wheel lugs are not tighten with uniform torque. You may have a look here

If there's a stronger impulse in the pedal and a thumping noise, inspect asap the wheel lugs for being properly secured. One or more wheel lugs may have came loose.

davolvo · Post by **davolvo** » 04 Dec 2014, 11:09

The only way I can explain it is that when I am on an open road and there is a stop sign I can hear a noise, it almost sounds like it coming from the front right, that sounds like my tire went flat. It is a real dull thud, thud, thud. However, when I am in town and am going at a slower speed, I do not notice it as much, if at all.

davolvo · Post by **davolvo** » 04 Dec 2014, 11:10

Oh, and there is no squeaking or anything like that. And I can sort of feel it in my brake pedal.

Post by **erikv11** » 04 Dec 2014, 11:36

Warped rotors I agree is most likely.

Another thing I have seen is buildup of brake pad material on the rotor over time. If you want to investigate this, there are two ways I know of:

(1) Do like 10 hard stops in a row 60 mph to 5 mph (but don't come to a complete stop), then drive for 10 minutes to let the brakes cool. By hard stop I mean stomp the pedal until the ABS kicks in (make sure ABS is working first! And no icy roads!!). The hard stops will heat up the rotor and burn off the accumulated material. If you come to a compete stop while they are hot that will just make it worse, there will be more material stuck to the rotor, so don't do that.

(2) Get the rotor turned. They can check it for warpage too.

Post by **oragex** » 04 Dec 2014, 11:44

Inspect your wheel lugs for properly torqued asap with the lug key that's in the trunk. I had this noise when braking and the lugs were completely loosened (it was caused by a bent wheel bearing hub).