98 V70XC thumping noise and burning smell Topic is solved

[dmcfan]

I am getting a loud thumping noise in front when I get to 45 mph and it sounds like a flat tire. Then when I got out of the car I smelled a strong burning odor.

Thoughts!

Now I have more time to write this up.

So as I reach 45 there is an audible thumping noise as if I have a flat tire. It gets worse around 55 to where I can feel it in the car and pedal. If I put it in neutral when the noise is occurring it does not go away.

Also when at a stop I could hear what sounds like a milk carton popping but every 5 secs or so. If I increase the throttle in drive it speeds up that noise.

Not sure if the two are related but when I got out of the car it had a strong burning order much like metal on metal abrasion.

I somewhat recently had one axle replaced and one repacked. Timing belt was done 20k miles ago.

[dmcfan]

The burning smell definitely came from the front driver side brakes but the pad is ok and same thickness as the passenger side.

Now also the thumping noise is gone.

[dmcfan]

My abs light went on. Could a bad module cause the noise?

[Clemens]

Just my 0,02$

If you hear it at a stop and it changes when revving up the stopped car it has to be the motor or the tranny in front of the torque converter (or clutch if MT). If it were the brakes it wouldn´t occur at a stop and when revving the motor. Same goes for the driveshafts.

As it is also connected to road speed I would guess it´s the torque converter wearing out or a Problem with the overdrive.
But this is just a wild theory. At least better than nothing, I hope

[dmcfan]

I appreciate it. Then on that therory I would be looking at more than 1 issue because the smell was definitely from the front driver side brake pads. So something is causing the pad to stick or think the ABS needs to kick in frequently. That is why I was wondering would a bad ABS module cause the one caliper to think the ABS needs to engage on that one wheel and the thumping is because the wheel is trying to rotate against force.

It is completely intermittent. Like today half way in my 20 mile commute I was ok and no noise. Then the noise started but no ABS light. Since then going to lunch no noise.

[Clemens]

I believe the abs module can't make the brakes stick because it only opens up, but won't lock it. The locking comes from pressure to the pedal.
I had a broken abs sensor ring once that would cause strange vobrating noises from the abs. Never smelled though. Never heard it when stopped. Was not rpm related.
Very strange. I hope someone smart chimes in.

[dmcfan]

I disconnected the ABS module and the fuse. Thumping came back. Once again at about the halfway point of my commute.

[scot850]

Do you still have the prop-shaft installed?

If you do, check the front U-joint and the center support bearing. Chances are one of them has failed. Also check the bearing at the front of the VC housing.

I think the issues are un-related. The smell and the knocking. However they may be one and the same issue.

When did you last replace the rubber hoses to the front )or all) of the brake calipers? It could be that one is collapsing on the inside and jamming the caliper on.

Also check the engine mountings, in particular the one under the crank pulley and the top torque mount.

Neil.

[sleddriver]

I wonder if you either have air in this caliper, which greatly expands when hot OR you might have water there, which boils when it becomes hot, thus expanding enough to cause your pads to contact your rotor with no input from the pedal. Once the air/water cool off, it'll go away.

Whens the last time you flushed the brake lines?

I've never owned an XC, so don't know anything about the drive-line differences.

[dmcfan]

It ended up all being from the front left caliper. It was frozen. Replaced with a rebuilt Volvo for $47 at he local store.