bizzare drivetrain prob - banging scraping shaking (SOLVED)

[rallysam]

EDIT - Solved, see posts further down

Hey guys,

There's a constant scraping/grinding sound combined with an occasional BANG sound from the area of the driver's front wheel. The scraping goes with wheel speed, not engine speed, definitely a wheel or drivetrain issue. It makes all the noises even at a crawling pace.

Now get this - If I lean out the window while the car crawls along, I can SEE the driver's side wheel SHAKES each time there's a bang sound and the car actually felt like it was being slightly held back. This was bad enough that I thought I couldn't make it a few blocks before something in the wheel or drivetrain nuked.

It started when I got an alignment. It was done by a really good shop, and we haven't found anything caused by their work so far, so the problem could be unrelated. I just throw that in there as clue. Left the shop with the car sounding fine and drove 45 minutes at highway speeds. It wasn't until I slowed down to city street speeds that I noticed the racket.

Debugging on the side of a street in downtown Baltimore:
* Wheel is not rubbing on anything - nothing is even close (caliper, strut, fender, knuckle, etc)
* Lugnuts were tight. I even took wheels off, re-torqued them, and the car still made the racket
* Wheel bearings seemed ok. I shoved the wheels and no loose movement. Also this is a clue that the alignment bolts are not loose either.
* All bolts used during the alignment were still tight... at least with a hand wrench
* No lost tools found in engine compartment
* A different garage did a full inspection of the drivetrain and didn't find anything wrong with it either.
* The only thing that we've found wrong was that the alignment tech forgot to clip the front passenger ABS wheel speed sensor under the camber nut, so the wire was dangling loose. But, note that was not the wheel that had problems.
* I am getting an ABS light now, presumably due to abuse of the wheel speed sensor cable.

THE KICKER:
I had the car towed to a garage around the corner, and it made the noises as we pulled off the flatbed, but then after sitting still for a a couple hours, THE CAR WAS FINE! No noise or anything. He did a full inspection of the drivetrain on a lift, ran it on the lift, and road tests, and found no problems other than the wheel speed sensor wire. And this is a completely different garage, so he's got every incentive to find fault with the first garage

Oh man, it's great that the car is not making the noise now, but how long will that situation last??? I can't drive hours away from home this weekend with this sort of unsolved mystery!

[BAC5.2]

So it no longer makes the noise?

Hmm....

Did you inspect axles and such? I can't imagine it being anything alignment related, unless the camber bolt fell out or some nonsense like that.

You have group-N tops, so I wouldn't imagine that the top could have been no-good.

Without inspecting it and hearing the noise, it's a tough call. If it happens again, you know where to bring it to get it looked at.

[vrg3]

Hm, until I read Phil's second-to-last paragraph I was gonna say it might be strut top mounts. Maybe it is though... if somehow something got into the bearings or something.

Did the steering wheel pull to the side when the bangs happened? If not, I wonder if it's a wheel bearing problem somehow.

When the car was towed, was it tied down? If the struts were held compressed for a while, maybe that could have masked a problem with the strut's internal lubrication (kind of like how jacking an STi up can temporarily cure a strut clunk problem).

[rallysam]

There was definitely nothing obviously wrong with the alignment - all bolts were not only present but also tight! (except the dangling wheel speed sensor line). And, the local guy inspected the axles and the whole rest of the driveline too.

Top mounts, eh? Well, I actually have stock, original top mounts, stock springs, and AGX struts that have seen years of rallycrossing. So, you're right to be worried about 'em. But, the noise (scraaaaaaaaaape... bang!) went with road speed. It would happen even when I was literally crawling down a perfectly smooth road - slower than walking pace - like parrallel parking speed. It even made a quiet scrape/bang when the car was being winched up and down the polished flat-bed (real slow). I didn't think a bad strut or top mount would make noise when there is no road vibrations because they shouldn't know the car is moving. What do you think?

I can't say as I noticed much steering wheel vibration, which seems pretty weird! I could see the damn front wheel jumping around from the drivers seat!

When it was towed, it was on a flat bed with chains to the tow hooks with tow straps wrapped around all the wheels. I don't remember whether the wheel straps or tow-hook chains were carrying the load.

The inner-city tow truck driver knew all about Subaru and rallies, and he was really digging my beater.

[vrg3]

Yeah, I agree that if you're moving slowly on a smooth road the suspension shouldn't know the car's moving...

Hrm.

I say you jack up that corner, take the wheel off, and take the brakes off. It'll take you half an hour but there's a good chance you'll find the problem.

You probably would have noticed this by now, but what if they left a wrench somewhere in the vicinity? On the brake bleeder, perhaps, if they bled your brakes for any reason? One time I was following my brother on a test drive after we had worked on the Supra and was shocked to see sparks coming from under his car. I spent the next ten seconds trying to figure out what could make that happen -- just before this I had been under the car -- when the answer came flying at me, literally: the 10mm wrench I had left on the clutch slave cylinder's bleeder popped off and flew just inches past my side mirror.

[rallysam]

Yeah, I agree that if you're moving slowly on a smooth road the suspension shouldn't know the car's moving...

Hrm.

I say you jack up that corner, take the wheel off, and take the brakes off. It'll take you half an hour but there's a good chance you'll find the problem.

You probably would have noticed this by now, but what if they left a wrench somewhere in the vicinity? On the brake bleeder, perhaps, if they bled your brakes for any reason? One time I was following my brother on a test drive after we had worked on the Supra and was shocked to see sparks coming from under his car. I spent the next ten seconds trying to figure out what could make that happen -- just before this I had been under the car -- when the answer came flying at me, literally: the 10mm wrench I had left on the clutch slave cylinder's bleeder popped off and flew just inches past my side mirror.

Well, I'm ALL about forgetting tools in the engine compartment! But, this time I took the wheels off (while parked illegally on a downtown street) and poked around everywhere around the caliper and knuckle. No wrench, nothing looked out of place. I can try actually getting into it this weekend and opening up the caliper.

Are you saying I should get the rotor off too? I'm familiar with that one but not a fan I'll ask my coworker to bring his sledge.

[vrg3]

Yeah, I was thinking you should remove the rotor too. Just because.

It shouldn't require a sledgehammer. If the rotor is stubborn, just thread a pair of M8 bolts into the two holes on the hat, tightening them evenly until they pop the rotor off.

[tahiti350]

possible binding in the CV joint caused by them turning it to full stop, maybe popped a ball out of socket???

With the wheel visibly moving every time it "popped" I'd definately be looking at the drivetrain area.

Also why was the sensor wire removed for an alignment??

I'd be looking at the half shaft and hub to see if something was removed or replaced. If they had the half shaft out it may not have been properly seated when you got the car back.

my .02 worth, and good luck

Tahiti350
Subbie nubbie, but 30 years of wrenching under the belt

[rallysam]

Thanks for the help guys. No, they didn't do anything during the alignment except turn the camber bolts and toe bolts... I watched. The wheel sensor cable is held in place by the camber nut, so that's the only reason it got messed with.

I just drove the car 35 miles and it sounds fine. WTF??? My best guess now is that it has something to do with that wheel sensor cable being loose since that's one of the few things we changed.

[douglas vincent]

I have had this happen before. It was the outer CV joint. It would come and go, but finally it just WENT! I could barely make it home.

The bang is most likely the joint binding up, then being forced to spin.

I lay odds when you pull your axle, there will be ball bearings missing from the outer CV joint.

[rallysam]

I have had this happen before. It was the outer CV joint. It would come and go, but finally it just WENT! I could barely make it home.

The bang is most likely the joint binding up, then being forced to spin.

I lay odds when you pull your axle, there will be ball bearings missing from the outer CV joint.

Can that be inspected on the car easily? Like by just pulling the rubber boot back and taking a look as opposed to removing a bunch of parts?

[rallysam]

SOLVED

The ABS sensor wheel inside the hub is obliterated. Maybe it was rusty and a rock got caught in there to finish it off? Regardless, as that sensor wheel destructed, chunks of metal were getting horribly caught between rotating parts and stationary parts (explaining why the driver's side wheel was jolting as it banged!!)

Now, there's not much left of that sensor wheel except these little bits that are still being held on by bolt heads. The rest of the wheel material is long gone!

Oh well, that problem solved itself.

Credit to gearboxtech.com for identifying the problem while I was in the shop for some other work.

And, for the record, if I had had the free time to actually follow Vikash's advice earlier, I would have noticed it then