title about sums it up. I have aquired a wonderful rotational/grinding type noise from the rear of the car. here's how...

Few days ago i was driving into Holland, leaving a highway fuel station i was forced into a curb by a clueless Aston Martin driver. I'll skip trying to explain the nitty gritty as that isnt the point anyway.

Point is, i hit a ~5" curb on the drivers side. Hit front and rear wheels nearly squarely, so there is no body damage no curb hopping etc... rashed up the OE wheels which i dont care about, and whacked the alignment.

*** see my next generation artistic portrayal. note how i've drawn how i caught the curb squarely, but at a glancing angle, not perpendicular into the curb.


The next day i got the car on the lift, the alignment equipment was out of calibration so i couldnt correct that yet. But otherwise there was no visible damage of any kind other than the curb rash on the face of the wheels. The sound I am developing was not reproduced by free spinning the wheel on the lift. The sound is also very odd in frequency/speed of the rotating/grinding... it is obviously tied in frequency to wheel RPM not engine/tranny. But the frequency is significantly slower than wheel/hub rotation speed.

I figure the 2 most obvious things are the hub and the rear end itself. The sound, although not an obviously noticable one, most definately comes from the rear of the car(axle area). Although i think it's probably hub/diff related, the speed of the sound and the fact i was unable to reproduce it by spinning the wheel/hub makes me want to see if anyone else has other ideas to look out for, or how i can test the diff sinc e it doesnt work the same when spinning wheels in the air as it does on the road...?

 

Gotta think wheel bearings.

 

yeah thats the obvious one.... and i think i simply cant roll the wheels on a lift and replicate because i cant spin em fast enough, or because theres virtually no load on the bearing comparatively..

just thought i'd throw it out to see if there were any other thoughts. that hub is getting replaced and i'm gonna peak at the diff all as soon as its viable for my schedule

 

oh, i also kinda threw this out here just to see if anyone would comment on the Aston Martin....

fwiw thats the 3rd such car that has almost plowed through me... the others were a Ferrari California and some older model... 355/Testarosa looking. i see a LOT of nice cars out here. havent seen a Veyron, but pretty much anything else i think i've seen around

 

I think I see the problem; your rear right wheel is significantly smaller than the others!

But seriously, I didn't see this covered, but maybe you have a bent wheel? Try balancing the two that got whacked? I know that doesn't necessarily account for the grinding noise, but could it be influencing the bearing?

 

lolz. sorry i dont have Alfy skills

wheels arent bent, still balanced. bent was my initial big fear till i got em on the machine

 

That would appear to be about a 16" or less!

 

How about the ujoints on your rear half shaft are fractured. It's amazing how long a u joint can go busted, but it's gotta be u joint inside or outside on the half shaft. It could also be the wheel bearing or rear diffeferential bearing.

Next time let the Aston Martin hit you; Oh, I see you're not in California so you actually try to drive responsibly!

 

i thought about the universals on the drive shaft, but by the time that much shock/flex would be delivered i'd already have other issues also. could potentially still be possible i suppose.

this is my first solo incident of any damage, i've been tagged in the parking lot before though. but i've been in more than a couple off road excursions avoiding collisions. and out here in the areas i like to go drive, more often than not its those type of vehicles* that are the worst dangers on the road
*Aston Martin, Ferrari, Porsche high ends, Lambo, Maseratti, etc...
theres a Gallardo here in Mons that tears it up once in a while but ive never seen that one wreckless

 

Put the rearend up on jackstands and run it in gear

just make sure the front end isn't pointed at anything you care about

 

like the shop?

i didnt do this when it was up because i was under the impression that without being under a "load" the diff wouldnt operate properly anyway, perhaps enough to verify a symptom, but not enough to rule one out

thanks for mentioning it though, i'll give it a go also

 

When I had to get a wheel hub bearing replaced I was also unable to reproduce the noise on the lift. There was just not enough load being put on on the walls of the hub-bearing contact point. It sounded like I was driving with mud tires on. I replaced that whole hub and the sound was gone.

* I'm using 'load' in terms of weight, not drivetrain load

 

Use a chassis Dyno instead

I wouldn't recommend wearing a neck tie when you crawl under there ...

You do own a mechanics stethoscope don't you? It can assist with pinpointing specific noises you might not pick up on otherwise.


.

 

^^ yep, exactly what i was thinking about the hub

if i knew where one was.... i'm sure there are some around with Spa being less than 90 minutes away, but i dont know where yet

 

Sorry, forgot you were knee deep in sauerkraut and weiner schnitzel

 

almost, i'm up to here in chocolate, waffles, and the best beer in the world!! Germans can keep their schnitzel though i do like kraut...

and hey, whats to be sorry for? I'm in the middle of SpaFrancorchamps, Nuremburgring, Hockenheim, Zandvoort, and half a dozen other tracks in single day trip distance

oh and the best ***** F'ing fries you've ever had in your life!

 

Should be a little play in the wheel if the bearings are damaged.

 

not any that was observable

 

Ok then, you suck

pulling the hub and changing the bearing is a lot of fun, trust me on this one .... you will be much better off getting a good used upright/hub assembly because for all you know the upright is tweaked too.



.

 

Not if the bearing in-question was simply flat-spotted.

 

yeah i was looking at it in the FSM, bad juju.... i think a call to Mazmart may be in order

 

Does the noise change under cornering loads ?

 

i would say yes, in general. but not always.

 

I know you say the noise is from the rear but if you haven't taken the front wheel off and checked the front bearing you should . I spent months trying to diagnose a sound I could have sworn (along with several other people) was from the rear and it turned out to be the front bearing.

 

Truth.

Not a day goes by that I don't think about Brugge.

Wheel bearings move around their race at a fraction of wheel rotation speed. That is why the sound is off.

That said, there are a bunch of things to check with regards to something simply making contact when the suspension is loaded.