Pelican OT, you're my only hope! BMW problem

[onewhippedpuppy]

So Bimmerforums hasn't been any help, I thought I'd seek the advice of the Pelican braintrust. The car is a '93 BMW 325i with 150k. The problem is this:

A strange clicking/light knock, that increases with both RPM and speed. I can feel it in the shifter, and it is still present while coasting with the car in neutral or the clutch pressed in. Probably at it's loudest while under acceleration. The noise frequency coincides with RPM and/or speed. Jacking the rear up and running it does not duplicate the noise. Doesn't seem to change while turning either direction. No longer noticable above 60 MPH. It started quietly a few weeks ago, and has steadily gotten worse.

So, any suggestions? Guibo has been replaced, I just did the center bearing this weekend, but no luck. U-joints felt ok when I was under there. I was thinking maybe CV joints, because I have no record of them being done, but there's no obvious tears in the boots (grease caked), and the sound doesn't change while turning. Transmission and diff fluid have both been recently changed with synthetic. I don't have the money to blindly start replacing stuff, so some direction would be appreciated.

[VaSteve]

Unbalanced tire? I have an issue like that with my 944, with the track tires it's fine...with the road wheels I notice it. I don't notice it when going fast.

Does it do when you rev the engine at a stop? You didn't say that it did.

[Joeaksa]

Still there when you press in the clutch? If so then that isolates it to the gearbox or drivetrain and not engine.

Would get underneath and look at the driveshaft and CV joints.

[onewhippedpuppy]

Only while in motion, still there with the clutch in. That's one of the first things I checked, so I know it's from the transmission back.

Joe, I just did the center bearing Sat/Sun, everything else looked fine. U-joints felt tight, I marked the driveshaft prior to disassembly to keep proper alignment, everything felt ok. At that time I could not see any OBVIOUS damage to the CVs, because I looked. I know they can be bad/dry and show no obvious outward signs. The weird thing is, normally CVs are worse when you turn towards the bad one. This is the same, straight or turning.

Steve, it doesn't feel like an unbalanced tire, but I suppose I could try rotating them to see if it changes.

[TerryH]

If not tires/wheels, maybe rear end or wheel bearings? Have you raised the rear and spun the wheels? Maybe even run the car in gear with the rear wheels off the ground or find a dyno. Probably won't sound similar without a load.

[onewhippedpuppy]

I have ran the car in gear with the rear lifted, no noise. Grabbing the rear wheels and jerking side to side or up down there is very little play.

[Dottore]

Sometimes it's the really simple things....could you have picked up a nail or screw in one of your tires?

[onewhippedpuppy]

You have a good point there. I once replaced all my u-joints and rebuilt the locking hubs on an F150, only to find that the noise was from a piece of metal jammed between the wheel and brake rotor. I'll try rotating the tires tonight, they're due anyway.

[David]

We had a rear wheel bearing go out on our 99 323i. I had the tire shop replace the tires thinking that was the problem. Nope it was a wheel bearing.

It could also be that someone put a zip tie on your driveshaft

[Tim Hancock]

Matt, FWIW, I have 271,000 on my '92 325i manual and I have never changed the trans or rear end oil and am still on my original wheel bearings, cv joints and clutch.

Hopefully it is just your tires!

Wheel bearings would tend to make sense if the noise was not present when run off the ground like you stated though.

The only noise I ever heard from the rear end was due to a frozen up parking brake mechanism (we rarely use it). I just put new rear pads on last month though and while I was in there, I freed up and lubed the parking brake shoe activator, so that little issue is gone for awhile. It did not click, you could just hear a rub and maybe an odd noise when when starting out or reversing direction.

[LeRoux Strydom]

If it perhaps is an engine noise, a sticking vanos actuator is known for making a ticking noise. Worth a look-see?

[GeorgeK]

I had that type of noise on my M5 touring, and it turned out to be an out of round rear tire due to a torn inner carcass.

[onewhippedpuppy]

It's not engine related, when I coast with the clutch in the sound is still present.

Wheel bearings would be best case, and not out of the realm of possibility. I suppose I could tear into it this weekend and inspect them.

[onewhippedpuppy]

Ok, after a bit of reading, it looks like the bearings take some digging to get to. Anyone have a reliable method of inspecting wheel bearings? Is the old top/bottom wiggle trick my best bet?

[VincentVega]

If they arent sealed bearings, like the rears, you can simply inspect them. Otherwise, the wiggle test is the way to test.

[Tim Hancock]

I read thru this again and the part about "feeling it in the shifter" is kind of scary sounding. Are you sure you used the proper oil when you changed it?

I assumed you meant the sound was coming from the rear. Maybe to save some guesswork, you could ride around the block in the trunk and try to at least isolate which side the sound is coming from. I know this sounds ridiculous, but it might help.

[SLO-BOB]

I'm guessing it's one of three things-

1-Despite your inspection, the u-joints could be binding. I've had this happen and it makes that kind of noise. You will feel it in the gear lever. No shop could find it. I ended up swapping driveshafts and it was gone. I'm betting it's this.

2-CVs. As you noted, the sound should change around corners. But, they will make a clicking noise when they are failing. It's also a fairly easy, if not inexpensive fix.

3-Wheel bearings. Again, like cvs, the noise should change with load and cornering. However, it's a maintenance item that you may choose to address regardless if they haven't been repacked/replaced in recent times.

Good luck.

[Superman]

Rock in the tread?

No, I'm not kidding. Here is some elimination info: U-joint problems are much faster. That is, with a real u-joint and a drive shaft that runs to a rear differential, the drive shaft spins too fast. A balance problem would be a buzz, not a click.

Same with tranny noises. If this is purely speed-dependent, then it's a problem with a tire, wheel, brake rotor....that sort of thing.

Wheel bearing problems almost always make a rumbling sound. Well, not really rumbling. More of a growling sound. Growling/howling.

Rock in the tire tread. Kinda kidding. Kinda not. This might be something too simple for the inspectors to have noticed yet.

[on2wheels52]

I don't know how much trouble it is to pull the driveshaft out of your car.
But I've run across drive shafts that felt fine in situ but after removing the binding could easily be felt.
I would think bad wheel bearing to be more of a constant noise.
Diagosis was easier when I had access to a hoist.
Jim

[Rick V]

Next time you climb under the car look and see if the shifter is hitting the driveshaft. Also check and see if any of the soundproofing , or metal shield below the driveshaft is rubbing anywhere.