A150 [w169] intermittent squeal

[Ian_T]

Hello all, I'm hoping someone can help me. I have a 2006 A150 CVT auto that has an intermittent squeal / screeching noise that seems to come from the right hand side front of the car in fairly specific circumstances.

The engine is normally warm, speed between around 40-50mph and engine revs are somewhere around 2k.

For the most part it seems to do it as I come off the gas in light 'cruise' and marginally decelerate.

I have replaced the serpentine belt, both idler pulleys and the tensioner pulley, which was fun, and while that got rid of a slight squeak at idle revs when cold, this noise is different and more metallic sounding.

When it comes on, I have tried jumping on the brakes but that doesn't clear it, so I think I can rule out both the front brakes and wheel bearings, but I'm still at a loss otherwise.

AC is switched off, makes no difference whether it is on or off. The pitch of the screech / squeal seems to be road speed dependent, but doesn't seem to vary with rocking the steering wheel, or braking of any strength.

Ideas welcome.

 

[Ian_T]

I should perhaps add to this. After I fitted the new pulleys and belt to it, I drove it to Birmingham and back, expecting it was fixed. Not far into the journey it squealed and I almost turned back, but with the engine warm and at highway speeds there was no noise whatsoever, so that led me to feel it might be safe. Probably a bad assumption.

Either way, I drove there and back without incident and since, it's back exactly to its old form. While it was in bits last time, it was clear that someone has suspected the AC compressor front bearing, as there was a good deposit of some kind of copperslip type spray grease that had come out of it (very obviously alien to the car). So perhaps that's a possible route.

On starting it up and driving it locally last night, I found I could hear the onset of that squeal even at idle with the gearbox in 'Drive' and handbrake on. The noise seems to come out of the engine bay pretty uniformly with the bonnet open and could even be coming from the CVT box (hope not!). I'll check the fluid level today and see what I find. There's no fluid loss sign under the car. I'm perfectly happy to drain and replace the fluid, filter and gasket if needed, as I don't know when that was last done (it's on 65k miles and the service book has sadly only been visited by a local garage to the first owner since the last time M-B touched it at 15k miles.) I'll start with the expectation that it's never had a fluid change, poor thing.

 

[Blobcat]

I would have said idler pulley and/or tensioner - but as you've changed them already it's probably something else on the serpentine belt

 

[Ian_T]

I'm off work this week so will put some more effort into it. I have another perfectly serviceable car so won't be running this poor thing into the ground.

That was my thought too. The only things on the serpentine belt that I haven't changed are the crank pulley, water pump, alternator and compressor.

Obviously someone suspected the compressor previously, as it was lubed up with spray grease behind the pulley, which had a near-zero chance of making it to the bearing. It's a variable displacement compressor (so no clutch) and the air conditioning works perfectly.

So... Crank pulley - I've heard that the main seal can come out and make a screeching / squealing sound on the back of the pulley, so I will have to have a look and see if I can see anything with my inspection camera.

Water pump - I didn't touch it other than seeing if there was obvious play in it - it seemed OK, but it looks like swapping the pump is an involved job!

Alternator - seemed completely normal to me. No appreciable end float, pulley seems to be clean and in good condition.

AC compressor - would have to be my favourite suspect, the pulley can be removed by removing the sacrificial 'clutch' plate and then removing a circlip and pulling it off. I guess that while that's an unpleasant job due to access from under the car, it would be a good thing to rule out. When I replaced all of the other stuff, I did rotate it by hand and it felt like it was engaged (as it should) but it wasn't really practical to determine if that big front bearing was still OK without pulling it to bits.

All suggestions welcome. I started the car again this morning and couldn't be sure where the noise was coming from. The periodic belt squeak that I started out with from cold disappeared when I replaced the belt and pulleys, but I'm left with the more worrying fault.

I have a MB autobox dipstick here that I will use to check the CVT fluid level this afternoon. I'd hate for something to be wrong with the box.

 

[Ian_T]

A little video always helps, right?

 

[Mike111s]

Hi Ian

Did you manage to identify the issue? I am experiencing a very similar problem with my manual A170 (w169). Cold start squeal at idle which a belt & pulley replacement fixed, but now left with this intermittent squealing which seems to come from the right hand side of the car and isn't affected by engine speed. Sounds very similar to yours and recently has become more frequent and louder.

Thanks,
Mike

 

[Ian_T]

Hi Mike, too early to say, but I'm being optimistic.

I have been catching up on 'post-purchase' maintenance and changed the fluid in the autobox as there was no history of it being changed. The filter was indeed dated 2006. No change to noises, but I didn't expect any.

I then went through the front brakes to see if there was anything there, any sticking or similar. Everything was in great condition and nothing was seized or noisy. Reassembled and no change.

Some YouTube later I wondered about the OSF wheel bearing and, because I also had a badly perished aftermarket CV boot on the outer end of that driveshaft, I thought I'd inspect the wheel bearing as well. The outer side is completely hidden by the hub / drive flange, but the inside (and ABS sensor) is visible around the end of the CV joint. I found that was quite dirty with some rust from the knuckle surrounding it and that some of the dust seal around the outer edge was hanging like a thin thread around the outside edge. I cleaned it up as best I could and rubbed grease into it and went for a drive. Instant change, no squeal whatsoever except when almost stationary, there was a slight high pitched noise.

I ordered the CV boot and a wheel bearing and replaced both, no noise so far, but I'm waiting for a camber gauge to arrive so I can reset the camber (as I chose to separate the knuckle from the strut). Once that's done (hopefully Friday) I should be able to drive it much more and see if it's truly fixed.

The bearing was internally just fine and didn't look contaminated. Externally there was that inner dust seal (ABS magnet ring side) that was obviously degraded and once I had removed the drive flange from the bearing, I could see that the inside edge of the large circlip had some 'slightly polished' appearance in one place, which *could* have been the source of all the noise.

Hope this helps you. I'd try checking the visible side of your bearing and smearing it with grease. If that silences it, I think you have the choice of replacing the bearing like I did or trying harder to clean and protect it (for a while at least).

 

[Ian_T]

I took some photos while it was in bits, poor thing.

 

[Mike111s]

Hi Ian, thank you for the detailed write up. Glad to hear you made some good progress, fingers crossed this has resolved the issue. I will take a look at my wheel hub this weekend to see if I can spot anything that doesn't look right.

 

[Ian_T]

You're welcome - here's what I saw. You might find your CV joint is larger than mine - mine has a diameter of 75mm, whereas the parts in EPC and available from factors are all 81+mm diameter. Sadly I had to use a universal boot as the rest of the joint is fine.

If you look at the slightly shiny ring around the CV joint, that's the dust seal (with integral magnets for ABS, which is a Hall sensor rather than old fashioned reluctor ring). I cleaned that up and it comes up shiny as it's either bright plated or stainless. I couldn't do anything to fix the thread of soft plastic seal that had become detached, so I just pulled it out and greased all the way around the outside edge. That cover rotates with the drive shaft, so only the outer edge needed lubricating. You'll see the 'finger' of the ABS sensor at the top-right of the image just above and behind the CV joint, it's not a substantial thing and while quite tough, not indestructible either.

I think that Stevie Wonder fitted that CV boot.

Despite the state of the boot, the joint inside was still nice and clean.

After reassembly, it's all a little happier:

 

[mioba]

Got a bit of a lip on the fring disks there OP.....

 

[Ian_T]

Got a bit of a lip on the fring disks there OP.....

Yeah, they're not all that bad really, they've been on the car for a while by the looks of them and there's a good bit of rust there where the pads don't quite wipe. The thickness was well in spec, though, so I thought I'd just let sleeping dogs lie (I've been known to knock that rust off).

I did set the camber and toe today, though, all seems good and definitely no sign of any squeals yet.