Technical Identifying a grinding noise

[Brian j]

My 2013, 140k mile, Panda MJ 4x4 has developed a noise which has me stumped.

The noise:

• sounds exactly like the sound of a slightly binding brake pad grinding on a disc.
• Starts at about 15mph, and gets louder the faster you go
• Sounds like it is coming from the N/S front wheel.
• Varies with road speed
• Is not changed by dipping the clutch
• Is not changed by turning off the engine
• Is the same whether in gear or neutral
• Started about 150 miles ago and is getting worse.
• None of the wheels is getting warmer than the others

I have checked all of the brakes. Pads are good, callipers are free, wheels rotate fine, Front discs are perfect, rears are good with just a little edge ring of rust.

I have checked the wheel bearings and there is no play on the wheel, and they are silent and smooth. (I even took the hubs off to check.). It has had two MOT tests at different garages in the last month and neither can find an issue with the wheel bearings.

I noticed that if I jack both front wheels, spinning one spins the other the opposite way easily, as I would expect, but if i jack just one, turning it also turns the prop and there is a significant resistance to it turning.

I was going to throw some wheel bearings at it just in case, but I can’t get any tool I have to push the drive flange out of the bearing, so I have quit on that.

Does anyone have any ideas where I should look? I think the fact that dipping the clutch or changing into neutral makes no difference should rule out the box, but I can’t see any other cause.

 

[The Panda Nut]

I fitted new discs and pads. Had the same. Even after looking closely twice I still didnt see it. BUT the edge / corner of the back plate sits very near the disc and had ben bent EVER SO SLIGHTLY and was touching the disc. Oddly making noises only at certain speeds and steering angles. Easily fixed. And, OH what a horrid noose.

 

[Brian j]

I will check that. Good shout. I didn’t see a shiny patch on it though when I had the hubs off so doubt it.

I should have also said, braking (either gently or hard) does not make a difference to the sound

 

[The Panda Nut]

I will check that. Good shout. I didn’t see a shiny patch on it though when I had the hubs off so doubt it.

I should have also said, braking (either gently or hard) does not make a difference to the sound

Yep sounds right for this issue. You may have to look very closely. The back plate was very thin metal and a good wash from a pubble would have bent it! Id put money on this being the cause.

 

[jackwhoo]

I think @thepandanut means the disc splash guard not the back plate of the brake pads.

 

[Herts Hillhopper]

Given this is a 4x4, it’s also worth checking the propshaft centre bearing - or more accurately its rubber support. I’d almost put money on that being the cause of the noise and it tallies with your description of varying with speed and in neutral as well as in gear, and not altered by braking. If it’s the original shaft and support, you’ve done well to get to that mileage with it.

Take a look at the first photo in my post here for the issue: (look closely at the top part of the circular support. Where you should see a rubber part you can see straight through it)
https://www.fiatforum.com/threads/sharing-my-experience-of-a-4x4-propshaft-replacement.516946/

Mine was replaced before the rubber ring had completely broken away, so there was never any metal-to-metal contact. But if the rubber completely goes, there definitely will be.

(It could also just be something caught in the ‘protection cage’ around that part of the propshaft)


By the way, yes, if you just jack one wheel there is enough ‘stiction’ in the rear differential for that to make it hard to turn the raised wheel. If you raise all four wheels, turning one will easily turn the other three, with those on the same ‘axle’ turning in opposite directions

 

[Brian j]

The prop was sent away to have a genuine centre bearing installed and re-balanced about 4 months/3000 miles ago so I hope it isn’t that but I have a bunch of avenues to check that are much more DIY friendly and less £££££ than I feared.

Thanks both!

 

[Herts Hillhopper]

The prop was sent away to have a genuine centre bearing installed and re-balanced about 4 months/3000 miles ago so I hope it isn’t that but I have a bunch of avenues to check that are much more DIY friendly and less £££££ than I feared.

Thanks both!

OK- very unlikely to be that then.

 

[Panda IIs]

The prop was sent away to have a genuine centre bearing installed and re-balanced about 4 months/3000 miles ago so I hope it isn’t that but I have a bunch of avenues to check that are much more DIY friendly and less £££££ than I feared.

Thanks both!

Let me know if you find the source; I have a similar squeal from a rear wheel. Sounds like it's a pad wear indicator (its a bent tab that rubs on the disc when the pad is worn) only it isn't that. I've stripped and lubed the caliper/pads but to no effect.

 

[Brian j]

OK- very unlikely to be that then.

By the way. Thanks for the description of the suction in the rear differential I was worrying but it seems like that is actually normal.

 

[euroben]

It sounds very much like the metal guard at the back of the brakes. Mine made the same noise. Not easy to see unless up on ramps

 

[AnthonyH]

Did the check the mud guards / wheel arches aren't rubbing?