Audi S4, rumbling/vibration under braking
Discussion
My, 2014, 40k miles Audi S4 Avant, S-tronic/DSG has developed a rumbling/vibration under braking. It has been doing it for a while (maybe always has?) and I always thought it was due to wide/low profile tyres and stiff suspension but it seems to have got worse recently.
I had all the wheels off and checked the brakes, could find nothing wrong and, yesterday it went for an MOT. Whilst there I got the garage to check it over as I thought it might be the brakes?
However it passed the MOT with no advisories and they say the brakes are fine as is the steering, wheel bearings etc. and so they think it it might be transmission related, to add the MOT garage is not an Audi specialist, rather a tyre & MOT station and didn't investigate much further.
It only does it under braking (which I find odd if transmission related) and is more noticeable when braking hard, also does it in neutral if that makes any difference? but the car stops fine, nice & straight and plenty of braking power.
All discs are original and whilst they have a small wear lip around the edge it is nothing significant, front pads are good having been changed around 14k miles ago, rear pads are original, tyres are all good with plenty of tread and car is kept garaged and so no corrosion on anything brake related.
The rumbling/vibration could be described as 'pulsing', hard to say where it's coming from just general rather than through the steering or definitively front or rear.
As for transmission, everything works as it should and the gearbox oil service was done (early) at 30k miles due to there having been a small oil weep from the rear of the box due to, it seems, insufficient sealant having been used when built.
Any ideas?
I had all the wheels off and checked the brakes, could find nothing wrong and, yesterday it went for an MOT. Whilst there I got the garage to check it over as I thought it might be the brakes?
However it passed the MOT with no advisories and they say the brakes are fine as is the steering, wheel bearings etc. and so they think it it might be transmission related, to add the MOT garage is not an Audi specialist, rather a tyre & MOT station and didn't investigate much further.
It only does it under braking (which I find odd if transmission related) and is more noticeable when braking hard, also does it in neutral if that makes any difference? but the car stops fine, nice & straight and plenty of braking power.
All discs are original and whilst they have a small wear lip around the edge it is nothing significant, front pads are good having been changed around 14k miles ago, rear pads are original, tyres are all good with plenty of tread and car is kept garaged and so no corrosion on anything brake related.
The rumbling/vibration could be described as 'pulsing', hard to say where it's coming from just general rather than through the steering or definitively front or rear.
As for transmission, everything works as it should and the gearbox oil service was done (early) at 30k miles due to there having been a small oil weep from the rear of the box due to, it seems, insufficient sealant having been used when built.
Any ideas?
Given the age and relatively low miles, I'd bet the discs are warped. Easy to do if held on the footbrake after a few decent hard stops, or if it's been sat unused outdoors for periods of time. The OEM discs aren't great quality and tend to rust up quite badly.
I haven't got my car file to hand, but from memory I had Brembo discs and pads fitted all round and they've lasted very well, if you were thinking of replacing. A decent old school garage should be able to measure the runout on your existing discs to see if they are warped, before making the leap to replace?
I haven't got my car file to hand, but from memory I had Brembo discs and pads fitted all round and they've lasted very well, if you were thinking of replacing. A decent old school garage should be able to measure the runout on your existing discs to see if they are warped, before making the leap to replace?
Adrian E said:
Given the age and relatively low miles, I'd bet the discs are warped. Easy to do if held on the footbrake after a few decent hard stops, or if it's been sat unused outdoors for periods of time. The OEM discs aren't great quality and tend to rust up quite badly.
I haven't got my car file to hand, but from memory I had Brembo discs and pads fitted all round and they've lasted very well, if you were thinking of replacing. A decent old school garage should be able to measure the runout on your existing discs to see if they are warped, before making the leap to replace?
I suspected that, and the chap at the MOT garage also suggested it but they reported no problems with them after the test?I haven't got my car file to hand, but from memory I had Brembo discs and pads fitted all round and they've lasted very well, if you were thinking of replacing. A decent old school garage should be able to measure the runout on your existing discs to see if they are warped, before making the leap to replace?
Maybe they only relied on the brake test machine? I could test them myself, I've got a dial gauge etc.
I was going to suggest warped discs but Adrian got in first.
OP: is the shaking noticeable when the car is stone cold, on the first braking? It’s possible there is a slight warp which is almost negligible when the discs are cold but then when you get heat into them, they expand slightly, the “Pringle”-shape becomes more accentuated as they expand, and the shaking increases.
OP: is the shaking noticeable when the car is stone cold, on the first braking? It’s possible there is a slight warp which is almost negligible when the discs are cold but then when you get heat into them, they expand slightly, the “Pringle”-shape becomes more accentuated as they expand, and the shaking increases.
BlackWidow13 said:
I was going to suggest warped discs but Adrian got in first.
OP: is the shaking noticeable when the car is stone cold, on the first braking? It’s possible there is a slight warp which is almost negligible when the discs are cold but then when you get heat into them, they expand slightly, the “Pringle”-shape becomes more accentuated as they expand, and the shaking increases.
Not noticed, I'll check next time out.OP: is the shaking noticeable when the car is stone cold, on the first braking? It’s possible there is a slight warp which is almost negligible when the discs are cold but then when you get heat into them, they expand slightly, the “Pringle”-shape becomes more accentuated as they expand, and the shaking increases.
catso said:
I suspected that, and the chap at the MOT garage also suggested it but they reported no problems with them after the test?
MOT tester is the wrong person to ask.You're looking for runout that could be a few thousandths of an inch. Initially on the brake disc surfaces (manual states at 3 points spaced across the surface), and if that doesn't show the runout then the same measurement on the mating face of the hub.
If the vibration is only through the brake pedal you probably have a distorted disc/s, but may also have hub or wheel issues.
Dr G said:
MOT tester is the wrong person to ask.
I'm beginning to agree with that, though I thought they might be keen to sell me new brakes and as such, look a little harder.I'll get the wheels off and get a DTI setup on the disc faces, any idea how much runout is too much? Also, I'm assuming it's most likely to be the front discs but will check the rears too.
So, today I have checked the runout on the disc surface and got the following numbers:
Front right; 0.15mm
Front left; 0.11mm
Rear right; 0.03mm
Rear left; 0.025mm
A quick google tells me that up to 0.05mm (0.002" for the old school-ers) is generally considered acceptable so it looks like new front discs are in order.
A shame because there's still plenty of metal left on them and, despite the age I would have expected better at only 40k miles. Plus, I've never had to change discs for anything other than wear before. Pads also still have plenty of material on them but will, obviously replace whilst doing the discs.
Any advice on best disc/pad combination? It seems the OEM discs are not that great.
Front right; 0.15mm
Front left; 0.11mm
Rear right; 0.03mm
Rear left; 0.025mm
A quick google tells me that up to 0.05mm (0.002" for the old school-ers) is generally considered acceptable so it looks like new front discs are in order.
A shame because there's still plenty of metal left on them and, despite the age I would have expected better at only 40k miles. Plus, I've never had to change discs for anything other than wear before. Pads also still have plenty of material on them but will, obviously replace whilst doing the discs.
Any advice on best disc/pad combination? It seems the OEM discs are not that great.
Thanks, after looking at the various options, I've gone for Brembo Xtra line discs/pads, cost a bit more but, hopefully better than OEM especially WRT heat dissipation so less chance of warping?
Plus, I always like to take the opportunity to upgrade when replacing, makes me feel better about spending the money when I end up with something better...
Plus, I always like to take the opportunity to upgrade when replacing, makes me feel better about spending the money when I end up with something better...
I run Brembo Max Xtra and have had no issues. Quiet, not dusty, and better bite/feel than standard pads.
Warping with excess heat is far less common than other factors. Damaged hubs, wheels, or dirty/corroded mating faces are more common root causes. I've seen people replace brake discs multiple times while failing to spot other factors. Sitting with your foot on the brake not good either.
Cook a brake disc you're more likely to crack it than bend it.
Warping with excess heat is far less common than other factors. Damaged hubs, wheels, or dirty/corroded mating faces are more common root causes. I've seen people replace brake discs multiple times while failing to spot other factors. Sitting with your foot on the brake not good either.
Cook a brake disc you're more likely to crack it than bend it.
To update for anyone interested - fitted the new, fancy drilled Brembo discs and pads today, probably the easiest discs/pads I've ever changed, just took my time and paid special attention to cleaning up the mounting face of the hubs to ensure no corrosion remaining to put the disc out of true.
Just been out for a quick test drive and can report all is good, normal smooth braking has been resumed.
Seems a shame to have had to swap them because there was plenty of disc and even more pad remaining but if they're not running true then needs must.
As an aside, the original outer pads are stuck to the inside of the caliper (presumably for ease of installation?) so they need to be levered off and the inner surface of the caliper cleaned, but the garage that fitted the replacements a few years back had only taken the material of the pads off, leaving behind the alloy plate, still stuck to the caliper, meaning there was a double plate on the outer pads.
Can't see that it caused any problem (other than slightly less engagement of the locating pin) but certainly not what I'd expect.
Anyway, should be good for a good while now as I'm not a high mileage driver.
Just been out for a quick test drive and can report all is good, normal smooth braking has been resumed.
Seems a shame to have had to swap them because there was plenty of disc and even more pad remaining but if they're not running true then needs must.
As an aside, the original outer pads are stuck to the inside of the caliper (presumably for ease of installation?) so they need to be levered off and the inner surface of the caliper cleaned, but the garage that fitted the replacements a few years back had only taken the material of the pads off, leaving behind the alloy plate, still stuck to the caliper, meaning there was a double plate on the outer pads.
Can't see that it caused any problem (other than slightly less engagement of the locating pin) but certainly not what I'd expect.
Anyway, should be good for a good while now as I'm not a high mileage driver.
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