Vibration under braking

SteveX

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Hi Guys,

Now, this has nothing to do with the rear brakes I changed the other day.

Firstly the front discs are worn a bit and have a lip around the edges. I was just going to order some today, but thought I would double check.

For the past couple of months, I've had a slight vibration when braking but NOT under normal driving, only if / when I want it to happen (which is never to be honest unless I test it is still there).

That is to say, braking any speed under 60 mph light, hard, whichever is perfect. Braking over 60 mph is also fine if you apply moderate pressure or brake hard. However, if I gently rest my foot on the pedal so hardly any braking is being done I get a vibration.

In normal driving circumstance this doesn't happen, and so hasn't worried me. However, I am just about to part with £1200 for a set of discs and pads, and would like to be doubly sure that the front brakes are to blame.

I'm going to have a look underneat for any worn busings etc but any tips would be appreciated. I would hate to spend out £1200 and then test and still have the same issue!
 

television

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This to me sounds like a disc out of true, and I have had the same with the bump bump bump if you touch the brake pedal, this does confirm that it is a front disc as well as the rears require more pressure to bring them into contact with the disc.
 

brandwooddixon

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My first thought would be that the discs are slightly warped or have a rough spot on them.
At £1200 I can understand your reluctance to just replace them if there is no need.

I'd be inclined to jack the car up and remove the front wheels so that you can have a better look at the discs.

A close inspection may reveal a rough spot or rust within the drill holes (I'm assuming AMG cross drilled discs), inspection of the back of the disc is a little more awkward.

To see if the disk is warped and assuming that you don't have dial gauge handy, it is possible to jury rig a straight edge up close to the disc surface (but not touching) and with the aid of some back lighting look at the gap between the disk and the edge to detect any warping as you turn the disc.

This may be easier with a second pair of hands turning the disc.
 

television

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Why £1200 for disc and pads, there are OE out there much cheaper or go to another good brand
 
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SteveX

SteveX

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Thanks for the replies guys.

These are the 'AMG performance Package' discs, along with the 6 pots the discs are floating.

The disc size is 340 x 30 not the usual fixed 345 x 28. Only Mercedes can get this size disc I beleive.

So far:

- Jacked the car up, checked for play in the wheel - solid as a rock other than slight side to side movement with the steering rack which is to be expected

- No worn bushes that I can see, roll bar, upper and lower arms all look good

- Rotating the driver front disc half of the disc seems to bind quite a bit, the other half rotates more freely

- Discs have aprox 1mm lip, but the surface is 'ridged'

- I have the option of trying to get these skimmed locally to see if it is the disc surface


Next calliper to be removed and checking of pads and pistons. I'll try your sugestion with a block and light to see what I can see too.

Malcolm what do you mean by 'bump, bump' I have noticed an almost like dull clonking in with the vibration.

The weird thing is, it's only reproduceable at 60+ and gently resting my foot on the brake which I don't normally do :)

Thanks :)
 

4-DANES

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Hi,

Just joined and thought I would help out. It may be advisable to get the discs skimmed first hence saving you some money.

In order to do a sight test jack the car up and remove the wheels, back off the callipers and spin the wheel,holding a screw driver or something similar just off the surface of the disc and see if it spins true.

Might be advisable to check the ABS sensors to see if they are clogged up.

Hope this helps.

TJ
 
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SteveX

SteveX

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Thanks, pads look ok pistons not stuck, everything looks ok. Only tell tale is the disc not rotating the same on the whole of the surface.

I sprayed brake cleaner on the discs, took it for a blast and could hear 'tisch, tisch, tisch' when braking lightly at slow speed although couldn't be felt through the wheel, Went up to 60, lightly touched the pedal and the vibration was there pretty much in time with the slight noise.

Skimming is an option although the chaps at the garage said it's more difficult to do floating as they expand.
 

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Not easy to skim on the car as the back plate is in the way, with only a 1mm lip its worth doing I feel
 

brandwooddixon

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The fact that the disc was binding on one section indicates to me that something is out of true.

I didn't realise that they were floating discs, this will have a bearing on whether they can be machined or at least how they are machined.

with only 1mm wear these discs are nowhere near done yet, so skimming would be a definite route to take.
 

brandwooddixon

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These guys cover "CAMBRIDGSHIRE, SUFFOLK, ESSEX, HERTFORDSHIRE, BEDFORDSHIRE, NORFOLK, LINCOLNSHIRE, NORTHAMPTONSHIRE" and do a mobile service.

I can't say whether they're any good or not.
 

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Hiya
You can buy a dial gauge quite cheaply from Axminster. This may help you determine which disc is causing the issue
 
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SteveX

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Thanks for all the replies guys, all the advice given has been taken into consideration.

I'll agree on a plan of action this evening and I'll let you know how everything goes :)


Cheers,
 
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SteveX

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Thanks all, I took everything into consideration and it was pointing towards bad discs. The disc was binding when rotating through aprox 60% of the rotation, even after cleaning everything up and reseating the pads and pistons. Micrometer showed uneven deposits and surface thickness accross the faces. Contacted a local place to skim, but they all said they couldn't guarantee the results with floating discs.

All suspension components and bushes check out, hub bearings are good, wheels are good, so it's pointing toward the front brakes.

The inside seems to have been worn more than the outside once I removed them from the hub, lots of rust around the hat which I knocked off of them, but a lot of material has been comprimised.

So, discs and pads on order, tucked her away in the garage for now ready to have everything put back on when it turns up.

I'll confirm back once I've fitted and done some testing.


Cheers,
 
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SteveX

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Fitted new discs and went round the block, it instantly cured the problem. So I came back and fitted the pads too.

Everything is sweet now, no mysterious vibration when resting my foot on the pedal over 60.

The old pads had about 70% of them left, but I thought it best to put the new ones on with the new discs.


Cheers,
 

Pathfinder

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Sounds good and you sorted it yourself !
 
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SteveX

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Yup always a bonus :)

I was actually thinking of facing up the old pads and keep them as spares, no point in binning £100 odd quids worth of pads that have tons of meat on them if it's at all possible.

I'll have to wear a mask and go careful though!
 

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It can take 500 miles to bed old pads to the disc so that complete coverage takes place. No point in trying to face them, as they will sort themselves out.

None of these brakes are 100% true regarding how they wear, once your disc are worn, then you can pop the old ones back in and use them up, you can see on the disc when they have 100% faced.
 
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SteveX

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It can take 500 miles to bed old pads to the disc so that complete coverage takes place. No point in trying to face them, as they will sort themselves out.

None of these brakes are 100% true regarding how they wear, once your disc are worn, then you can pop the old ones back in and use them up, you can see on the disc when they have 100% faced.

Cheers, the new ones are ATE so they should be good quality and last a fair bit. The old ones are Jurid, so they are expensive ones too, worth keeping as a set of spares :)
 

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Vibration on CLK when braking 60 - 40mph

I've had the front discs and pads replaced, then noticed vibrations and sometimes a clonking noise coming from the rear on braking from 60 - 40. So I had the rear discs and pads replaced, as the indi reckoned they could be warped (they were pretty worn). But the noise and vibration is still there - any ideas?
 


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