Warped discs - again - W203

[markjay]

Vibration during braking is usually described as warped disks, but it is not always the case - and rarely do garages actually bother to measure the discs' run-out.

(see also: http://www.ebcbrakes.com/automotive/check_brake_rotor_runout.shtml )

The vibration can of course be down to warped front discs, but also due to other issue with the master cylinder or clippers, suspension components (bushes, wheel hub, etc) or even rear discs.

The funny thing is that front discs replacement will often resolve this for the short term. I had this problem on a previous car. But the problems comes back...

 

[merc07]

So do you think the discs will need replacing again if there is another fault with the car ?
I was hoping the pagid pads were not as hard and maybe they would actually wear out before the discs this time.
Anyone else had a similar problem ?

cheers
Adam

 

[markjay]

So do you think the discs will need replacing again if there is another fault with the car ?...

Yes. Sorry I can help more, I never resolved the issue on mine at the time - When braking (even mildly) at moderate to high speed, a rather violent vibration was felt through the steering wheel. Initially I replaced the front discs and the wheel hubs (inc. bearings) and all was well for a short while, when the vibration came back I was advised to replace the front lower wishbones, I did buy the parts but never got a chance to fit them and no longer have that car.

 

[merc07]

Hi Adam,

Thats REALLY strange as warping 2 sets of discs (especially if 1 was nearly new) is not normal.
the discs are under warranty and would be replaced with no quibble, but i have a feeling you are just going to warp another set...

Anybody got any suggestions about the cause?

I'll get the front end checked out asap.
What is the warranty on the discs ?

Also never heard that holding your brakes on at the lights is a no no.

Thanks,
Adam

 

[corned]

I heard the heat soak issue with holding on the (hot) brakes 20 or more years ago.

You would think these days, particularly with systems such as SBC (the hold feature especially), that this issue would have been engineered around to prevent such possibilities.

So hopefully it is not that.

To me (and I'm no expert), it sounds like other components may be at fault. Are you absolutely sure that your wheel bearings, caliper mountings, brake pad locating dowels, anti-squeal shims, suspension joints, etc, are all perfectly OK?

 

[BlackC55]

I think you may have warped hubs. This is quite a common issue on 203's and 209's. Corrosion builds up on the hubs and they don't get cleaned prooperly. I use an abrasive wheel on a grinder to get them spotless when doing disc and pad replacement everytime.

 

[merc07]

How can you tell if the hubs are warped ?
I just took it to an Indy for advise and they drove it round the block, removed the wheel and disc then charged me £24 to tell me 'it's the discs mate, cheap discs all do that'

Cheers
Adam

 

[hotrodder]

With the same dial test indicator you'd use to check the disc run out although in practice you'd typically get the hubs spotlessly clean prior to fitting discs (as said) and then measure the run out on the disc. Obviously the wheel bearing endfloat needs to be within specs (can use a DTI to measure that too)

As has been said 'warped' discs/hubs aren't actually physically bent*. The problem is thickness variation either due to uneven pad deposits as discussed on pg 1 or rust/a spec of grit/burrs preventing the disc form sitting on the hub squarely causing excessive run out which can result in DTV TECH ARTICLE # T004 – DTV – Disc Thickness Variation | Disc Brakes Australia


*unevenly tightening bolts can distort things but that'd probably on be a real issue if we were talking about something old and/or French

 

[BlackC55]

How can you tell if the hubs are warped ?
I just took it to an Indy for advise and they drove it round the block, removed the wheel and disc then charged me £24 to tell me 'it's the discs mate, cheap discs all do that'

Cheers
Adam

It's very difficult to tell. I would put money on the hubs being distorted as the corrosion is normally very heavy causing high spots. Put a new set of hubs on with either MB discs and pads or Pagid and I'm pretty confident your problem will be sorted. I have had issues with this before.

 

[merc07]

With the front jacked up, spinning the wheels by hand, there is a tight spot where the pads rub.
I removed the wheels and callipers and measured the runout with a dial gauge attached to the calliper bolt hole and touching the disc about 5mm from the edge.
The discs were only held on by the torx screw but still solid to the hub so the measurement should be good enough.
I then removed the discs to find the hubs that I spent a good time cleaning up just 2000 miles back, full of rusty crud again.
I used a wire brush in a drill and plenty of elbow grease with 200 grit paper to remove the mess.

I then measured the runout on the hubs.

Here are the results:
Drivers side - disc 0.18mm / hub 0.05mm
Passenger side - disc 0.54mm / hub 0.06mm

Are the hubs within tolerance ?

I fitted new Pagid discs, replaced under warranty but didn't measure them as they still had the paint on them.

Why is it mainly the 203/209 that have the hub problems ?

Cheers
Adam

 

[hotrodder]

Dunno about the 203/209 but the maximimum laterial hub run out for w124s is 0.03mm. The single torx screw ain't really good enough for measuring disc run out, it's there to keep the disc secure (bolt holes lined up) when the wheels off nothing more. You don't need all the wheel bolts torqued up or anything but the rotor needs to be evenly nipped down considering how small the numbers are supposed to be. The other advantage of using the wheel bolts is that the rotor can be 'clocked' i.e. rotate it by one bolt and repeat. At some point the run out of each part might 'add up', at other points they might cancel each other some

 

[merc07]

I did put 1 wheel bolt in the disc with a spacer and a ring spanner - all I had to hand as the bolt is obviously too long ! This made no difference apart from making it more awkward to measure with a spanner in the way.

As I said, the disc was pretty much solid on the hub and needed knocking off. Also the part that rubbed on the pads when the wheel was spun coincided with the high point on the gauge

Granted, it's not the most accurate way to measure but the 2 tests back each other up.

As for the hub it looks like is is more or less ok although why isn't it made from something that doesn't rust in 5mins ?

I'll have to wait and see how long this new set lasts...

Cheers
Adam

 

[NigelOB]

Never heard that before. Point taken and stored for future use. Not that I've ever had warped discs but an interesting point nonetheless.

This is quite right your also putting strain on the diff and prop shaft ect..

As for your discs Merc pads are hard and may warp poor quality discs. I haven't had the prob with my w140 or W 201 but have Experienced the prob with a Saab Turbo pre GM the workshop manager of our local Saab dealer told my to use cheap pads as the Saab ones had a high brass content and wore the discs prematurely. I was given the same advice from Vauxhall when a Cavalier GSI I had used to go through a set of discs every 6 to 8 months..

 

[merc07]

Oh well, here we go again.
Same as before, and just another 1800 easy miles.

I think the only thing I can do now is to fit genuine discs.
The hubs were spotless and measured 0.05mm runout.
Maybe I will change these as well.

Anyone know what the cost of the hubs are ?

Cheers
Adam

 

[SJX]

I Second AMG Fan's suggestion of caliper trouble. If the pistons are carrying some muck/pitting they may be sticking in the bores. This usually happens more often when they are very hot (after hard braking - motorway or decent) and makes it difficult to detect when poking around them stone cold during a service. (When new, the caliper pistons will withdraw fractionally by the action of the rubber piston seals relaxing when you lift off the brake, maintaining a very small clearance disc to pad.) Consistent pressure from a pad riding against the disc after heavy braking until the friction material wears down allowing the correct clearance again is going to induce unwanted heat into the rotor - time and time again week after week... and its likely that it may be the cause of the warping.

All the best Steve

 

[jaymanek]

We had issues with a W203 sport pack, exact same issue although the issue recurred very quickly, like less than 100 miles... We tried Pagid 4 or 5 times until Euro refused to change them under warranty. We tried dealer discs but they were the same.
We tried pads and we checked the calipers too.

In the end the customer never came back, I think he must have gone elsewhere so not sure what the outcome was...

My theory was that one of the caliper pistons was sticking causing the brakes to overheat... Caliper issues are common on the sports pack cars.

 

[Geoff A]

I've recently done discs and pads on C270 with sports pack brakes and am now encountering the same problem after a couple of thousand miles.
Jacked the car this morning to start looking for clues and it seems there's some play in both front wheel bearings and I think this could be enough to cause the shake when braking (I guess if the wheel isn't sitting totally true on tight bearings, the disc could be pushed/pulled by the pads under braking?)
Looks easy enough to do - slacken the retaining clamp on the hub nut and give it a tweak.....(guidance appreciated though)
If this doesn't work, I'll pull the pads out and put more clearance on the edge of the backing with some sandpaper, and double check piston movement too. After that, I'll be out of options.

I'm a long way from home at the moment and have limited tools so I will see how I get on..... First step is to buy a pack of Allen keys so I can tighten the hub retaining bolt.
It'll get me back, but it's just not nice when braking. It drives perfectly as long as I don't touch the brakes

 

[bolide]

I think you have to go back to first principles here. If the car is juddering and there's a lateral vibration then the cause may be imbalanced brakes but the vibration is coming from the front suspension

I'd look at wheel bearings, rod ends, wishbone bushes, etc and see where there is play and compliance. Once you've got rid of the play look at the compliance in the suspension

The brakes may set the vibration off but it's the compliance in the system that allows it to develop

Nick Froome

 

[BlackC55]

I can say that it will be the build up of corrosion hubs causing it. Seen it loads of times.

I use a 4" abrasive disc to clean them up.

 

[V12]

I can say that it will be the build up of corrosion hubs causing it. Seen it loads of times.

I use a 4" abrasive disc to clean them up.

I had to do that on my 209 clk...never seen it on any other mercs that badly.

Sent from my GT-I9300 using MBClub UK