Rusting discs.

[John]

I am used to discs which have a substantial lip on them and are in need of replacement.

What I am not sure is, if the discs are rusting, at what point do you need to replace them?

I've also noticed cracks around the cross-drilled holes.

 

[carat 3.6]

Rusty Disc's are not a problem as such, as long as they are above the min thickness your ok.

 

[John]

There is a small lip on them but hardly any.

What about the cracks? Presumably these are from too much heat?

 

[carat 3.6]

Yes, looks like normal heat fatigue to me. How deep is the lip?

 

[John]

Hard to measure but I used the metal end of the tape measure flat against the disc near the lip and the lip felt slightly more - the metal end measured just under 1mm.

So I would say 1mm.

These discs are 4 years old now (I'm obviously not trying hard enough but I don't tend to use my brakes a lot believe it or not ).

 

[AMGeed]

If you get some time, I'd whip the wheels off and use a cordless drill to unblock those drilled disc holes. Did it to mine a while ago and they have stayed clear. They look a lot better cleared out too. Looks like yours will last a while longer.

 

[kianok]

I just jet wash my discs from time to time to clean out the holes.

 

[BlackC55]

Cracks are not ideal. According to MB they need replacing if cracks show.
In reality tiny cracks are not the end of the world.

Measure the disc. The min thickness is stamped on the hub of the disc.

 

[Reggie-rock]

If it was my car I would change the discs together with a new set of pads after all safety first.

 

[rifiki]

Had similar problem, take the discs off and file the lip.

 

[Alps]

id clear the holes with a drill as suggested, this will help the cracks to not get worse.

small cracks should be fine, I have a few little ones on mine now. 1mm lip should be ok.

you could just change them next time you do the pads.

 

[Simon_M]

Normally MB discs have a little dimple to indicate when they need replacing. Once the disc is worn down the dimple goes and the discs need swapping. It should be on the outer edge. But as said clean out those holes.

S

 

[John]

I know what I will be doing this weekend!

I will have a look for the dimple

Thanks all.

 

[John]

So I have something for the 'what did you do to your Merc today' thread.

I think this is what they mean by 'living the dream'...

I got the wheels off respectively and drilled out the brake dust in the holes.

It definitely needed to be drilled out as it was too tough to just push out.

What I did notice was, and I presume the friction was caused by the brake dust being a friction material, was it made the drill bit red hot and it melted it to the point where it twisted the end of it round. It still worked even at the end but I can't really drill holes with it anymore!

I noticed this clogging problem was worse on the OS disc than the NS, and the insides of both were worse than the outsides.

Whilst drilling, I noticed rust from the vents dropping out as I rotated the disc after drilling, so clearly the rust build up is getting bad.

I will see how the car performs on Monday.

Is this the dimple you were talking about Simon?

 

[Mrhanky]

Just after I bought mine MSL checked out the discs for me as they where corroded. They advised to change and I'm glad I did as when the removed the caliper the inside front pads just fell apart.

My advice is to change them, not worth taking any chance, however small.

Also agree with the pressure washing the holes. I do this once a week during the wash and always surprised how much black dust comes out of the front ones.

 

[Simon_M]

Is this the dimple you were talking about Simon?

I don't think so, it should just be a hole that looks like it hasn't been drilled through on the disc, still within the same pattern as the other holes. It almost looks like a marker for a hole that wasn't drilled as it was too near to the edge of the disc.

If that makes sense...

 

[Will]

I think the discs on these cars are pretty cheap - at four years old, lipped, corroded, cracked and with blocked vent holes surely a replacement set would be the way forward? Especially on a ~ 500bhp heavy performance saloon

Usual online suppliers seem to show these discs at £50-60 each, I would think MB may not be too bad in this instance with a bit of discount

 

[John]

Yes, I'd already decided to get them done after seeing the condition of them yesterday with bits of rust dropping out.

I've definitely had my money out of them!

Shame they rust so quickly really as there isn't a lot of wear.