Hot Discs....

[Sullivj]

Have just had my brakes inspected and washed out as part of a recent service on my 1998 S Class (Which I've only owned for about 1 month so far).

I noticed at the weekend how, even after a short journey, the front discs get reallly, really hot - too hot to touch. The back ones are warm but by no means this hot.

I wasn't being hard on the brakes so it seemed odd. Is it usual for the front discs to get this hot? I guess it is about 2 tonnes to stop! If it is usual for them to get this hot, it's going to eat the pads off in no time - more expense!!

Apart from that, I am still loving it. She has about 5 coats of polish now and is starting to look appreciated.

Any comments on the discs would be appreciated.

 

[SUE.]

Discs will get hot especially on an automatic,the front do more work than the back so they will get warmer..

 

[pascal]

How Hot is Hot?

John, I know that they get hot ok, and as Sue says the front ones have more work to do, thats why many front discs are vented.

But to be honest I've never being inclined to put my fingers on them just after driving .

 

[mlc]

Two things come to mind from your post.

The first is what does "washed out" mean as part of the brake service? The second is much more worrying and Pascal has beat me to it - brakes turn kinetic energy into heat, who would be daft enough to stick their fingers on a brake disc to see how hot it is!!

That said heavy car + big brakes = hot discs, nothing to worry about.

Mark

 

[mercman_1]

Check to see if the brakes are binding.Simple to do just jack the front up and see if the wheel turn freely! if so nothing to worry about.if they are tight to turn some gentle tapping with a hammer on the calipers may free them off.

 

[Sullivj]

Thanks MercMan

Thanks MercMan, I will give it a go. :mrgreen:

I am indeed stupid enough to touch my discs!! Only because I sprayed the car to wash it and was worried about the immense amounts of steam pouring off the front discs.

As for 'inspect brakes and wash out', I have no idea what it entails. It's what is listed on my recent service invoice. Yes, yes, I know I should ask exactly what it entails, but if I wanted to be a mechanic, I would! That's why I take it to those who know! My talents are very much, elsewhere!

Glad it seems I have nothing to worry about. When I'm in the mood, I'll drive it hard and see if I can get them to glow red!!!! :wink:

Thanks.

 

[jberks]

If I wash the car 15 mins after driving, I still get clouds of steam off the discs. Its perfectly normal. If they were binding it would likely be only on one side and you would find that it pulls to one side or the other. Its probably fine.

 

[SUE.]

Water should not be sprayed on hot discs as you will end up with them warped.....

 

[tom7035]

Don't you drive in the rain, Sue? LOL!

 

[davidsl500]

apparently an average car stopping from 60mph generates enough heat on the front discs to boil a pint of water..

And i have had my front discs glowing a nice cherry red on my Golf GT TDi many a time.

Spraying water on hot disks is not a good idea as Sue says, as you will get differential cooling since you are unlikely to spray the whole surface evenly at the same time. If they are very hot you may well induce stress in the cast iron which will lead to a fracture at a later date. If it raining then the disks will be all wet so there isnt a problem as they will still cool equally. (though if you braked really hard and landed in a deep puddle then there could be problems...)

Still puzzled by having the brakes washed out though.. I wonder whether it was a brake fluid flush and change?

 

[jberks]

Just for the record folk, I don't make a habbit of around spraying water on my brakes, but the odd drop tends to reach them when you're cleaing the wheels and if I haven't been back long - I get steam!. Not a frequent occurence and yes, doing it regularly could warp the discs but it does happen from time to time and it does indicate that they get rather warm which was the point of this thread.

 

[Richard Murray]

Total guess, but if you had your car brakes inspected and 'washed-out', could it be that they've just dismantled them and completed a de-dust and clean procedure? Might be worth calling the garage to find out exactly what they mean - surely it will be itemised on your bill.

Regards the discs heating, the discs have contact with the pads at all times, but shouldn't bind or drag. Have a look at your discs, any scoring on the disc surface or heat spots should alert you to a problem. However if they're clean with an even, smooth surface - then I wouldn't worry.

Richard

 

[LANDR0VER]

Don't you drive in the rain, Sue? LOL!

Driving in the rain is a bit different from pouring water onto hot discs don't you think,Tom...

 

[turnipsock]

Am I missing something here, why not just wait until the brakes cool down!

or, you could try not using the brakes like us good drivers.

 

[SLinKyjoe]

brakes may well be hot to the touch but that doesnt mean they are really hot..........really hot and they start to smell too, then you know you have been driving.


i feel a pic coming on.

hot brakes and washing dont mix....

ps. i should point out these are carbon disks.....steel explode alot better.

 

[Acloud]

How Hot is TOO HOT

i have a 3 year old E320 CDi and have major problems with extreemly hot disks, to the extent that the alloys where glowing red too. This too happened after a Mercedes dealer service to replace worn disc pads all round, and a fast drive home on a motorway..

Problem has resulted in damage to all 4 alloys and claim in at present with MC. Oh! car is back in for rear break problems.

So how hot is TOO HOT

 

[jberks]

I would say that on anything this side of a racer, brakes are not supposed to give out light! Any form of glowing is definately a bad thing.

 

[pascal]

Acloud,

Sounds like your brakes were binding severely, unless you drove home with the pedal supressed:evil:

Good luck with that claim. Keep a log of everything: Phone calls/dates/times etc. Too be honest, I've never seen disks going red on a road going car.

Pascal

 

[mlc]

not only have I never seen road brakes glowing but I would have expected the brakes to have failed before the alloys got glowing. I know brake fluid has a high boiling point but for the wheels to glow the calipers must have been seriously hot.

Clarkson (God bless him) had the brakes on an SLR burning but they hardly fall into the standard group.

One last question - if the brakes were binding this badly - didnt you notice that perhaps the performance was just a little bit under the weather?

Mark.

 

[SLinKyjoe]

glowing brakes....on a road car....fantastic....to get the steel to glowing you will need to be in excess of 1000C. no road brake is ever going to generat this type of temp without the entire pad disentegrating.

as stated above the SLR after repaeted braking did catch fire...but it was the copsite pad materail and if they have driven gentle around a bit it would have cooled. the wheels are designed to flow air in to cool the brakes...

carbon brakes generaly glow around 500C and above. but this is the temp they work most effeciently at. if the exceed 800C then the compsite material starts to braek down and they fall apart...this why cooling is an important thing on race cars.....


a road car will be hard pressed to generate more than 200C in most conditions. altho it is possible for it to raise above the boiling point of brake fluid it is very unlikely indeed that you will see them glowing...

even magnesium alloys that the very expensive alloy wheels are made out of starts to melt at around 1000C. so the brakes will not get anywhere near this temp or your wheels might go all floppy and saggy like.