Brakes quickly fade

[MancMike]

Hi,

On occasions where I do some heavy repeated braking, I've found the brakes fade very quickly. It's as if they're poorly cooled. The alloy wheel is warm and I can feel the heat from the discs, so they're getting screaming hot, but heat isn't able to easily dissipated.

Is this typical, for my wheels at least? As they're quite enclosed. (the standard elegance wheels like these)

When it comes to renewing my discs/pads, do you think drilled/grooved will make a difference, or is there anything else I can do? Maybe a change of alloys, to a more open design, like the AMG alloys, although I don't think these suit the elegance trim.

 

[moonloops]

If you don't burn your hand on the wheel, you're not trying hard enough

p.s. change your brake pads, they sound like cheapies.. Merc's from a long time have had strong braking systems..

 

[renault12ts]

If you don't burn your hand on the wheel, you're not trying hard enough

p.s. change your brake pads, they sound like cheapies.. Merc's from a long time have had strong braking systems..

Brake fade is caused by the overheating of the fluid rather than the pads. Or have I got this wrong?

 

[MancMike]

lol oh no the wheels have been pretty warm!


So pads? I thought if they're producing heat, they're doing their job?

I'll see how much meat is left on them and generally inspect the brakes at weekend, I've not had the wheels off this car yet.

 

[MancMike]

Brake fade is caused by the overheating of the fluid rather than the pads. Or have I got this wrong?

If you boil the fluid you'll have barely any brakes as the bubbles are very squashy.

I'm sure it's caused when the discs have so much heat in them that the pads no longer produce much friction against such a hot surface, hence the heat ratings on various racing pads.

I'm not sure when the fluid was last changed either, so I may change that too.

I've always upgraded my cars to DOT 5.1, is that suitable for Merc too? It has a much higher boiling point...

 

[stwat]

How old is the fluid?

 

[markjay]

I suffered brake fade on previous cars and upgraded the discs on one occasion to TarOx grooved discs and on another to drilled discs. In both cases it cured the fade.

So grooved and drilled discs do dissipate heat better.

But the cars were modified and I drove them hard (was a young lad back then...).

If you are driving the car normally and experience brake fade then this is more likely to be a fault - contaminated brake fluid, failed flexible hoses, etc.

As others said, start with fresh brake fluid. Also, check discs thickness - the minimum value should be stamped in the disc's hub.

 

[MancMike]

How old is the fluid?

I don't know, but the car has always been serviced regularly, every stamp in the book, so I'll renew anyway.

 

[MancMike]

Thanks guys.

I'll get the wheels off at weekend and inspect/replace fluid.

If the discs look a bit past their best and or the pads, I'll replace, with drilled/grooved, but hoping the fluid cures it.

 

[hotrodder]

Pad fade = pedal feels normal but the car won't stop. Can usually smell the brakes long before the Oh $*!@ moment
Fluid fade = pedal gone soft 'cause the brake fluid has gotten hot enough to either boil or, in the case of ancient fluid, the water it's absorbed over the years boils hence 'wet' and 'dry' boiling points. Less likely to require new underwear than pad fade as the brakes still work after the initial panicked pedal pumping

Both are types of brake fade

Drilling and/or grooving discs makes very little difference to a brake discs ability to dissipate heat*. Both, especially cross drilling, have their origins in the dim and distant past when 'pad outgassing' was very common. Grooving did a better job of 'cleaning' pads whose compounds were also prone to glazing than todays pads.

Outgassing isn't really a problem anymore due to improvements in pad technology but in the old days the 'glue' used to make pads would vaporise as the pads overheated and cross drilling gave an escape route for these vapours. These days, especially on a road car, it's mostly cosmetic and while it can improve 'bite' the penalty can be increased noise and discs that are more prone to cracking. On a race car the holes also save a few precious grams

Grooving is more useful than cross drilling as the slots allow an escape for debris, 'clean' the pads, improve bite and are more resistant to cracking than cross drilling

* switching from a straight vane ventilated disc to curved vanes makes a MUCH bigger difference to brake temps for example

 

[MancMike]

Thanks HotRodder, that's all very helpful.

It's what you described as pad fade that I have. Pedal feels the same, but brakes feel "oiled", I'm pressing harder to stop and starting to get nervous. Returns to normal after a short run without braking.

So, new pads? Are mine likely not MB then? I thought Pagid were OEM for most cars pads? I'm not sure I'm keen on the racey pads like EBC, etc. ?

 

[hotrodder]

Like pretty much all car manufacturers MB are gonna have several sources for most parts. Off the top of my head i think Jurid, Textar and probably Pagid have all supplied them with pads over the years and no doubt there are plenty of others too. Half the time many of the different brand names are all owned by the same company too... Pagid, Textar and Mintex are all owned by TMD friction. Sachs, Boge, Lemforder are all under the ZF parts umbrella- the last parts i bought were some new top mounts from a UK Sachs agent which came in a Boge box with a Lemforder sticker on it and had an MB part number cast into them although the MB star that should've been infront of the # had been ground off

Not all of EBCs pads are 'racey' but you can count me among those that aren't fans of them- about half of the internet raves about the low dust thing while the other half points out they often don't fit very well and/or have had them crumble

I've no idea if Pagid from eurocrap are the same compound as Pagid from the stealer (that's assuming the stealer doesn't sell you Jurid or whatever their current stock is), as you can't really see the calipers let alone the pads through your wheels easily it could be as simple as they're nearish to the end of their life... like discs the pads are mostly reliant on their mass and surface area for heat capacity & cooling i.e. pads that are down to their last few millimetres before the idiot light on the dash comes on will be less resistant to fade than newish ones of the same compound

 

[Sp!ke]

Rather than changing the brake fluid, I would test it first. You can get cheap testers on amazon for under £10 but if you like your tools, you might prefer a refractometer.

Then I would simply inspect the brakes and pads and also go round each wheel and do a quick bleed to ensure there's no air in the system.


You shouldnt be experiencing brake fade on the road at all.

 

[st13phil]

I'd expect changing the fluid to make no difference whatsoever for the reasons mentioned by hotrodder. It's definitely worth inspecting the pads to see if they're on their last legs though.

 

[MancMike]

I have several refractometers.

Thanks guys, I read the fluid should be changed every 2 years as per the service schedule anyway, so I might flush it through just to give me something to do at weekend. It'll give me the opportunity to get the wheels off, where I can inspect the brakes properly.

I've always been very happy with the grabby-ness of Pagid pads, so I'll get prices from MB and ECP and go with whichever is best priced and get what I'm given, as MB pads should be good whoever makes them, and I'm happy with Pagid, so either way I'll be chuffed with the purchase.

 

[Del80y]

I ordered from the bay member name is dcparts2006 which is Mercedes Edinburgh dealership great prices compared with just phoning them up
Got pads and drilled discs for my C220

Better price than ECP
delivered next day
Interior, Interior Trims items in Mercedes Parts Edinburgh store on eBay!

 

[rorf]

Looking at your pic of the wheel it looks like your discs are too small - anyone worked on these before - what is the year and mileage? Pad fade, then cheap pads or maybe even grease/oil on the pads.

As mentioned Mercedes cars generally have excellent brakes - maybe the brake booster is not working too.

 

[MancMike]

That picture isn't of my car. My car is red, in my avatar. That is a back wheel too, so smaller brakes. It was just to illustrate the wheel design (it's pretty full face, not a lot of openings)

It's a C280 (3L V6 Petrol) 08 plate Elegance, 82,000.

The brake master cylinder is fine, the brakes are very nicely assisted, it's just that when I get a good run, late evening and get to "enjoy the engine", I can get the brakes to fade, where I have to press the pedal harder to stop when they're screaming hot.

I've not done my investigating today, I'll do that tomorrow.