Brakes not using all the disc

samZ4M · Post by **samZ4M** » Fri Dec 16, 2016 1:13 pm

Easier to look at the pic, but my pads aren't gripping the entire disc on the real axle. It's done it for a while, so I'm not sure on the negative effects, I suppose there is more braking coming from the front (rather less from the back).

But, what is the fix? New discs, pads and calliper refurb?

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Paulr · Post by **Paulr** » Fri Dec 16, 2016 1:21 pm

I would certainly be looking at the pads as a start, that would be the main target of my investigation. Then seeing if the calipers are pushing them on the the disc evenly. Then looking at the discs.

Depending on what I find, I suspect I would be replacing just the pads first to see if that makes any difference.

Might not need everything changing if you are adept at DIY. A garage wll change everything.

samZ4M · Post by **samZ4M** » Fri Dec 16, 2016 1:24 pm

All my tools are in storage and frankly, brakes are the one thing I don't like to work on!

There is a very well rated indi local, I can get it to them for a check over. Concern is, if I put new pads on, they'll only then be braking on the 'raised' bit.

Paulr · Post by **Paulr** » Fri Dec 16, 2016 1:35 pm

Not easy to see on that photo, but if they have scoured the disc and you have significant raised areas, then replace them.

obewan · Post by **obewan** » Fri Dec 16, 2016 2:04 pm

I had similar on mine (not an M admittedly) See topic here
viewtopic.php?f=45&t=89242

I replaced with new discs and pads, didn't see anything obviously wrong when taking apart
Was all ok afterwards

samZ4M · Post by **samZ4M** » Fri Dec 16, 2016 2:26 pm

The lighter area is contact, the rusted bit is where there seems to be no contact. So this pad is going to look very weird if you ask me!

There isn't a massive lip, so I might get away with new pads, to even the disk out. But might end up needed an other set of pads once the disc is even, as the 1st set will be mis-shaped.

Fishy Dave · Post by **Fishy Dave** » Fri Dec 16, 2016 2:32 pm

Mine are exactly the same on the rear since changing to genuine BMW discs and EBC Blue pads a few hundred miles/3 months ago. The area not being swept is getting less with each time I use the car though. I can't tell if it's the pads or the disc that is not flat (running APs btw).

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samZ4M · Post by **samZ4M** » Fri Dec 16, 2016 2:36 pm

Mine has been like this for some time and isn't improving. Whats stranger is it's on both sides, exactly the same wear. Could have been heat warped them? even then, for both sides to be the same is rare, non?

Argenta · Post by **Argenta** » Fri Dec 16, 2016 2:43 pm

No they're used too little so, 1. they rust and 2. When you changed to new pads it takes a very long time for them to grind to the shape of the disc, which is formed by the old pads. The biggest pressure of the braking pad is always in the middle where the cylinder in the caliper is. Thats why the disc eventually gets thinner in the middle, hence thats where you'd end up with a rusty trail with new pads. IF you dont go out on track and brake intensly and wear them in.

So the same wear on both sides is completely logical too.

samZ4M · Post by **samZ4M** » Fri Dec 16, 2016 2:51 pm

Makes sense Argenta. Pads were swapped and still (in 18 months and 18k) haven't got to the shape of the previous pads.

They do get some heavy braking frequently enough, I'd have figured it'd be sorted by now. I suppose the answer is to swap discs & pads at the same time...

D4dawg · Post by **D4dawg** » Sat Dec 17, 2016 2:15 am

Evening all

Thought you were going to sort these after our car meet with Matt etc buddy

As to me it looks and dear God with your sized ridges,
The calipers all need pushing back in and see if come out cleanly and go back in freely
If not they'll run continuously and warp discs

Discs need taking off and skimmed if enough meat left on them place on Witney does that can't remember name but Matt will as they are well known
If meat left this will flatten the surface area again
If not enough, sorry you'll need all new discs.

Now, providing calipers and pistons all moving freely
Clean them with brake cleaner, lune with small amount of copper grease along pad contact areas and slides

Fit new discs and new pads as old ones aren't even fit for bin, now carefully bed in the pads slowly and carefully for 200 miles with a progression of pressure and a few good 70-50mphs to bed fully

Plus Alot of people forget about thermal shock a major destroyer of cars discs
This is hot disc and either roadside deep puddle or car wash 200c -10c in seconds with ice cold pressure washer or puddle and the disc warps

Ref your shocking amount of untouched disc fishy
I'd skim disc and shave pads if lots of meat left
Check pistons then clean mounts and slides, then rebed

Z4M-2006 · Post by **Z4M-2006** » Sat Dec 17, 2016 9:36 am

Poor wear like this on a single piston caliper is usually the slides seized or worn, or the pads tight/ partially seized in the brake pad carrier ...

Overhaul and new parts as needed

Fishy Dave · Post by **Fishy Dave** » Sat Dec 17, 2016 9:38 am

D4dawg wrote: Ref your shocking amount of untouched disc fishy
I'd skim disc and shave pads if lots of meat left
Check pistons then clean mounts and slides, then rebed

It's strange as both pads and discs were brand new before my trackday at Anglesey and you'd think that the drive up and back plus the trackday would have bedded them in? I'm more inclined to think it is a pad issue as I can't believe BMW would issue concave braking surfaces on their discs? All four pistons moved smoothly in the rear calipers, with no corrosion that I could see and the pads were greased.

D4dawg · Post by **D4dawg** » Sat Dec 17, 2016 1:34 pm

On my way to tell sadly is by taking the pads off and having a look buddy as your loosing not far off a third of your braking

Beedub · Post by **Beedub** » Sat Dec 17, 2016 3:27 pm

Fishy Dave wrote:Mine are exactly the same on the rear since changing to genuine BMW discs and EBC Blue pads a few hundred miles/3 months ago. The area not being swept is getting less with each time I use the car though. I can't tell if it's the pads or the disc that is not flat (running APs btw).
20161204_151606_resized.jpg

something not right their dave... my AP sweep right across the friction service. That inner rust ring ( closest to the bell) suggest the pads are the wrong shape or size. the pads i have seem to almost overhang the rotor slightly.

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