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why do my discs get glazed over

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discs glazed
2K views 13 replies 6 participants last post by  rd350lc 
#1 ·
I am my second set of front discs and pads in 6 months on my 2007 laguna 2.016v and am experiencing brake judder from them again ( like warped discs ) .
On inspection of the discs the outer surfaces look fine and the pads have bedded ok , but the inner faces on both discs are really glazed badly .
Could there be a caliper problem that is causing this ?
What is the correct procedure for bedding new discs/pads ? I am obviously doing something wrong here .

thanks in advance
 
#3 ·
Are you putting the wheels on, BEFORE you press the pedal, to reset the callipers.
Its discs, then pads, then wheel, then press the brake pedal... Most people press the pedal, to check brakes are working, but this pulls the disc away from the hub slightly on the opposite side of the calliper, this then slightly jams the slides, but enough to warp the discs, and locks the calliper slightly
 
#5 ·
Fair enough.
Discs (and pads) glaze generally from friction.
Which sounds strange but a rubbing pad will be polishing the rubbing surfaces, continually hot, glazing.
Similar if a pad isn't pressing on the disc firmly when braking.
Both can be result of sticky calipers.
 
#6 ·
Check the piston is not sticking,, long reach socket inside the piston, put one brake pad in the calliper, press the pedal, until hard, the design of the seal will bring the piston back slightly, so once its pressed, and released, the piston retracts, you should be able to move the pad, it will only be a slight movement ,, but it will be a movement...
 
#8 ·
If discs haven't warped, I'd have at them with some emery cloth and bust the glaze......
After I'd checked calipers, pistons like Ourkid says and greased the slides.
Make sure pads are free to move in the calipers as well.
Often a touch of paint or burr on the ends can jam them.
 
#9 ·
Hi


Brake pad / disc glazing is caused when the brake pad friction material is overheated.
This results in crystallized friction material on the pad surface and the brake disc, from probably worn or sticking caliper guide pins caused by their incorrect lubrication.



Caliper guide pins must only be lubricated with proper silicon caliper grease not ordinary grease.


Alan
 
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#10 ·
Caliper guide pins must only be lubricated with proper silicon caliper grease not ordinary grease.

Alan
It does get rather confusing.

Red rubber grease, lithium grease and copper grease; surely if the aim is to prevent rust, they are all oil based and very similar? I still use a tub of grease that is probable over 10 years old.

I can hear my brakes squeal when I reverse, I am going to check them now.
 
#14 ·
Update here , stripped the calipers down yesterday and the slide pins looked good to me , they were not very well lubricated bur no signs of corrosion etc . I spent about an hour each side trying to emery the glaze , but also there were pad marks in 2 places on both inner faces which didn't look great . The discs were very cheap (£30) a pair so maybe that doesn't help.
Re-greased the slide pins ( with the wrong grease naturally !)
Will try the suggestion of the sticking pistons as that seems a very valid point as if the pad is not releasing when off the brakes when I put the correct grease in !

All put together so will know very shortly in new discs and pads are needed.

Thanks all for some great advice .
 
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