Changing disks and pads

[tk72tk]

I have a specialized crosstrail disc and the brakes are making an awful screeching sound when braking hard. Any advice on changing them. Should I change pads and discs or just the pads for now. Also is it an easy enough DIY job or is it worth getting it into local bike shop to do.

Thanks

Terry

[NATURAL ANKLING]

Hi,
A picture posted here will help alot.

[mattsccm]

You tube is your friend.
It may just be muck. Clean the discs. Have a look at the pads. If they are worn or reallymanky swap them.

[reohn2]

You tube is your friend.
It may just be muck. Clean the discs. Have a look at the pads. If they are worn or reallymanky swap them.

+1

[tk72tk]

You tube is your friend.
It may just be muck. Clean the discs. Have a look at the pads. If they are worn or reallymanky swap them.

+1

Anything to clean them with or just water?

[reohn2]

You tube is your friend.
It may just be muck. Clean the discs. Have a look at the pads. If they are worn or reallymanky swap them.

+1

Anything to clean them with or just water?

Alcohol,nail polish remover,acetone,meths.Apply with an old toothbrush or wipe with kitchen roll,it evaporates very quickly

[tykeboy2003]

I've done over 10,000 miles on my tourer which has disk brakes, I'm only on my 3rd set of pads and there is only slight wear on the disk so I'd be surprised if there's anything wrong with the disks unless the pads have worn down to the metal and been used significantly since. Replacement of pads and/or disks is not difficult.

[chris_suffolk]

General advice seems to be to change pads when they reach 25% of new - which is probably about 4mm- i.e. at about 1mm. Vernier gauge needed to be accurate. My guess is, so long as there is meat left on them, they will be ok to just change pads.

Wear can be very subjective - ride in wet sandy conditions and the pads may not even see the ride out. Keep them clean, and don't brake alot (live in the flatlands) and they will last ages.

[Grandad]

I've seen several suggestions that pads need replacing when they are the thickness of 3 credit cards.

[Brucey]

General advice seems to be to change pads when they reach 25% of new - which is probably about 4mm- i.e. at about 1mm. Vernier gauge needed to be accurate. My guess is, so long as there is meat left on them, they will be ok to just change pads..

this is much thinner than is recommend by most brake manufacturers.

The usual advice is that the pads are worn out not when they are worn to 1mm, but when they are worn by 1mm.

So they start out ~4mm total thickness (~1.8mm backing and ~2.2mm friction material) and they should be replaced when they are worn to 3mm total thickness. The absolute limit is often 2.5mm.

You will note that there is normally about 0.7mm lining thickness remaining at this point; why can't you use this? There are two reasons;

1) the remaining friction material is apt to come off the backing in one go.... not good
2) any pad springs (eg in mechanical disc brakes) tend to get snarled up with the disc when the friction material is worn down past this point.

Disc brakes can be noisy for all kinds of reasons, but worn pads don't have to be very worn before they are ready for replacement, and failure to replace them is a very common cause of problems.

BTW there are some brakes which will wear the discs out almost as fast as the pads; two sets of (standard) pads and the discs are done too, at or below minimum thickness. Measure the discs for total thickness and even-ness of wear each time the pads are checked/changed.

cheers

[chris_suffolk]

New to discs myself, but this link suggests minimum pad thickness of 0.9mm

https://www.parktool.com/blog/repair-help/disc-brake-pad-removal-installation

and this one suggests 0.5mm

https://si.shimano.com/pdfs/si/SI-8J50A-002-ENG.pdf

[Brucey]

that refers to the friction material not the total pad thickness.

0.5mm is only even possible with perfectly even wear, and in any event is practically suicidal in most cases because of point 1) in my previous post.

cheers

[pedals2slowly]

Manufacturers will err well on the side of caution.

I have adopted a penny pinching and risk taking attitude over 15 years of riding a wide variety of disc braked (cable and hydraulic operated) touring, gravel, mountain, commuter and tandem bikes.
You can happily leave the pads down to 1 mm thickness or less (but heed Brucey on the spring clearance, and uneven wear)
The brakes do still work even when the pad material is completely gone! So not suicidal..............I hope
I've never had to replace a disc.
I usually carry spare pads as they are easy to replace on the road/trail, so i don't have to waste money throwing pads away with plenty of wear on them.
First sign of screechy metal to metal noise - inspect.
No probs

[tk72tk]

[img]

IMG_20200820_095113.jpg

IMG_20200820_095154.jpg

IMG_20200820_095113.jpg

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Pics of the discs.

[NATURAL ANKLING]

Hi,
Last picture disk one, if you can feel those grooves on the outer edge then you're going to need new discs.