A 'Clunk' from the front.

[Tuga2112]

so this is now the second time it happens to me. and i believe its happening for the same reason.
I'd like to get some suggestions on how it can be resolved.

the issue appears to be that when I rebuild my front calipers. i removed the rust from inside the sliders by abrasive means. (sandblasting or sandpaper drums in a dremel)
as a result the gap seems to get bigger and allow some play. which then given the archimedes principle becomes a visible movement at the opposite end of the front calipers.

this has happened to me now twice, and the first time i just swapped the caliper pair with a spare, but this is now happening to one of the currently installed calipers.
the odd thing about it, is that it started now... after changing the front wheel bearings. which means.. i have not done anything to the calipers apart from removal and refitting.

I Have spare sliders from rockauto. which interestingly enough. have sleeves, so i can see the sleeves are sliding in and out fairly easily.
im pondering making my own 'oversized' sleeves on the lathe, or potentially use threadlock on the outside of the existing sleeves to prevent movement.. but the threadlock approach seems unlikely to be a long term repair.

but if anyone has other suggestions to prevent this movement at the caliper, or warnings about my potential fixes. I am interested in hearing your views.

[chrism]

Hi Tuga. I reckon you're right; my clonk disappeared after I put new sliders and springs in. Let's face it they do get a bit cruddy in between the yearly? two yearly? services that these calipers seem to need.

I reckon it's rude not to automatically renew sliders + springs as part of the brake service. I reckon weak springs could have contributed towards my clonk too, since the new items were more difficult to push down on when the caliper was set up.

The sliders are folded into a rounded shape/circle so why not ease the fold a little bit further apart with a screwdriver after scraping off the rust? Granted too far apart might not let the pads move back...

I think my latest springs + sliders were stainless steel; I wonder they they'd have needed so much abrasive treatment?

I wonder, also, if your piston is a a bit sticky as well, not pushing out so far and leaving a small clonky/loose gap which allows the pads to move against the (weak) springs. Just a thought...

Perhaps, too, the quality of the items our dealers provide?

Seeyer

[Simon_P]

Tuga, you don't say anything about the clunk.

which then given the archimedes principle becomes a visible movement at the opposite end of the front calipers.

Archimedes won't have been anywhere near your calipers.

Why are they rusty and why on earth are you sandblasting or grinding them?

[Tuga2112]

Simon,

the clumk happens because theres play in the sliders. when i brake. the caliper tilts slightly and i can hear it. I will do a video to show. but this really seems like a tilting of the calipers movement clunk, instead of the common issue with the pads.

im not sure why you find the calipers getting rusty surprising ? my car is driven all year long and is often not in the garage because something else is being worked on.

why was I sandblasting/sanding with a drum (unsure why you describe grinding)? to remove the rust in order to prevent that from happening again.
I followed up with a bath in phosphoric acid to prevent further corrosion and caliper paint.

i dont recall exactly if the slider holes had rust or not, but everything was treated the same, in order to allow the phosphoric acid to create a layer barrier of iron phosphate to prevent rust

I Will post a video of the movement to show. i think i can make it do the clunk noise by hand.

[Tuga2112]

[Simon_P]

im not sure why you find the calipers getting rusty surprising ?

I don't - that isn't what you wrote.

i removed the rust from inside the sliders by abrasive means.

It doesn't appear that you have followed the WSM. If you do, you will notice that it refers to special grease and sealing which would prevent the sliders from becoming rusty.

i removed the rust from inside the sliders by abrasive means. (sandblasting or sandpaper drums in a dremel) as a result the gap seems to get bigger and allow some play.

There is some play by design (you may have buggered it up and created too much play) but I suspect what is happening is the piston is sticking and retracting when the pedal is released or the disc is warped and pushes the piston back - There shouldn't be enough piston retraction to allow you to move the calliper by hand... so it can't move enough to clonk. Rebuild it properly and it will be ok.

which then given the archimedes principle becomes a visible movement at the opposite end of the front calipers.

not sure how a buoyant body displacing it's own weight is applicable ?

[Tuga2112]

There is some play by design (you may have buggered it up and created too much play) but I suspect what is happening is the piston is sticking and retracting when the pedal is released or the disc is warped and pushes the piston back - There shouldn't be enough piston retraction to allow you to move the calliper by hand... so it can't move enough to clonk. Rebuild it properly and it will be ok.

I Fear i may have done just that, but i will give it a try regreasing the sliders.
i use the brake grease that is provided in the kits. i still have some left.

which then given the archimedes principle becomes a visible movement at the opposite end of the front calipers.

not sure how a buoyant body displacing it's own weight is applicable ?

im refering to a different one from archimedes (the one regarding leverage) i can see how filling bath tubs with water can be rather confusing
https://www.socratic-method.com/quote-m ... -the-world

[Simon_P]

Put your foot on the brake
take it off
is there that much slack?
If yes take the piston out and polish it.
What can happen is that the piston sticks to the rubber seal. If it sticks the rubber seal will pull the piston back too far -the pads should be touching the disc and there should be no movement. This is also how the front brakes adjust for wear.

[peteoddcar]

Have you got this type of pin retaining the pads ?

EBay description
FRONT BRAKE PAD FITTING KIT PIN FOR: VAUXHALL ASTRA MK1 MK2 80-92 SOLID BPF0975B

[Tuga2112]

I have to check, but I don't think I have that style of pin installed.

I'm pretty sure the type I have installed at the moment is the solid core with a flange and a retaining pin on the opposite side

[peteoddcar]

Joao
Looking at the video the pins seem to be a bit loose in the housing that’s all - I think mine has the split pin type