Replacing BRAKE Pads

stevieb · Post by **stevieb** » 03 Mar 2006, 14:03

Kowalski wrote:I've heard of one method for detecting worn brake pads its a metal tab that sticks up inside the friction material. When this tab contacts the brake disc it makes a screechy type of noise, the same sort of noise your pads make when they get down to the metal backing. I think this may have been an american idea.

I suspect my 406 may have something akin to this at the mo. The brakes have just started to gently sqeak - completely out of the blue. So I assume it's just wear.

I'm not really a fan of the warning light idea. I had a binding pad on the 405, but the dumb pad, not the live pad - which is the one with the wire. The damb pad wore right down to the metal with no warning at all. Luckily I knew the sound of metal to metal as soon as I heard it and replaced the pads straight away, but I wonder how many non-mechanical people would assume that no light = no problem. Having said that, these are the kind of people who would carry on driving even when their braking is virtually non-existent, so maybe some kind of warning is better than none.

8304 · Post by **8304** » 03 Mar 2006, 14:23

my zx has new front and rear pads and discs and it is squeaking - (out of the blue)

i spose they just need bedding in........

the front drivers alloy is getting very hot over the last week obviously a sticking slider... but its a pain as the mot is next week - typical it should happen just before it!!!!

stevieb · Post by **stevieb** » 04 Mar 2006, 11:50

Judgin by the amount of meat left on my pads I'd say my 406 isn't dure new pads yet, so that's my earlier theory out of the window.

One trick for eliminating squeak is to nip up caliper bolts by a small amount - or slacken them a little if they're already too tight.

It's all to do with resonant frequency. If the tension in the bolts creates the necessary tension in surrounding components then you end up with a "ringing" effect (like rubbing a wet finger round the rim of a wine glass). A quick tweak of the bolts can be enough to alter the tension and therefore the frequency - hopefully to a point that isn't reached in daily use.

Having said that, I didn't bother with mine last night, even though I had the front wheels off to change the front anti-rollbar droplinks. Mainly because I was ankle deep in snow by the time I'd finished...

AndersDK · Post by **AndersDK** » 04 Mar 2006, 13:54

Do NOT play with the caliper bolts please

If the brakes are squealing its because of the pads shaking against the discs, caliper piston and slider at a high frequency. Its still possible to purchase damper pads - thin damping material - to put between pads and piston/slider. That will instantly cure the squealing.

Most pads are manufactured with a rather thick layer of "paint" on the back face - exactly to work as a damper pad.

BonceChops · Post by **BonceChops** » 04 Mar 2006, 15:59

AndersDK wrote:Its still possible to purchase damper pads - thin damping material - to put between pads and piston/slider. That will instantly cure the squealing.

I thought they made baked beans in tins so you could make such shims easily at home

fastandfurryous · Post by **fastandfurryous** » 04 Mar 2006, 17:11

A bit of crinkly baked bean tin, and some coppergrease on the back of the pads works wonders for nasty squealy brakes, and I agree with stevieb that changing the tension in the caliper mounting bolts can help in extreme cases... WITH the proviso that you take the caliper bolt right out, and put some fresh threadlocking fluid on the threads. A caliper bolt is NOT something you want coming loose! (trust me.. I've had it happen!)

One thing that's not been mentioned so far is the benefit of having a wear lip on the outside of the brake disc. The backing of the pad tends to be larger than the friction material, and so the backing will touch the wear lip before the friction material is completely gone. I once managed to drive about 300 miles back from Leeds with the backing *just* touching the wear lip on a brake disc. I drove not using the brakes, but was safe in the knowledge that I had a teeny tiny bit of brake pad left and could use it should the need arise.

Sure enough, got the old pads out, and there was about 0.5mm of friction material left on one of them. My own fault for not checking the pads more frequently, but at least it wasn't full-on metal-to-metal.

Kowalski · Post by **Kowalski** » 04 Mar 2006, 17:28

My Xantia has one of the anti-squeal shims missing from the rear brakes, i.e. it only has the shim on one caliper. My rear brakes were squealing so I went to the Citroen dealer to see if I could buy just 1 shim. He got on his computer and after quite a bit of head scratching he denied that the shims exist at all. I insisted that they did exist, the fact that I had one in my hand at the time convinced him that I hadn't just imagined the part, eventually he looked in a box of genuine Citroen Xantia rear brake pads and the kit contained 2 shims and 4 brake pads. I didn't need pads at the time so I didn't bother buying them just to get 1 shim especially when the Citroen dealer wanted twice what GSF or ECP were charging for pads. To cut a long story short, I took the corrosion off between caliper and suspension arm and the noise disappeared.

I've had new brake pads before that have had a tarry or rubbery coating on the back of them. You can also buy self adhesive rubbery sticky material to go onto the back of the pads to stop the squeal. There is even special white brake grease for the job too. Brakes shouldn't squeal but the fact that they often do for no obvious reason means that various methods of disguising the fault that makes them squeal have arisen. Personally, I wouldn't be happy adjusting the tightness of caliper bolts, if they aren't tight enough, fair enough tighten them to the correct torque, but messing about and trying to under or over tighten bolts to avoid a squeal sounds like madness to me, especially when there is a well know problem with rear Xantia brakes that makes them squeal.

fastandfurryous · Post by **fastandfurryous** » 04 Mar 2006, 18:15

Kowalski wrote:messing about and trying to under or over tighten bolts to avoid a squeal sounds like madness to me

Talking about no more than a couple of lb-ft difference here... not enough to make a safety difference, but enough to change the natural frequency of the system.

But I agree... it's not the sort of thing you really want to "experiment" with.

As regards the cause of brake squeal... Asbestos. Or rather the lack of it. Brake pads always used to have asbestos in them, and brake squeal was almost unheard of. When asbestos was removed due to health issues (asbestos dust being generated by every car on the road... NOT good!) brakes suddenly started to squeal a lot. The car that springs to mind with this issue is the Cavalier MK2/3. These brakes were designed before 1981, when asbestos was common, and then had to use asbestos free pads.

Another thing that can cause brake squeal is pads that are too hard or too soft. A friend with a 406 has just made the mistake of fitting "super cool racing pads mate." Mistake! you can now hear him coming a mile off.

Mandrake · Post by **Mandrake** » 04 Mar 2006, 19:30

Kowalski wrote:My Xantia has one of the anti-squeal shims missing from the rear brakes, i.e. it only has the shim on one caliper. My rear brakes were squealing so I went to the Citroen dealer to see if I could buy just 1 shim.

They're more than just anti-squeal shims, they help ensure even brake pad wear by biasing the braking force onto the trailing edge of the pad. (Which no doubt helps prevent squealing as well

)

When mum got her Xantia, the first time I checked the rear brakes I found one of the shims upside down

and that pad was completely poked - it had not only worn badly compared to the other 3 pads, it had worn at at least a 10 degree angle

How it managed to wear at such an angle when the pad could no longer touch the disc over most of the area is anyones guess, but it did...

Moral of the story, take extra care to put the shims up the right way

Regards,
Simon

Mandrake · Post by **Mandrake** » 04 Mar 2006, 19:36

fastandfurryous wrote:Another thing that can cause brake squeal is pads that are too hard or too soft. A friend with a 406 has just made the mistake of fitting "super cool racing pads mate." Mistake! you can now hear him coming a mile off.

Yep,

I agree. The rear brakes work so lightly compared to the front (especially if you usually drive around with an empty boot, as I do) that if you put hard pads in the rear they NEVER get a chance to bed in, so they squeal and also aren't very sensitive due to a combination of never bedding in, and the hard surface.

I always put fairly soft grade pads in the rear - not only do they bed in, but it makes them a bit more sensitive and improves the rear to front braking sensitivity thus preventing the rear from lifting under braking. (Which is critically affected by the front/back braking balance)

Even with a soft grade they still outlast the front pads 2 or 3 to 1....

Regards,
Simon

stevieb · Post by **stevieb** » 05 Mar 2006, 20:20

The other trick to eliminate squeak is to wire-brush the calipers off. Obviously taking the necessary breathing precautions. It's worked for me before. It might just work for me this time, but it's just too cold, so I'll have to live with a slight squeak.

On the subject of nipping up caliper bolts, I've personally never had one come loose, but always tighten mine to a point where I'm happy that they're tight. Not to the specified torque - which never seems quite enough for me. I should say I never get brake pad squeak any more. The squeak I've got now is from the previous owners pad installation - I haven't had these out yet.

Clearly, before the days of thread-locking compound and torque-wrenches this is the way everybody worked. Still works for me.

drewmunn · Post by **drewmunn** » 06 Mar 2006, 10:46

mine that i got off ebay came with white wires