Brake squeak then screech!

[Hilux]

Filing the sides off the pads is a botch

Why?

I had some plate lift before the brakes were sorted and it was a bu**er to get the old pads out and the new pads in but it cured the problem.

To take a portion of a mm off each side or lip where they rest or bind will not compromise the pad but will ensure it doesnt bind (especially with heat)

Every pad I have fitted on my cars that include Porsche, Westfield, Ginetta, Golf, Suzuki off roader, classic Rovers that has been `tight` in the caliper rests/seats I have `eased`and used Coppergrease and that includes Ferodo, PF, Textar, Green Stuff, Pagid blah blah.........................

Strange thing is they stop making noise when heated up, surely they have expanded by then? Confused.

Exactly my point about the pads heating up and binding in the caliper rests. Once heated they dont move around or vibrate at high frequency so much when applied.

 

[zcacogp]

Paul,

It's a botch because it treats the symptoms, it doesn't solve the problem. If you have plate lift then one of the symptoms is that the pads will be tight. If you cure the problem - address the plate lift - then the pads will no longer be tight. If, alternatively, you grind the sides off the pads then they will work, but the plate lift will still be there and will continue to get worse, until something serious happens (possibly the plates snapping - I don't know what happens in the limit.) And, if you ever do cure the plate lift, you will have to buy some new pads as the ones you have ground the sides off will be too narrow for the calipers.

Same applies to tightening a worn-out wheel bearing. You will perhaps stop the drone, but it doesn't solve the problem, just masks the symptoms.


Oli.

 

[scam75]

Quick update on the situation. Took the pads out again last night and took the edges off as per Oli. Re-applied copper grease and re-assembled. Have not replaced any pads yet, wanted to see if this edge removal thing would work!

Went for a drive last night and no noise. No noise this morning either. Not going to get too excited as the copper grease alone achieved this the last time only for the noises to return a few days later.

Will update again in a few days.

Stuart

 

[zcacogp]

Hope it continues well Stuart. I can't vouch for the technique having never used it, but I have heard of it working well elsewhere.

Keep us posted.


Oli.

 

[Hilux]

ORIGINAL: zcacogp

Paul,

It's a botch because it treats the symptoms, it doesn't solve the problem. If you have plate lift then one of the symptoms is that the pads will be tight. If you cure the problem - address the plate lift - then the pads will no longer be tight. If, alternatively, you grind the sides off the pads then they will work, but the plate lift will still be there and will continue to get worse, until something serious happens (possibly the plates snapping - I don't know what happens in the limit.) And, if you ever do cure the plate lift, you will have to buy some new pads as the ones you have ground the sides off will be too narrow for the calipers.

Same applies to tightening a worn-out wheel bearing. You will perhaps stop the drone, but it doesn't solve the problem, just masks the symptoms.


Oli.

I needed to change pads when I first realised I had plate lift, it got me out of a spot entirely safely until I had it resolved. The new PF pads were a tight fit and bound slightly on newly refurbished calipers so I `eased` those too! It did 6 track days without issue. The road use Textars were ok though

What if aftermarket pads are tight (without plate lift) ?? Are you going to suffer it as they will bind when hot? You may not notice it but on track they do need to rest away from the disc to help lose heat. It may be just me but I need to know the pads are free to move. I`ve never had issues in any of the cars on road or tracks over some 15 to 20 years.

 

[zcacogp]

Paul,

I'd say that if the callipers have no plate lift and the pads are still tight then you need to take the edges off to make them fit ... especially if (as you say) they need to be looser for track work than normal road use.

Grinding them to accommodate callipers which are exhibiting faults (plate lift) is however a botch.


Oli.

 

[sawood12]

Aluminium calipers have a higher coefficient of thermal expansion than the steel backing plates of the pads so they may be tight when cold, but maybe loosen up with use - though the pads might get hotter than the calipers so that might cancel things out!! But then again the brake fluid in the caliper gets pretty hot, so maybe not.

In anycase - are the caliper plates actually spring plates? the operative work being spring? Maybe the pads should be tight-ish going in as they are up against the tension of the spring plates? Maybe the pads are supposed to 'float' within the caliper against the pressure of the two spring plates. I don't know, just adding 1 & 1 and probably ending up with 5.

 

[zcacogp]

Good points Scott. Particularly about the coeff. of thermal expansion. (Not being able to think like that explains why I failed a Mech Eng degree, eh?!)

No, the calliper plates aren't spring plates. At least, they are spring steel but are flat against the calliper body in normal use, and they shouldn't move, hence no 'spring'. I have often looked at the design and not quite understood why they are as they are; there is a lip at the bottom of them to constrain the pad from going too far in (and resting against the disk bell) but that's about all. The only conclusion I came to was that the plates are there to prevent the pad backing plates from wearing out the (comparatively soft) aluminium of the calliper body - which I guess they could, over time.


Oli.

 

[sawood12]

Oli - you see, you've just demonstrated there some Mech Eng thinking!! That is exactly the purpose of the caliper plates - it is to prevent the pads from wearing into the soft alloy caliper body. From what I can see with the monoblock calipers off the later cars where the caliper body is a one piece casting, there are two steel (I assume they're steel) dowels that locate onto the pads to stop the pads edges from wearing into the caliper body - they also prevent the pads from being slotted too deep into the caliper body too.

I think i've seen the plates referred to as spring plates somewhere which is where I thought that maybe they do have a spring effect, but if they are flat against the caliper then that is clearly not the case.

 

[Super_Marv]

I think i've seen the plates referred to as spring plates somewhere which is where I thought that maybe they do have a spring effect, but if they are flat against the caliper then that is clearly not the case.

Yep - they're called Spring Plates by Porsche.

Anyway, I still reckon it's the pads!

 

[sulzeruk]

We will find out tomorrow as Stuart is coming over for some ramp time tomorrow morning!
Alasdair

 

[scam75]

Well, after a couple of days driving the little squeaks started to come back. Today we took the Oli'd mintex pads off the back and stuck on a new set of pagids that just happened to be there. No noise from the rear now. Took the car for a blast to check brakes and the high pitched screech returned from the front at slow speeds when pads where heated up.

Under normal driving conditions I now have no noise at all, however if I get some heat into the pads the fronts screech at low speed braking and come to a standstill braking. This phenomenon has manifested itself since putting the pagids on the front, with or without copper grease and with or without the edges coming off as per Oli.

Strangely the new pagids in the rear have been silent. Taking the edges off the old rear mintex pads made no difference either.

Will now get some non pagids for the front and see what happens. Or turn the stereo up, for ever.[]

Stuart

 

[zcacogp]

Oh dear. Sorry my idea wasn't the solution. I was kind of hopeful it would be, shame it wasn't.

However, there MUST be some reason why this is happening. I can't imagine what it is, and I am assuming you have checked everything - tightness of all bolts, disk run-out and so on.

I guess it could be 'one of those things', that may yet go away with time. I hope it is (for your sake.)


Oli.

 

[scam75]

It was an interesting experiment and I noticed quite a few pads come like this now, so no harm done. The squeaky pads on the rear that got chopped would have been replaced anyway. The front pagids may settle in as you say, the fact that under normal driving conditions I have no noise now is progress.[] For final piece of mind I will replace the fronts with non pagids out of curiosity, although the rear pagids seem to be fine![&:]

It's all part of the enjoyment interacting with other owners looking to fix odd issues.[]

However, this technique will be known as Ollying your pads from now on!

Stuart

 

[zcacogp]

ORIGINAL: scam75
However, this technique will be known as Ollying your pads from now on!

[]

(And will also be known as ineffectual!)


Oli.

 

[Super_Marv]

Some interesting findings there - as I think I said previously, I've got OEM pagids fitted to the rear calipers on my car. They don't squeal either. Perhaps it's because the rears don't work as hard as the fronts, so don't get upto the kind of temperature where they'll start to squeal?

 

[scam75]

After yet more tinkering with brake pads we have more data to analyse! I found two of my old Textar front pads at Alasdair's so we swapped over the front driver side ones. These Textars are VERY loose as they had been modified previously to suit a heavily plate lifted caliper, probably 2 or 3 mm of freedom in them! No difference whatsoever, still great shrieking when pads heat up particularly when coming to a halt.

Got back home and had the brainwave of putting the new pagids back in front driver side along with the 2 good shims I had left. This time I still got the shrieking and also got the car pulling left under braking due to the shimless side braking stronger. Aargh for the umpteenth time!

Back home again, shims out the drivers side and then took out the front passenger side pagids and stuck in the used Textar's. Went out for a drive and wait for it, nothing, no noise at all, fast, slow, cold, hot, nothing at all. Music to my ears if that makes sense.

Got home and examined the removed pagids to find one of them very shiny down one edge (can't explain, got to be rubbing against something) and also a chunk about 1/4 the size of a 5p missing off the braking surface. A duff pad maybe?

Anyway, now got new pagids in 3 corners and old textars in the other. Won't celebrate prematurely. Taking car a long drive today/tomorrow. Will report back after then.

Fingers crossed![]

Stuart

 

[scam75]

OK, squeak returned today same as ever once a bit of heat in the pads.

New pads at the weekend then mental asylum if still squealing.[&:]

Seriously, wtf else can it be? There is nothing left!

Stuart

 

[zcacogp]

ORIGINAL: scam75
Seriously, wtf else can it be? There is nothing left!

That's a very good question. One to which I don't know the answer.

I'd suggest an eMail to Hartech (Barry Hart) - what he doesn't know about 944's isn't worth knowing. And he's friendly. And may well be happy to make some suggestions. I know he posts on here occasionally, but not that often; an eMail direct to him (via this site) could be a good idea. (You could just point him at this thread and ask him for his comments or thoughts.)


Oli.

 

[Hilux]

OK, squeak returned today same as ever once a bit of heat in the pads.

New pads at the weekend then mental asylum if still squealing.

Seriously, wtf else can it be? There is nothing left!

How old are the discs?

Basic check for runout is to hold a nail etc close to the disc and rotate it and see if it is warped.

Got back home and had the brainwave of putting the new pagids back in front driver side along with the 2 good shims I had left. This time I still got the shrieking and also got the car pulling left under braking due to the shimless side braking stronger. Aargh for the umpteenth time!

Back home again, shims out the drivers side and then took out the front passenger side pagids and stuck in the used Textar's. Went out for a drive and wait for it, nothing, no noise at all, fast, slow, cold, hot, nothing at all. Music to my ears if that makes sense.

Got home and examined the removed pagids to find one of them very shiny down one edge (can't explain, got to be rubbing against something) and also a chunk about 1/4 the size of a 5p missing off the braking surface. A duff pad maybe?

How did you bed in the new pads? There is a required technique namely 5 or 6 0-50mph emergency stops with a very brief interlude between each and then dont apply again but let cool down naturally - if still no good repeat - the pads should be smoking nicely (alarmingly) when you finally stop and on new discs the discs should have blued with the heat input.