Brake squeal without touching the pedal!!

[The AJP Griff]

I have a problem with the brakes on my griff,which otherwise work fine,ie they dont bind,pull to one side or anything like that,and they also stop the car effectively enough.
The problem i have is that the brakes squeal for some time after i've taken my foot off the pedal,even after a mile or two.The squeal can come and go,again,without touching the pedal,and on occasions it seems to come from different wheels.I'm afraid i'm struggling to tell if the noise is from front or rear,and suspect that its either.The rear calipers are new,and the fronts are rebuilt and all pads and even the discs are new.I'm thinking that theres little left but to replace the master cylinder,but could it also be down to the proportioning valve or the servo?

[HRG]

Copper grease on the back of the pads?

[PhillipM]

Do they have anti-rattle springs on the pads? They're either tired or not working very well if so.

If not, there's your problem

[GreenV8S]

If the noise changes/stops when you ease the handbrake on slightly, it's the rear brakes. If it makes no difference, it's probably the fronts.

[The AJP Griff]

Cheers chaps,some thought provoking replies thereI dont think there are anti rattle shims/springs fitted,so i'll see if you can get some for the fronts(Alcon 4 pots).Can you get them for the std ford rear calipers?I know that Joo put some copper grease on the rear of the front pads which seemed to make a difference for a short while,but now ive put more miles on and bedded them in fully theyre worse than ever.I know the rear pads are Mintex,which if i recall,do have a bit of a reputation for squeal?The front pads are Pagid road compound,and i know nothing about these.
What i still dont understand is why they start to squeal without touching the pedal?I could understand it if it happend on pressing the pedal,but cant understand how it happens for some time afterwards?

[The AJP Griff]

Went out for a run last night and discovered that the cause seems to be vibration.When at a certain rpm on part throttle the squeal is present,but you can drive out of it by increasing or de-creasing the revs.I could make it happen at will.I think i'd better check that everything is tight!

[PhillipM]

The pads are still touching the discs even after releasing the pedal, so they are vibrating with the discs when the discs rotational speed brings into resonance.

[The AJP Griff]

Thanks Phillip,how do i stop this happening?I'm guessing were back to coppaslip and shims?

Edited by The AJP Griff on Friday 22 August 18:54

[Uncle Fester]

Wheel bearings allowing the discs move and come into contact with the pads, even though you haven't touched the pedal?

Do you ever have symptoms of pad knock off?

[The AJP Griff]

Never get the symptoms of pad knock off,but i have just discovered what may turn out to be a small leak coming from the o/side caliper area,so perhaps that is related to my problems?I'll have to sort this first,then we'll see what happensCheers,Mike

[PhillipM]

May be, sometimes you'll get it regardless with some pad and disc combinations though, you can help damp it down sometimes by having grooves machined in the discs, or more succesfully by having 3 small semi-circular slots cut around the circumference with a key cutter - leaving about 3mm of the braking surface for continuity of course, which will break up the resonance wave in the disc.

These are last stop resorts of course, first stop is a complete disassembly and check of the existing setup for any play anywhere.

[The AJP Griff]

Cheers Phillip.I cured the slight weep from the one caliper,and took all the pads out and gave the backs a decent,but not too thick,coating of coppaslip.After doing this the squeal under vibration was still there initially,but after a few miles has now disappeared!I did notice some 'witness' marks on the top edge of the metal pad backing,so this might also have been something to do with the problem.Either way i'm happy now,although i would have liked to have identified the problems cause,more conclusively!