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MG MGB Technical - Screeching brakes

I had a problem before with the front brakes screeching after I had fitted a set of new pads. The calipers were not in the best condition so when replacing them I thought I would go all out and replace the discs and a different make of pads also. Initially the brakes worked well and quietly but after awhile the old screeching has come back again.. it only happens at low speed like pulling up at traffic lights etc. which can be quite embarrassing as heads turn at the noise. I have run out of ideas. Please help.
Trevor Harvey

Did you fit shims with the new pads?
They aren’t always supplied with new pads, but can make a difference if you do experience squealing brakes.

Simon
S Holt

On recommendation here I used the 3M stick on type (available on ebay). Doesn't look much, but cured the squealing.

https://www.ebay.co.uk/itm/274644968043?epid=1448148486&hash=item3ff21da26b:g:5vMAAOSwP41dRAZJ
Peter Allen

I fitted the 3m stick on ones previously before the latest rebuild and after a while the screeching came back. On inspection the pistons had cut through the stick on shims causing them to screech again.
Trevor Harvey

OK, Trevor, I've that issue then yet to come!

I've found regular metal shims haven't worked.

I wonder if some sort of thin hard, but flexible, plastic shim would work. Obviously, it's going to abrade as the pads move. Say, make them from the sort of plastic that oil cans are made of - this might be a bit too thick if the pads are new, but that sort of thing.
Peter Allen

Huge amount of info and many suggestions elsewhere. After working through several of them including the standard metal shims (not always provided with new pads), chamfered pads, copper grease and Bremtech self-adhesive pads (Mintex and EBC alternatives not tried) but it always came back. Along the way I realise that the pads were a bit of a sloppy fit 'rotationally' but had some offcuts from the Bremtech so stuck that down the edges of the metal backing and finally silence and has been for eight years so far. That soon gets deformed against the pistons and the caliper, but there seems to be enough left behind to damp the vibrations.
paulh4

I would second what Paul has done. After fitting new calipers and pads the screeching appeared and I never had this before with original components. Cut to size some 3M shim pieces and stuck them on the calipers where the pads slide. That was 4 years ago. No brake screeching since. I just think that it is a basic design going back decades and the pads are a loose fit.
Craig M Harvey

I have never had this problem. The car has EBC Greenstuff pads with some copper grease on the back. The braking performance is good with no fade on track time, bit of of a frying smell afterwards though :-), and no problem with road use when they are cold.
The trade off is sticky black dust on the wire wheels.
Stan Best

I have never seen metal shims for the standard calipers on a Mgb.
I have tried the 3M stick on ones that worked well for a short time until the pistons cut through them and the screech returned.
Paul, are you saying you fixed a small sliver of shim to both ends of the pad or to the calipers where the pad goes in. If this works do you think the screech is generated by metal to metal contact from these areas.
I never had any problems from original front brakes with screeching before I decided to update the pads, maybe the originals were a better fit.
Trevor Harvey

I thought the screech was from lack of contact, air vibrations/pressure, I thought the idea was to insulate from sound loss.

Thing is with new pads the screeching can take 1,000 miles or so to go away, that's if pads, shims, discs and installation was fine.

I've no idea for Trevor but for some MG owners 1,000 miles could be a very long time and this assumes normal road use braking.

A few decades back I had screeching front brakes on my B, it was very loud, annoying and embarrassing, I tried shims, grease and other stuff but nothing worked - until the noise just went away by itself, not to return, I was so relieved I didn't bother about why.
Nigel Atkins

Apologies, it is the V8 pads that have the shims, although I have read they can be fitted to 4-cylinder calipers to give a little more friction surface area. They are 'handed' in the V8, in that there is an inner and an outer in each caliper, denoted by the A and the B at the corners. Fine until you get three of one 'hand' and one of the other in a box - BT, DT!

The second image shows a rubberised 'gorilla snot' coating on the back of 4-cylinder pads - used showing the witness-mark of the piston.

Yes, the sliver of stick-on shim down the edge of the backing-pad to 'wedge' it into the caliper. I did wonder if it was too much clearance between the side of the pads and the jaws of the caliper as without that extra shim they rattle about, and it does seem to have worked with this set of pads and these calipers (replaced) at least.





paulh4

I have always thought that the screech is caused by a harmonic vibration set up in the disc itself. I didn't have any noise when I had Greenstuff pads, but since I fitted Mintex I get an apologetic squeek when lightly braking to a stop. It doesn't happen when braking normally at any normally speed. But then I don't have standard discs on my car. Mine are large ventilated discs from a Peugeot 504 I think.
Mike Howlett

Funny you should mention Peugeot. It has been said that circular shims with some Peugeot pads can be used in MGB pistons with good effect, similar to these used with the MG ZS 180 (one per caliper). I didn't change the pads on that enough times to test the theory in all four pistons!

At the end of the day the variety of calipers, discs and pads and their condition in use today quite likely gives a range of solutions, and each of us only needs the one that works for us.

paulh4

Paul, do you think the V8 shims would fit the 4 cylinder engine calipers or be made to fit it. I have tried copper slip, 3m pads etc. All worked for a short time but eventually the squeal came back, haven’t tried the slivers down the side yet but would like to do this and fitting metal shims at the same time.
Thanks all for your feed back. Trev
Trevor Harvey

I haven't tried it, Trevor, and wouldn't like to guess.
paulh4

Was informed today by a neighbour that cutting a slot about half way through the pad with a hacksaw would cure the screech. He was an engineer before retiring so it’s a possibility. Have noticed on the pads of several modern vehicles that they have slots in them so it might work. Any thoughts?
Trevor Harvey

Were the brake pads you're proposing to saw made, and with the same materials, as when your neighbour was working as an engineer?

My personal experience is that engineers can make very poor mechanics.
Nigel Atkins

ETA: How Brake Pads are Made - https://www.youtube.com/watch?v=H1WXlHONorw

See particularly from 12:43

Nigel Atkins

And at 18:38
Nigel Atkins

From a local company, see at 6:11 "slots for improved heat expansion performance, shims for reduced brake noise". (2008 video) - https://www.youtube.com/watch?v=e0GbTN0wVYU
Nigel Atkins

Nigel, this neighbour of mine was a mechanic engineer, looked at the video and noticed that almost all of the pads had a slot down the middle, there are no metal shims made for the 4 pt MGB, I have tried the 3M stick on pads, the calipers piston cut through them and the squeel came back, I have used copperslip, made no difference. Everything has been replaced discs, pads ,calipers,pins, springs. The pads are made by Delphi who I believe bought out Lockheed, they have a pad material attached to the back and the pistons have not cut through them, they look good quality. So as you can see I am running out of ideas as where to go next.
Trevor Harvey

Did you look at the Chris Fix and EBC videos and my comments?
Nigel Atkins

Slotting could be as much about getting rid of gases with non-drilled discs as being an anti-squeal measure.

The attached are the latest V8 discs I bought with a pronounced chamfer, said to be for anti-squeal, but didn't work.

"running out of ideas as where to go next." Slivers of stick-on down the edges?

paulh4

Can only get one sliver down, with them on both edges the pad will not go in properly. Have cut a groove in the pad, only time will tell if it will work.
Trevor Harvey

If one sliver takes up the play that might be enough. Might be better on the edge that rotation of the disc pushes against the caliper though!
paulh4

Paul,
see my post of 02 October 2021 at 15:15:40 for the slotting.
Nigel Atkins

Tevor,
if you've sawn your pads now fair enough, that would concern me but I'm not a mechanic engineer, perhaps the slotting as well as possibly improving heat expansion performance will also help with reducing noise. Tome most of the noise reduction seems to be about what's behind the pads.

If the slotting is OK and the shimming stops the noise you've achieved what you were after, I hope it does, good luck to you.

Meant to say Delphi's part of ... and I can't remember, - just dropped into brain as I typed that - BorgWarner.

Nigel Atkins

This thread was discussed between 23/09/2021 and 03/10/2021

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