MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Brake squeal

Hi everyone,

I'm getting bad front brake squeal on my factory V8. This is just after replacing the brake pads and pistons. The new pistons have cut outs on the rim of the piston that contacts the back of the pads which are presumably to prevent squeal. My question is what position should the cutout be in? On the leading edge (bottom) or the trailing edge (top) or should they be in one of the quarter positions. (top inner / top outer / bottom inner / bottom outer) My previous car came with some anti squeal shims which were flat sheet steel the same shape as the backing plate of the brake pad but with one quarter cut out. Unfortunately I can't remember what position they were installed.

Thanks in advance

Phil

Phil

Done the copper slip on back of pad trick yet?
Stuart Robson

Not yet, maybe I'll do that too while I'm resetting the piston positions. I want to set the pistons correctly so that i don't risk uneven pad wear and / or braking.

Phil
Phil

Did you have your rotors cut or replaced? Sometimes a rotor can cause the same problem.
Mike MaGee

Phil - If all else fails, try the "greenstuff" pads. I haven't had so much as a tiny squeak for the front brakes on our MGB since swiotching to them. Good luck - Dave
David DuBois

Hi, Phil - I suppose your True Problem is brake squeal, but your One True Question was how to orient the pistons so the recesses are pointing the right way. Many people won't search out the One True Question, but - at least - their hearts are in the right place. So, this is kind of like feng shui for disk brakes - - - listen, Grasshopper, and learn - - -

The relieved area should meet the leading edge; that is the rotor rotates into the recessed side of the caliper piston. Thus they should be mounted in the housing with the notch oriented toward the road.

Now, whether that will help your squeal, who knows. Best of luck - - Alec
Alec Darnall

Verbatim from the MGB manual "the cutout must be located at the inner edge of the calliper i.e. towards the hub. " To make this plain there is a sketch showing the cutout close to the lugs , and it's centre point equdistant from the mounting bolt holes.
I too have Greenstuff pads and no squeal. Noises audible by the great pedestrian unwashed are an under researched area, the rattle of a Ducati 996 dry plate clutch as the hoi polloi mill past the red traffic lights and redder fairing while you straddle the coolest bike in the universe is the other example that springs to mind.
S Best

Hi, Phil - bit of controversy here, and, to Mr. Best's credit, I did find a reference to "the cut-away facing inwards" in a Chilton Manual that covers the MGB. My prime reference, however, was the British Leyland Workshop Manual AKD4021 that covers the midget. As I'm sure you know, the brakes are almost a carbon-copy of the MGB's, and this publication specifically says to, "Check that the relieved face of each piston is correctly positioned downwards, and fit the friction pads into the calliper."

But, I was still nagged with "Why", so I did some research on the Internet. Here is my first find:

http://s2.pegasusautoracing.com/108.pdf

Look in the area marked Girling Caliper Repair Parts, and you’ll find the text, “Notch in piston face is to be positioned towards leading edge of pad. This reduces uneven pad wear.

OK, that matches what I believe, but some more confirmation would be nice. The next site (a Porsche one) was more clear:

http://vista.pca.org/sch/tech_articles/caliper_rebuild/caliper_rebuild.htm

- - Installation notes for brake caliper piston with notched face.
- - Some calipers utilize pistons with a notched or recessed surface that presses on the brake pad. The purpose of the notch is to attempt to even out the pressure applied to the pad, since the leading edge of the pad would otherwise do more work than the trailing edge. When installing these type of pistons, orient the notched portion such that it faces the leading edge of the pad. This would generally be facing upward if your caliper mounts on the leading side of the rotor, or facing downward if your caliper mounts on the trailing side of the rotor. To be more technically correct, there is a Porsche alignment tool to set the orientation, but the above guideline will get you pretty close.

Now we're talking - but does this notched piston have anything to do with brake squeal? This next site elaborates on that subject, and even shows the alignment tool, from the factory manual:

http://www.pelicanparts.com/techarticles/911_caliper_rebuild/911_caliper_rebuild.htm

I hope that answers the "Why", and I do apologize for not citing my sources beforehand. Best of luck - - Alec

Alec Darnall

Alec,

I too like to understand "why?" and salute your research.
2 things spring to mind, the disc surface rotates faster at the outer edge compared with the inner, which may demand more thought about "leading edge" effects.
Secondly, the Lockheed people probably knew their stuff so I took a look, scan from the 69 BMC manual here,
http://homepage.ntlworld.com/richard.maile/MGB/pistonorient.gif
This is for the 1800, I don't have the V8 version so don't know if it's different.

I fitted Greenstuff pads last time and have about 1000 miles on them. They are OK. Not amazing but better feel than the Lockheed ones that came off. Maybe I have weaker legs these days or the traffic is faster but they seem no better than 30 years ago. I suspect what may have happened is the loss of the (slight) asbestos content lead to harder pads and these new high tech ones have now caught up with original spec with regard to feel though I cannot test if they are genuinely better in respect of fade etc.

There's simply no room for anti-squeal shims with them so I made sure they were free in the caliper and smeared a little copper grease on the pads' backing edges and backs as usual and they don't squeal. Claims as to less dust seem exaggerated and the stuff ends up all down the sides of the white paintwork let alone the wire wheels. Next time I'll try the new Mintex material.

Rich.
Rich

To hazard a guess as to the reason for the cut-away portion perhaps it's to stop judder/squeal by reducing the amount of pressure applied to the slower moving inner surface.

Just as with shoe linings, it's also usful to chamfer the leading edges of the pads friction material to stop them grabbing and causing squeal. I've done this for years using a big bastard file ... cough.. splutter..watch the dust...


Rich

The Leyland Cars MGB Workshop manual AKD 3259 (15th edition) reads exactly as S Best quoted and the drawing is the same drawing referenced in Rich's post.

Clifton
Clifton Gordon

Looks like Porsche are 4 pots and may be used for gas build up rather than using unequal pots.

Research by Ford has indicated that unequal torque on fixing disc is usually the cause of shudder.

Squeal happens with New formula Greenstuff with or without shims copper Ali grease and stick on shims, but fades after extended use.

Paul
Paul

Hi, All - This subject just popped up on the S&M boards a few days ago, which made me *think* I knew the answer - now it seems there is no ONE answer <sigh>. That was for a Midget with the big surface upgrade: Spitfire rotors and MGB calipers, so would you orient them the way the Midget manual says, or the way the MGB manual says?

Rich, I believe your theory of the outer edges moving faster has merit. I wonder if this is why the Porsche solution has the notch canted 20 degrees? And, yes, I've always "broken" the sharp edges of disk pads, but I've used a bench grinder and held my breath. Those organic pads aren't supposed to be a health hazard, but they sure do stink!

Maybe, since you can get pistons either notched or flat, it really doesn't make that much difference? - - Alec
Alec Darnall

Thanks all,

I'll have a go at the pads over the weekend. Anyone else out there going to Beaulieu this weekend?

If you see someone walking round with a sign on their back saying "Wanted Elva or Willment cylinder head for Ford Sidevalve engine" that'll be me.

I think the porsche solution to cant the slot at 20 degrees is designed to set the slot radially to the disk which puts them on the slot on the leading edge side of the fence.

The way i look at it the leading edge argument makes more sense than the hub side. If squeal occurs when the front edge of the pad grips, tucks under, releases and then regrips at very high frequency then the idea of taking force away from the leading edge of the disk makes a lot of sense.

Phil
Phil

This thread was discussed between 10/05/2005 and 12/05/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.