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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 Midget and Sprite Technical - Drilled discs

Why does putting holes in brake discs make them work better?
Guy Weller

the gases escape and it helps keep the rotor cooler
Props Black Hole

Plus they look cool & Prop doesn't have them.


Brad (Sprite IV 1380)

but if used hard they are *very* prone to cracking and breaking up around the holes, race cars don't have them
David (davidDOTsmithAT stonesDOTcom)

On this rare occassion I agree with the obervaions of David. :-)
Robert (Bob) Midget Turbo

So why do the holes make them work better? I am not planning on fitting any, just wondered why they do that?

Guy
Guy Weller

Perhaps the same reason why condensors appear to repair all ignition related problems. :-)

And I almost forgot and vizarding your SU adds about 300 BHP.....
Robert (Bob) Midget Turbo

drilled discs tend to crack more when a normal disc is drilled
when the holes are cast in the disc they do not

i prefer dimpled and groved witch have the added bonus that if the diples and grooves start to disapear they indicate de disc is worn and should be replaced
Onno Könemann

Onno is right about discs cast with holes being tougher than drilled discs. As for dimples and grooves, don't they become clogged with brake dust and so don't work any more? Stick with plain discs is my advice.

Guy, the discs with holes or grooves are supposed to be more resistant to fade under extreme use. The theory is that the hot brake material gives off gas which on a plain disc MIGHT come between the pad and the disc. In normal and even quite heavy road use this is not going to happen. Generally even if you have to make an emergency stop, you only do it once so fade is not a problem. If you made emergency stops repeatedly from high speed like a formula one car, then the brake performance would fall off and a disc with holes MIGHT just delay that happening. In my opinion its just a way of extracting more money out of the unsuspecting buyer.
Mike Howlett

Thanks Mike,
It was purely out of interest. I have no intention of fitting drilled discs. Just wondered what the theory was behind the claims.

Guy
Guy Weller

I always thought the drilling of discs helped the cooling because it increased the surface area of the metal to AIR and so aided the cooling/heat transfer.
Also, I am not a metalurgist but have been involved in investigation of crack failures in metals components, and the cracking from the drilled holes will generally be caused by poor deburring of the holes after drilling (milling would be preferred) Most cracking can be eliminated if you dont provide a stress riser, all well explained in Caroll Shelby's Engineer to win, an excellent book for us laymen.
Surface finish is one of the holy grails where highly stressed metal components are concerned.
Ian
Ian Webb '73 GAN5

Mike,
totally agree, but for an extra £20 boy do they look good through the minilites, also Prop hasn't got them,so thats worth the extra.
Brad (Sprite IV 1380)

>>> also Prop hasn't got them,so thats worth the extra. <<<

Give him time...

-:G:-
Gryf Ketcherside

can somebody explain why what they look like matters? who spends time looking at brake discs anyway?
David (davidDOTsmithAT stonesDOTcom)

Brad

your correct, I dont have the ones for the midget ...I got spitfie from triumph (yeah Im a sell out) I just dont have them installed yet

Prop
Props Black Hole

Are drilled or slotted discs worth the effort?

Well you pays yer money and you takes yer choice.

Suffice to say we have solid discs on the racer and we have absolutely NO brake issues. In fact, if anything we are over-braked.

First time I raced the Midget at Snetterton I was hooning along the Revett Straight at around 130mph, got to what I thought was the normal braking point, braked and WTF????? Had to accelerate to the apex!

Drilled/Grooved discs are a waste of time, effort and ££££££ IMHO.
Deborah Evans

Deborah
Was that with a std set up or a big brake kit
And what pads do you use.

Got my groved and dipled set with the car (thanks po)and it looks nice but indeed that is it it does not brake anny better than std
Onno Könemann

A grooved / drilled disc won't increase braking effort at low-med temps (relative to the pad spec). But once the pad is hot and starts to emit gas, then (so goes the theory) without vents the trapped gas reduces the contact between pad and disc and so brake effectiveness. It makes some kind of sense and I have drilled (FL) discs on BRB.

I'd be interested to know what the majority of racers use (of course, racers will have high temp pads in the first place, so will suffer less in the 'trapped gas' dept).

For those of us that use their cars on the road, we need a pad that works OK at low temps and yet will withstand the kind of heat that can be generated from enthusiastic track days (with 140+ bhp and full weight too).

So maybe vented discs are primarly for road / track-days cars?

A
Anthony Cutler

As far as brake disc cooling goes, all manufacturers now use the twin disc with a gap between them - look through the wheels of your modern car. That's what I have fitted on my MGB.

Deborah, I would be interested to hear your views on what are good brake pads for road use. I have Greenstuff, but they don't seem to have a lot of bite, and they make loads of dust.
Mike Howlett

BIN the bloody Greenstuff.....!

Mintex 1144 for spirited road use and 1155 for racing. That is with std discs and rear drum set up and as Deborah says, hit them hard and you slow down far too quickly....

No servo, No drillings or grooves, No tricks, NO BULL...!

Mark.
M T Boldry

I use bog standard brakes with Greenstuff pads on my race Midget and have had no issues with braking. If you want to improve your brakes fit stickier tyres.
Mike Allen

I use EBC Greenstuff pads on an otherwise standard front brake system on my 72 and have no complaints. My understanding was that the early ones had major dusting problems, but that the composition has been changed since then. I have no complaints about braking or dust with mine.
David "not my thumb" Lieb
David Lieb

Having raised the question of how drilling works; I use standard discs, no servo and Greenstuff pads. They work really well. Prior to switching to Greenstuff pads the brakes were very good but did tend to fade a bit with spirited driving down some of the Lake District passes. Greenstuff don't seem to actually brake any better, but don't fade as much. I am very happy with the braking and as it is it will outbrake most modern cars as they are so much heavier. It is all down to proper adjustment, particularly at the rear.

Guy
Guy Weller

dimpled an groved discs with greenstuff here no servo and old combined MC

servo : don't need it don't want it!

dimpels an groves : never felt anny advantage next season they need to be changed and plain are going back

Greenstuff : i need mor bite from cold but like them when hot and like the wear (only need to change onece a year)

how is mintex 1144 from cold and do they wear fast?
Onno Könemann

Guy
Mintex 1144 very good from cold as Mark says, I run the metro vented discs on mine and so they are probaly extra cool in normal use, and the 1144's always have plenty of bite.
I agree with you rear adjustment is important, I think for a good balance, I get annoyed when I see it said " oh the rear brakes do nothing anyway" they are very important for the overall brake performance.
Ian
Ian Webb '73 GAN5

Mike,

WRT your MGB, personally I wouldnt touch Greenstuff pads with a bargepole! While they are good at not producing dust, as you say they lack feel and bite (apparently EBC changed the compound a couple of years back so they are supposed to be better than the original Greenstuff). Furthermore they are not very fade resistant and glaze very easily. On my mgtf I was running SBS carbon-ceramic front pads with Greenstuff rears (the Greenstuffs were fitted by the PO) and found after a Track Day at Silverstone that I had cooked the rear pads so badly that their surfaces had cracked. I now use Mintex 1177 on the rear.

For fast-road work a pad with good initial bite is the Mintex 1144, which is available for the MGB calliper. Other options would be the Hawk HP Plus or HPS or the Ferrodo DS3000, which I know are available for the MGB calliper. Another option is the highly rated Pagid RS4-2 (known as the Pagid Blue) although whether these are available for your callipers I cant say.
Deborah Evans

On the Racer we use modified Austin Allegro discs at the front (the bell of the disc is modified to take the Midget hub and the disc is machined down from the stock 246mm to, IIRC, around 9”) with Austin Princess 4-pot callipers running Mintex 1177 compound race pads. The Princess callipers are a direct bolt-on replacement for the standard Midget Lockheed calliper.

At the rear we use Wolseley 1500 drums with twin leading shoes. Being a Class B car we are required to use drums.

This is then set up with carefully selected M/C sizes for front and rear as well as a brake balance bar (Tilton pedal box).

AFAIK not one single Class B car uses drilled or slotted discs. Most are using the 9” Spitfire disc that Peter May sells with a variety of callipers – Wilwood, AP or even Girling Type 16. Some cars are using a modified Metro Turbo set up with vented discs and some are using (I believe) GT6 or even MGB discs).


The reason we went with this set up is because it was available to us ‘off the shelf’ as a direct bolt-on replacement. However, while we have no braking issues (and indeed in some respects we could be said to be over-braked) the Princess arrangement IS heavy and contributes massively to the unsprung weight at the front of the car.

Accordingly I am developing a system similar to that on the front of my Ginetta G15 Racer using Ford Capri 2.8i 245mm vented discs (ie a shade under 10”) along with Wilwood Dynalite alloy 4-pot callipers running either Wilwood Poly-A or Mintex 1177 race pads.

This should give excellent braking with a much-improved reduction in unsprung weight. However I am going further in using alloy front hubs (as with the Ginetta) and have recently machined these up out of billet aluminium alloy (shown alongside a stock iron hub):

Obviously I have yet to drill them for the wheel studs and disc mountings and I need to machine up a spacer to go between the disc and hub as well as a plate to mount the callipers onto the front upright. Although this is well in hand and I have all the relevant measurements, I just have been too busy at work to get down to the machine shop and get on the mill.



Deborah Evans

More:


Deborah Evans

Lastly:


Deborah Evans

Ian
You are right!
the rears are verry important!

they don't help the braking but properly adjusted they make the pedal feal so nice and make the fronts work so good ;P
Onno Könemann

"hey don't help the braking but properly adjusted they make the pedal feel so nice"

Onno,

Set the rears up right and the braking is waaaaaay improved!
Deborah Evans

I just got my MGB calipers ordered for the big brake kit....Powdercoated in stop sign red color, Nice! Im going to use Ceramic pads (no dust, and super cool aka. little to no break in issues) but with the MGBGT V-8 pads, 20% more braking surface area...and no mod work to fit the bigger pads.

I got the drilled and slotted spitfire rotor, not that much more expensive, but adds greatly to the cool factor.


Now all I lack is the Barry king wishbone pans and my front brake and suspension modifcation set up is complete...other then getting the FL kit re-powder coated in bright warning yellow color.

Prop


Props Black Hole

Sorry I forgot to add,

I also am going to upgrade the wheel studs to 7/16" from 3/8" and have the hubs re-drilled to 110mm PCD being that my wheels are slotted from 4x4 to 4x110 PCD

Prop
Props Black Hole

Prop,
Are you getting the Barry King wishbones? Aren't those the ones with some negative camber built in? You do realize that your Frontline upper arms ALSO have been designed to add negative camber, right? I fear that both together could be a bad thing for you.
David "cautious soul" Lieb
David Lieb

Prop, the Barry King wishbones are not generaly negative camber, black ones are std camber.
There was a small batch of NOS wishbones which were neg camber, these are in blue hammerite, and do not have the improved lubrication or the additional strengthening plate (because they were made years ago by Barry's father)
Ian
Ian Webb '73 GAN5

Now i'm curious about the rears

i do adjust the rears properly but the only thing it seems to change is the position of the pedal (higher if properly adjusted)
The car feels a little bit more stable but that is it.

When considering where all the weight is in a midget and that under braking the weight shifts forward.
I just don't see how the benifit can be made with the rears

please enlighten me
Onno Könemann

Onno
You answered the question youself:

"The car feels a little bit more stable but that is it"

That really is it, the car is more stable/balanced front to rear, it really only makes a difference when or if you use the brakes hard.

If some people think rear brakes are not important, clamp them off or disconnect them and try that.......not on the public road of course !!
Ian
Ian Webb '73 GAN5

This thread was discussed between 22/08/2009 and 24/08/2009

MG Midget and Sprite Technical index

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