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MG Midget and Sprite Technical - Brake Shudder - Metro Vented Discs

The Minor has Metro 4-pot calipers, with Metro 8.4" ventilated discs and Mintex 1155 pads. Before that it had Metro solid discs with 4-pot calipers and 1155 pads. It has a 2.2:1 boost servo - I know the comments, but jumping out of a 'modern', it's nice to not have to remember to eat my spinnach first!! The pedal has a good solid feel to it. Also the Minor is a bit heavier than a midget.

The brakes are excellent, no fade on tracks or coming down innumerable hairpins on this year's Euroclassic.

BUT there is a shudder on the initial bite (there was before we started on the Euro). Have just checked the discs and there is a total of 0.004" runout (i.e. +/- 0.002") and a disc thickness variation of 0.0015". Pads about half worn.

The runout seems fine, but would 1 1/2 thou thickness variation cause shudder? I can feel a slight uneveness on the brake pedal at low speeds, coming to a halt in traffic. The vented discs have never been as smooth braking as the solid ones.

I know MIntex 1155 are not officially 'road' pads, but I did get occasional fade with 1144's and the solid discs, so switched to 1155 with the solid discs, now 1155 and vented.

I like the idea of the Metro set-up as it as sort of period, but is it the time to change? (I need the brakes to fit inside steel 13" wheels).

Richard
Richard Wale

Richard. I'm also experiencing brake judder, but on the first application from stone cold it doesn't do it. It gets worse the hotter the brakes get and, like you, I get the pedal uneveness and jerky stopping at lights etc.
What I'm thinking in your case is that although the runout etc is acceptable when measured, it may be much bigger when the brakes are hot thereby giving you the judders. Brake judder is almost always down to a warped disc. The only other thing I can think of is a wheel bearing, but that would normally be noisy.
I eliminated the rears by applying the handbrake whilst in motion and I didn't get the low speed jerking, but I can't decide which front brake it is because I have braided hoses which can't be clamped off, not that it matters as I will obviously have to fit a pair of discs. I would just like to know which one it is.

Bernie.
b higginson

Sorry about your problems with everything Richard but just a quick one

What mods did you need to do to fit the vented disks to Midget/ Moggy hubs?
Robert (Bob) Midget Turbo

Bernie, I've just found some data on Metro discs, which is probably typical of discs this size? The maximum runout is 0.006", so mine are within that, but the maximum width variation is only 0.0005", so I am outside the tolerance.

Have just checked a new pair for thickness and they look fine - will change them and see if it makes any difference. Annoying as the discs are not even 50% worn yet.

Richard
Richard Wale

Richard
I would also be very interested as how you fitted Metro turbo vented discs to your hubs ? any pics etc.
Rob Newt

Sometimes if the car hasn't been used for a while you can get a little bit of corrosion where the pads were. Result: light judder due to the disc being a little bit thinner there.
Paul Walbran

Brake judder can also be caused by not bedding in the new disks/pads, resulting in uneven deposits on the disk surface. What you might feel is not a warped disk but uneven friction surfaces on the disk.. Please read this VERY interesting website:

http://www.ipdusa.com/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System/blog-102

I've solved numerous brake judder problems by following the instructions.
Willem vd Veer

Richard
I too have this set-up (on a midget) also with 1144 pads and I also do experience a little light juddering. I have always suspected the wheel bearing to be the culprit as by their very design they
will always have a little play in them.

But having read Carroll Smith's article (thanks Willem) it could well be some light surface deposits, as the car is only used occasionally.....I must pay attention next time I feel the judder, and try to notice if the judder dissapears with use or stays at the same level all day.

I also find it an excellent set up, so long as the rear brakes are at working really properly, otherwise the fronts will lock before the rears in the wet.
Ian

Ian Webb '73 GAN5

Ian what mods did you do to the vented disk to make it fit the Midget hub?
Robert (Bob) Midget Turbo

Willem. Thanks for pointing us to that very interesting article. It's made me promise myself to have a serious look at my discs to see if there are any uneven deposits, as they have only done 4000 miles and should not be warped.

Bernie.
b higginson

Looks like its TOP SECRET INFORMATION Bob !!!Lol
Rob Newt

I was thinking that last night, I think the purchase of a metro vented disk is in order. LOL.
Bob Turbo Midget England

<<Looks like its TOP SECRET INFORMATION>>

SSSSSSH!

Quick, here it comes whilst no-one is looking!

I have detailed drawings of the mods required to the Spridget steel wheel disc brake hubs to take the Metro vented disc.

It involves machining the hub to provide clearance for the standard Metro 4-pot vented caliper and machining the Metro disc so that it will bolt on to the hub, using the standard Spridget 4 hole fixing. This means that you can revert to standard Spridget disc at any time, if required.

If you email me at richardl dot wale at btinternet.com, I will send you copies of the drawings on the same basis as they were sent to me by the original author - for your own use only, not to be used commercially.

I also have details of mounting the caliper on to a drum braked car (the Minor never came with discs as standard!).

I don't know what is involved in mounting the Metro disc to the Spridget upright. The mounting hole centres are 3.5" against the Spridget's 3.25", so not a direct fit, but does Ian have the details?

Finally you will need to get a brake hose conversion to connect the dual line caliper to a single line feed. eBay have them, as do some of the Mini mods suppliers.

Richard

Richard Wale

Willem,

Yes I have the myth busting article - very interesting indeed!

Unfortunately I did bed the pads in using the Mintex reccommended process, and they seemed OK, but not totally 'smooth' with new pads on the new discs. I have re-bedded them twice since then using the same process, but it has not made any real difference.

Even after a track day session, when the brakes get nice and hot to burn off the pad residue, they are not judder-free.

The RH hub has a little bit of bearing play, so will replace the bearings and am going to fit a new set of discs.

Richard
Richard Wale

Hi Richard thanks the metro caliper is not a problem simply needs one mounting hole pluging (interference fit plug) and then redrilling for correct spacing, I thought.
However I was not sure of the mounting of the disk. Think by the sound of it I will simply obtain a disk and then I can see for myself and pop it into the public domain :).
Bob Turbo Midget England

Bob, sorry couldn't post earlier, been away a couple of days. I believe I used the same drawings as Richard which came from Mark in Leamington (sorry Mark cant remember your Surname) I dont have an electronic file just a paper one, which I would be happy to photocopy and send you if Mark is agreeable.
The conversion is not to difficult if you are or have somebody who is handy with a milling machine and a lathe. The calipers need the holes slotting (not enlarging) on a milling machine which if done correctly will be virtualy as robust as original intended. the discs need drilling and re tapping again should be done on a mill IMO.
Best to buy decent quality discs though. As Richard says the hub needs turning down slightly ....which is the only part of the conversion I dont like, as it makes the area of the mating face face between hub and wheel smaller, but then, in 5 years it hasnt caused me any problems.

I am currently looking for one Metro LH 4 pot caliper for NON vented discs if by chance anybody has one for sale; note a LH caliper on a metro is a RH on a midget & vice versa ....because on a metro it is fitted at the front of a hub but on a midget its fitted at the rear. This is a fun excercise to fit 4 pot caliper to the standard midget disc ..... should be a very cheap conversion for a car where the heavy breaking isnt used frequently.
Ian
Ian Webb '73 GAN5

The brake judder on my car appeared a while after getting the 9inch brake kit.
after 2 years fidling arround with it i bought new discs and pads.
After a while again the judder.
Then new wishbones, brake pads, discs and calipers and... after a short while again brake judder...

Then I replaced it with the 10inch brake kit from Frontline: vented discs and new calipers.
I thought vented discs are harder to be warped/bent as they are double discs put together but again, after a while brake judder. :(

I couldnt understand why, my mg garage at the time either and no one else I knew.

Untill Coen of the Classic Car Clinic pointed out to me its the stubaxles causing it: happens when they wear out.

And he was right, no brake brake judder at all anymore.

It was that easy/simple, while I was all the time completly focused on possible warped discs and that kinda stuff. :)
Arie de Best

Arie. That's another avenue for me to go down. As mentioned above I'm going to have a look for uneven deposits on my discs but I've not had chance yet. I really hope it's not the stub axles as they, like the disc were new in 2008 and have only done 4000 miles. I'll have to do it soon though before I splash out on new grooved discs and 1144 pads.

Bernie.
b higginson

Richard - Sent you an e-mail. Thanks
D Rock

Bernie, have you tried giving the stub axles a really good greasing, and then test the brakes? The grease might just fill up any wear in the stub axles long enough to clear the symptoms.
Tarquin

Ian,

Yes, I machined the first hub to the drawing dimensions and did not like the bearing area for the wheel at all - might be OK for alloys, but not for steel.

So have moved the caliper 1mm inwards and machined the hub to leave 141mm diameter for the wheel bearing face, instead of the 130mm on the drawing. Also reduced the amount removed from the hub flange to leave 9.00mm instead of 6.75mm.

They have done about 6,000 miles and about 10 track sessions (this year's Euroclassic had 5, including 3 of the Nurburging in a private session - superb!!).

For the disc machining you will need a lathe that can swing the 8.4" disc o/d (too big for a Myford!) and an operator who can bore the i/d to within +/- 0.002" and face the end off, whilst keeping the actual disc face running within a total runout of a maximum of 0.006" - aim for 0.002" TIR.

Drilling the 4 new 3/8" UNF tapped holes is very straightforward using the the hub as a jig - spot though 1 hole, drill and tap it, fit 1 bolt and then spot through the other 3, followed by the same drilling and tapping. I use a bench drill for drulling the holes, as these break through into a 1/2 hole, and with a hand drill this could end up with a broken drill and less than good tapped holes.

The hub machining is very simple as all that is being done is removing metal to provide clearance for the caliper - so no requirement for tight(ish) tolerances.

The first set-up I did with Metro calipers was using the Midget solid discs - much easier, and no machining of the hubs required, as there is plenty of room for the narrower caliper.

I have electronic copies of the drawings, but respecting Mark's request at the time, all I would ask for is the same assurance about commercial use that I was asked for and gave, before receiving the drawings.

Richard
Richard Wale

Tarquin, the greasing up the stubaxles might help but if realy worn it wont be of any use anymore.
Arie de Best

Hi Richard, Ian

No problems about sending the drgs. Just to let you know the modified hubs have been used on a few race cars over the years without any problems, but of course they have been using alloy wheels.

Ive now moved onto alloy wilwood callipers as they are lighter and not much different in price to the metro ones, just less work and no disks to modify!!

Interesting about the disks, on race cars different brands of disks wear very differently to others, some only last one season!!

Richard where are you in oxfordshire? As you can see ive moved a few miles closer!!



Cheers

Mark
Mark Turner

Hi Mark,
My hubs have actually been fine using steel wheels...I just keep a close eye on them.
What is the Wilwood part number ? I have seen them and as you say not much more money (IIRC I paid 119 for a pair of fully reconned calipers)

Bob, I have some drawings spare, now that Mark has given the OK I can send them to you if you want them.

Ian
Ian Webb '73 GAN5

Mark,

No so far away, in Islip, the one near Oxford! There is one near Northampton as well.

Bob,

I can email you electronic copies (pdf) if you would like them?

Richard
Richard Wale

Richard
I have emailed you for copies, perhaps I have wrong email? mine is rob at cornishconnectionpasty.co.uk
Thanks in advance.
Rob
Rob Newt

Rob,

On the way!

Richard
Richard Wale

This thread was discussed between 03/10/2010 and 11/10/2010

MG Midget and Sprite Technical index

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