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MG Midget and Sprite Technical - Disc brake rear

Hello all, and happy 2014.

Could some one please point me in the right direction to find information - instruction and pictures (for dummies) about converting a drum brake rear end to a disc brake one. I am working on a Mark III Austin Healey Sprite/Mark II MG Miget. Ideally I am not looking to buy a kit, rather source suitable (and recommended) parts from a wrecking yard and manufacturing any necessary brackets.

Any help or assistance would be greatly appreciated.

With thanks
Jeff.
Jeff Moore

here is a kit

http://www.ebay.co.uk/itm/AH-SPRITE-MG-midget-REAR-DISC-BRAKE-CONVERSION-KIT-NEW-/300787525295#ht_4759wt_758

and

http://www.frontlinedevelopments.com/products/midget/reardiscbrakekit.shtml
mark 1500 nearly on the road

As far as I know, there are no diy parts out of a salvage yard to convert to rear disk brakes

But... a possibility might be a 1st generation mazda RX 7 GLS (1981?)

They had 13 inch wheels but the PCD was differant so that would have to be delt with...but my 13 inch wheels incased the brake system fine

Just a matter of welding the caliper to the axle.. then modding the brake disk will fit the midget hub.

The good news is the caliper does both braking and parking E. brake

To add to your confusion... the mazda axle assembly above can be cut down and becomes a good fit in place of the old midget ....it has lots of aftermarket gear ratios, LSD, rated to 300 hp, only slightly more weight then the midget, and looks almost exactly like the midget

So for a few extra dollars, you get alot more bang for the buck

At least thats my plan

Prop
Prop and the Blackhole Midget

If you want to do it yourself, here's what we are doing to our current Midget project using MGF rear calipers. These particular pics happen to be of my MGB, but the set-up is almost identical on the Midget version. http://www.mgparts.co.nz/about-us/our-cars/joseph-s-rear-disc-brake-conversion/
Note that we are running 14" wheels, so for 13" a smaller disc will be necessary.

The Brembo site has full specs of all the discs they do, so once you work out the offset you need all it takes is a bit of time plugging them in to their search routine. As you are unlikely to find one which is exactly the dimensions you identify you will need a workable range of each dimension to successively try. It can end up with quite a few combinations but keep plugging away and you should find something to do the job.
Paul Walbran

Hey paul

Very cool... just a simple question considering you have done all the hard work. Would it be possiable to just chuck the disk into a lathe and turn down the disk.by an inch to.fitninside.the a 13 inch wheel.

Sure seems like that would be a fast and easy way to get to the same place your at without reinventing the wheel (or brake disk) once agian

Prop
Prop and the Blackhole Midget

On the disc that I used for the B it would be too narrow for the pads if 1/2" was taken off all round. Also, the offset from the end of the axle housing to the hub face is a bit less on the Midget. Discs (and Brembo no's) on my short list were
Toyota MR2 86-89 08.A140.10
Ford Focus 08.4931.24
Peugot/Citroen 08.2938.24
Fiat 08.9460.10
As well as the MGF rear disc.
All these discs had a smaller centre than the Volvo one so could probably be reduced down to the approx 240mm diameter size which would fit insode the 13" wheel and still retain good pad coverage.
Paul Walbran

Gee paul

Arent you the poster child for a real kill joy this morning....hahaha

Back to the drawing boards

Thanks

Prop
Prop and the Blackhole Midget

See bias bar pedalbox thread on K series Midget for a disc which has been used with these calipers.
Paul Walbran

Paul, very interested in your conversion as I have an MGF sitting on the driveway going scrap.

How did you mount the caliper? Is it a custom bracket and do you have dimensions?
R McGeown

We made the bracket up out of 10mm alloy plate.
In the centre there is a recess which repicates the oil catcher of the original drum brake backplate. (see photo of unfinished bracket)
Large ID of recess = 68mm. This locates on the ridge on the axle housing flange.
Small ID (of oil retention lip) = 56.7mm. This has to be as small as possible but just big enough to allow the slinger on the hob to fit through it.
Depth of recess 8.5mm, leaves 1.5mm thickness for the lip.
Basic OD of plate = 145mm.
Mounting holes for caliper (yet to be bored in the example attached) are 84mm apart and the distance from the centre needs to be worked out according to the OD of the disc used. Calculate as:

(Disc radius less 0.5mm) - (distance from pad extremity to the line between the mounting holes).
The 0.5mm places the pads just inside the outer edge of the disc.

Paul Walbran

Hi Jeff,

Late last year I did the same conversion have looked at Paul Walbrans site. The discs you can use are from a VW, Brembo no. 08.4177.10 . I made my discs mounting plate from a 8mm stainless plate with a packer on the front to bring the calliper in line with the disc.

Phil Lawson

You need to rotate the calliper about 10 to 15 degrees so the hand brake linkage is in the right plane. If you need any more info drop me a line.

Phil

Phil Lawson

I meant to add:

Rotate the bracket round the axle to optimise clearance bewteen cliper body and car body. This will be with the caliper only just clear of the spring - which is slightly below horizontal. To gain more clearance, cut off the big mounting lug which secured the MGF outer handbrake cable. It's not needed for the B/Midget as the rods/cable pull directly on the caliper lever.
Paul Walbran

This thread was discussed between 03/01/2014 and 08/01/2014

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