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MG Midget and Sprite Technical - AP Master Cylinder

Does anyone know the part number for the AP Brake master cylinder to fit a midget?
Peter King

You dont say what Mark your Midget is. Whether or not it's discs or drums at the front as there are two sizes of cylinder depending on the front brake configuration.

The original cylinder (Drum Brakes) was a 22.00 Bore GMC109 and the later (Disc Brakes) was only 19.00 Bore GMC112.

AP apparently don't currently do not have the Disc Brake GMC112 version in production but if
you need the other version GMC109 go to eBay and you
will find a GMC109 for sale at 86 by Vehicle. Brake. Spares who buy directly from them.

If you cannot find a stockist with what you require try a post on the MGA site as I believe they favour a supplier, of GMC112, for their cars.
Alan Anstead

apologies for thread hijack - Peter are you still looking for a n/s front wing?
David Smith

Or do you mean 1275 & 1500 single circuit, or dual circuit?
Dave O'Neill 2

It's a mk111 with discs
I'm running with a tandem but not good for competition.
Peter King

Hi Dave,

Yes still looking for N/S/F wing.
Peter King

Assuming you want a tandem cylinder:

If you want the manufacturer of the good MGA type MC (which is the GMC109, and has a 7/8" bore), it is Caparo. The AP ones din't have a good reputation (they often seem to have problems), but the Caparo ones are usually just great. I fitted one last year, and left it standing after fitting for a couple of weeks and it had bled itself - how about that for a stroke of luck!

The GMC112 has a 3/8" bore and doesn't work well in an MGA as the pedal travel is then longer to compensate for the smaller amount of fluid being moved (about 15% less). I guess if Caparo makes the GMC109 they probably make the GMC112 as well.

So you need to measure your bores first (if you have an old cylinder)

Do a search in the MGA BBS archives as the AP cylinders come up a lot, and over the years there has been a fair bit about the Caparo ones as well. Bob West (Mr. MGA) in Pontefract sells the Caparo one and is a really really nice guy to deal with too.

dominic clancy

Gentlemen, terminology, please!!!
GMC109 and 112 are dual cylinders.
The riders sit one behind the other on a tandem, not alongside. The tandem cylinder is used on late 1275 and 1500 cars to provide split circuits.
I think Peter wants a GMC113, or a GMC166 with a separate remote reservoir.
Peter you have email.
David Smith

My info about AP Caparo is for the tandem master cylinder. The Tandem refers to the dual master cylinder fitted to earlier cars. 7/8" dia for drum
and 3/4" for disc. Some catalogues show 0.70" for discs. The Brand is AP Caparo. My info above near the start of this thread is actually copied from a letter from them.
TRW are the brand causing problems with leakage and residual pressure.
If a Tandem cylinder is not suitable for competition then a Sebring pedal box and seperate cylinders is available from Archers Garage at Birmingham. That system was used on competition cars in period. It is, of course, possible to make a copy of the system yourself, as i have done a couple of times, if you have the necessary ability. It also allows use of Girling etc seperate cylinders for brake and clutch.
Another alternative is to have the original cylinder sleeved by a company such as Past Parts or a local engineer.
Alan Anstead

Alan I apologise as I did not make my post clear enough.
Peter has a Mk3 Midget. He neither wants nor needs a tandem, or indeed a dual master cylinder. He has the later pedal box, he wants a single master cylinder, part numbers per my previous post.
Yes I did see that Moss call the dual cylinder a tandem cylinder, we all know how grossly inaccurate they can be.
David Smith

Peter King

Thanks for all the info.

I don't want a Tandem as I've got one and it gives a long pedal no good for competition. GMC151 is the OE but I want to see if I can get an AP racing cylinder, if not then I will go for the GMC151.
Peter King

Hi Peter

If you want AP racing cylinders try Merlin Motorsport, Trident Racing Supplies or Raceparts.

Standard master cylinders try from Powertrack brakes.

M Wood

to research your requirement start here:
David Smith

This thread was discussed between 26/08/2014 and 27/08/2014

MG Midget and Sprite Technical index

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