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MG Midget and Sprite Technical - Piston diameter on Princess Calipers

Does anyone know the piston diameter used on the Austin Princess caliper that was such a popular upgrade a few years back for midgets? I'm looking at some Wilwood calipers but I'm really not sure about how compatable they would be with my master cylinder and there are several piston diameters to choose from in that style. I sent an enquiry to Wilwood a couple of days ago, but no response from them.
B Young

I bet deb evans would know, she is a big fan of the princes calipers
Prop

She might well do but she's in America so won't!
rachmacb

I can measure up a set when I get home, but that won't be for a while.

The Wilwood Billet Dynalite calipers that we use on the racer have 1.75" (44.5mm) bore pistons. The Princess calipers, IIRC, have 38mm bore pistons.

However, you can get the Wilwoods with 1.62" (41.1mm) and 1.38" (35.1mm) bore pistons.

We ran the Princess calipersr on a 0.75" bore Master Cylinder which gave a good, firm, pedal. With the big Wilwoods we are looking at using a 0.875" bore Master Cylinder to get the pedal firmness back.

I would warrant that the 41.1mm Wilwoods would work fine with a 0.75" bore Master Cylinder.


One point to be aware when using Wilwoods: the brake line inlets are 1/8-27 NPT, so you will need an adapter and this will need to be a right-angled type owing to the fact that the inlets are on the sides of the calipers and not the ends.
Deborah Evans

With the 35.1mm bore calipers you'd get away with a 0.7" M/C.
Deborah Evans

Thanks Deb, that helps a lot. I was thinking that the 35.1mm bores would be a bit small for my .75" master cylinder. That's the largest bore in the caliper I was looking at, the Powerlite, which looked the best as far as fit inside the 13" wheels with the stock disc. I can always drop down to a smaller bore master cylinder with the Powerlites, but I'd like to find something that would work with the .75 master as that would also work with the stock master cylinder as well. From what I read in the catalog the Dynalites are for a wider disc than the stock Midget disc, so those are out for now. Why can't someone make a new batch of Princess calipers in alloy for us?
B Young

Bill-
Can you tell me what is the point of all this fiddle-faddle while keeping the stock disc? It makes a little sense to use something like the Princess calipers as a bolt on, IF they are readily available.
But, seems to me the miserable toy disc is the limiting factor for decent brakes. There are plenty of cars with 13" wheels and real discs. Hardly like your car meets anybody's rules now!
Deb, what discs are you using?
I was working on a system, but life interfered and I haven't gotten back to it yet.

FRM
FR Millmore

FRM, I was hoping to find a caliper that would be a "bolt on" like the Princess unit was so that it would appeal to more Spridget owners who could start with the caliper and then upgrade to a larger disc later on by using a different mounting bracket and pads. I also didn't want to have to space out my steering arms like the well known "big brake" kit does as that does affect ackerman and bump steer a little bit. I realize that with the stock small discs the mechanical advantage is reduced from even a disc that a half inch larger diameter such as the Spitfire disc.
Just trying to get a little improvement in braking with the least amount of modification necessary.
Wish there was a new Princess caliper available, I'd go for that in a second and I think a lot of other guys would as well. A properly designed new caliper could actually be a bolt on with a modified dust shield for a Midget using the original brake line and all.
B Young

FRM - with the Princess calipers we were using modified Austin Allegro (just sub 9") discs.

The current set up with the Wilwoods is a (just sub) 10' vented disc - obviously that is overkill for a road car!

Another option is to use a 9" (Spitfire) disc with a set of Girling Type 14 calipers, or even a 9.5" (GT6) disc with a set of Girling Type 16 calipers.
Deborah Evans

This thread was discussed on 02/08/2011

MG Midget and Sprite Technical index

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