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MG Midget and Sprite Technical - Calipers from other manufacturers that fit Midgets

Any knowledge of calipers from other manufacturers that might fit midgets?

In particular, the Ford M16 caliper fitted to Escorts, Cortinas, Capris and early Sierras.

My reasoning is this. MGB calipers fit Midgets. Princess and SD1 and some Land Rover fit MGBs. So Princess calipers fit Midgets. And Princess calipers fit Escorts, Cortinas etc. as do SD1 calipers. Escorts etc. normally use the Ford M16 caliper .... so the M16 caliper fits Midgets? It even has the same diameter piston as the MGB (though not identical). Infact the M in M16 means "Metric" and was a metric equivalent to the P16 caliper used by Triumph on some of their cars.

They all have one thing in common in that the mounting lugs are spaced 82.55mm apart (3 1/4 inches in old money).

But what are the other dimensions of the M16 caliper? How do they differ from the MGB caliper.

Is there a reference anywhere on the www that contains engineering drawings of the different calipers from different manufacturers?

Rob
Rob aka MG Moneypit

Rally design and hi spec callipers have drawings on their sites.
Rob Armstrong

Hi Rob, yes seen those and Wilwood also has drawings.

I'm more interested in information about 'normal' calipers from the likes of Girling and Lockheed. They must have had technical publications of their calipers or car manufactures wouldn't know where to put the caliper mount lugs when they design a new car.

I've looked on the www but so far not found anything but details of alloy after market types.

Rob
Rob aka MG Moneypit

Rob,

There are at least 5 basic dimensions that control the fitment of a caliper:

Mounting bolt centres - Midget = 3.25" + what others
Mounting bolt diameter - Midget = 3/8", others??
Disc offset
Caliper pad radial distance from stub axle centreline - varies with disc diameter and other variables
Disc thickness

The 3.25" hole centres is only one of them, and the other dimensions are not easy to find, if available at all.

Sorry not to be more helpful, but it may help to explain the lack of readily available data to enable identification of potential alternative calipers for the Midget.

I think it's more down to what people have tried in the past, than being able to work it out from base dimensions.

Richard
Richard Wale

Richard. Yes it's proving very difficult to find the sort of information I'm after. I can find a lot of information about Girling and Lockheed hydraulic devices including line drawings but nothing that shows dimensions. I may have to resort to lurking on eBay and buying used examples to measure.

Rob
MG Moneypit

Rob, why not just buy the most likely ones from an online company like eurocarparts and take the measurements you want. Then if it is wrong you just return it for a full refund.

Bought online, they have to refund you in full without you having to give a reason. Even for online sales done as a click and collect so there needn't be any delivery costs for sale or for return.
Guy W

Why do you want to use anything other than the MGB caliper?
Daniel Stapleton

You don't really gain anything from using an MGB caliper other than it uses bigger pads, which add nothing to stopping power, and bigger pistons, which adds 13% more clamping force at the expense of slightly longer pedal travel.

I suspect the centre of pressure of the MGB caliper/pads is exactly the same distance from the disc centre as Midget calipers/pads, but that is one of the things I could determine if I could find the right information.

In the end stopping a car is down to tyres, reliably stopping a car is down to pads/discs and tyres.

And the subject is very interesting.

Rob
MG Moneypit

I found that the braking torque of the MGB caliper and V8 pad was considerably greater than that of the Sprite/Midget caliper. I'm also always interested on an ongoing basis of everyone's brake torque figures which are mandatorily produced at the annual MOT test.

My memory on converting to the MGB caliper is that pedal travel did not increase but rather it was shorter and harder - in any event something addressed by a change in master cylinder size as required.

An upgrade to the MGB caliper (and Spitfire disc) was using Hawk friction material which has impressive initial grab and bite such that a shorter stopping distance is produced but produces no noticeable difference in braking torque (but the MOT tester noticed the initial grab and bite - assumedly by how fast the needle moved on the measuring equipment to other vehicles tested).

The key factor in stopping a car is more than just what you've stated and at first principle is down to the ratio of braking torque to vehicle weight. For any given caliper, pad and disc the less the car weighs the greater the braking performance in all respects will be.

If you mean repeatable braking peformance rather than reliable braking performance that's really down to the disc and caliper being able to run with a consistent temperature range without overheating the fluid or friction material.

Braking performance and stopping performance are not the same thing as stopping performance is not just down to tyres but the grip they can generate which will vary according to the road surface and condition as well as the tyre itself. At speeds above, for example 60 mph, the grip will also vary with the amount of front end lift of the car (a spoiler will reduce lift). Not least poorly performing dampers also increase stopping distances though my testing experience with dampers wasn't in a Sprite.

The real downside to the MGB caliper is it's weight, with even Ti pistons (asuming they are available or could be made) unlikely to make a massive difference - with the detriment to handling - unsprung weight.
Daniel Stapleton

Interesting comments about the MGB calipers reducing pedal travel. Was that compared to standard Sprite brakes or other calipers (eg Princess)?

From a piston size point of view the MGB has a 54mm piston compared with the Midgets 50.8mm (2 inch). This gives the MGB as having 13% extra area which if retaining the standard Midget master cylinder should give a longer pedal movement.
This extra piston area should raise the brake torque, is this where some of your extra braking torque came from? (the rest from pad material?)

Yes, I meant repeatable rather than reliable and appreciate in simplistic terms the relationship between discs, pads, fluids and temperature, but when dynamics enter the equation things tend to get complicated in a way that doesn't (to me) always seem intuitive.

What about alloy calipers rather than cast iron? Hispec offer them with 3 1/4 inch lug mount as copies of the Princess caliper. They also offer a 4 pot version for replacing Ford M16 calipers with the same 3 1/4 inch lug mount spacing, which brings me back to the start of this thread.

Wilwood are popular but I couldn't find any with 3 1/4 inch lug mount. They seem to do 3.5 inch lug mount or radial mount.

How much heavier is the Spitfire disc compared to a Midget disc? and along with MGB calipers is there an appreciable increase in unsprung weight?

Rob
MG Moneypit

I havd the mgb calipers with ceramic mgbV8 pads (about 2x) the size of midget pads and rhe rotors are drilled vented and my master cly is a tilton set up

Ive got a fl suspension with barry kign wishbones on red poly with a 3/4 inch roll bar and angular 30 degree bearings

The only thing left is aluminum hubs

But someday ill bolt the whole thing up it should be amazing

My mgb calipers are completely rebuilt with stianless steel piston and the calipers are powder coated

Prop



1 Paper

JLH Aluminium hubs, alloy 4 pot calipers and carrier, and a massive vented 260mm disc. 2kg lighter per side than standard, immense stopping power. Uses the same master cylinder. Yes it's more expensive than an MGB caliper, but it's lighter, has more pad area, twice the pistons and no fade at all. No need to mess about spacing the steering arms out and it takes proper taper roller bearings.

I completely forgot to ask my MOT man for brake readings off them. But they can lock up warmed up 185 track tyres with a decent shove on the pedal.

Rob Armstrong

Good for you Prop, now run along and let the grown ups continue their conversation.

As for the brake discussion

Imo tyre grip is most important. With all tyre's I've used (165wide and considered sticky) I can lock up the fronts with standard calipers and mintex 1155 pads on a dry road.
With regular brake fluid flushes I've never had any fading problems.

So the only real reason for a caliper change would be a weight reduction. The MGB conversion certainly does not give that with a heavier rotor and caliper.

So to make use of more braking torque,which can not be consistently measured at an mot given the difference in exerted pedal pressure (the human factor) you need a lot wider wheels and tyres (weight penalty) of a compound like a Yoko A048 (don't get caught in the rain)

Maybe pad life should be taken in to the equation.
As mine don't realy tend to last more than 7000miles
O K

weight reduction is a bonus, but also fade. Those vented monsters won't fade, ever. My standard discs with green stuff pads I could fade on the road, which is about 30% of the abuse my brakes get on track.

But then, I'm quite heavy. And mad.
Rob Armstrong

ooh, I'll add, I agree with the tyres thing. No point having monster stoppers on 5.20 crossplies.

My MOT chap presses till the wheels lock up - do they all do that?
Rob Armstrong

Here in Holland they do.
But you can not expect the MOT guy to exert the exact same amount of pedal pressure each time.

Green stuff can indeed fade never had that problem on the 1155's.
Perhaps the mintex pad absorb more heat in the pad material instead of boiling the fluid?
O K

Not quite on topic, but for years (pretty much since computerisation)my MOT man has taken my Midget out for a road test to do the brakes (My Mini too)with one of the old gimballed gizmos. Something to do with my cars not being on the system for do it on the rolling brake tester ???
I thought it must be the case for all Midgets but it seems not ??? Does he just want to drive my cars I wonder !!
G Hawkins

Yes I remember those. The first Midget I owned (a 1965 C reg in Red) got tested with one of those. The MOT man remarked the brakes were good because the brake tester shot off the passenger seat into the footwell.

Before MOT exemption our Frog was never on the database so the MOT man always asked me how heavy the Frog was so he could put it on the brake tester. I suspect your MOT man just wants a spin in yours.

Rob
MG Moneypit

Hi Onno,

On 175/70 tyres standard calipers and discs but with Mintex 171 friction material I could fade the brakes. I told Mintex this and they told me it was impossible to fade 171 with road use.... A decent ring road system with dual carriage and regular roundabouts with speeds varying from 100/110 and down to 50/40/ zero would start to get the job done (Bracknell as I recall).

It's not locking up/nearly locking up the wheels at 100+ that reveals the limitations of the brakes but when you do it in reasonably quick succession (the Bracknell ring road) that reveals a better braking combination would be better.

The MOT brake tester, as far as I know does produce the same braking torque measurement because it measure the amount of braking torque generated against the rollers. So a full 'input from the right foot' pressure will get the same figures. The only variable is the temperature difference in the brakes and tyres between each test.

The faster the car is going/the more it weighs - the greater the amount of braking torque that is developed. At a speed of 115+ in the 3rd lane when a car moves from the middle lane to overtake a car doing about 60 but is only doing about 65 itself I suspect the difference between MGB caliper/Spit disc and standard brakes is a collision or brown stains in the trousers.

Hi Rob,

In relation to standard brakes (albeit like for like braided steel brake hose). The extra braking torque is not from the friction material.

I won't pass a public opinion on some aftermarket calipers because I'm obligated not to while with others I have no experience or informed engineering data from braking professionals.

I haven't got any weights of spit disc+ adaptor + king pin spacer + caliper and pads - its a penalty I'm prepared to live with. With unsprung weight it's not just the weight itself but the ratio of unsprung to sprung. So the lighter the rest of the car gets the worse the ratio of unsprung to sprung gets.
Daniel Stapleton

Tapley meter....
David Smith

Daniel, you appear to be in a hurry a lot given your stated road speeds !
Might I ask what HP your car is producing ? and if you have considered a parachute as a back up ?
P Bentley

BHP is over a 100 and the car is more aerodynamic than your average Sprite.

Daniel Stapleton

Daniel, that even looks quick !
lots of neg camber too.
P Bentley

This thread was discussed between 30/12/2016 and 06/01/2017

MG Midget and Sprite Technical index

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