OEM front break caliper piston diameter

There are two sizes in the front. The larger measures 38.78mm and the smaller one is 27.86mm. That is with a digital caliper, not a micrometer so that really is only approximate but I doubt that the minute difference in measuring devices is significant?

Thank you very much.

Anytime.

Interesting that they don’t really seem to be either a standard metric, or inch size…

Wild speculation is that the bore is a standard size, and the pistons are undersized because the O-rings are what is the real bore interface?

Rocky

Your guess is as good as anyones. There are so many small details on the car that logically make little sense.

What I think is that geneally speaking, someone took over the overall engineering details on the car, like Ford Engineering, and rather then do actual engineering calculations on what the size of a component should be, modeled those decisions (copied an existing car) after another.

If you start closely comparing the 65 Mustang to the Pantera as far as dimensions like this, things become very suspicious.

The '65 Mustang front caliper is close enough to make me think that an engineer in Italy, just took a cross reference and picked out something that was "close enough" and available in Europe and went with that. That likely would get easy approval from both the Engineering department and the Accounting department.

If I was a prosecuting attorney, I could show the relationship of those two departments to the point of making you doubt they were not the same people?

That caliper does fit the scenario which both of us have just described. Take something that already exists and has been in production, and make it work, as inexpensively as you can.

Look at the spindle and the front bearing sizes. Those are all '65 Mustang dimensions and the bearings interchange.

I think the Legal Department sometimes was the Engineering Department and that one person was also the Accounting Department? Delara was long gone from these decisions.

Rene,

What makes you wonder about the piston diameters?

Not to mention all the Fords produced in Europe for Europe we never had in the US…  steering column , steering wheel and ignition lock from the Ford Capri on the Pantera and…

What was it determined that the steering rack was from?

I have actually seen this type of thinking and application on some of the Italia's.

One of them when I looked seemed to be a Mustang with a custom body on it?

I actually like that type of engineering.

Having built my own version of the EPS, reducing the engine cabin bubble and lowering the floor pans (and accommodating power seats), actually having to fit anything into the Pantera without butchering it up is seemingly almost alchemy? I can respect that when done well.

@larryw posted:

Rene,

What makes you wonder about the piston diameters?

To compare the volumes of fluids needed to operate the front calipers and my new rear calipers, since the diameter of the two parts of the master cylinder are the same.

Another question, does anyone know what length of travel of the caliper pistons is taken into account to calculate this volume? I guess it's around 2 or 3 tenths of a mm?

@panteradoug posted:

What was it determined that the steering rack was from?

I have actually seen this type of thinking and application on some of the Italia's.

One of them when I looked seemed to be a Mustang with a custom body on it?

I actually like that type of engineering.

Having built my own version of the EPS, reducing the engine cabin bubble and lowering the floor pans (and accommodating power seats), actually having to fit anything into the Pantera without butchering it up is seemingly almost alchemy? I can respect that when done well.

Sorry, my mistake! The steering column is supposedly from the Ford Capri and the steering rack is Ferrari 308

that was my understanding so far

it seems like there were quite a few Ford Taurus  and Ford Granada euro models parts used ( Deauville & Longchamp)

@rene4406 posted:

To compare the volumes of fluids needed to operate the front calipers and my new rear calipers, since the diameter of the two parts of the master cylinder are the same.

Another question, does anyone know what length of travel of the caliper pistons is taken into account to calculate this volume? I guess it's around 2 or 3 tenths of a mm?

You may actually be getting to what I was thinking? I don't see the reason that two different sized pistons were used in the front calipers unless possibly it was felt that the master cylinder could not adequately operate the caliper if all four pistons were of the larger size?

I still have my original master cylinder stored in my Pantera parts drawer.

I went to the master cylinder that Hall Pantera sells. It is definitely a Ford item and likely will interchange with a Mustang.

It has no issue with supplying pressure to the calipers but what I have learned through the years is that you can modify both the pressure and the volume by using different diameter pistons and piston bores in the master cylinder.

From memory, I think that the bore in the original Pantera translates to about the stock size of a regular production Mustang. 7/8"?

This balances the pressure that you feel in the brake pedal with adequate pressure to the calipers.

When I went to fully manual brakes in my 68 GT350, I changed the master to a 1-1/8" bore. That was from a F250 truck application. It made the pedal high and hard but reduced the travel of the pedal to the point that you just touched the pedal for braking. This desensitized the brakes for racing so that it was more difficult to lock up the brakes in a panic stop and it kept the car braking straighter.

Eventually I went back to the power brake set up and added rear disc brakes. The master bore wound up a 15/16".

As far as the OD of the caliper pistons that I am using in my Pantera, the front uses 4 @ 49.327mm (1.942") and the rear are 4 @ 41.275mm (1.625"). Considering how big those are in comparison to the stock originals, I don't think that you should have an issue with lack of capacity with the stock master cylinder and stock calipers? I don't think that there is any kind of an issue there? Why the original piston bores are two different sizes is a mystery to me but really doesn't matter?

The original master cylinder has a diameter of 24 mm or +/- 15/16'' and is common with the Ferrari 308.

It is certain that as with all semi-industrial or semi-artisanal cars, it's as you want, De Tomaso used parts from existing mass-market models, this is what made it possible to obtain a very low price for performance equivalent to that of Ferrari, Maserati, Lamborghini and other Porsches of the time. The engine is the most significant, +/- 300 hp at the time in Europe was reserved for very expensive brands.

Small pistons have less pounds per square inch on the brake pad surface to rotor to make the brake less snatchy / chattery . Small piston is usually the front one first to be approached by the disc

That helps with even wear of the brake pad

Multi piston calipers are directional!

Another interesting element that this thread implies, but doesn’t explicitly state is….

The motion required for the pistons within the calipers is much smaller than that of the Master Cylinder….  BUT…. You have to remember that the fluid forced out of the MC has to completely actuate four (4) sets of calipers!

So there is a large element of fluid volume supply / requirement in the design of brake systems…. Only now is this made obvious to me!!!

Thanks Doug, Rene & (possibly) Roland!

Chuck (aka Rocky)

I think everyone is over reacting just a bit to a non-issue.

For example, consider the front caliper that I am using on my car and the size of the pistons. 1.942" od  x 4.

That set up was used on the big Fords with essentially the same master cylinder bore on a 7,000 pound car since 1965.

It has no issues in stopping that monster. There is mechanical advantage working here. Why is that suddenly questioned even on a smaller caliper like the original Girling Pantera caliper?

Simply stated, there is no issue. The original braking in the car is "adequate". Many of us are just looking to improve it.

I think that Rene is just very analytical in reviewing the original design, looking for an original engineering/design flaw, which I don't think exists. He just seems to want to verify that. That is fine for his own peace of mind.

Incidentally, on pistons sizes, Ford never had an issue with using four equal size pistons in their production vehicles. The 65-7 Mustang caliper is essentially a scaled down version of the "Big Ford/T-bird" caliper and they are equal bores as well.

Varying the caliper piston sizes is just a design option some felt would reduce the likeliness of pad squeak. Since those days, other methods of eliminating pad squeak have been developed. For instance, using the pad adhesive is very effective and inexpensive.

That works. "If it ain't broken...don't fix it!"