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!"

After checking by a professional, it turns out that my brake booster needs to be changed. Given the difficulty in getting it repaired or buying one in Europe and the cost and given that I replaced the original rear calipers with 4-piston Brembos, I decided to remove the Mastervac and install a system with double master cylinder and mechanical distributor between front and rear. I also removed the shuttle valve which was no longer working correctly and is of no use from my point of view (if there is a brake problem you can notice it without needing a warning light for that).

I bought two master cylinders and the distributor for less than €150 and I made the support.

I now have a hard pedal and it brakes quite well but you have to press quite hard on the pedal which is normal with the removal of the Mastervac. To reduce the effort on the pedal, I ordered a set of Porterfield R4-S front pads for which I read very good reviews on the forum. However, I have a question, what is the coefficient of friction of these pads? I couldn't find the answer on the Porterfield site?

Running without a brake booster will be a workout 🏋️…

If you go with more aggressive brake pads will increase the wear on the brake discs considerably… there is no free lunch…

I learned that with my Corvette… needed brake pads AND discs due to massive wear so I went back to original setup…  💰

you seem to be pretty mechanically inclined.. what stopped you to use a brake booster from another more available car manufacturer?

or use something like that..

@LeMans850i posted:

Running without a brake booster will be a workout 🏋️…

If you go with more aggressive brake pads will increase the wear on the brake discs considerably… there is no free lunch…

I learned that with my Corvette… needed brake pads AND discs due to massive wear so I went back to original setup…  💰

This is true. I was observing street cars at a club high speed event and genuine "vintage" Trans-Am cars at the same track, the same day.

The T/A cars literally went through three sets of brakes, some four IN PRACTICE.

The street cars in the high speed events, none.

I have the Porterfield R4s pads and also still have what we used to describe as "semi-mettalic heavy duty pads".

I actually think that the "semi-metallic" pads are better UNLESS you are going vintage racing.

Under those conditions, the semi-metallics will glaze the rotors. The R4S will just coat the wheels in grey dust as they literally disintegrate.

My opinion on the Pantera useage is to run the "semi-metallics" in the rear for both uses.

Switch to mounting the rear rotor OVER the axle flange so it is simpler to service.

There it is also adventageous to use the two piece assembly. Seperate hat and rotor. That will help on reducing the cost in the rear under a "non-sponsered" racing condition.

The front pads depends on the useage. You don't need the Porterfields for high speed events. Semi-metallics are fine for that.

I have original Ford service pads for both the fronts and rears here. I honestly can't determine what they are but they do not look like the "semi-metallic" compounds I have for my GT350's.

On those you clearly see the metallic content in the compound. The Pantera pads you do not.

So really it is a "trial and error" basis. Unfortunately these days "trials" are very expensive.

Sorry, I do not know the coefficient of friction on any of the pads. The fact is, no one lists them and the manufacturers do not readily give you that information.

One of the reasons I went with the 69 Ford T-bird brakes in the front is that the parts are still serviced. The entire rotor is around $70 so compared to burning up a Brembo or Willwood, it is a better cost break.

Brands like Pagid, Mintex, Ferrodo or Carbone Lorraine indicate the coefficient of friction, often they even publish the variation curve of this coefficient as a function of temperature.

I opted for the dual MC system to be able to easily adjust the front/rear distribution, due to the replacement of the OEM rear calipers with 4-piston Brembos.

I don't think disc wear is a big problem, I don't plan on driving tens of thousands of miles a year. But if that's the case, I'll make the changes to the disk mounting suggested by Doug.

I like your analytical approach to everything. I like and enjoy your problem solving ability. It seems obvious to me that you have an Engineering background and quite a bit of experience. "Carry on!"

Indeed, I was an engineer

I ran a full race, manual brake set up on the street in my '68 GT350.

I was using a 1-1/8" bore master.

The brake pedal was firm but didn't require much travel and there was no issue with leg effort driving it on the street.

The stopping power was really effortless and it seemed like I could not lock up the brakes at all.

The car stopped and it stopped straight, so I would comment that it is possible to use a fully manual brake system with no power assist safely and effortlessly on the street.

It is just a question of having the correct components together.

Those were with Porterfield r4s street pads and there was less pad wear with them.

The only issue, if it was in fact an issue, was those pads do generate more dust on the wheels.

You are re-engineering the system so expect some quirks that you must adjust for.

In the Pantera I would expect any kind of larger rear brake pad/caliper combination to need the pressure to them dialed way down. Where it winds up to your satisfaction is up to you.

I chose an MC of 5/8'' for the front and 11/16'' for the rear to have a pressure on the rear circuit lower than that of the front circuit with a 50/50 adjustment and to have a slightly greater volume of liquid displaced at the rear than at the front since the pistons of the rear calipers are larger than the front ones.

For the moment I have completely ordinary pads at the rear but my rear calipers come from a Renault Mégane RS II which is a very sporty car often used in rallye and on tracks, there is a large choice of pads more efficient.

I have to receive the Porterfield pads tomorrow and I hope that it will finally stop raining so that I can do some testing on a really dry road, which I haven't been able to do yet.