914 Brake Caliper info, Whats the internal pin for? They stick Options

[Thorshammer]

Okay,


So I am rebuilding a set of calipers of a customers 914 FP racecar.

One front is a standard "M" caliper with 3 inch spacing and a center pin internal of the piston. This pin sticks out from the center of the caliper piston bore and the piston center has a rubber seal and the pin sticks into the piston.

Anyone know what this pin is for????

I also have another front caliper which has no center pin and the caliper piston is not cupped on the fluid side, so the second caliper has less fluid in it. I found a caliper in the customers spares kit which had a 411 XXX XXX part number on it. From my VW days I deduced this is probably a 411 VW caliper. Same piston diameter and 3.0 inch bolt spacing.

The rears are standard early front calipers from a 914-4.

Here are the questions:

What calipers will bolt onto a 3.0 inch bolt spacing that are two piston calipers??? for the front.

What calipers are the same bolt spacing as 914 front calipers, and are the same piston size?

Observations:

When rebuilding the standard 914 calipers (with the center pin) the caliper pistons move really hard, even with use, or new with Brembo caliper grease.

The "411" caliper pistons move very easily, and I mean this is a big difference. They also retract better, when on the car, you can actually turn the wheel much better than the other calipers.

I am at a loss for whether a piston design that has a cup on the fluid side (more fluid volume) will be better for heat dissapation, or if a piston design that has an almost flat back side (fluid side) will (less fluid) work better. Does anyone make a ceramic insert so the pads will not transfer heat to the pistons to the fluid as easily.

Obviously I am looking for a performance improvement, In two ways:

One piston retracts much better than the other, so less rolling resistance

One piston design that will keep the brakes cooler

This is my dilema.

Erik Madsen

[Eric_Shea]

I've been talking to Ate about these pins last week. I should have a definative reply back tomorrow AM.

The pin device is supposed to pull the piston back faster and pull the pad off the rotor.

In a racing situation I've been told by more than one person to remove the pin. In extreme temps it can actually bind. They (Ate) are discussing the option of removing them in a pair of S-Calipers we're working on now. Re-anodizing the calipers will ruin the steel pin. Most later calipers went with a dished piston for more cooling surface area and no pin (A-Caliper picture included... no pin).

Another bonus would be to remove the dampening device on the piston once the pin is gone. A little c-clip and out they come. You'll get more fluid volume up toward the dome of the piston.

I'll weight in tomorrow if I can get an answer back from Manfred at the factory.

On to your other questions:

You talk about M-Calipers (48mm pistons) and 411 calipers. The 411 caliper is probably a later 914 caliper. The M-Caliper was 911 issue only so, what struts and rotor offset are you looking at?

The 914 caliper is a 43mm piston. A later (1984 on) rear M-Caliper has a 42mm piston but no others in Porsche land that I know of come that close. Maybe DaveP will weigh in here on various VW units. Regardless, if they're going on teener struts you'll have offset issues.

What's allowed in FP? Tell me more...911 Struts? 914 struts? 43mm 914 calipers is a lot for the rears...