Front caliper piston question

The front calipers are pretty much straight forward. Just buy the seal kit which has a new dust boot and piston seal. Do not split the caliper unless you buy a set of the "square" O-rings which are sold seperately. Stick a piece of flat wood in the calipers and apply compressed air to the brake line hole and pop out the pistons. One will come out 1st then you'll need to either put a rag into the piston that came out and use compressed air for the other piston. Now if after inspecting the piston bore you see corrosion then you'll need to split the caliper and hone out the bores. If they are clean just wipe them down with clean brake fluid and reassemble. Good luck.

 

OK sorry I got your point now. I recall that the notch needs to be oriented in a certain way. As I recall when you get the rebuild kit there are instructions on where this should be set. You can also make a template out of cardboard to insert and align the piston. It is not a big deal and is straight forward.

 

Remember, the calipers are Ate brand and are the same as used in the old Porsches of the same period (fronts are same as 914 IIRC, check the JWise thread for cross-reference). There are Porsche parts dealers that sell them for a lot less than with Ferrari labels on the packages. And when I was rebuilding mine, I found that getting replacement pistons was actually very cheap. So if the pistons are scored or corroded, don't fool around with them. Just order a new set. You can pick up a set for both calipers pretty cheaply. Get stainless, if possible.

 

When you get the rebuild kit from ate, it explains that there is a special tool to align & remove the piston, it connects to that notch, I had no problem getting the pistons out with a lil compressed air.
The ATE kit assumes you wont be splitting the caliper or removing it at all, it is based on in car maint, so I guess they took into account the fact that you would have no leverage within the tight confines.
The rebuild is quite simple, the parts prices are pretty high from ferrari vendors, especially considering the kit for porsche 911 is 13 dollars at napa & is an ate part, & is all you need for the front calipers, except the lil o rings for the caliper split.

The rears are also porsche parts, but have no seals for the handbrake parts, & the vendors are charging a very high price for this kit, but what the hey, you can always get it from europe for 1/2 the price if you can wait for a few weeks. I needed mine now as it was leaking like a sive & I do support our sponsors, so i bit the bullet & paid the price.
that being said, the rear was a torturouse ordeal, to get at some of the clips & springs & i developed a few tips to make the job eaiser, but have yet to photograph it.
feel free to PM me & I will guid you through it.

 

If you're unlucky enough to have a seriously stuck piston, as I did, you can get them out but will have to replace with new. I very carefully drilled and tapped a couple of M8 holes through the piston back face about 1/2 to 3/4 of the piston face diameter apart. I then gently screwed in two good clean M8 cap-head bolts, tightening them evenly so that they pushed the piston out squarely. Make sure the ends of the bolts are ground smooth and slightly domed so they don't score the back face of the cylinder too much. As it was the piston that was corroded, rather than the cylinder bore, I was able to just replace with stainless from Superformance.

Note, when I tried to fit the new pistons initially, even though they had lots of fluid to lubricate the new seals, the back edge of the piston caught on the seal and tore it up. When I compared old with new I found that the old piston had a much greater radius on the circumference going into the cylinder. I put the new ones up on a lathe and turned them the same and all was well with another new seal in place.

 

I use an "old indian trick" to remove stubborn pistons.

I have a brake fitting that I have mated to a grease zerk fitting. You screw it into the hydraulic port and pump grease in (a grease gun will develop 1000's of psi) until the piston moves.

In a multi-piston caliper you need to be creative. Some pistons will move first, I hold them back with a c-clamp or a block of wood that I cut to the size required to hold the pistons back until the stubborn one is out.

When you're done you have a greasy mess to clean up but NO DAMAGE to the caliper or piston!

 

Anyone know the technical reason why these piston contact surfaces are not uniform around the entire circumference, but instead have a ridge that sticks out from the surface that goes around maybe 2/3 of the way. Apparently, the entire piston surface will NOT contact the back of the pad. Why?? And, does it matter HOW this "horseshoe" surface is positioned when it eventually will contact the pad back?

OK, here is what I mean....
http://www.pelicanparts.com/techarticles/911_caliper_rebuild/pic15.JPG

in this photo, the guy is checking angle. Apparently, it does matter, (dont understand why), but, gees, in that photo, how would one turn the piston around if it is not the correct angle, once it is in the caliper? Kinda difficult to do .....

 

The notches are for the removal tool, the directions supplied with the ate kit explain the theory, I dont have anymores but i believed the angle was related to noise & tapered wear issues. Important on a dialy driver,but not my car

 

Thanks guys for input. But, not to belabor the problem, but these low relief "shoes" on top of the piston surface, or notches, are what actually contact the back of the pads. Cant figure that they also double purpose for removing them......Oh well, kinda like motor oil, v debatable........

 

Any thoughts on this?

Here are some pics of my calipers (if that part could talk ). The "contact surface" was on the top side of the caliper (pic 1).

I had massive amounts of taper in my rotors so I thought maybe the horseshoe should be on the outside concentrating force on the outside of the rotor making the wear more even (pic 2).

The Pelican article referenced shows the "contact surface" on the bottom side with a slight 20 degree angle.

Any thoughts? ... I'm thinking of putting it towards the outside to try and even out wear I'm seeing on my discs but usually info at Pelican is pretty good.

cheers
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FWIW, this is how mine looked when I took them off the car:
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See the figure in post #1 of this thread -- seems to match Peter's "as removed" condition:

http://www.ferrarichat.com/forum/showthread.php?t=85703

 

Thanks guys thats what I'll do.

That's the same as the Pelican article and it's the same as my basic Porsche repair manual shows.

cheers