I've searched/read every post I can on rebuilding calipers, but I came upon a few stumbling blocks today in my project.

1) What is the trick to getting BOTH pistons to pop? I can get one or the other, but not both. I used the grease-gun method, followed by the air compressor method. No luck!

2) Having used the grease-gun method, how do you get all the grease out?

3) As you are not supposed to split the calipers, how do you get a hone in the bores to clean up? My bores look good, but there is some varnish in there (car sat for many years).

The grease gun method sounds like asking for trouble... I don't think I would ever do that. I think you're going to have to split the calipers to clean them out now, which means finding the seals. But then they'll be easier to hone.

The grease gun method worked very well. Air wouldn't budge one of the pistons, but the grease did the trick. There only appears to be two small passeges going from one side of the caliper to the next. I'm thinking of pressure washing these openings with the hose from the parts washer...?

Calling Salmon Boy to the White Courtesy Phone ..... Paging Eric Shea to the White Courtesy Phone.

Brake-Kleen or similar .... rags

Yeah, Eric is going to be re-building the rears, but I figgered I could tackle the fronts.... Live and learn...

I haven't has a problem using compressed air.


Did you put a block in between the pistons? The last time I rebuilt calipers (they were "S's" but the procedure should be the same), I put a block of wood in between the pistons and pressurized it. Both came out a bit instead of one or the other coming out totally.

Yes, I used wood, but it doesn't allow the pistons to expand enough to remove by hand. I experimented with different thicknesses of wood and, if too thin (e.g. paint stirring stick), one piston pops, if too thick, they don't come out far enough to get a grip on. I guess I need some "thin-nose" channel locks, as regular channel locks don't fit inside the caliper well enough to grip the piston tops.

The following is generally applicable to front calipers, but can be used with the 914 rear calipers with some modifications. My opinion is that it is best to leave the rear 914 calipers to someone that has the experience, tools and parts.

I've rebuilt dozens of calipers, and have never used grease, and very seldom use air. Most calipers tend to have sticky pistons, and if you use air, then when they do start to move, they generally go off like a cannon. I have an aluminum bar to sit where the rotor goes, and use wood shims between the aluminum and the piston. I allow only a little movement each time. The steel pistons I can grab with locking needlenose Vise-Grips and gently work out the last little bit.

My preferred method is to use a spare pedal cluster, master cylinder and reservoir. Doing it hooked up to the car is also possible, but the use of a lot of fresh fluid can be a problem. With my off-car set-up, the use of fresh fluid is not required. The pistons are easy to hydraulically push out since the pressures involved are many times that available with air alone. Secondly, once the piston is past the seal it will leak, and you will loose a lot of pressure. There is no cannon effect to worry about. I use a special C-clamp to hold one piston back while pressing out the other.

I have used dental picks to scrape rust from the bore outside of the seal area, and inside of the seal recess. Use Q-tips and rubbing alcohol to clean everywhere. Use generous amounts of alcohol to flush everywhere and blow clean with compressed air. I use a special brake lube to reassemble with new seals. Pistons can be generally cleaned with a green scrub pad and alcohol. If they are pitted, they need to be replaced. Be sure to thoroughly flush the mechanism inside the pistons. Generally the outer piston and bore will be rustier than the inside. This is usually due to inadequate flushing with fluid when bleeding the brakes; nothing forces fluid into the outer circuit during bleeding.

Why?

Dave's got the right method. The determining factor in getting the stuck pistons out is "fluid" it does not compress like air does.

Grease is perfect for the home mechanic that does not have the elaborate set up Dave uses. The el-Cheapo Harbor freight grease gun simply screws right in. You can literally have your hand in the pad cavity when the piston "plops" out. Very safe. Very much a pain in the ass to clean up but... jobs done. Get some paper towels and get on with life. Actually, paper towles, brake cleaner and compressed air.

To answer the question; you'll need to c-clamp one of the pistons as Dave mentions to keep it where you want it. Then you'll need to make a cap for the open bore once that piston comes out. This can be accomplished by going to Lowe's and getting the large rubber washer. Find and cut some flat stock steel to fit the cavity and clamp that in place while you pump out the other piston.

Go ahead and split the caliper. I'll send you some o-rings. Not a big deal at all. I'd call it a 1 on a 10 scale.

-or-

I'm thinking of offering a front caliper kit for the CSOB. You could be the first to purchase one!

It would include 4 freshly plated caliper 1/2's and polished pistons and all of the goodies needed to bolt them together. You'll need a brake caliper hone and a torque wrench. $124.00 plus shipping, plus your cores.

Yikes... no-no.

Are these the late style fronts? If so I have a "very" simple solution for you. The later pistons have a ridge that the dust cover sits in. Once the dust cover is off you can see this ridge.

BE VERY CAREFUL TO GET THE RIGHT AREA (proceed)

Use a large screwdriver and place it under the THICK area of this ridge. There is an almost paper thin section you want to avoid. You can lightly pry in various areas around the piston to get it out.

Again...

* This is for 1973 and later front calipers.
* This for pistons that are almost out or to help free stuck pistons while using air (be careful).
* You should not attempt the entire piston removal this way.
* Do not pry on the thin section of the piston. You "will" break it.

Greetings Eric,

I was just about to e-mail you when you posted.

The calipers are "early" (71). I will try the block-off plate trick.

How much do you want for the seals? I was going to purchase from Pelican ($2.71/ea.) but shipping would make it un-economical (can't they just throw 'em in an envelope with a stamp?), so I went to the local Porsche dealer...are you sitting down? $7.81 ea.!

So...I still need seals. Name your price!

The reason I'm going "cheap" with this rebuild is that I'll eventually (sooner than later) be converting to a full 911 front/rear suspension set-up. I don't want to spend a lot on the current brakes, as they'll end up on the "spare parts" pile. I do need brakes, however, to move the car around, road-test & deliver to the shop for the MFI tune & valve adjustment.

$7.80

No...

$2.70!!

PM me your address... you'll owe me a

Update: I used a large washer and a piece of self-adhesive rubber to seal the "opposite" caliper piston hole. Applied air pressure and "pop" goes the piston.

Grease cleaned right up with some Brake Kleen.

Eric sent some replacement o-rings and everything went back together easily. Not a difficult job (rears are another story...gonna send those out).

I wanted to do a quick front brake job and not split the caliper last week, (it's tricky to hone it without splitting but i didn't have those o rings), but one cylinder got stucked, i tried to get it out with air but the pressure in my "hobby" compressor was just not enough so nothing happened, my final solution was to use the grease method but I didn't look forward to that as I only had seals for the cylinder and wanted the car ready for the weekend so ordering caliper seals was not an option. So I got an crazy idea, I bought a new greasegun and a bottle cheap brakefluid, filled the greasegun with breakfluid and voila, it worked, no messy grease to take care of... the grease gun leaks the breakfluid so latexgloves and somthing under everything to thake care of the fluid is my tip

My wife shouted trough the window if that was some stuff that would be bad for her grass (she loves the garden at least as much as I care for my 914) I replied, no problemo, it's just breakfluid



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You're lucky. Those hand crank type guns don't have the pressure needed to get the really stuck ones out.

Yes, I tought about that, there was very little oxide on the cylinder so it couldn't be to badly stucked compared to some pictures of heavy rusted cylinders that I have seen, but the greasegun (15$ cheapest I could find) stated that it would handle about 5000 psi, so it can't be that bad compared to my sh-t compressor.