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Posted by: skline Oct 14 2006, 05:54 PM

Alrighty, I am rebuilding 4 911 m calipers, for vented rotors. On some, the piston will not push itself out with air pressure, they are stuck.... Help! I need to do this myself and I am cheap lol. Heat maybe?

BTW this is DRIFTERJAY...not scott...

Posted by: Aaron Cox Oct 14 2006, 05:55 PM

got a grease gun?

use hydraulic pressure to make the piston come out (gee... thats how a car works )

hook it back up to the MC if you can... and just pump fluid

Posted by: Lou W Oct 14 2006, 06:02 PM

Posted by: davep Oct 14 2006, 07:47 PM

Like Aaron says, hook it up to a master cylinder. Hydraulic is the only way to go. Air is far too dangerous with stuck pistons. Never use heat.

Posted by: Joe Ricard Oct 14 2006, 08:03 PM

PB blaster around the piston to caliper interface.
Rust forms there and is probably the Number one reason for calipers sticking.

atany rate make sure your fingers are not in the pistons path when it decides to let go.

I rigged up a 17mm M/C on my bench got it plumbed with a resevoir and everything. Works good to test the caliper after rebuilding.
I just did Derek Kim's Calipers today and it went well after I fixed the rear adjuster. Freaking little spring !!!!!!!!!!!!

Posted by: Lou W Oct 14 2006, 08:23 PM

QUOTE(Joe Ricard @ Oct 14 2006, 07:03 PM)

Posted by: mihai914 Oct 14 2006, 08:38 PM

QUOTE(Lou W @ Oct 14 2006, 10:23 PM)

Posted by: Lou W Oct 14 2006, 08:51 PM

ok, thanks

Posted by: rhodyguy Oct 14 2006, 10:16 PM

get the pb blaster. it's great stuff. call around to see who stocks it locally. our shucks stores carry it. they are partnered with kragan(sp) and checkers.

k

Posted by: dmenche914 Oct 14 2006, 11:03 PM

rusty pistons / bores is a good reason to use brake grease on the piston when rebuilding. it helps prevent rust on the exposed surfaces that are outside the seal rubber. besure to use the correct brake grease that works with rubber,adn brake fluid, wrong grease can destroy your brakes.

Grease gun idea i hear is good. although air can work, the grease gun is recommended, If you use grease, the caliper halves need be split to replace the halve seal, it is rubber,a nd the grease will ruin it, or the solvent you clean out the grease will. you might try air fisrt, if it don't come out easy with moderate pressure, then move up tot he grease gun , or hook up to the master and pump.


good luck

Posted by: Eric_Shea Oct 15 2006, 09:31 AM

You'll have no or limited luck with PB or any penetrant on a stuck piston. You simply can't get enough at the problem area.

Air compresses, liquid doesn't. The el Cheapo Harbor Freight grease gun has the proper fitting for a Porsche brake caliper. Simply screw off the nozzle and thread the hose into the caliper. (must have air)

You can do it on the car with the M/C but you will have a difficult time popping out one then closing off the bore and popping out the other. Then there's the fluid all over the place etc. That is best done in a vise.

If you have time. Buy a gallon can of Gunk carb. and parts cleaner. You can "just" squeeze an M-Caliper in there. Let it sit 3-5 days then try air again. The piston can come out at quite a velocity as Dave mentions so make sure there's no fingers in there and, stuff a shop rag in there to protect the piston top. I've "never" seen a piston come out of the brake pad/rotor opening so I'm going off the assumption that, while it makes a lot of noise, it's relatively safe.

I keep a gallon can of the Gunk cleaner around for the tough ones. It's now in the $19-24 range though... I had a rear M-Caliper that was cooked. The pistons were S-T-U-C-K. Even the grease wouldn't budge them. I literally gave up on it but otherwise it was a fine caliper. I let it sit for 4 days in the Gunk and both pistons came out with air.

Eric

P.S. You'll probably have to to that with the engine you have sitting here as well

Posted by: skline Oct 15 2006, 11:56 AM

thanx eric, and everyone else, when I have the money I will get that motor out of there....it took me 3 months to have the spare money to buy 4 caliper rebuild kits....Money is tight right now.

-Jared (DRIFTERJAY...not skline..)

Posted by: Lou W Oct 15 2006, 01:35 PM

Okay Jared, you can borrow mine that I just bought from Harbor Freights for $12.95, on sale. I'll bring it with me to the Wienie roast and swap meet on the 29th. Just don't let Scott use it.


Im gonna try it out on my front "m" calibers today.


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Posted by: Lou W Oct 15 2006, 04:14 PM

Update: well it didn't go too well, the pistons didn't move, so now the caliber is sitting in Carburator cleaner.

Posted by: Aaron Cox Oct 15 2006, 05:04 PM

it didnt budge with hydraulic pressure???

no way.... and you did the compressed air trick too (less effective than hydraulic tho)

musta had a hardlife (rust or heat got em stuck )

Posted by: Lou W Oct 15 2006, 05:14 PM

The hubs themselves actually look to be in good shape, no exterior rust or anything out of the ordinary, I'm going to let them soak over night and try them again tomorrow. I'm leaving Thursday and was hoping to get them apart by then so that I could take them up to get powdercoated.

Posted by: Eric_Shea Oct 15 2006, 06:02 PM

Posted by: Lou W Oct 15 2006, 07:06 PM

No I should have tried that, I think I was too impatient....

But, I let the calipers soak, took a pair of channel locks and squeezed the pistons in to "unfreeze" them, yes there was some resistance at first, hooked up the compressor and they did not pop, they "POPED", it kinda startled me one piston came out first, so I put it back, propped a piece of wood in there while it was in the vise(limiting the amount of travel for the one piston), and the other poped out.

I am currently soaking the other front calipers and will duplicate this again.

Eric,
My next question is the rear calipers, I got them apart, however, Im having trouble getting the spring clip that is holding the "hat and the adjuster" out, my spring clip doesn't have the small holes like the ones that you took pictures off in your directions, they are more like a "C" on each end of the spring clip. Update: I got that part done, the hat seems to move some.

Can I push on the hat to relive pressure on that clip? Update: Yes it does.

and secondly, will the E-Brake lever come out?


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Posted by: Eric_Shea Oct 16 2006, 09:32 AM

You have a very late rear caliper. 75 or 76. I hate those clips. Looks like you've got it tackled but for future referrence, I use a pick and a small blade screwdriver. I use the pick to pull up the corner and slide the screwdriver under the clip and pop it out.

Does the handbrake arm come out? Yes. You will have to destroy the 25mm welch plug to do it though. We don't mess with those unless there's an obvious problem. Repair kits for that section alone are $49.00 from your favorite Ferrari vendor (read: more than a decent core is worth).

If you're insistent then here's what I do: Take a dremel with a carbide cutoff wheel and etch a notch "just" through the surface of the welch plug. The end of the arms is on the other side so... just enough to cut through. Get a large screwdriver and peel the welch plug out. Take the small clip off the end of the arm and the arm and rubber seal will slide right out. You may be able to reuse the seal if it's not in bad shape but... if it's not in bad shape, what the hell are you doing all this for?

Seriously... you may be able to reuse it if you find a 25mm welch plug. PB Blaster touts itself as a seal restorer. It's actually a seal sweller. A small bit of PB plaster on a cloth to clean off the seal should make it work but, make sure you get it in the groove and put back together asap.

This is good info for those having a small adjuster o-ring leak. A little PB blaster on that area may swell the seal just enough to fix the problem. Any fix like that should be viewed as temporary but...

Posted by: davep Oct 16 2006, 09:45 AM

Lou, you didn't say you were trying this trick on the 914 rear calipers. It is a bad practice to just use hydraulic pressure on 914 rear calipers alone. It is far better to use the adjusters along with pressure. Adjust a little , then force a little. You can permanently damage adjusters by using pressure alone.

Posted by: Lou W Oct 16 2006, 12:08 PM

QUOTE(Eric_Shea @ Oct 16 2006, 08:32 AM)

You have a very late rear caliper. 75 or 76. I hate those clips. Looks like you've got it tackled but for future referrence, I use a pick and a small blade screwdriver. I use the pick to pull up the corner and slide the screwdriver under the clip and pop it out.

Does the handbrake arm come out? Yes. You will have to destroy the 25mm welch plug to do it though. We don't mess with those unless there's an obvious problem. Repair kits for that section alone are $49.00 from your favorite Ferrari vendor (read: more than a decent core is worth).

If you're insistent then here's what I do: Take a dremel with a carbide cutoff wheel and etch a notch "just" through the surface of the welch plug. The end of the arms is on the other side so... just enough to cut through. Get a large screwdriver and peel the welch plug out. Take the small clip off the end of the arm and the arm and rubber seal will slide right out. You may be able to reuse the seal if it's not in bad shape but... if it's not in bad shape, what the hell are you doing all this for?

Seriously... you may be able to reuse it if you find a 25mm welch plug. PB Blaster touts itself as a seal restorer. It's actually a seal sweller. A small bit of PB plaster on a cloth to clean off the seal should make it work but, make sure you get it in the groove and put back together asap.

This is good info for those having a small adjuster o-ring leak. A little PB blaster on that area may swell the seal just enough to fix the problem. Any fix like that should be viewed as temporary but...

QUOTE(davep @ Oct 16 2006, 08:45 AM)

Posted by: Eric_Shea Oct 16 2006, 05:59 PM

Good call on the handbrake arm. I rarely find the need to replace those (and they're not causing any leaks).

I'm not a fan of powdercoating. What are you trying to make them look like?? There's Brembo covers available on eBay!

The seal should be able to take the heat of powdercoating but the only one's I've powdercoated we did remove the arms just in case. Also, the powder would effectively go everywhere and bind the arm when is cures. All of the openings should be plugged (bleeder, piston bore, Arm bore, fastener holes, fluid input, etc...) When you remove the (9 or more) plugs it leaves ridges all around. Not a clean installation in my book.

I would encourage you and/or anyone else reading along in the comfort of their humble abode not to powdercoat your calipers... do the right thing and plate them. There's a guy down there in SloCal that does them cheap...

Posted by: Lou W Oct 16 2006, 06:23 PM

I was planing to do them in dark grey, the covers on e-bay are red


Thank you for taking the time to respond. I now realize that it makes more sense to have them plated.