Can't push caliper piston back
 

I decided to change the brake pads on my '86 Carrera today and ran into a bit of a problem. On both the front left and right calipers, the outer piston will not retract enough to get the new pads in. The outer piston pushed back easily with just a spreader against the pad, but the outer piston will not budge at all on either caliper. Any suggestions?

Put a C clamp on there...use something between the piston and the c clamp...screw slowly, it'll back off.

are you opening the bleeder screw when you push it back?

No. I removed the cap on the master cylinder and took out a little fluid to give it some room for any back flow.

Yikes. Just loosen the bleeder screw and gently push the piston back. Some fluid will squirt from the bleeder, so attach a hose or something to that effect. Don't forget to bleed your brakes properly afterward.

Thanks for the advice. I didn't even think of doing that...

you should buy a couple of kits and overhaul them if they're stuck that bad. a couple of hoses too. best to try and free them up first so air pressure can pop them out. i use a snapon 3 foot long pry bar with an angled tip on the stubborn ones. with just that one pad removed (all 7 others in place) try pumping the pedal once to at least get it moving outward if there's room between piston and rotor to get your pry bar in. pry it in all the way and them pump it out 3 pumps, pry it in and repeat until it's moving easier.

put the pad back in on the good side and use the brake pedal to push the stuck on e out.

+1
 

Of all the things on the car you want to work perfectly, every time, the brakes are at the top of the list. If even one caliper is funky, (stuck piston), do them all, including the rears, rebuild them or send them out to a quality outfit like PMB.

You will sleep better :-)

If a piston starts to stick again, after the pad replacement, you will have varying pedal height, possibly pulling and shorter pad life.

While you are in there, check the disc thickness and surface condition - you may need to have them resurfaced or replaced.

Likewise, your front wheel bearings are likely in need of cleaning/repacking.

Any time the calipers are off, it is a good time to check the flexible lines and going to stainless is a nice move, (imho).

I would suggest a power bleeder or vacuum bleeder rather than the old manual, (foot) bleeding because after tens of years, debris accumulates at the end of the master cylinder stroke, (not to be confused with bottoming out the pedal). This crud sits there, just waiting, (with malice aforethought), hopeing to nick or tear up the master cylinder piston seal, when you try to push out all of the old fluid and air in the system.

I have seen this happen on maybe 5% of the brake jobs that came through the shop before I caught on to what was going on.

If you have been manually bleeding the system every year or every other year, you probably don't have that pernicious filth waiting to smoke your MC. Good on ya.

If you use different colored fluids for your annual bleeding, you will easily be able to see the completion of the flushing operation, as the ejected fluid changes color.

hth,
chris

I have the same issue with my 1988 Carrera 3.2 Targa G50. At first per directions in both Bentley and 101 Projects, I attempted to use a spreader to push the pistons in. The inner one went in fine but the outer would not budge. To the point I bent my spreader. So I thought, maybe I should unscrew the bleed nipple to relieve some pressure, so I did. Still the piston won't budge. At this point I gave up and put the old pads back in, figuring I'd throw in the towel and take it somewhere. But now the situation has gone from bad to worse and I have no pedal, so obviously can't drive it. In the process of opening the bleed nipple could I have drawn air into the system? I thought this job could be done without bleeding.

Make sure the piston is going in straight and isn't "cocked". It shouldn't take that much force to push back in, I've had that happen before.

Opening the bleeder is not necessary as the fluid just goes back to the reservoir when the piston is pushed inward. If it is stuck until the bleeder is opened and then it moves, suspect a swollen, blocked hose. I'm seeing a ton of solidly stuck calipers lately, so a lot of new ones are getting installed.

Thanks John. Having the bleeder opened or closed didn't make a difference. I have already ordered a new set of calipers and hoses. Just concerned about the lack of pedal. Did I likely introduce air when I opened the bleeder, or is it possible to damage the master cylinder by putting excessive force on the pistons?

air.
you can open the bleeder and let some fluid run out. that can get the air out.

do like i said. put one pad in and put something thinner than the pad on the other side and use the brake pedal. just don't let the piston pop out

I would expect that opening the bleeder introduced air into the system. Bleed that line and see if the pedal firms back up. I bet it does.

Use an old pad on piston side but its impossible to get force and a flat connection on the outside of the caliper. It is VERY easy using a C Clamp to get it at the wrong angle and it will go NOWHERE like that. Try applying brakes to get it to close. The lube up the sides of the piston and try it again. Gentle back and forth is better than force. good luck, been there

This happens quite frequently when people baby their precious 911. They drive it gently, the pads wear out very slowly and thus the pistons don't move all that much in the caliper bores. Eventually the pistons get stuck in the bore, just outside of the pressure seal area.

Add to that a lot of people tend wash their car, dry it off and then put it away still wet. All that wetness in the wheel wells and chassis is inviting things to rust. I'm a big promoter of washing the car and then take it for a short drive to get all the water out of the cracks and crevices and dry out the brakes.

Where did you order the new calipers from?
What do 4 new calipers run these days?

PMB if you want to restore. For me, I purchased a full set of calipers, front and rear(Porsche Classic) from Suncoast. I looked at restore, plus shipping both ways, and for me, new was the way to go. Just sayin'

Ok, so a brand new caliper is $225 from Suncoast. Are these OEM?
Isn't that cheaper than getting them rebuilt?
http://www.*************.com/product/911FCAL.html