seized caliper piston?

[Guest]

got three pistons to retract ok but one just wont go back in?

am i looking at a caliper rebuild or is this common? any advice appreciated

 

[Fred Hindle]

Will it move at all? That is to say does it come out when pressing the pedal. Place some packing (old disc pads or piece of wood) between piston and disc and get some one to press pedal whilst you watch. If pads are very worn then piston can 'keck' a bit and jam - same as most disc brakes.
Try twisting the piston in the cylinder.
Cheers,

 

[Guest]

disaster - pumped the brake pedal to push the pistons outs and only one piston came out, tried a little more and the piston came out completely and is now leaking brake fluid out [][]

can i push it back in without damaging it or am i going to have to remove the caliper?

(only wanted to change the discs and pads!![])

 

[Guest]

have got piston back in and attached caliper to the housing with the old pads in but there is no brake pedal, i assume there must be air in the system now?

 

[944Turbo]

yes lots of air I would imagine,
Tony

 

[Diver944]

Get yourself an Eezibleed or similar and a tin of brake fluid from Halfords. Its very easy to bleed all the air out. You won't have damaged the piston (unless you jumped up and down on it and rolled around in the gravel when it fell out [])

 

[sawood12]

Those ezibleed kits are the dogs danglies, make the job a doddle. It is probably prudent to replace the fluid at this point anyway (unless you've had it done recently). Just a pointer, when I replaced my fluid I thought i'd got all the air out then but gave the caliper a good thump with my fist and a load more air bubbles came out so make sure you give the calipers a good thump as you are bleeding the brakes to make sure all the air is coming through.

 

[Guest]

cheers everyone will resort to the brake bleed (inc thumping technique!)

was about to try last nite but had ran out of brake fluid (and patience!)

have got some braided hoses to fit also so might as well do everything at once now there is air in the system

just hope I can free that seized piston. read the article about these calipers and how the guides get corroded so you cant get the new pads in (was also experiencing this problem) mine dont seem corroded just slightly bent so hoping to be able to bend them back slightly - anyone know the easiest way to resolve this?

 

[Diver944]

Unfortunatley it's the corrosion underneath the plate that swells and causes it to bend, so you will have to remove the plate (it's a bu66er []) wire brush away the corrosion, plaster the area in copperslip and reattach the plates (possibly new ones if they won't flatten out [])

 

[Hilux]

Did the piston have any corrosion around it?

If so dont push it in as it`ll bugger up the seals, change it/them.

Bleed caliper furthest away first then progressively closer to cylinder and then re bleed. Eezi bleed is best bet but be aware of max pressure from tyre IIRC its only 20 psi max []

 

[sawood12]

If you can slide your pads in and out as intended then your caliper plates should be pretty straight. As the corrosion builds behind the plate, which acts like a spring, it pushes the plate out and will eventually bind on the edges of the pad and restrict their motion. Removing the caliper plates is a real pain in the bum and there seems to be two methods employed as the allen screws are invariably siezed. One method is to use heat to heat up the screws. You might want to protect the pistons with some plates of metal - use a pad as a template. This heat should melt any locktite stuff used and loosen the screw from the corrosion in the threads. Another method is to use a chisel or something like that to work the screw round. I don't like the idea of this method as there is a danger of shearing the head off then you really will be bu@@ered. In fact I don't much like the first method either which is why I paid my indy to do it for me!! He used the heating method and they were still a bu@@er to get out. It cost me 3 hours labour in total but he ususally says you usually need to allow 2hrs per caliper. My caliper plates didn't need replacing as the corrosion was quite mild and the plates sprung back into postion, but in more severe cases they will have bent too far and will need replacement.

 

[os951]

I managed to get a sized piston out using my air compressor. You just have to place other three pistons to their cylinders and support them so they won't move when you put compressed air into caliper. I have restored a lot of these calipers and i must say they are old fashioned and you have some trouble with them, for example those sliding plates bends easily. So many people change pads to the calipers which have bend plates. They force pads in and after that most likely pad will not move as it should. Actually it's much easier to change pads when you remove caliper. I do not put pads from that side where that fastening spring is. When you remove caliper, it's easy to check out the condition of seals and sliding plates. What causes these piston stucks is usually pad brake fluide. If you have not change your fluids within two years most likely you have water/brake fluid mix up. This water causes also problems to the clutch functions. I can see that easily here in land of polar bears where we have so much problems with clutch slave cylinder among the 944 drivers who drive also during winter months. Old dirty brake fluid with water just destroy all seals and also clucth/caliper pistons. Brembo used metal pistons with 951's, it also causes difficulties, because caliper cylinders are aluminium. I have solved these problems by moving to newer Monoblock calipers, GT2 front & GT3 rears. They have ceramic pistons, no sliding plates, so they perform much better. I also change brake fluid after every driving season.

 

[zcacogp]

Will echo the comments about corrosion bending the spring plates. If they look bent, it's probably 'cos of corrosion ... if it's mild, get the plates off and clean them as it is much easier than when they are more serious. (I learned how to do this two weekends ago, and be warned, it's not an easy job. You will need a decent workshop, bench with vice and small blowtorch. BUT it is possible to do it at home if you are gung-ho enough.)

Good tip about thumping the calipers to get air out. Thanks.


Oli.