Help... front brake piston stuck

[SoCal Craig]

I was changing the front brake pads this morning and I accidently over-extended one of the pistons when depressing the other. Now it is stuck. How do I correct this? Do I need to take off the caliper? I've changed front pads before, but this is the first time I've gotten the piston stuck

Is there a tool made to easily depress the multiple pistons on a fixed monoblock caliper?

[SNKEBIT]

I think you pushed the piston out past the seal, prolly have to take it off to get it back in. On single pistons I use compressed air into the port for the brakeline. I don't know if there's a tool to do multiple pistons,,,, sorry.

[Steve-Indy]

Please do not take my question as an insult as you are probably a better mechanic than I...but, have you opened your bleeder valve so as to decompress the system while you attempt to slowly rotate piston ? I did have one piston pop out once, somewhat of a surprise, but was able to carefully reseat it (after opening bleeder) after checking the seal and dust boot...all with caliper in place, though I think it would be better/easier to remove caliper.

[Tom, F&L GoR]

I second Steve's comments. As long as the piston and seal are lubricated (as they would be with the brake fluid) and there's a place for the fluid (or air) behind the piston to go (bleeder open or brake line off,) the piston should press in by hand. I've learned this with the 38mm conversion of the rear calipers- the OEM seal groove in the bore is not a square cut, it's tapered to twist the seal in a direction to easily allow pistons to be pushed in, then squish to form a good fluid seal when the fluid behind it is pressurized. (Square cut seal grooves with perpendicular faces will have their edges sheared off when trying to insert pistons; at $11 per Brembo seal it was an expensive education.)

Try and put a block of wood between the other opposing pistons, so they don't jump out while you do this. Worst case is to remove the caliper from the car and turn it over on the bench and do it.

[GTS Dean]

Is there a tool made to easily depress the multiple pistons on a fixed monoblock caliper?

Yes, it's like a big pair of pliers with flat plates on the jaws. When the handles are clamped, they spread out.

I use a less elegant, but much cheaper approach. Pull one pad at a time out of the caliper. Reinsert it into the caliper with the short dimension pointing toward the hub. Use the pad as a lever against the pistons and the rotor OD as the fulcrum. When two pistons on that half are retracted, install the new pad and do the same thing on the other side of the rotor. This won't work if you have 6-piston calipers.

[SoCal Craig]

Please do not take my question as an insult as you are probably a better mechanic than I...but, have you opened your bleeder valve so as to decompress the system while you attempt to slowly rotate piston ? I did have one piston pop out once, somewhat of a surprise, but was able to carefully reseat it (after opening bleeder) after checking the seal and dust boot...all with caliper in place, though I think it would be better/easier to remove caliper.

No insult taken... I suck as a mechanic. But I have changed pads before on all three of my cars with no problems. I just goofed by letting one of the pistons hyper-extend. I tried opening the bleeder valve to push it back in, but it didn't budge. I didn't try rotating the piston. How do you do that, with channel-locks? The fronts normally just push in.

Haven't tried removing the caliper (3 bolts?) yet.... decided to wait until I received some input from you guys.

[SoCal Craig]

Try and put a block of wood between the other opposing pistons, so they don't jump out while you do this. Worst case is to remove the caliper from the car and turn it over on the bench and do it.

I think I remember one of my friends (Dearing) telling me to hold one piston while pushing the other back in... Now I know why

[SoCal Craig]

[quoteYes, it's like a big pair of pliers with flat plates on the jaws. When the handles are clamped, they spread out.

[/quote]

Like the kind the racers use on Speed Channel? Where can I buy one? I've searched various racer parts, brake tool, and brake (Brembo, StopTech) websites, but cannot find that tool.

[Chuck 98 RT/10]

It sounds like the piston is on the very edge and is cockeyed in the cylinder. Take the caliper off and look at the piston very closely. If it looks like one side of the piston is higher than the other, put channel locks on the high side and squeeze. Keep the bleeder valve open. It'll make a mess so have some towels near by.

[SoCal Craig]

Thanks Chuck. I'll try that tomorrow.