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Retracting rear brake piston

7244 Views 12 Replies 7 Participants Last post by  AlexGS
I removed my rear brake calipers and pads this weekend to check the wear. When reassembling, I had no problem retracting the passenger side (starboard) piston using a large C clamp and a large channel lock to turn the piston clockwise back into the caliper.

The drivers side piston however was a bear. I really had to torque on it with the channel lock and a pry bar suck in the caliper to turn it. I only was able to turn it ~3/4 of a turn (enough to get the caliper back on).

Do I need a new drivers side caliper, or am I missing something here? I'll be getting new discs and pads too.
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Was the master cylinder full to the top? You may have needed to take some brake fluid out of the MC to retract the other caliper. If that is not the case, you may need a new caliper, but I really kind of doubt it. They can be fairly difficult to retract from my experience. :eek:
Crack open the bleeder screw and see whether you can retract the piston easier. If yes, then something wrong with the hydraulic line. It could be the proportional valve - you should be doing the bleeding with the rear suspension under load (i.e. support under the strut). If the piston is still hard to turn with the bleeder screw open, then it is possible that the piston seal is gum up due to corrosion or the parking brake mechanism inside the caliper has some problem.
Yes, where is my brain. Leave opposite side wheel on the ground, jack up the car on the side you want to work on, support that side and then jack up under that strut to put weight on the suspension. If you follow the brake line, it leads to a proportioning valve in the center of the rear axle. That valve closes off if weight is not on the rear suspension. It should not be a problem then. Look under there and you will see how it works. ;) You must bleed the rear brakes with weight on the rear suspension as well.
So, I should have had weight on the suspension when retracting the piston to allow a release for the fluid?
So, I should have had weight on the suspension when retracting the piston to allow a release for the fluid?
The last time I did mine, I raised both sides and supported the struts to ensure the proportioning valve was completely open.

The wife complained about the car "Being up on blocks". I thought it matched the upholstered chair on the front porch. ;)
Finally had a go at this.

Tried jacking up the suspension as suggested, no luck. I then removed the caliper from the car and put it in the vice, no luck.

I can get ~15 degrees of turn until the piston stops, both ways. I can't retract it back into the cylinder or remove it.

One item of note is that my pads were worn almost all the way. So the piston is out just about as far as it goes. Make a difference? I don't know but either way, I'm not able to do anything with it.

Unless someone has some great idea, I'm planning on getting a rebuilt caliper.
Sounds like it is probably frozen from rust and corrosion ...

Have you tried pop the lever (as in the picture below)? Can you move the lever back and fore (I do it with a plier)? It would pump the piston out when you move the lever and I think it will stop when it reaches some max extension - I always stop when I the piston didn't appear to move out more. Take a look at the inside of the rubber seal to see how much corrosion and dirt is in there on the piston wall.

Have you tried it with the bleeder screw open too? It is still possible that one side of the proportional valve (or the rubber brake hose) has some problem!


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Yes, I cracked the bleeder screw with the suspension jacked up. I then removed the caliper from the car and have it in a vice, so the hose is unattached and fluid is free to flow out.

Yes, the handbrake lever moves. I had to move it in to remove the cable.
Did you use a C-clamp to apply pressure to piston as you rotated piston with curved jaw vise grips or water pump pliers?
Sounds Like frozen caliper.
I use this tool for the rear calipers, makes things very easy.

Picture is a bit wrong in that the wrench provided is a double sided wrench with a 15mm (for pins) and the large section shown.

I have rebuilt calipers or good used ones if you may need one.

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Thanks, I had already called APE and they are sending me a used one.
Thanks, I had already called APE and they are sending me a used one.
One thing I didn't spot in this thread - when I attempt to wind-in rear caliper pistons, I always slacken the handbrake cable fully first (i.e. undo the nut at the lever until the cable is really loose). I only retighten the cable once I have operated the footbrake about 20 times.

On my FIAT Stilo, one side piston had to be wound in anticlockwise, the other side clockwise. I have never experienced this on any other car so I presume that all 164s are clockwise-only both sides.

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