M caliper rebuild question

[Davz912/911]

Hi All,

Due to Covid... and some squeaky brakes, I find myself needing to rebuild my calipers.
Left front first... found this... seems the brass bushing is stuck to the pin. Currently soaking
In PB blaster.
Question, since the piston “came apart” and it seems the washer that holds it in place in the piston
Is peened in place, do I need to replace the piston?

Thanks in advance,
Dave

[Jim Breazeale]

Hi All,

Due to Covid... and some squeaky brakes, I find myself needing to rebuild my calipers.
Left front first... found this... seems the brass bushing is stuck to the pin. Currently soaking
In PB blaster.
Question, since the piston “came apart” and it seems the washer that holds it in place in the piston
Is peened in place, do I need to replace the piston?

Thanks in advance,
Dave

Those pistons don't have a clip to hold the "knock back" device in place like the earlier ones. Yes, I would replace them.
You may want to call me at 510-504-3333 and I can give you options.

Regards

Jim

[Davz912/911]

Thanks Jim,

Great talking to you. New piston on order from PMB, along with some new rubber brake lines ��.
Was able to get the knock back device off the pin too.

Cheers,
Dave

[Davz912/911]

The saga continues... the knock back device doesn’t slide over the pin.
Seems the spring inside it is deformed. Any ideas would be appreciated.

Dave

[davep]

The knock-back device is supposed to grip the pin. In use, the piston is forced out by hydraulic pressure from the master cylinder when you put your foot on the pedal. When you remove your foot the pressure is released. When the piston is forced out, the K-B moves with the piston, and the internal spring is compressed. When the pressure is released, the spring pushes the piston back into the bore; with some assistance of the sealing ring. This re-establishes the venting clearance of the pad to the rotor so that the brakes are not dragging. As the pads wear, the piston must move permanently along the pin, so the K-B mechanism does have to creep along the pin. This means that the K-B mechanism is difficult to manual move along the pin while servicing, but perseverance is a virtue. This means the the K-B mechanism is essentially 4 parts: the outer portion that is either peened in place or held by a circlip, the spring, the inner gripper portion, and the pin.

[Davz912/911]

Dave,

Thanks a million for your fantastic description.
I get it now. You now, after watching 20 YouTube
Videos... yeah, that desperate, there are a lot of holes in the
descriptions.
Thanks for sharing the knowledge... much appreciated!

Dave