Rear Brake locking up

Because this milling in that position is on top and helps to bleed air out of the piston’s inside?
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mkmini said:
So now I don’t understand why the groove on pistons pad side has to be horisontally upside.
How does that matter?
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I believe it is two things.

One it reduces the tendency for an air pocket to hide in the deep recesses below the circlip inside the piston and the groove engages the tab on the back of the pad which keeps the piston from rotating as the ebrake system and the hydraulic system drives the threaded portion along to compensate for the wear of the pads.

Others will be along shortly to expose my ignorance I am sure :)
 
Anyway so far I still don’t understand how self adjusting happens.

I think that got it.

When brakes are pressed and pads worn out, that central thing with inner thread screws off. And there is always same amount of movement for ebrake and brakes.
 
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It is a bit hard to make out from your photos, but if you look at the inside bore of the piston, you will see that it is not circular. The scalloped out part should face up (corresponding with the groove facing up), and is there to reduce the chance of air being trapped inside the piston.
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Boom. There is the exact answer. Thank you, I had missed that detail as I havent pulled one apart for a while (since around 1983/4....)

ng_randolph said:
It is a bit hard to make out from your photos, but if you look at the inside bore of the piston, you will see that it is not circular. The scalloped out part should face up (corresponding with the groove facing up), and is there to reduce the chance of air being trapped inside the piston.
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For those who are thinking of refreshing their calipers:
1.it is very easy job if follow instruction
2.new pistons are empty, withou rachet mechanism, so disassemble all, to be sure that it won’t be cheaper to buy new caliper
 
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Regarding a couple of your questions.
I believe the pistons are the same for left and right; it was coincidence the clips were that way.
As you said, the milling inside the piston - same as was @ng_randolph said.
I think your idea about how the adjuster works is correct.

Those pistons appear to be corroded and scored. Might be best to replace them (but I think you already have). ;)
 
Pistons and internals are same.
When placing a washer before lockring, place it horisontally to prevent air being locked in piston.


Yes i installed new pistons and all seals

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Looks like you've used copper grease in the handbrake mechanism? I've only seen Moly grease used here - could there be a problem with the copper grease softening the rubber boot long term? 😕
 
I didn’t like the rust under grease what there was prevoisly ang got hard to scratch off.

I don’t know is copper grease better or worse.
But chassis will corode faster than that boot I guess 😬
 
EricH said:
Next time it locks up, try cracking the bleeder open. Chances are that you'll get a spurt of brake fluid and then it will unlock for a while.

You can try replacing the hoses (they can collapse trapping fluid under pressure in the caliper) and rebuilding the offending rear caliper (a real pain because of the e-brake mechanism).

I'm not going straight to master cylinder replacement because only one of your two rear calipers is affected and the problem goes away when the car sits and rests. An MC problem would affect both rear calipers and generally doesn't clear itself.
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Had a similar situation with a Fiat 500. Ended up being the hoses that were collapsing on the inside (not visible) because of old age and, as mentionned, trapping return fluid. Replacing all hoses in the system corrected the problem.
 
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