What makes a brake caliper release? - Alfa Romeo Bulletin Board & Forums

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Old 03-27-2009, 03:21 PM
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What makes a brake caliper release?

Right rear caliper is sticking a little on the Spider. I can turn it with a long screwdriver for leverage between the lug studs but can't turn it with my hand.

I replaced the pads on all 4 wheels not too long ago. Would it be a seal or a hose or what?

I checked & made sure the e-brake isn't stuck. It's on the left on my car anyway.

I wonder if Midas or Schwabs would charge me anything just to look at it.
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Old 03-27-2009, 04:08 PM
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The pistons in the calipers are gripped by the (square cut) seals. When you apply the brakes the seal distorts slightly then, when you release the brakes the seal pulls the piston back (slightly). As the pads wear (or when installing new pads and the pistons have been fully retracted) the piston will slide through the seal - making them 'self adjusting' (when everything is working properly).

Another possibility for a non-releasing caliper is a faulty brake hose. They can collapse internally or delaminate and act like a one-way hose. Brake pedal pressure will push fluid to the caliper but the restriction in the hose can prevent the seals from being able to pull the piston back. To test this possibility try applying & releasing the brakes then (with no pedal pressure applied) crack open the bleed screw. If you get a squirt of brake fluid and the caliper releases then the hose is suspect.


I'm sure Midas or others would be glad to look at it but I doubt they've ever actually worked on an Alfa. They are no different than any other cars but I'd be leary about letting them 'learn' on my car. Why not find a competent Alfa mechanic? How about the one in your mirror?
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Old 03-27-2009, 04:20 PM
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If the brakes were working OK and there is no evidence of leaks it could be dirty pistons. Try this: remove one pad and have a trusted assistant gently apply the brakes (doing this by hand instead of foot is a good idea) while you watch the piston where you removed the one pad. Tell your assistant to stop when the piston has moved out about 1/4" to 1/2". Do not allow the piston to move out so far that it gets ejected from the caliper's bore.

The Alfa calipers have a dust boot over the pistons so you will have to carefully remove that to get to the piston.

With the piston extended, use an old toothbrush or a soft rag moistened with brake fluid to clean off the exposed portion of the piston. I use a strip of rag in a 'shoe shine' fashion to clean off the piston. Then apply a bit of clean brake fluid - enough to slightly moisten the piston & seals and push the piston back in. Have your assistant again work the brake pedal while you watch the piston to 'exercise' the piston. You should be able to see the piston move out when the brake pedal is moved and retract slightly when the pedal is released. If this works, reinstall the brake pad and do the same for the other piston.

Clean any brake fluid off the rotor and retest the brakes.
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- -~ 1981 GTV-6 ~
Mebane, North Carolina

L-jetronic Spider diagnosis (1982-1989)
L-jetronic V-6 diagnosis
OK injectors - fuel injector cleaning
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Old 03-27-2009, 04:49 PM
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Stellar. Thanks so much Eric, i'll try that.

BTW i did contact a local brake shop and he just said "replace the calipers, it'll cost less than having me rebuild them".

If there is something i can do myself, i'll do it (as evidenced by the numerous requests for help on this forum when i get stuck )

*edit* I wish i had known that tip wrt the pistons when i had them all apart not that long ago. I replaced all 4 pads when i installed a new (used) rear diff.
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Old 03-27-2009, 04:50 PM
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Here's a couple of picture I stole off somebody here (sorry, I don't recall who to give proper credit).

These are of a split caliper. Note that it is generally advised to not split the calipers for routine service.

The first photo shows the parts disassembled. L>R = seal, piston, dust cover, dust cover retaining ring

The second photo shows the caliper re-assembled. Note the dust cover. Also note the cut out section of the portion of the piston that will contact the back of the brake pad. That cut out should be properly positioned when assembled. Look here for info and a template you can print out.
Attached Images
  
__________________
- - Eric
don't read this
~ 1984 Spider Veloce ~
- -~ 1981 GTV-6 ~
Mebane, North Carolina

L-jetronic Spider diagnosis (1982-1989)
L-jetronic V-6 diagnosis
OK injectors - fuel injector cleaning
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