caliper woes

[JJH]

1979 BMWR65  
I recently found that my front brakes were dragging rather dramatically on the wheel.  I confirmed that the small return hole on the reservoir was open, and just for fun I bleed the brakes.  Seeing no improvement I thought I would have a look at the caliper and pistons.  Well one side did not move at all.  I engineered a work around and finally removed both pistons from their bores.  The bores were filled with disgusting fluid, lots and lots and lots of brown solids.  The outside of one of the pistons (the dust seal area) was covered with dried yellow solids, which I assume is dried brake fluid?  I cleaned everything up the best I could.  I fitted the cleaned pistons into the clean bore using brake fluid, but they can not be moved in and out with just hand pressure. The seals in the bore actually looked very good, but there is quite a bit of corrosion in the bore, and to some extent on the pistons.  The question is what can be done?  Does this require a new caliper, or can the bores be re-honed.  I assume that there new pistons are still available.  I know that one can still purchase seals.   Also I have a embarrassing question/ confession.  when I was driving out the pin to remove the pads, upon removing the first pin I heard a ping, and the sound of metal landing on the floor.  I found a  pin, the cross piece spring, but also a conical shaped spring.  Is this something that should be there, or was it just a bit of mechanical flotsam or jetsam that exist in my garage.  Thanks,  John

  

[Mike V]

JJ,

ATE' calipers?

Sounds like your calipers need a good cleaning and rebuild.  Clean the pistons and caliper internals the best you can with clean brake fluid. You can use a green scotchbrite pad or similar.  As long as your pistons and caliper bore aren't pitted they should clean up well. Pay particular attention to the square o-ring groove and make sure it is surgically clean along with the rest of the caliper internals. You can use a plastic or wood pick to get into the corners of the square o-ring groove or even a metal pick if you are careful. Don't worry too much about your pistons unless the middle is pitted.  The square o-ring contacts only a small portion of the piston.  Purchase a rebuild kit which consists of new square O-rings and dust seals. Be sure everything is very clean, personally I recommend not using water or solvents which can leave behind harmful residue.  Water is a brake system's enemy in any form.

I'm guessing the metal piece you are referring to is the retainer clip. It helps keep the pads in place and restricts movement and high frequency vibration. The small rivet often corrodes and separates itself.  They are available from many sources.

If you need to replace the caliper fluid gallery o-rings after you separate the caliper halves I have several I can send you.  They are NLA.

If you can - post some pictures of what you have so we can better help and lend some opinions.  
  

[Barry]

Corrosion is common with the ATE pistons. The critical part that must have a good finish is the part of the piston that contacts the seal. The bore of the caliper serves no function other than to guide the piston so that may clean up OK.  When you reassemble I would not coat the outer end of the piston with brake fluid as that just attracts moisture even though it's under the dust seal and the corrosion then works it's way down to the seal area of the piston. Red rubber brake grease will be better to keep the corrosion at bay.

I found a  pin, the cross piece spring, but also a conical shaped spring.  Is this something that should be there, or was it just a bit of mechanical flotsam or jetsam that exist in my garage.  Thanks,  John

The conical shaped spring is a puzzle unless it the part that fits on the end of the pin to act as a retainer.

[Barry]

Corrosion is common with the ATE pistons. The critical part that must have a good finish is the part of the piston that contacts the seal. The bore of the caliper serves no function other than to guide the piston so that may clean up OK.  When you reassemble I would not coat the outer end of the piston with brake fluid as that just attracts moisture even though it's under the dust seal and the corrosion then works it's way down to the seal area of the piston. Red rubber brake grease will be better to keep the corrosion at bay.

I found a  pin, the cross piece spring, but also a conical shaped spring.  Is this something that should be there, or was it just a bit of mechanical flotsam or jetsam that exist in my garage.  Thanks,  John

The conical shaped spring is a puzzle unless it the part that fits on the end of the pin to act as a retainer.

[Mike V]

Spring ...

[Bob_Roller]

If you are reusing the old square section seal the the piston goes through, that may be your  issue, I would replace the rubber parts, they may be originals .

Post a picture of your spring, I don't think it is from an ATE caliper .

[JJH]

Thanks for all the information.  It sounds like the little conical spring is not part of the brake system.  I will pay special attention to the square o-ring area.  Mike V.  thank you for your offer for the little o-ring.  
Best regards,
John

[D Mann]

Here is an article that can keep you on the right path. http://bmwmotorcycletech.info/brakes.htm

[mrclubike]

If you decide to get a new caliper assembly.
Don't worry there is a very reasonable alternative to the Crazy high priced OEM.
http://www.mgcycle.com/index.php?main_page=product_info&products_id=1034
remember this also has new pads and has a larger bore size giving better braking