The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: NorR65 on October 09, 2010, 11:15:29 AM
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I can not push the pistons back in the caliper, not even with pliers.
I have opened the bleed screw and then pushed the pistons back but with no success. The calipers need to be overhauled.
My first question: My Hayes book tell me to split the caliper before I removes the pistons. I think I read in an article by Snowburn that it can be difficult to align the two halves and avoid leaks.
Can I get the pistons out without splitting the caliper?
Any good ideas how to overhaul the calipers as easy as possible?
Thanks
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There's an o-ring between the caliper halves, that should be replaced .
With the caliper assembled, I don't think you can get the pistons out of the caliper.
If the pistons are seized in the caliper, disassemble the calipers and use air pressure to remove the pistons .
Use caution when doing this, as the pistons can come out with a lot of force, make sure you have something to stop the piston and contain the fluid that is still present in the caliper, otherwise you will have a real mess to clean up .
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It is probably just a real mess inside. That is what I found.
I had no issues with alignment. Although my 1979 came with ATE calipers, they are for the most part identical to the Brembos.
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fwww.pbase.com%2Ftomfarr%2Fimage%2F75975722%2Fmedium.jpg&hash=59ee6bea3d8234792428b1ab11d8a7e386a78988) (http://www.pbase.com/tomfarr/r65_brakes)
click for more pictures
Do yourself a favor, and rebuild the entire system at this point. That includes replacing the flexible line.
Most folks go with stainless steel braided line, these days.
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My calipers are ATE. Do they too have an o-ring between the caliper halves? If the calipers and hoses looks as messy as the master cylinder reservoir inside then its a wonder that the brakes functioned at all.
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My calipers are ATE. Do they too have an o-ring between the caliper halves?
Yes
If your pistons are stuck in the caliper the only way your going to get them out is with pressure behind the pistons. Safer with hydraulic pressure if you can so don't drain the fluid out before you start. Just use the brake lever to force one of the pistons out. When I overhauled my caliper I managed to force the RH piston out before splitting the caliper then replaced the O ring with a rubber disc to block off fluid from the RH side of the caliper after reassembly which then allowed me to pump out the LH piston with hydraulic pressure.
I had no problem with leaks from the O rings. Actually if I remember correctly it's a square section ring.
If you have some corrosion on the piston and it's not too bad you can polish it out and you will be OK. It's the piston seal that keeps the fluid in not the piston itself. The caliper bores have to be good though.
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My master-cylinder is dead, will not hold pressure.
I guess I have use some form of air to free the pistons.
I start to take the brakes apart tomorrow. Then I will see what parts I need to order.
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Sorry
I hadn't read your other thread on the master cylinder problem.
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No need to be sorry Barry.
I am really happy for all help I have got from you and everybody else on this forum.
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Nor65,
Here's some photos of what you can expect when and if you get inside your ATE' calipers. Best way to free the pistons is secure the bleeder valve, insert a loose fitting block of wood in-between the pistons with the pads removed, secure the caliper in a vice carefully and apply compressed air through the delivery line port. Be VERY careful, the pistons will release with violent force. Keep your fingers out of harms way. Be sure to clean everything very very well. Rob's pictures look a lot like mine when I opened up my calipers after 15 years of storage. Looks a lot like gravy in there. Cleaning things thoroughly is key. I don't use any lube other than brake fluid for re-inserting the pistons and new square o-rongs. Be sure to line-up the pistons with the bores as close as possible. I've always been lucky with my caliper rebuilds, the pistons and square o-rings have gone back in with thumb force. Don't use a hammer! The small caliper o-ring for the caliper halves are unavailable as far as I know. I think Bob was able to find some in a specific kit somewhere if my memory serves me correctly. If not, I have hundreds of replacements that will work fine you can have for free. I'm more than happy to mail them to you if needed. Below are some links to my brake rebuild and an essay (pdf attachment) on the o-rings I wrote up a while back with Oak's review. Hope the pictures help or at least give you an idea of what to expect.
http://s428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Front%20Brakes%205-09/?start=0
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Nice write-up, Mike! I remembered someone having a bag of o-rings, but I couldn't remember who.
I did mine before yours, and I ended up re-using my small o-ring. I didn't remember it being a square section, though. But that was 4 years ago...
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Motobins has the o-rings for those of you in Europe, or OZ .
The o-rings that go between the caliper halves a round in cross section, the seals that into the caliper and seal against the piston are square cross section .
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Motobins has the o-rings for those of you in Europe, or OZ .
The o-rings that go between the caliper halves a round in cross section, the seals that into the caliper and seal against the piston are square cross section .
Mike V's PDF write-up seems to indicate he found a square section o-ring between the two caliper halves, and he settled for a more typical round cross-section o-ring.
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Rob,
The old caliper o-rings I removed seemed to be square in profile. Don't really know if the originals were round or square. I looked at them very closely - it's very possible they were originally round and over the years formed themselves to appear square under years of compression. The replacements fit perfectly with just the right amount of bulk for good sealing compression. I have over 1500 miles on the bike since the rebuild and since the article was written. No caliper drips, leaks or errors. I couldn't be more pleased with the brakes on this bike! It's one of the things I enjoy most about riding the R65...it's ability to stop with very controlled lever modulation and good feel & feedback. Don't understand why the ATE's get such a bad rap.
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Don't understand why the ATE's get such a bad rap.
It is the "swinging" ATE's on the /6 & /7's that had the bad rep. But I think that is because they required a special logic to setting them up to work best.
Here is a picture (http://www.stephenbottcher.net/BMW/R100T-Dateien/frt_new.jpg) from Stephen Bottcher's website.
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Mike V
Thanks for the offer of o-rings. May be I will need 2 o-rings.
When I bought the R65 I got a few spare parts, including some small o-rings for a Brembo caliper, I will measure them, may be they fits ATE calipers also.
Since I have no compressed air, is there another way to loosen the pistons? Pliers? Grease gun?
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I didn't have compressed air either. Grease gun sounds a good idea though.
If they are tight I doubt you will do it with pliers without damaging the pistons.
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If you don't have an air compressor (buy a cheap one, you will need it), take the calipers to a car repair shop. They will blow them out quickly, and probably not charge you very much.
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The ATE caliper pistons are no longer available from BMW, they are specific to the R65, the larger bikes had larger diameter pistons .
So treat the pistons with care .
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The ATE caliper pistons are no longer available from BMW, they are specific to the R65, the larger bikes had larger diameter pistons .
So treat the pistons with care .
Motobins has them in stainless steel, as does that guy who I posted about some time back, but I don't know if his measurements are correct.
Or Justin could probably whip out a few dozen quickly....
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I checked Motobins, they removed them from their online catalog about 6-8 moths ago, just checked again today and I couldn't find them .
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Oh. Sorry. I wish places would tell me these things so that I could keep my memory updated.
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Justin could probably whip out a few dozen quickly
Yeah, right... ::)
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I have got one caliper off the bike, splitted it and pushed out the piston with a grease gun. It was a lot of hard work. Both pistons have some pitting at the top and bottom, not in the middle of the piston. The caliper did not leak before I took it apart so I think it will perform OK with new seals. Do you agree?
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Nor65
My guess is you'll be fine. The piston is in contact with the square o-ring mainly in the center portion of the piston and a very small travel area at that. Try cleaning the pistons of grit and gunk and corrosive buildup with a green scotch brite pad or 00 steel wool soaked in brake fluid. Flush well with brakekleen and re-polish. Kind of a wet lubricated non-abrasive polishing affect. Don't scratch or burr the piston surface where it contacts the square o-ring. The corrosion you're seeing is probably the outboard portion of the piston exposed to the elements. Be sure to clean the inside bore of the calipers very well and with a sharp plastic or wood (non-abrasive) tool clean the inside corners where the square o-ring rests in place. The better for reinstallation of the piston and seating of the square o-ring. Be sure to replace the old square o-rings with new ones.
Clean, clean, clean...
http://s428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Front%20Brakes%205-09/?action=view¤t=81R65Restoration001.jpg#!oZZ30QQcurrentZZhttp%3A%2F%2Fs428.photobucket.com%2Falbums%2Fqq8%2Fgruntyman66%2F81%2520R650%2520Restoration%2FFront%2520Brakes%25205-09%2F%3Faction%3Dview%26current%3D81R65Restoration002.jpg%26
http://s428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Front%20Brakes%205-09/?action=view¤t=81R65Restoration05-19-09008.jpg
http://s428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Front%20Brakes%205-09/?action=view¤t=81R65Restoration001.jpg
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I got new seals for the caliper and seals for the master cylinder from Motobins. Cleaned everything and installed the seals.
My brakes is much better than before. The caliper pistons was more pitted than I liked. I guess I need new pistons which I can not buy anymore.
Maybe other mc or cars use 36mm pistons? Any ideas?
Or can I use calipers from other BMW`s?
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Brembo calipers from the LS will work on bikes that originally had ATE calipers, the pistons for the Brembo's are still available .
The aluminum pistons don't seem to exhibit the corrosion problems of the chrome plated steel pistons the ATE's have .
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I guess I need new pistons which I can not buy anymore.
Maybe other mc or cars use 36mm pistons? Any ideas?
Brake pistons are relatively simple cylindrical lumps of metal with the correct dimensions. Any decent machine shop could make new ones in stainless steel using yours as a pattern.