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Front caliper pistons not retracting !!!

guzzijimbo

guzzijimbo

Tuned and Synch'ed
GT Contributor
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Location
Maleny, Queensland, Australia.
Can any one through some light in to this dark corner: A 10 year old B11 that's done 50,000 kl, I noticed some resistance when I pushed it across the shed floor, with front wheel off the ground I found the pads were handing on to the discs, after some on bike testing I removed the calipers and pressurized them with air to find that they were doing the same thing with no possible influence from the master cylinder or lines. Both performing similarly.

I dismantled inspected, cleaned, lubricated and remantled, (if that's a word) the result was a slight improvement but still a long way from right. The discs are approx. 5mm I inserted a 7mm disc to prove that (not apparent) pad ware had not put the pistons in an awkward position, same result.

It's all new to me but the only explanation I can see is that the seals have swollen with age?? and are inhibiting the retraction of the pistons. Am I missing some thing !!???
 
Since you have done all the appropriate things (cleaning etc) have you ridden it at all ?....do the discs get overly warm over a short distance( 2miles) ?

They never move very far from the discs because of the very small piston movement at the lever end.
 
I had trouble with my Breva 1100 front brakes a while ago, it turned out to be a tiny spring in the dust boot on the brake lever. The rubber boot had perished and part of the spring had somehow got behind the piston and was causing it not to fully return (I'm talking 0.5mm) and therefore keeping the brake on, albeit lightly. After a short ride, brakes got hot the fluid couldn't return and the brakes went on harder until it almost locked up the front. I couldn't get just the boot and instead put a small washer to stop the spring riding over the circlip.
 
"I dismantled inspected, cleaned, lubricated and remantled,"
Re assembled would be the term.
Anyway, did you replace the piston seal? If not, do so.
I have never had a calliper still seize once it has been properly cleaned and the piston seal replaced.
What actually happens is the seal is sitting on a small ridge in the calliper and when the piston slides out, it deflects the seal ever so slightly.
When the pressure is released, the seal returns to centre and brings the piston (and pad) off the rotor.
Because this is a very small movement, it's critical the seal is good and the seat is clean...clean...clean.
Also, you can clean the inside of the calliper cylinder (gently) with 0000 steel wool to make sure the bore is smooth.
 
I'm with Kevin on this one. Caliper problems are usually the master cylinder. When they are tight against the rotor, do they detract if you open a bleeder? If so the issue is at the master cylinder.
 
Keith Broughton said:
"I dismantled inspected, cleaned, lubricated and remantled,"
Re assembled would be the term.
Click to expand...

Well, I kinda like "remantle." Then, again, I did just write "kinda." ;)

Seriously, I think the OP was kidding comma but ...

See https://www.google.com/#q=remantled, which would seem to indicate some support for the commonsensical construction. :happy:

On the merits, really appreciate your comments and the others', as I get what clues I have about wrenching from such threads.

Bill
 
Nice work Bill, I like that !!!
I've restored many a caliper, usually from a poor state, this one looks like new inside, all the evidence points towards the seals being the culprit, it can't be the master cylinder as I get the same result on the bench. I've been reticent to buy new seals to date as they are bloody expensive for what they are and too often, (once is too often) over the years I've replaced the wrong part.

As Keith points out there is little room for error, and 10 years on... while they look perfect they may well be off their game.

By the way if you can dismantle why cant you mantle?
 
I am also having probs with front caliper seizing - all down to crud sticking the pistions. i got the bike just over a year ago and whilst i checked the pads i have not had the caliper off. just noticed that there are no seals on the piston external of the caliper - Brian Uk raised that. probably when piston has jammed up.

i need to get new seals but i dont know the caliper model - the seals are pretty expensive for what they are so i dont want to order up wrong ones
 
jim mac said:
I am also having probs with front caliper seizing - all down to crud sticking the pistions. i got the bike just over a year ago and whilst i checked the pads i have not had the caliper off. just noticed that there are no seals on the piston external of the caliper - Brian Uk raised that. probably when piston has jammed up.

i need to get new seals but i dont know the caliper model - the seals are pretty expensive for what they are so i dont want to order up wrong ones
Click to expand...


Jim,

If the resource section does not have the parts manual for you bike, Check Leo Tamer's site http://www.tlm.nl/en/parts/new-parts/partsmanuals/
 
Got the seals ordered, now cant get the bloody torx bolts out so that i can split the caliper. Is there a trick to this or just plenty of loose oil and a bit of bashing ?
 
guzzijimbo said:
Nice work Bill, I like that !!!
I've restored many a caliper, usually from a poor state, this one looks like new inside, all the evidence points towards the seals being the culprit, it can't be the master cylinder as I get the same result on the bench. I've been reticent to buy new seals to date as they are bloody expensive for what they are and too often, (once is too often) over the years I've replaced the wrong part.

As Keith points out there is little room for error, and 10 years on... while they look perfect they may well be off their game.

By the way if you can dismantle why cant you mantle?
Click to expand...
My apologies if I pointed out the obvious but your OP did say "new to me" but then you say you have restored many callipers.
Anyway, if one goes to the trouble of taking a calliper off the bike then dismantle it, might as well replace the seals.
Then..er..remantle them and place them on your mantle to lift the mantle of responsibility off your shoulders :rofl:
 
jim mac said:
Got the seals ordered, now cant get the bloody torx bolts out so that i can split the caliper. Is there a trick to this or just plenty of loose oil and a bit of bashing ?
Click to expand...


Use a 50/50 mix of automatic transmission fluid and acetone as a penetrating oil. Last resort a little heat. Do be advised there is an o-ring between the two halves that should be replaced. Hopefully it is in the rebuild kit for the caliper.

For your information:


April 2007 "Machinist's Workshop" magazine comparison test wrote:
They arranged a subjective test of all the popular penetrates with the control being the torque required to remove the nut from a "scientifically rusted" environment.

Penetrating oil ...... Average load ..... Price per fluid ounce
None .................... 516 pounds
WD-40 .................. 238 pounds ...... $0.25
PB Blaster .............. 214 pounds ...... $0.35
Liquid Wrench ......... 127 pounds ...... $0.21
Kano Kroil ............... 106 pounds ...... $0.75
ATF-Acetone mix ....... 53 pounds ...... $0.10 (50/50 mix)

The ATF-Acetone mix was a "home brew" mix of 50 - 50 automatic transmission fluid and acetone.

Note the "home brew" was better than any commercial product in this one particular test.
 
Thanks Brian, I was a bit worried about your sense of humor but I see I have no need for concern!!

The "new to me " comment relates to the fact that I've had success with the procedure described above on many an occasion and was perplexed and looking for something that I missed. There are no other suspects so new seals it is.

Thanks for your thoughts men. And Jim, follow John's advice, the home brew is a winner and go easy with the heat, nice hot water can't get you in to too much hot water.
 
Right, got the new seals fitted, but now cant get the front to bleed at all. Trying usual method, pumping levere, hold ,turn bleed screw, release air, tighten - but not gettng anything through, fluid remians in the reservoir.

Will try reverse bleeding tomorrow, told cold to do anymore todqy

Is the ABS anything to do with it,?
 
Get a 60 mil syringe and some tubing and inject brake fluid from the calliper bleed port up stream into the lines.
Make sure the master reservoir cover is loose and do it SLOWLY to avoid spraying brake fluid out the top.
I tried this on my last calliper re- build (re mantle?) and won't do it any other way from now on.
NOTE: this was not an ABS brake system.
 
Wow Big thanks Keith. I use "Ed's Red" for cleaning a lot and it is great.

25% ATF + 25% Acetone + 25% Kerosene + 25% Mineral Spirits

Now I don't have to screw around purchasing WD40 and all I have to do is make up a pint.
 
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