Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: florence on June 06, 2021, 11:58:19 AM
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Having taken apart my front caliper and replacing the piston and seal, I am contemplating re-assembly. I want to put something on the threads of the two large bolts that go through the caliper so that I can undo them next time it needs servicing. Would a very slight smear of high melting point grease be OK, I don't imagine it will get anywhere near the pads or disk?
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Or Copper slip ,that's what I use
Sent from my SM-A750FN using Tapatalk
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Thanks John, I did think that but I haven't got any and wanted to finish the job today.
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Any grease temporarily then coppaslip as soon as you get some
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Thank you Bryan.
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well, I have assembled the brake caliper, very easy and quick but suddenly realise I may have made a mistake. The new piston is stainless steel rather than the original chrome steel type and therefore will be prone to electrolysis with the aluminium and the bike spends most of it's time outside. Although the old type of piston goes rusty after a few years, it doesn't affect the caliper. Has anyone had problems with this and should I order an original piston?
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Put a stainless piston in my front brake in 2007, it's still fine, the piston is separated from the alloy by the seal.
Cheers
Dennis
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Fitted loads and never yet had a problem
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It needs to be assembled with silicone grease as this prevents an electrolyte forming from water and salt in the gap between the piston and caliper bore. There is no weather sealing on this type of caliper and this takes it's place as best as can be provided.
It's even in the first 750 KO manual as direct instruction.
Don't assemble with brake fluid as lubrication for the seal, it's hygroscopic (absorbs water) and just promotes accumulation of moisture to facilitate electrolysis.
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OK, thanks for the advice, looks like I will have to take it apart again before winter and get myself some silicon grease.
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You can just get small pot size from plumbers merchants or something like this
https://www.amazon.co.uk/PROUNOL-Silicone-General-Purpose-Dielectric-Waterproof/dp/B088361TCJ/ref=psdc_303918031_t2_B086QBNSRT
It's generally very useful anyway for all sort of things as inert to most materials, and so safe to use.
Particularly good on electric connections on old Land Rover systems too. ;D
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Car mechanics use this.
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Not in UK we dont just copperslip. You wont find many car mechanics rebuilding calipers usually exchange rebuilt ones are fitted due to cost of labour
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well, I have assembled the brake caliper, very easy and quick but suddenly realise I may have made a mistake. The new piston is stainless steel rather than the original chrome steel type and therefore will be prone to electrolysis with the aluminium and the bike spends most of it's time outside. Although the old type of piston goes rusty after a few years, it doesn't affect the caliper. Has anyone had problems with this and should I order an original piston?
Galvanic corrosion as you know occurs when two disimilar metals are in contact so both types of caliper metals will have this issue be it your new stainless steel calipers or the original chrome/steel type.
On the outside you will have water / salt road grime helping the corossion process on the inside you might have water if you are using mineral brake fluids due to the hygroscopic nature of most brake fluids. Certainly on cars it is my experience that calipers seize or stick due to moisture getting past the dust seals causing the chrome to pit etc.
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"Certainly on cars it is my experience that calipers seize or stick due to moisture getting past the dust seals causing the chrome to pit etc."
That's one of the issue here, they have no external seal at all, dust or otherwise.
It's just straight into the bore between the piston and caliper until it meets the only seal. You get a creeping corrosion that also travels round behind the seal into the machined groove, ultimately compromising the seal ability to retract the piston in use and resulting in brake binding.
The silicone greaee is the external protective boundary if they are assembled dry (no fluid) with it.
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Not sure of its relevancy here but I met an Austin Mini owner at a car show it was a 998 Cooper that was just like it had left the factory he had one front wheel off the car to show the gleaming brake disc, hub & caliper. He trailered it to events using WD40 spray to prevent any oxidation of the bare steel parts. Not sure what the brakes were like with WD40 on the disc but it seemed to work.
I believe there are sprays (GT85 PTFE based) for use on pedal cycles where you spray the Shimano mechanism after a wet or mudy ride that are very effective at keeping,chains, cranks, pivots from rusting. After a winter ride a spray avoiding the discs might be effective.
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"I believe there are sprays (GT85 PTFE based) for use on pedal cycles where you spray the Shimano mechanism after a wet or mudy ride that are very effective at keeping,chains, cranks, pivots from rusting. After a winter ride a spray avoiding the discs might be effective."
That field is complete and utter bog of wonk opinions on what should be used on any of the components, supplied by manufacturers selling "special" potions in tiny bottles starting at something like £8.99 for half a fluid ounce. ;D maybe a soapbox view, but they really are nuts in there.
Working on a lot of that equipment, I treat the calipers the same as these bikes as they also have zero weather protection for the pistons. Calipers with 2, 4 or 6 piston in aluminium, stainless, phenolic or titanium all are fine with silicone grease. Also it's imperative that the seals are free and retract the piston promptly as pushing any drag along in a brake is purgatory.
As you point out though, keeping anything clear of disc and pad material is primary as it stops them working very quickly. Even cleaning the surface with brake cleaner has quite a dramatic affect on brake bite specifically and you have to put them through some duress and heat cycles to bring them back to designed efficiency.