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edlithgow
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PostSubject: Silicon Grease for Brakes?   Sat Aug 24, 2013 2:56 am

Someone mentioned silicon grease for lubricating door hinges.

Reminded me that I've been thinking I should try and get some of that for my brakes, since my car spends long periods without moving (currently in the monsoonal/typhoonal rain of Taiwan) and I'm slightly concerned that the brake pistons will corrode, as happened to a similarly immobile truck I had in the UK.

I'm assuming that a silicon grease will tend to be rubber-friendly, and so should be OK to use on the brakes.

I'm in Australia at the moment so it should be easier to find stuff than it is in Taiwan.

Any recommendations?
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Father Tiresias
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PostSubject: Re: Silicon Grease for Brakes?   Sat Aug 24, 2013 11:59 am

Generally speaking when refurbishing brake calipers the seals are lubricated with a silicone based grease. Anything that is external to the caliper is better lubricated with copper slip grease as this is temperature resistant and works as an anti seizure compound.
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Justwatching
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PostSubject: Re: Silicon Grease for Brakes?   Sat Aug 24, 2013 7:02 pm

When calipers seize, it's because they corrode inside the caliper bore or on the piston surface that mates with the bore surface. Both of these are internal and cannot be lubricated. Clean, uncontaminated brake fluid is the only way to protect against internal corrosion in the brake system.

Applying some silicone grease might help keep the external seal (dust boot) from perishing, but that's it really.
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Father Tiresias
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PostSubject: Re: Silicon Grease for Brakes?   Sat Aug 24, 2013 10:35 pm

Justwatching wrote:
When calipers seize, it's because they corrode inside the caliper bore or on the piston surface that mates with the bore surface.
Thats not always the cause of seizure. On a floating/sliding caliper often they can also seize on the two slides.  Lubricating this with copper slip reduces the chances of that happening.
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edlithgow
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PostSubject: Re: Silicon Grease for Brakes?   Sun Aug 25, 2013 3:04 am

Thanks all for replies so far.

I didn't see the truck problem, just had it described to me as an advisory by garage doing an MOT prep, but I'd noticed one of the front brake drums was pretty hot on arrival, presumably because it was stuck. They said they had to clean up the piston due to corrosion, and had applied some grease to it. I asked what kind of grease they used and they said something like "general purpose grease", perhaps looking slightly shifty while doing it.

I suspect they used a mineral-oil based grease, which I thought could attack seals and O-rings and lead to failure of the wheel cylinder. This was a bit worrying, since a 4 ton truck could make quite a mess of a bus-queue, though I'd hope the failure would not be sudden/catastrophic, and I suppose the corroded piston could also threaten seals.

This kind of thing is one reason why I don't much like getting other people to work on my vehicles, but I didn't have much choice in this case, the truck being rather big, and my (illegal) London residence at the time.

So I'm after a high-temperature (rubber-friendly) silicone-based grease for the piston sides. Ideally, it should also have anti-seize properties so I can use it elsewhere in the braking system.

A bit of Googling suggests Permatex Ceramic, Molycote M-77 (though spec says "compatible with many elastomers - test for compatibility" - Oh yeh? HOW exactly?, so probably not that), or Sil-Glyde as possibilities. The last is cheapest but doesn't seem to have anti-seize properties, so the Permatex looks to be favourite.

Might not have time now for mail order to an address in Australia so I'll have to see if I can find it in the shops.

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edlithgow
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PostSubject: Re: Silicon Grease for Brakes?   Sun Aug 25, 2013 3:33 am

Oh, and there's Bendix ceramlub, which may be the same stuff as the Permatex.I've got personal objections to Honeywell so that'd be a last resort.
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Justwatching
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PostSubject: Re: Silicon Grease for Brakes?   Sun Aug 25, 2013 12:55 pm

Father Tiresias wrote:
On a floating/sliding caliper often they can also seize on the two slides.
Good point - completely true. The garage told him they lubricated the piston though, which is BS.
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Justwatching
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PostSubject: Re: Silicon Grease for Brakes?   Sun Aug 25, 2013 1:19 pm

I've lost track a little of exactly what part needs lubricating. If it's slider pins on a caliper, then red rubber grease. I'll put a link below with some info if you'd like to read up on it.

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If for any reason you couldn't get hold of the above, CV Lithium-Moly grease should be an acceptable substitute.

If it's drum shoes or brake pads then it needs to be copper grease.
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edlithgow
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PostSubject: Re: Silicon Grease for Brakes?   Tue Aug 27, 2013 4:52 am

Justwatching wrote:
I've lost track a little of exactly what part needs lubricating. If it's slider pins on a caliper, then red rubber grease. I'll put a link below with some info if you'd like to read up on it.

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If for any reason you couldn't get hold of the above, CV Lithium-Moly grease should be an acceptable substitute.

If it's drum shoes or brake pads then it needs to be copper grease.
Thanks. I was aware of the existence of the rubber grease, in fact I took it as partial justification for my dodgy DIY veg oil tyre treatment, since its rubber-compatibility is because its castor oil (and, I think, bentonite) based.

It'd no doubt do the job, but I'd guess its the "traditional" solution, and castor oil, while good stuff in many ways, is less stable than mineral, synthetic or silicone based-grease. It seems possible that there may be better products available now.

The pictures in your link seem to show it being applied as an assembly grease to the piston sides, suggesting that this procedure is not universally regarded as "bullshit".

That's my main current intended application, but I'd like to find a "general purpose" solution if possible.

This article

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is a bit low on specifics but suggests Silicone or PAO synthetic based lubricants able to withstand 400 degrees F for cylinder / piston use, and dry lubricants with graphite or molybdenum for other external areas. PAO may have better rust and temperature resistance, and incorporate solid lubricants.

There seems be an implication that such a PAO grease could be general purpose, in the statement ” can be used for both assembly and external lubrication”.

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Dow Corning list 32 different products for brakes. From this visual guide, the best general-purpose candidates seem to be Molycote PG-54 Plastislip or 111 silicone compound, but, as you note, drum brakes seem to require dry lubricants or pastes.

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The bendix ceramlub looks like it may be a “general purpose” PAO-based lubricant incorporating solid lubricants.

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permatex 24125 (purple) looks like it may be another,

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Permatex 24110 (green) looks to be another synthetic lubricant with a less extreme temperature capability. The manufacturer doesn’t seem to claim a solid lubricant content.

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The Permatex 24112 (red) is silicone-based, so has lower high temperature resistance, but it contains solid lubricants so may have some general purpose application.

Permatex 24125 looks favourite at the moment, with the silicone-based 24112as a second choice.

I hadn't thought of the CV greases but as a substitute but it makes sense, since they have to be compatible with the rubber CV boot.
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edlithgow
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PostSubject: Re: Silicon Grease for Brakes?   Sun Sep 01, 2013 12:13 am



I could only find the Bendix (= Honeywell, unfortunately) Ceramlube stuff (In Repco, which AFAIK doesn't have a UK presence). They had it in big 1000 years supply bottles/tubes for 35AUS$, or wee one shot sachets for a couple of bucks, so I got a couple of the latter. Sod's Law would suggest I'll find the Permatex stuff in Taiwan next week for half the price.

Alladdin's Cave-stylee tool stores are everywhere here (probably like the US, though I don't remember being in one when I was there.) Going to miss that back in Taiwan.

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