stallie Posted December 12, 2020 Report Share Posted December 12, 2020 (edited) I have been away for the last 2 months so disconnected the battery and had parked it up. I opened the bonnet tonight to reconnect and discovered that the clutch master cylinder was half covered in the by product of some form of reaction. Nothing was done differently, previously the car had been parked for a couple of months during the austral winter (I live in the hills out of Melbourne and winter is cold and wet, like a UK summer ) and no corrosion, then I drove it for a while back in September and for the past 2 months it's been in a dry garage and daytime temps rarely below 15-20C. The battery terminals were both fully disconnected. Any ideas? Edited December 12, 2020 by stallie Quote Link to post Share on other sites
Mike C Posted December 12, 2020 Report Share Posted December 12, 2020 I get white salty corrosion like that in a much milder form on the clutch cylinder- might be acid fumes from the battery venting? The painted steel around the base of the cylinder in mine also gets attacked locally by something, presumably the same fumes. Quote Link to post Share on other sites
Casar66 Posted December 12, 2020 Report Share Posted December 12, 2020 It looks like a kind of galvanic corrosion, the aluminum of the clutch cylinder ist (nearly) the most base one of all. I guess the engine compartment became wet maybe due condensation as a result of fast changing weather conditions. And the mass-cable was still on. Maybe even a charger was mounted? Quote Link to post Share on other sites
astontr6 Posted December 13, 2020 Report Share Posted December 13, 2020 17 hours ago, Casar66 said: It looks like a kind of galvanic corrosion, the aluminum of the clutch cylinder ist (nearly) the most base one of all. I guess the engine compartment became wet maybe due condensation as a result of fast changing weather conditions. And the mass-cable was still on. Maybe even a charger was mounted? +1 for galvanic corrosion, condition of mounting bolts is also a give away with rust! Bruce. Quote Link to post Share on other sites
JochemsTR Posted December 13, 2020 Report Share Posted December 13, 2020 (edited) In order for galvanic corrosion to work, both materials need to be far away from each other with their galvanic voltage. Combination of Magnesium and Gold is the worst. Aluminum lies directly to steel, but far from stainless steel. The bolt are rusted, but the washers beneath not. If these are stainless steel, then this could cause it. Replace them with zinc plated ones. Jochem Edited December 13, 2020 by JochemsTR Quote Link to post Share on other sites
Mike C Posted December 13, 2020 Report Share Posted December 13, 2020 Galvanic corrosion requires that the two materials be immersed in a conductive solution, what do you think it is? I'm interested - as I have a lesser version of the same problem It can't be dry air. Quote Link to post Share on other sites
RogerH Posted December 13, 2020 Report Share Posted December 13, 2020 Aluminium and many of its alloys are very reactive. Pure Aluminium is continuously trying to corrode on its surface. In doing so it creates a barrier that then slows down the process. The MC with the white deposits is simply the Alloy trying to protect itself !!! It takes only a very small amount of moisture to set up a corrosive environment - Oxygen in the atmosphere then reacts with the Aluminium in the alloy and you get those white deposits. The best way of stopping it is to Anodise/Anodize the part (or paint the outside with Alochrom 1200). This would help to preserve the surface of the piston bore from wearing. Roger Quote Link to post Share on other sites
Z320 Posted December 13, 2020 Report Share Posted December 13, 2020 This is for shure not pure aluminum, a short test in my wife's kitchen indicates a density of about 3 g/cm3. Probably copper it added, more likely zinc. And the zinc does what zinc usually does. Quote Link to post Share on other sites
RogerH Posted December 13, 2020 Report Share Posted December 13, 2020 Hi Marco, the alloy is obviously suitable for casting. There are very many Alu alloys that fit into this class. Some are better than others. Some less prone to cracking some less to corrosion. If the Aluminium part of the alloy decides to corrode then it will. Not all do. As I mentioned above - Anodising will stop or seriously limit any corrosion. Roger Quote Link to post Share on other sites
astontr6 Posted December 13, 2020 Report Share Posted December 13, 2020 3 hours ago, Mike C said: Galvanic corrosion requires that the two materials be immersed in a conductive solution, what do you think it is? I'm interested - as I have a lesser version of the same problem It can't be dry air. Moisture in the air is good enough to start it! Bruce. Quote Link to post Share on other sites
ChrisP Posted December 13, 2020 Report Share Posted December 13, 2020 Could old deposits of brake/clutch fluid contribute to this if drips or smears haven’t been cleaned off ? Quote Link to post Share on other sites
DaveN Posted December 13, 2020 Report Share Posted December 13, 2020 5 hours ago, RogerH said: Aluminium and many of its alloys are very reactive. Pure Aluminium is continuously trying to corrode on its surface. In doing so it creates a barrier that then slows down the process. The MC with the white deposits is simply the Alloy trying to protect itself !!! It takes only a very small amount of moisture to set up a corrosive environment - Oxygen in the atmosphere then reacts with the Aluminium in the alloy and you get those white deposits. The best way of stopping it is to Anodise/Anodize the part (or paint the outside with Alochrom 1200). This would help to preserve the surface of the piston bore from wearing. Roger Or Alocrom 1000 if you don’t want it gold coloured! Quote Link to post Share on other sites
Casar66 Posted December 13, 2020 Report Share Posted December 13, 2020 I had this corrosion several times. since I use protection wax for all kinds of blank metal it is fine. Quote Link to post Share on other sites
stallie Posted December 14, 2020 Author Report Share Posted December 14, 2020 Interesting points all around. What I found interesting in all of this is that is appeared to be worse in a warmer drier time of year with the battery disconnected, whereas when the battery was left connected throughout winter (and not driven) it wasn't noticeable. Quote Link to post Share on other sites
Casar66 Posted December 14, 2020 Report Share Posted December 14, 2020 It is no just about the absolute temperatur, it is about (fast) changing temperatures during weather changes and the occuring condensate. Quote Link to post Share on other sites
RogerH Posted December 15, 2020 Report Share Posted December 15, 2020 11 hours ago, stallie said: Interesting points all around. What I found interesting in all of this is that is appeared to be worse in a warmer drier time of year with the battery disconnected, whereas when the battery was left connected throughout winter (and not driven) it wasn't noticeable. Hi Stallie, the battery should make no difference as the MC body is attached to the earth - there is no PD present at any time. As I mentioned above it may simply be a characteristic of the alloy. Give it some Oxygen and off it goes. The constituents of the alloy help the process along. Some Alu alloys exhibit a corrosion called 'exfoliation' corrosion. This is where the corrosion digs in deep along the grain boundaries and the metal breaks up into sheets. The comment above about the brake fluid covering it, may actually protect it as it keeps the Oxygen off the surface. Also the heat treatment (it's temper state) will affect how it may corrode. Keep the MC clean but with a smear of light oil (3in1 would be prefect). Roger Quote Link to post Share on other sites
Casar66 Posted December 15, 2020 Report Share Posted December 15, 2020 Condensation (and as a consequence corrosion) of metals due weather change is not a winter-only phenomena. Typically in the the transition times between autumn /winter/spring it can pops up during fast weather changes at any time, very often when a strong warm front comes along. In this November it happens two times here. The roof of my barn (metallized sheet) und all the blank metals in the engine compartment or brake disks were soaking wet. First I thought there is a hole in the roof. Quote Link to post Share on other sites
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