Jump to content

Corrosion / reaction Clutch MC


Recommended Posts

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?

IMG_0692.thumb.jpeg.384e1cdf29d77eafa54a96ea2d37fe5a.jpeg

Edited by stallie
Link to post
Share on other sites

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.

Link to post
Share on other sites

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?

Link to post
Share on other sites
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.

 

Link to post
Share on other sites

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 by JochemsTR
Link to post
Share on other sites

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

Link to post
Share on other sites

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

 

 

 

Link to post
Share on other sites
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.

Link to post
Share on other sites
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!

Link to post
Share on other sites

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.

 

Link to post
Share on other sites
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

Link to post
Share on other sites

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. 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.