Mounting onto the firewall

[SimonNicholson]

Last night I was making a doubler plate to attach the brake reservoir to the firewall. Is there any problem making this out of Aluminium and mounting to the stainless firewall?

[Greg_Marlow]

Last night I was making a doubler plate to attach the brake reservoir to the firewall. Is there any problem making this out of Aluminium and mounting to the stainless firewall?

Looks good, and I don't see a problem with it. But this is the internet, someone probably will.

[Battson]

Just paint in between. Mine has given no trouble with paint, for my remote oil filter.

I don't think you need a doubler for the reservoir, by the way. I haven't missed it, not having one. It's very light.

[whee]

Aluminum and Stainless Steel are far enough apart on the galvanic potential chart that the SS will cause accelerated corrosion of the AL. I wouldn’t use an AL doubler on the firewall, SS is too easy to source and work with. If you want to do it anyways you should isolate them from each other.

[SimonNicholson]

Just paint in between. Mine has given no trouble with paint, for my remote oil filter.

I don't think you need a doubler for the reservoir, by the way. I haven't missed it, not having one. It's very light.

I noticed you had one on your park brake though. Any reason for that?

[svyolo]

It is generally OK to use small steel (fasteners) or other metal parts on large pieces of aluminum, but not vice versa. There is a small current flowing from the AL to the steel. The small aluminum acts as a sacrificial anode for other metal. With a big piece of AL onn small "other" parts you just get a little oxidation between the two. With small AL on big "other" metal, the small AL becomes like the zinc anode that needs to be replaced periodically as it just slowly disintegrates.

When I was 18 I fixed up an old Ford van as a work vehicle. I ended up using AL screws to mount paneling to the steel van. All the AL screws turned to white powder and failed in well under 6 months.

When I was in my late 30's I worked on a lot of AL sailboats masts, mostly 10-30 years old. All had SS fasteners. The fasteners were a PITA to remove (AL corrosion under the head and threads), but they were all intact if you got them out.

The doubler mounted to the firewall won't turn to dust any time soon, but will probably get pretty ugly within 6-24 months.

[Battson]

I noticed you had one on your park brake though. Any reason for that?

Lack of experience, frankly. It was one of the first jobs I did.
There's no force on it so a doubler is superfluous.

There are dozens and dozens of aluminium rivets in the stainless steel firewall and tunnel. In my case none has corroded, could be that the Cad plating works, or that they're too pure (Al) to form an effective anode.

[svyolo]

The rivets also go through the aluminum flange, which is connected to the aluminum cowling. Lots more aluminum to donate electrons to the cause.

[bergy]

Doesn't the dissimilar metal junction have to be in long-term wet conditons before an electric current (and associated corrosion) occurs?

I just remembered .... my wife has had a couple of SS cooking pots for years with a thick layer of aluminum bonded to the bottoms. No sign of corrosion and no insulating layer between. ????

[Archer39J]

Doesn't the dissimilar metal junction have to be in long-term wet conditons before an electric current (and associated corrosion) occurs?

I just remembered .... my wife has had a couple of SS cooking pots for years with a thick layer of aluminum bonded to the bottoms. No sign of corrosion and no insulating layer between. ????

Yeah an electrolyte is needed to facilitate ion transfer between materials, so if it's dry it's not an issue. In theory ionic reactions can occur between solids but it's not a practical issue for any materials we use.

[whee]

If you live in a dry climate then you shouldn’t have any trouble for a long long time. If you live where it’s humid then eventually you will. Like Battson said, all it takes is a coat of paint in between the layers. Personally I just don’t see a reason to use aluminum instead of stainless when making the doubler.