A few month ago I bought a replacement passenger side-view mirror as the '90 Cherokee did not originally come with one. The mirror I bought did not come with threads in the attachment posts and the only instructions with the mirror said to use self-tapping screws. When I originally asked this question here, someone told me I HAD to use stainless steel screws if they're gong into aluminum posts.

Finally getting around to attaching the mirror, I did a little more research and the sources I found said that stainless steel and aluminum are a TERRIBLE combination as together they'll cause galvanic corrosion. I started getting deeper and deeper into it to the point where I found "Trilobular stainless steel self-tapping screws" suggested but couldn't find any for sale that were actually self-tapping. Plus I was way in over my head with the science of why those would be okay.

Then I found there are "black coated" stainless screws at Home Depot for use on aluminum sliding doors and wondered if those would work...

Can anyone explain what screw I should specifically be looking for that won't cause the aluminum of the mirror's base to corrode and fall off on the Freeway in 6 months? Hate to have bought a nice new mirror and watch it go bouncing down the shoulder...

Thanks in advance.

CJ

 

If you can find them aluminum screws are the best option (they do exist but are not easy to find).

The second best option is likely galvanized steel with thickly zinc plated steel as a close third (the zinc prevents the steel from contacting the aluminum) though you're probably better off drilling and tapping the threads separately with these options, as self-tappers are more likely to strip off the zinc coating leaving exposed steel in contact with aluminum.

Stainless is better the regular un-galvanized/un-plated carbon steel, but only slightly, the stainless generally won't corrode, but the aluminum will.

Un-plated carbon steel and brass are the worst options as they will cause corrosion in both the aluminum and steel/brass.


Of-course manufactures (auto, motorcycle, power equipment, etc.) use carbon-steel screws in cast aluminum all the time (which usually leads to them snapping off when you go to remove them years later) even though it is a horrible practice (anything to save a few bucks), so anything will likely hold the mirror on fine (it will take a long time to corrode badly enough to fail just sitting there), it just may be a real pain if you ever want to remove it.

 

A Mercury outboard's block is aluminum, all fasteners on the mota are stainless...

Freakin screw it and forget it..

 

Like said, I wouldn't sweat it, it's done all the time. Maybe goop it up with that newish polyurethane, E-6000. Glues patches on my 501's and maybe would leave a breakable, unpenetrable layer...

 

You might try using NOALOX or OX-Gard on the screws. Both are used in the commercial electrical industry to coat Aluminum wires when installing them.


Both have Zinc dust and additives included to prevent moisture intrusion.


These can be bought at Lowes or Home Depot.


I use this stuff to coat steel bolts being installed in Aluminum castings, such as the bolts that hold the AC compression on to the bracket and the bolts that hold the transmission isolator on to the transmission TC adaptor.


Compressor bolts:


https://www.cherokeeforum.com/g/picture/4014686

 

Thanks, guys. That coating looks perfect, Ken, since I've hunted and cannot find any aluminum bolts.

Best,

CJ

 

You never want to use Aluminum bolts/screws anyway. Stainless Steel in non-structural applications - yes, but not Aluminum.


Cheers