8 replies to this topic

[K7MDL]

If you have an aluminum body truck like the 2015+ Ford F150 and soon the 2017+ Super Duty trucks, here is a Ford bulletin on the recommended way to install attachments like our camper hold down eyebolts to an aluminum truck bed.  Just ran across this today, not sure I have seen it referenced on this site yet.

 

https://www.fleet.fo...-html/Q-222.pdf

 

I elected to use nylon washers and bushings to isolate non-zinc coated steel eyebolts and washers from the aluminum truck bed and aluminum backing plates. 

Edited by K7MDL, 21 July 2016 - 03:46 AM.

[Bill D]

Thanks, great info.

 

The same applies to replacing screws or attaching items to our aluminum campers.

Edited by Bill D, 21 July 2016 - 03:58 AM.

[K7MDL]

Fixed, tnx. 

[Rusty]

interesting that they recommended an isolator plate above the bed but recommended an aluminum washer and a steel nut....in direct contact....below the bed....somebody not thinking this through to the other side

 

I have to deal with this issue with a heavy, welded aluminum boat.....marine stainless fittings recommended there...but not here??

 

good quality Stainless nuts and bolts....not Chinese....work well...and are used exclusively in aluminum outboard motor construction where galvanic corrosion is the engine destroyer

 

this sounds like a liability position statement...where the engineer knows about the difference between grades and manufacturers of stainless nuts, bolts and screws... 

Edited by Rusty, 21 July 2016 - 04:11 AM.

[BILL98388]

Rusty (By the way, good name to be discussing corrosion. ;-)):

 

Looking at the diagrams closely I see that in the recommendations they require an "air gap" around all non-aluminum fittings (like SS bolts), their way to stop the galvanic corrosion.

 

Of course the steel nut and the aluminium washer shown in both diagrams will corrode.

 

You would think a better answer would come from the manufacturer.

 

Do you use the oversize hole method for an air gap in your boat?

 

Bill 

[Beach]

I love the air gap they show between the bolt and the truck bed. I wonder how long till the bolt shifts over and makes contact with the bed. Bolt should be sleeved or use a necked washer.

[K7MDL]

I went for the nylon sleeve appraoch due to concern for shifting with our sideways pull.  They do specify zinc plated steel, not regular steel, so that in combination with the aluminum washer does reduce the galvanic voltage and places it at the replaceable washer/bolt interface.  The big bed mounting bolts are likely zinc plated steel, have to look tosee if they use the aluminum washers or something/nothing else.  The bed bolts terminate in the steel chassis frame underneath so only have to pass through the aluminum sheet metal.  They use a foam-like adhesive pad between aluminum and steel flat parts like the underside of the truck bed. No idea if they use an air gap or some form of insulator under the bolt head.

[ntsqd]

If you look up a galvanic potential chart you'll see that zinc is a lot closer to aluminum than stainless is, by far. That means that the galvanic potential (voltage) is much lower than with SS. Lower galvanic potential = less/slower corrosion. The ocean marine guys that I know all say not to use SS with bare aluminum. It corrodes fast and locks up the joint requiring the bolt to be drilled out. Hard anodized with SS is a maybe, not a for sure.

 

With rare exceptions stainless is SAE Grade 2 or worse in strength so not using SS in loaded joints is easy for me.

 

The aluminum washers are probably intended to be sacrificial, they corrode first and save the bed.

[Bill D]

Will galvanic corrosion spread on its own like rust, once it had started?

 

Let say you notice it and then change materials etc. does the existing corrosion need to be dealt with?