Dissimilar Metals

[Pelican]

I have a Rugby bed hoist on my F-350 that's been giving me trouble. It has an electric pump that is powered by an old Delco style starter motor. The pump has an aluminum housing.

The Motor is bolted to the pump housing, and relies on this physical contact between the steel motor housing and aluminum pump housing to provide ground to the motor. Between the steel rusting and aluminum rusting, I have to remove the motor and clean the joining area almost anually to keep it working. The first time it happened I bought a new motor thinking it had burned out.

Is there a method to keeping this area from corroding? I know there are always problems between steel and aluminuym, but is there a solutioon to the corrosion? My alternative idea is to weld a bolt on the motor housing and run a ground strap to it from the truck frame.

[Garagekeeper]

Steve drill and tap a hole in the end of the motor housing near the end cap so you can use a 5/16 bolt with an external lock washer to install a ground cable directly to the motor case from the chassie of the truck. Make sure you also add a 2 ga. wire from the battery to get a good ground to the frame. Then you can put a nice bead of silicone sealer around the motor to pump housing to help prevent additional corrosion.
:rolleyes: John...

[Rick]

Why not just run a dedicated ground from the frame to one of the bolts that conect the motor to the pump?:huh

[Pelican]

For some reason those bolts are insulated Rick. It drove me nuts troubleshooting this thing the first time it quit. I thought for sure the motor had fried, but the new one wouldn't work either. I kept testing the ground at those bolts and it showed it was good, but the bolts are insulated from the housing. Who's have thunk???

Thanks for the tip John!

[Crash935]

Steve, dedicated ground back to the battery and a piece of duct tape between the aluminum and steel and you will be good for a long time.


Darn grounds will get you every time!

[Garagekeeper]

Steve here's a picture of the location you can drill and tap a hole in a prestolite motor without taking it apart. just grease the drill bit and tap up well to keep the chips out of the inside. Note that the pump housing gets grounded too as the coils for the cartridge valves are grounded thru it.
:rolleyes: John...

[Pelican]

Thanks John!! I was going to tackle it today but ended up spending all my time on one of the Scags. I looked at the one I had taken off and the end cap is aluminum too, so I'd have to ground the motor housing. I'll get it done this week. It will be easier not having to take out the motor to do it, thanks!

[Pelican]

I tackled this today and it went smoothly. I drilled and tapped for a 5/16 bolt and had a short one with a serrated flat head around. I put a star washer between the ground cable and the housing, never-seized the bolt and whala!! The body went up. Thanks again John.

All this came about because my left turn signal to the trailer isn't working. When I built the truck I put my wiring in an outdoor junction box. Unfortunately I used a pot metal box instead of plastic and it disintegrated. Now I have another project on my hands, to rewire my trailer connections. It never ends.....