Spring Plate Restoration

The “after” pic in our little story. Just waiting to have new bushings glued on. Passivated Zinc plating is a really sharp look while protecting these parts from corrosion.

My spring plates were in rough shape but it was also the middle of the Auto-X season. In the interest of time and adjustability I replaced the original spring plates on the car with an adjustable set from Prekom. They work great, and look terrific.

But what to do with the old plates and hardware? They were pretty beat.

Passenger side spring plate and cover. 36 years of “life” showing.

It seemed obvious to see about restoring them. It's a pretty simple process, and easy to DIY, not to mention cost effective.

The hardware is simple: degrease, remove any rust and then re-plate it. I used an ultrasonic cleaner to get the dirt and grease off of them. In my past life we sometimes just used the sandblaster cabinet to clean hardware. It works although sometimes it can rough up the finish. Pick your media carefully and test it out on some disposable parts to make sure you are going to get the results you want.

Next I soaked them in a strong acetic acid (vinegar) solution overnight to remove the rust. Just be aware if you have not used it before, it is gentle, but it will remove any plating. I started with 30% Vinegar from the hardware store and diluted it 1:1 for a 15% solution approx. That's a bit strong perhaps, but it worked well for me here.

Finally I tried out Evapo-rust which is a newish chemical rust remover from CRC, and it worked very well too. It is more gentle than the vinegar solution I used and so I am not 100% sure it would have gotten off the heavier rust. But it worked quickly and best of all, it is reusable. I will keep testing it out for sure. I love that I don't have to dump it, I can just re-use it.

The hardware was now all down to the bare metal and ready for plating. In the case of the custom hardware used to set the ride height, etc. restoring the old bolts can save you some real money and have the bonus of being "original" in case that matters someday.

The hardware came out very nicely, despite starting out with a fair amount of rust. If this car was going to fancy car shows I would maybe polish the heads of the bolts & the washers just to be extra spiffy. But this is pretty close to new as-is. Chase them with a thread repair die set to get them back to 100%.

The spring plates themselves are a bit more work. The original bushings are vulcanized on (installed with heat to bond them to the metal).

First you need a torch and a screwdriver or chisel to remove the old bushings. The heat is really key to getting them off, nothing new there, just confirming the CW.

The left side here has had the rubber mostly removed and is being cleanup up with plumber’s sanding cloth. The right side still needs to have the rubber residue removed along with any rust.

Next you can disassemble the spring plates into their two components & loose hardware.

To get the rest of the rubber off of them I used a combination of plumbers sanding cloth and a brass wire wheel on a drill. The plumbers cloth is really great on the torsion tube, it is designed to clean up copper pipes for soldering, and is perfect for cleaning up a round surface. It's an open mesh so it doesn't get clogged. I used 160 grit which left a nice finish.

Before and after, I cleaned up the RH one more after I took this, but it's a good comparison for where the plates started out and where they ended up after being stripped.

I was especially surprised at how well the torsion tube cleaned up. This isn’t the final finish, but pretty far along.

I used the torch a bit along with the wire wheel to strip off the surface rust from the plates. In hindsight I would probably try either chemical stripping (Vinegar or other) or send them out for media blasting; the latter to achieve a more even finish on the bare metal. The finish going in to the plating process has a big effect on the quality of the results you get.

Once the plates were all cleaned up and there was no rubber or rust left I took them to get re-plated. The Gold or Yellow plating is passivated Zinc. Zinc plating is normally silver and can be shiny depending on the finish. A layer of Zinc is applied via electrolysis, and you have galvanized the underlying steel by doing this. Porsche was fully galvanizing the 911's chassis by 1977 and offered a 10 year warranty on rust as a result. Non galvanized parts and hardware can still corrode, but having the chassis protected is a big advantage.

Passivation is treating the plated part chemically to create a layer of oxide. There are various colors available (incl yellow, black, white & blue), but the key thing is that this additional layer of oxide further enhances the corrosion resistance of the part.

Resources:

All about zinc plating: https://kdmfab.com/zinc-plating/

Passivation: https://artizono.com/zinc-plating-vs-passivation-whats-the-difference/

Plumbers sanding cloth (example): https://www.walmart.com/ip/Plumbers-Open-Mesh-Sanding-Cloth-180-grit-1-5-x-25-yd-Double-Sided-Abrasive-Roll-Emery-Crocus-Cloth-Sands-Deburrs-Copper-Pipe-Metals-PVC-Wood-Drywall/17303801112?classType=REGULAR

Concentrated Vinegar: https://www.tractorsupply.com/tsc/product/harris-30-pure-vinegar-extra-strength-vine30-128-1651585?BU=TSCO&campaignid=627558462&device=c&product_id=1651585&matchtype=e&bidmatchtype=be&network=s&keyword=default&msclkid=b2a364931aae144325920c7d818d4de3

Evapo-rust: https://www.evapo-rust.com/

Reliable Plating (Bridgeport, CT) www.reliableplatingct.com