More regarding painting or powder coating springs

Question:

Your latest issue (May) is great as always. There is an item in it about painting or powder coating springs. This rang a bell because I took the seminar put on by Eaton Detroit Spring at the Hot Rod & Restoration Show in March. Painting came up in the seminar. I got out my recorder and transcribed the information. Now, this is textbook stuff, but in the magazine world, sometimes that’s the best route.

Mike Eaton said that the top and bottom surfaces of springs should not be painted. While the thickness of a single layer of paint is inconsequential, when you paint the tops and bottoms of five to 10 leaves in a spring pack, it starts to add up to “measurable thickness.” And since the leaves are constantly moving on each other, the paint will eventually wear off and you will get sliding between the leaves. This will result in looseness in the center bolt area and when looseness develops there, the end result will be spring breakage.

Mike also said springs should never be chrome plated as it causes hydrogen embrittlement. First the chrome will start to flake off and eventually the spring will break. He told a story about spotting a car with this problem at the Hot Rod Nats in Kentucky. He left a note on the car and heard from the owner later. The owner saw the note and thought it was BS, but then he hit a dip in the road and his transverse leaf spring that had been chromed simply shattered and the entire suspension dropped.

The seminar did not include specific information on powder coating springs, so I have emailed Mike to get the skinny on this.

Answer:

Interesting information, though I’m not so sure that I agree with it.

With regard to paint adding “measureable thickness,” the additional thickness seems way too small to be consequential. For example, a 10-leaf spring has 20 top and bottom surfaces. If each surface has 2 mils of paint then painting each leaf adds about 40 mils of thickness. That equates to about 40-thousandths of an inch. Think about all of the chassis components that impact ride height and then think about how imprecise some of these are in old vehicles, and think about how age and use impacts their dimensions, and it seems logical to me to conclude that 40-thousandths of an inch more height owing to the paint won’t make any difference. For example, consider all of the rubber parts in the suspension, including the rubber in the spring shackles. How long would it be before the weight of the vehicle causes rubber bushings to compress 40-thousandths of an inch?

As far as the paint wearing off, in reality, there is very little movement of a leaf spring’s leaves relative to one another and most of what little movement there is takes place at the outer ends. The center bolt area is typically held very securely by the spring’s mounting brackets, with little to no discernible sliding between the leaves in the areas around the bolt.

With regard to Mr. Eaton’s advice to never chrome plate a spring, I would not paint with such a broad brush.

Chrome plating is extraordinarily hard and for this reason, among others, it is often used as a durability enhancing surface treatment for all sorts of mechanical components, including ones found in aircraft. While it is true that chrome plating can cause dangerous hydrogen embrittlement, which can in turn lead to crack propagation, there are techniques for dealing with this.

The steel can be shotpeened prior to plating to increase its fatigue resistance and can be heated to prevent hydrogen embrittlement. A correctly carried out heat treatment eliminates most of the hydrogen that was introduced by the plating process.