Thread: Renovating Leaf Springs

Painting.
I'm sure originally they would have been manufactured and then dipped in paint for speed. There was an article in a LR mag a while ago where the company assembled the spring then used a rattle can of paint.

Lubricating
I understand that using grease or an oily lubricant attracts dirt (especially on a 4WD vehicle). The problem would be if the spring pack opens up to allow dirt between the leaves which might happen on full articulation.
Early cars had leather gaiters fitted to keep dirt out Welcome to Wefco Gaiters
Some cars used zinc strips between each leaf.

Lubricate well and you'll need good shock absorbers but get a softer ride. Leave dry and the friction in the spring will damp out any oscillation after hitting a bump (most leaf sprung trailers don't have shock absorbers).

I just found the reference to not using oil because of degenerative effect on modern steels ???? Leaf Springs for 4WD
Sounds odd, maybe I shouldn't use modern oils in my engine either ?!


Cleaning
I'm not sure that abrasive blasting would lead to millions of stress raisers unless a very aggressive medium was used. Bead blasting wouldn't affect the surface at all but shot peening would stop the chance of cracks Metal Improvement | Shot Peening

I most cases hitting it with a rotary wire brush, degreasing , painting (with a brush) and then possibly lubricating would spruce things up. There is also the possibility of separating the leaves and following the same routine.


Colin

As I too am in the process of rebuilding a Land Rovers suspension, I went looking for a company able to reset leaf springs. I have read a vast amount about the subject, but (as always) tend to treat "internet wisdom" with some scepticism. Like Wikipedia, "truth by repetition" seems to be the norm, the more people say something, the more people believe it!

So, armed with the "knowledge" that springs must be re-tempered after resetting, I visited the spring shop. "Can you re-temper springs?" I asked. "No", came the answer, "There is no requirement to do so". He then explained why:

"The physical properties of steel are largely attributable to its chemical make-up (alloy). The tempering of steel changes its physical properties, as does work hardening, but only within the limits of its chemical make-up and only by a certain amount. So if steel is work-hardened it can be annealed, but there is a degree of work-hardening beyond which no amount of annealing will correct. Repeatedly bending steel within its elastic limit will very slowly work harden it. Bending steel beyond its elastic limit will also work harden it, but will not significantly affect the temper of the steel as a one-off process. So when a spring is reset, it does not automatically need to be re-tempered because it is not significantly altered by the resetting process. The problem is that bending a spring beyond it's elastic limits is hard to do, so most spring shops heat the spring to make it easier and this is where the problems start. The tempering of steel requires the metal to be heated to a particular temperature. Heating to below that temperature will still cause the steel to soften, but not change temper. So if you can control the temperature to which you heat the steel, you can soften it to allow easier re-setting, but not affect the temper and therefore not automatically need to re-temper it."

He went on to explain that some springs, because of their alloy, the degree of work hardening etc., will not "hold" a reset no matter what you do, and suggested that he can often tell these springs by the way they act during the resetting process.

I haven't, as yet, sat down and researched the metallurgy to see if this theory holds water, but it sounds logical enough. Unfortunately it could also be simply an excuse from someone who doesn't own a the equipment to re-temper springs. The only thing that stops me assuming it's an excuse is that this company started off making springs for carts, so they've been around long enough to know what works!

Edit:

Further reading suggests there may be some merit to his argument. Spring steel is hardened by heating to around 900C, then quenched in oil. It is annealed by heating to around 660C and cooling slowly. Tempering is done by heating to 400-550C (depending on the degree of tempering required) and cooling in air. Springs are hardened, then tempered. So it is indeed possible that if a spring is heated slightly too much to ease the reset, it could in fact reach the annealing temperature and end up being softened. However such a spring would not require re-tempering, it would actually require re-hardening THEN re-tempering.