What does re-valving shocks accomplish? When is it needed?
 

<iframe width="560" height="315" src="https://www.youtube.com/embed/IGCmAzSZz_k" frameborder="0" allowfullscreen></iframe>

I just watched this and had some questions.

When a shock leaks oil out, I understand that it no longer works.
What exactly is re-valving a shock?
What symptoms exist that indicate a shock needs re-valving?

At the 7:00 mark, he shows that he is replacing a bunch of washers.
What is the point of replacing washers?
I can understand replacing o-rings, but not washers.

It doesn't appear to be a complex part.
If a shock isn't leaking oil, and doesn't fail the manual bumper bounce test, it's working fine?

He's not rebuilding a leaky shock he's revalving to change the stiffness.

Rebuilding is required when the seals wear out.

Revalving is changing the piston orifices to get different shock forces at different shaft speeds.

A rebuild is necessary indeed if the oil leaks out, but also if the internal wiper on the piston fails. Basically if the shock isn't working so great anymore. They're wear items and don't last forever, nor do the usually fail all at once. They degrade over time.

A revalve is necessary if you change spring rates (torsion bars) a significant amount. It can be extremely complicated - back in the day, there was linear valving. Two one way valves and certain size holes. Force went up linearly with shaft speed.

Then came digressive valving, with multi-piece valving (shim stacks.) With digressive valving, forces ramp up quickly to give the good body control you get with stiff shocks, but "blow open" and knee off at high shaft speeds (bumps) for ride comfort.

Now cutting edge passive valving in the cubic megadollar range is using regressive valve curves - super fancy stuff that ramps up even faster at low shaft speeds, then actually more than just knee off but actually soften at high shaft velocities to let the suspension work to soak up bumps.

And then there's the active magnetorheological shocks, where there's a magnetic based fluid that can have it's viscosity changed several times a second by passing an electromagnet field over it. Neat stuff.

But I've gone too far. Yes, changing the valving on a shock isn't hard. Changing it to something that works for your application requires someone with pretty specialized knowledge.

Not all shocks can be rebuilt or revalved
not all Bilstein shocks can be rebuilt or revalved

Bilstein mono-tube shocks can be rebuilt and revalved.

In these shocks both oil and the pressurized gas can leak, if they do seals will be replaced and the shock re charged.

If the shock damping curve is to be modified for different performance say because of a spring change or a desire for different behavior then a re-valve is needed.

Here are what the oil ports look like for different curves, the oil of course is forced through these ports, the resistance is what damps the motion.
http://forums.pelicanparts.com/uploa...1450902930.jpg

Most older design shocks are linear(this includes all the Bilstein hd and sport shocks for 911), digressive is very popular for high performance and track use(Bilstein PSS are digressive), almost all new high end race shocks are digressive, Though at the bleeding edge other more esoteric strategies are used.

Here is what the shim stacks look like from the side
http://forums.pelicanparts.com/uploa...1450903285.jpg
http://forums.pelicanparts.com/uploa...1450903301.jpg

There are multiple choices for the shims, each has a different flow characteristic
http://forums.pelicanparts.com/uploa...1450903405.jpg

Bill, you never cease to amaze, my man!

So, what was the point of replacing the shim stack in the video?

Wait, does the "bounce test" even apply to torsion bar cars?

On other cars, it makes sense if the shock has no oil, there is no resistance, and a car will bounce on the coil springs when the spring decompresses.

I don't think a torsion bar would recoil and bounce in a similar way. For a torsion bar, when it's loaded, the bar twists, as it untwists, it should just snap back, if the shock damper is not working. But, it won't start to bounce, right? I'd imagine that a blown shock on a torsion bar car just means a sharper "bounce back". Is that right?

Is there a formula for specs on a re-valve. I have a 2600 lbs car with 23/31 TBs. I want to re-valve my rear Bilstein sports. If I send to Bilstein to do this,what info do they need?

Talk to Chuck at Elephant Racing, they re-valve Bilstien and test all shocks to match on a shock dyno.

Torsion bars and coil springs behave the same.

A coil spring is just a torsion bar wound into a cylinder shape.

A shim stack change is done to on a macro scale match a shock to a spring, on a micro scale change the handling characteristics of a car.

Elephant Racing refreshed & re-valved my 10 year old Bilstein sports to my new 22/30 TBs. Car handles great and controls the would-be faster rebound.

I installed Elephant Racing 21/27 TB's in my 82 SC without re-valving my shocks and I had porpoising in my car on one section of freeway which I've had porposing in various cars for this section of freeway. After having them re-valved by ER this went away and the care is much smoother. I provided them with the general setup of the car. Following the re-valving riders are surprised at how smooth it rides even with the upgraded TBs.

So I started reading this thread on my iPad and the first thought I had was "which thread was it that Bill Verberg posted that excellent picture in?" Scroll a little further down and there it is. Bill, you're like FedEx. Guaranteed to deliver. :)

Did you have front and rear re-valved with the 22/30 TBs?

If you mean me, yes absolutely.

fwiw even if an old shock seems fine the oil in the shock deteriorates with time.

Every few years we do a little preventive maintenance and have the JRZ, Penske and Ohlins rebuilt on our 3 race cars before they fail.

LOL,..That doesn't apply to anything and I'm sure it never did, much like kicking tires. :)

So what would the recommended rebuild cycle be for Bilstein shocks on a street-driven car (years or miles)?

Are you saying you've never heard of this, or that it's not accurate?

https://youtu.be/BiW0ISi8N-w?t=44s