Bernie S.

So, to update everyone. I have purchased a Bilstein shock that will be dedicated to this thread. I will use this to show you the internals of the shock, and also how to create different curves on the graph.

Here is the shock on the dyno being set up for the initial runs. At this point, I am setting the preload and about to adjust the IR temp sensor.

wannafbody

iTrader: (1)

So if I'm seeing this correctly based on the size of the shims, as the shock changes from compression to rebound and visa versa it's using different ports on the valve.

Thucydides

I'm a bit of a dummy, Bernie; could you retake that photo but with everything in a single line? Alternatively, could you tell me if the order is top to bottom and left to right, or something else if that's not right.

JustinHoMi

If you look at the picture in post #278 it will make more sense.

Thucydides

Ok, I think I get it.

When we're looking at your photo it actually looks like there are two notched shims.

1) Is that how the thickness is adjusted for the bleed shims - by adding or subtracting shims?

2) Are there bleed shims on both sides of the piston, or is bleed for both damping and bump adjusted from just one side of the piston?

3) Is bleed also controlled by other means; say differences in the bleed holes between different pistons, or different shim shapes?

4) Are the internals we're looking at the same as, or only similar to those within the yellow Bilstein's we're more familiar with for our Miatas?

Bernie S.

Maybe I'm missing something. Where do you see two notched shims?

The bleed is adjusted by the thickness of the notched shim, along with the number of notches. This one in the picture has 8 notches, but they also have them in 4 and 2 notch.

The other way I adjust bleed is by drilling the piston. I've included a picture below of a piston with a .060" bleed hole.

wannafbody

iTrader: (1)

Do you use a variety of shims from different manufacturers to fine tune?

Thucydides

Ok, Bernie explained the shim stack and I'll explain it to you.

Let's start with the second photo, the one with the completed piston assembly.

The red thing on the bottom - that's the droop bumper and it keeps the piston assembly from banging up against the top of the shock when the suspension goes into full droop mode.

Now let's move over to the photo of the various components. Imagine you have the shock shaft between your knees with the part of the shaft that's inside the shock body pointing up.

The first thing that goes on - at least for the sake of this discussion - is that red bumper. We're then going to take those various other shims and washers and put them on next - starting at the bottom row of the photograph.

On the bottom row there are two shims; one big and the other small. The big one, let's call it the "bottom plate", goes on first. It's job is to be the contact surface for that rubber bumper.

The smaller shim on the bottom row, let's call it the "top off shim", goes on next. I'll leave it to Bernie to explain what it does, but the "top off shim" comes in different diameters.

Moving to the next row from the bottom, the next shim to go on is the larger shim; let's call it the "main compression damping shim". Next is the smaller shim next to it, which we'll call the "pre-load shim". Again, Bernie will explain the function, but the "pre-load shim" comes in different thicknesses.

Ok, next the piston is slid onto the shaft, and then we move up to the row of shims above the piston.

The first to go on after the piston is another pre-load shim, but this one is for rebound damping; again, it comes in different thicknesses.

The slotted shim, which we've already introduced as the "bleed shim" is next. As Bernie mentioned this comes with different size and different numbers of slots. Interestingly, it's designed so that no matter how it's clocked on the shaft the same amount of bleed opening is exposed.

After the bleed shim comes the next large diameter shim in the row, which we'll call the "main rebound damping shim".

We're finally at the top row, and we'll begin on the right. The right most small shim is another "top off shim". Next to it, and next on the shaft, is the "top plate", and to the left of it, and the last on the shaft, is the washer against which the Nyloc nut that holds the assemble on the shaft rests against.

So, in summary, in order of assembly, we have:


Got it? Good.

wannafbody

iTrader: (1)

Fluid always passes both ways through the outmost ports of the piston?

Thucydides

Hang on, let me put down my Martini. Honey, where are my reading glasses? Damn, I can hardly see through this cigar smoke.

There it is, see those multiple lines....

Thucydides

Negative.

The inside circle of slots on one side of the piston is common (connected) with the outside circle slots on the other side of the piston.

Flow through the piston is from the outside circle of slots to the inside circle of slots and then past the shims.

85Dave

At the 6 o'clock position in the outer ring of slots, it looks like there is a hole. Is this used to allow a certain amount of fluid bypass for low speed comfort? Does this hole get adjusted?

Bernie S.

Yes, you are correct. This controls the low speed on the graph.

I drill the pistons with a selection of bits ranging from .010" - .060".

BAHKACK

Saw this thread and thought that perhaps I could rebuild my own bilsteins.

I am not thinking that any more.

The parts are relatively simple, but knowing what sizes etc is way beyond the diy'er without years of experience and a shock dyno. I'm happy that Bernie has the knowledge to do this.

wannafbody

iTrader: (1)

Do bilsteins break in?

Thucydides

Besides knowing what parts to install, there are two other issues.

First, there's a highly pressurized chamber at the base of the shock. This probably isn't as big a problem as it first seems because you can probably just drill a hole at the base to evacuate the chamber and drill and tap the hole for a Schrader valve. That's what Shaikh does.

The other issue is Bilstein stakes the end of the damper rod so the plain nut they use doesn't fall off. Removing the nut buggers up the threads and they need to be recut; again more an issue of having the proper thread chaser/die rather than a major problem.

But yeah, the bigger issues are what do you put on there and how to you test it. In the long run, even if it's just R&R seals without changing damping, it's probably easier and cheaper to just send it to Bernie.

BAHKACK

Bilsteins can be bought for under $400 shipped (NB HDsport).
Wouldn't it be cool if Bilstein would do a SD spec'd edition and give Bernie a royalty. It would make life easier and cheaper for everyone and give SD more time to do custom spec.

wannafbody

iTrader: (1)

Bilstein has files on hand and can revalve to questionable specs such as the R and FastMike versions. It's only $35 more to get Bernie to do the revalving.

Thucydides

Also, after speaking with Bernie, I'm pretty sure Bilstein isn't interested in being nearly as meticulous as Bernie is; it would take too much time and money. In Bernie's case his reputation is on the line in a way Bilstein's isn't; his customers expect a superior product and Bernie's got to deliver.

Bernie preps parts in a way Bilstein doesn't, and has some custom assemblies Bilstein doesn't use. Think of it as blue-printing your shock vs a factory job.

BAHKACK

+35 bucks per shock to get revalve? Do I buy my shocks and send to him or buy from him and add $35?
Dang that's good. I'm gonna wet myself.
I have an NA. I have NB hats, do I get NB HDsports? Or should I do NA HD and drill the hats (diy FMC hats)?
Forgot I was on mt.net. Give me a second to get my flamesuit on before replying to my dumb questions. Thanks in advance.