Are '99 Shocks rebuildable?

[DMadigan]

Just thought that I would ask before buying new. I have access to a shock dynamometer so I can match them. The guy who builds the dynamometers says off the shelf shocks are badly matched, even quite expensive ones.

[tcora]

They are not rebuildable

[DMadigan]

Looking at the Bilstein B6 and B8 (apparently no difference except the word "Plus" on the B8) they have a top nut that can be removed. The only question is whether any internal parts are available.
Sometimes they use off the shelf seals rather than having specials made.
Does anyone know it the stock shocks are tube inside tube or does the piston run directly in the lower tube? Modern motorcycle forks use a separate tube for the damper head to control the clearances.
Any idea who the original manufacturer was?

[tcora]

Pretty sure the OE was Bilstein. I replaced the OE struts in my 03 last summer - I don't recall seeing anything removable on the top of the strut. Thought I might have some pictures, but can't seem to find any...

[DMadigan]

Feeling in there with my fingers, the top has a V groove nut like the Bilstein pictures on Pelican so it would be possible to open them.

[tcora]

So then one has to ask: are rebuild parts available? Are the OE shocks worth rebuilding?

[DMadigan]

It depends upon what you mean by "worth rebuilding"? The only parts that wear out are the bushes and seals, maybe the damper head if it is contacting the tube. Better shocks have wear bands on the head.
You can buy adjustable shocks for the price of B6 Bilsteins. If they were made for a Porsche it would be four times the price. Bilstein's non-adjustable shocks for circle track cars are half the price. The only thing special about the B6 is the mounting and spring plate.

A loss of damping is usually from oil loss or worn seals. I am not building a race car, just restoring the stock damping, maybe a little better with higher viscosity oil. Plus, I can match the damping which you do not get with off the shelf shocks.

[Jeff Alton]

^^^^ Are we talking about a street car here?

When you get your new B6 and of B8 put them on the shock dyno you have available and see how mismatched they are, or aren't. Report back.

New B6 or B8 are not expensive.

Have you considered talking to Bilstein about replacement parts if you think they are worth rebuilding?

Cheers

[DMadigan]

As I said, not a race car, so yes, a street car. Bilstein said they cannot sell parts for OEM shocks due to legal agreements with Porsche. I replied asking about parts for the B6 and B8 which I think are not OEM. Bilstein list them on their site as aftermarket. Unless they have a different bore or shaft from the B4, which is not likely, The internal parts are probably compatible. Yes, the B6 are listed as "performance" and the B8 as "performance plus" but that may only mean different viscosity oil or damper head. They might not want to sell parts since they can sell the entire shock for a lot more.
Here is what Ohlins damper heads look like:
https://www.propilotsuspension.com/wp-content/uploads/2012/10/pistn-kits.jpg

I modified the internals of my '73 911 Koni's. Very simple really, a shuttle valve in the base sets the compression and rebound damping by the size of the holes and how many are closed off by the floating plate. Nothing like the reed valve dampers that I made for my motorcycle forks.

[DMadigan]

Well, nothing further from Performance Shock. Guessing they either do not want to sell parts since they rebuild them or maybe they think I want to go into the shock business. Not interested, I doubt there is any market for rebuilding B4/B6/B8 shocks since people are happy to pay $1000 for new shocks. Besides, I have far too many other projects that are more interesting.

[DMadigan]

So not rebuildable in the normal sense. Here is a picture with the top crimped-on cap removed:

The tube is crimped over the seal, a CFW DHSWV 25-46.5-3. I did not see this size in CFW's hydraulic seal listing so may be special. No matter as I would have to weld on a special seal holder anyway.
A couple minutes with a parting tool in the lathe you see this:

I am not sure if this is an inner tube or the top bushing holder. It does not move with a punch.

[DMadigan]

The piece you see inside the tube is the top bushing holder. A few pulls on the strut rod and it comes out along with the inner tube.


Standard double tube construction with a reed valve on the end of the piston, one set of reeds for compression, the other for rebound. There is a addition reed in the end of the damper tube. Probably a one way valve so as the strut operates it circulates oil through the reservoir and any aeration bubbles are pushed out the top into the reservoir.
The orange band is the topping stop. If you want to lower the car put in a longer stop. The black band around the piston is a wear band.
Would not be hard to re-valve. Making it externally adjustable would require gun drilling the strut.
Considering the time it takes to remove the struts it might be worthwhile.

[DMadigan]

Used a Dremel cut-off wheel to trim the peened stud from the nut. Here is the shim stack:


Top row is the topside of the piston (compression), bottom row is the bottom side (rebound). The small slots in the rebound disc allows the strut to move at slow speed without having to force the shim open.
The low speed control shim sits on the inner ridge of the piston, The smaller high speed shim next to the piston fills most of the space between the ridge and centre of the piston.
Changing the thickness of the shims changes the damping level. Changing the diameter of the high speed shim changes at what shaft speed it comes into effect.
The simplest modification is to add a fill port near the top of the reservoir and one on the bottom so the fluid can be changed and the shock pressurized.

[mistertate]

Cool info, thanks for posting

[DMadigan]

Checked with the shock dyno guy on what can be done with these shocks. He suggested adding an air bladder so the shock can be completely filled with oil, then it does not have to be pressurized to prevent cavitation.
Add a bung near the top where the body bulges out and one on the bottom so the fluid can be changed on the car..
He said they use 2.5 weight oil and modify the valving to work with it. Light weight oil does not change viscosity with heat as much as heavier oils. He said the NASHCAR guys would run WD-40 in the shocks.

[Driven97]

I mean I like that you're spending time on this and all, but may I ask why? Seems like pushing a boulder up a hill for slightly more shade for ten minutes one day every July.

Or maybe a better question, have you ever entered a turn and were like, "darnit, I feel like I have 3% less rebound damping on the left front than the right, I really need to get that fixed."

[DMadigan]

First, because I prioritize handling and braking over engine kilowatts.
Bilstein sells the stock shocks with the B8 at a higher price because people go for "performance" parts. They cost no more to make than the stock shocks. They could have made the shocks rebuildable with the top seal held in by a nut rather than folding over the shell to retain the seal but why sell a $5 seal when you can sell a $250 shock?
You probably would not throw away and expensive fountain pen because it ran out of ink but would throw away $2000 shocks because a $5 seal leaked?
Just cutting off the seal and welding on the threaded piece for the nut would cost far less than a new set of shocks.
Revalving the shocks to work with thinner oil will make them more consistent as they heat up.

[JFP in PA]

Yawn.......................

[DMadigan]

The opinion of someone who's skill level is "take it to your dealer for repair" or "replace parts until it works" is of little consequence to me.

[tcora]

Originally Posted by DMadigan

The opinion of someone who's skill level is "take it to your dealer for repair" or "replace parts until it works" is of little consequence to me.

Wow