Cockroach Suspension Logs/Notes 6/2 DIY Repaired Leaking AST Shock

[fattycharged]

Sam, you got it correct. Needle valve is super common on a non remote setup. I've got a nitrogen setup at the house if you don't have access to one.


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[samthejam]

Sam, you got it correct. Needle valve is super common on a non remote setup. I've got a nitrogen setup at the house if you don't have access to one.


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Awesome, if I have any trouble with my aircooled friends setup I'm borrowing. I'll setup something with you

[cobra]

Nitrogen pressure should not really be used as a tuning tool. In a monotube setup like that with no base valve, you probably need to run 150-250psi depending on valving. If you want to play around with it, try to machine the hole for a schrader valve and fill it with a bicycle shock pump.

[samthejam]

Nitrogen pressure should not really be used as a tuning tool. In a monotube setup like that with no base valve, you probably need to run 150-250psi depending on valving. If you want to play around with it, try to machine the hole for a schrader valve and fill it with a bicycle shock pump.

A lot of remote reservoir shocks will give the user a nitrogen fill port (schrader) for servicing, if the reservoirs have to be disconnected. Some use it for tuning but it's intended purpose is for service.

Also targets to aim for he said

"AST . They run they kind of high, too high if you ask me. But 150psi front..."

Good to know it can go up to 250, I'm hoping I can get a reading from the other damper.

My nuclear plan is if something happens to the self healing membrane is to take it to my dad and figure out to add a Schrader with his machine shop tools.

Again mainly trying to refill it to by me some time while I save up for something else, since the shock doesn't look majorly damaged just seems like it is leaking the nitrogen very slowly. Ideally new MCS 1 ways or a set of used 2 ways.

[samthejam]

The Nitrogen filling went well, the shock was only at 60 psi. I filled it to 150psi, and it needed about a 100lbs of force to begin opening the shock on my scale. I didn't want to poke the other "good" shock as it was kindve a fiddly affair and I just didn't want to create more problems as myself.

So my only way to match it was using the gas force. I had both out of the car anyways so this was easy enough. The "good" shock was 50-55lbs to open. So I just kept bleeding off the nitrogen until I was able to get it within 5-10lbs of the "good shock". Which ended up being 55-60lbs of force for the damper to move. I used a corner weight scale t to measure the gas force for all of this.

Stole the idea from FCM

Thank You @fattycharged for the nitrogen tank, regulator and lines

[cobra]

There is a good chance if you had the nitrogen leak out, it will leak out again especially after being poked. Just a heads up!
Several companies have moved to a screw with an o-ring instead, but that requires an even more specialized tool. Or a schrader valve which is the easiest.

[samthejam]

On this episode of being a dumbass and on a shoestring budget and deprecated dampers. One of the rear ASTs called quits on my last roadtrip.

With my 784lb rear spring, this left me in a tough spot. This was my solution.

From the middle of the shock “eye” to the end of the shock body:
AST: 14"
911: 13.5”
911 w/ Spacer: 14.75”

Full length of shock from eye to the very end of the shaft
AST: 25"
911: 25"

But the measurement that really matters is the eye to the end of shiny part of the shaft as that merits the true “top” part of the shock as far as the car is concerned.
AST: 23.5
911 22.5"

Shock 911 / 930 1972-89 - BILSTEIN - REAR - B6 - Clubsport / Race (220/180)
Part Number: 24-009676
Series: B6 (HD)
Position: Rear
Descriptor: Club Sport Model

https://www.rockauto.com/en/moreinfo.php?pk=6603144&cc=0&pt=7556&jsn=329

M12: Rear Shock mount

https://www.bimmerworld.com/Ground-Control-Urethane-Alloy-RSM-Set-12MM.html

EDIT: The Bilsteins were M10, but I used the bushing the shocks came with and shoved them into the GC RSM Housing with their supplied washers.

Shocks
$383.15
RSM
$161.24
Amazon Sleeves for 14mm to 12mm for Shock Bolt
$8.43

https://www.bimmerforums.com/forum/showthread.php?2207929-Detailed-Information-on-E36-Struts-and-Shocks

https://www.bimmerforums.com/forum/showthread.php?2136006-Mounting-Koni-8210-1159-rear-sport-shocks

https://workshop.bilstein.com/wp-content/uploads/2020/08/4_BILSTEIN-Klassik-Katalog-2019.pdf

https://forums.pelicanparts.com/porsche-911-technical-forum/1111488-bilstein-shock-question.html#post11591117

$552.82



TC Klines sells the single and double adjustable rear indiv. E46 M3 Rear Koni Yellows would work but be underdamped and springs would fall out. The Koni 8210-1159 would also work, but were backordered from FCPEuro. Other sites were a little more than I wanted to spend and I think they'd work but me maxed out.


Untitled by Sam DaJam, on Flickr
Untitled by Sam DaJam, on Flickr
Untitled by Sam DaJam, on Flickr

Car doesn't seem as easy to thrown around, it was a little too playful arguably before. We'll see how I like it on track but It rides better. I have the front shocks on 4 now and it feels decent. 2 feels okay, but just can't throw the car around like in a slalom the way I like.

It used to be 2 and 3 for street. I'd turn it up to 5 and 6 for the track and loved it, but was bouncy and too rough for the street.

I'll play with it more at Road Atlanta

[samthejam]

Just wanted to see if I could repair it, just to do it.

Got it apart, thanks to some wisdom from Pavlo
You actually have to have gas in it to loosen the dust cap. I initially degassed and was stuck. The dust cap threads onto the shiny aluminum piece, and without the gas pressure they rotate together. All the sealing is done by the seal head, and it's all held in with a circlip.

Working through sourcing the seals at this moment. It looks like it uses a custom two piece seal for low drag, for the main shaft seal. Looks like that was a selling point for the 4150 way back. I should be able to get away with a regular u cup seal? At work right now need to grab some more measurements when I get home.

Some info: I found on the seal

https://www.vorshlag.com/forums/forum/board-rules-and-announcements/announcements/6771-ast-suspension-purchases-moton-suspension

https://www.vorshlag.com/forums/forum/board-rules-and-announcements/announcements/6851-ast-4150-series-damper-announced

Worst case, I am just where I started but figured I'd share if anyone wanted to see what the inside of it looked like.

[samthejam]

Seal head dimensions:
22x5x14

Seal Head oring: 33x4.5

[samthejam]

Good news!
I found a hydraulic seal—it came in Friday.

It’s a U-cup seal like the original, but made from urethane and in a single-piece design (unlike the two-piece original). Specs below:

• Max Speed: 3.0 ft/sec (1.0 m/sec)
• Temp Range: -50°F to +230°F (-45°C to +110°C)
• Max Pressure: 6,000 psi (400 bar)

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A Bit About How the Shock Works


Untitled by Kurvenkamph Motorsport, on Flickr
Untitled by Kurvenkamph Motorsport, on Flickr

Part E is the shaft guide and main seal head. It originally sealed via Parts C and D, a special two-piece seal you can find in Vorshlag’s documentation. That seal’s no longer available, so I said screw it and went with a standard U-cup.

Now Parts C and D are replaced with the single-piece seal, which handles all the hydraulic sealing. It’s held in by Parts B and A—a washer and a circlip.

Part E also seals against the shock body with an O-ring, which holds both oil and nitrogen in. But this O-ring is a weird, obscure size—probably would’ve taken weeks to get from Europe. That would've killed my motivation, so I reused it.

The piston (anodized blue) also has an O-ring. It supports Part H, the wear band—a sort of hydraulic piston ring. VANOS fans will get it.

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My Approach


A lot of people go by: “Do it right, or don’t do it at all.”
I lean more toward: “Get it running, even if it’s wrong.”

That usually means doing things twice—and probably spending more—but it keeps the project from stalling.

For example: Part G, the dust cap with the wiper seal. I couldn’t figure out how to get the seal out without destroying it. And since I couldn’t source a new one, I left it alone. It’s not critical—just keeps crap away from the seal head. Yeah, it’s beat up, but it’s better than risking not being able to replace it.

Untitled by Kurvenkamph Motorsport, on Flickr
Untitled by Kurvenkamph Motorsport, on Flickr

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Why the Shock Had to Come Apart


The shock was leaking oil and gas pretty bad on the car—but it was still holding pressure, about 50–60 psi when I took it apart.

So I just ordered the shaft seal. It was the most likely failure point, and I could get it fast enough that I wouldn’t lose steam or get distracted by another project.

I wasn’t even sure I could reassemble it. And I made a dumb mistake: I pulled the dividing piston without measuring it. Don’t do that. You’ll be sad.

Another unknown: how much oil it takes. I saved what came out, but since it had been leaking, I couldn’t rely on that to get the fill right.

I ended up using 3wt racing shock oil from Amazon. The original was probably a Motul—red and lower weight—but close enough for now.

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Got it all assembled... then the nitrogen tank ran out. Luckily found a shop open Saturday that could fill it.

I matched gas force by feel, using the other (good) shock as reference—about 55 lbs of force. Both shocks rebounded at full soft in the same amount of time. Compression and rebound were smooth, no dead spots.

Reinstalled it, and have put 200 miles on it—still bone dry. I check by wiping the shaft with a clean paper towel. So far, so good.

Untitled by Kurvenkamph Motorsport, on Flickr


So I guess for Road Atlanta I'll be on ASTs, if it holds coming up to the weeks prior over Houston roads. I do enjoy having the adjustability for changing the cars handling balance.