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Old 10-01-2015, 03:31 PM   #1
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Default OTS Bilstein to motorsports ASN conversion

I've been thinking about converting the steel bodies on my shocks to the circletrack ASN offerings from Bilstein. The advantages of the ASN series would be the aluminum threaded body, and the ability to use 2.25" ID springs.

Anyone have some insight into what might be involved?

My shocks aren't exactly an OTS Bilstein, but instead they are a used set of FCM double adjustables with an external reservoir. This is what I think the procedure might be. I know that the ASN shocks use 46mm dia pistons, and that the ASN rod diameter is 14mm. AFAIK, the FCM fancy DA shocks use a 46mm dia piston with Black Magic (TM) and a 14mm piston rod. I have read also that while the piston and damping adjustment are proprietary designs, the bodies, piston seals, and rod guides/wipers are standard Bilstein parts.



Can anyone confirm my suspicions about this? Would it be safe to assume that because both OTS bilsteins and the ASN shocks use a circlip as a piston retainer and to hold the main rod guide/wiper in that they could be used interchangeably? The more I look, the more it seems like a definite possibility.
  • Depressurize external reservoir - bleed schrader valve
  • Remove dust cap on shock
  • Press the main rod guide/wiper down to expose the top circlip
  • Remove top circlip
  • Remove lower piston retainer circlip
  • Pull out the shock shaft and piston assembly.
  • Drain the oil from the shock
  • Remove the hose between the shock body and the external reservoir
  • remove the circlip that holds the bottom cap in the external reservoir
  • Remove the bottom cap from the external reservoir
  • Press the separator piston all the way up to the top of the external reservoir
  • Have a new hose made to connect the schrader port on the ASN body to the external reservoir
  • Fill the asn shock with oil
  • Install the piston/rod/etc. in the ASN body
  • Bleed the shock piston
  • Install the piston retainer circlip
  • Press the main rod wiper into the ASN body
  • Install the top circlip
  • Install the top dust cap
  • Install the end cap back on the external reservoir
  • Pressureize the external reservoir
  • done?
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OTS Bilstein to motorsports ASN conversion-80-126321_fatcat_double_adjustable_coilovers_small_55d9085cef7a939b2965ef8ad97a2367c8f7cbf9.jpg  
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Old 10-01-2015, 03:36 PM   #2
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Watching closely.
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Old 10-01-2015, 04:03 PM   #3
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I contacted Shaikh through his website with some questions about this undertaking.

The TL;DR is that the conversion for the shock shaft to the ASN housings is no problem. The placement of the schrader valves is where my issue lies.

I don't know if I can just pull the whole piston/rod/rod guide/wiper/dust cap out of my shock and put it right into the ASN shock body, but it sounded like it was a possibility. Otherwise, I'd need to take the piston off, and slide on the new dust cap, wiper, rod guide, seals etc. Not really a huge problem.

Basically the schrader valve positions on the ASN shock bodies are very low, and may actually contact the miata control arm or the swaybar mounting tabs. It is really close to the sway bar mounting tab in the front and may be inside the pocket for mounting the shock in the rear. Also, the ASN bodies use a 1/2" bolt while the miata bolts are 12mm. The front mounting ears would just need drilled out slightly for the larger bolt, but the rears have a captured nut and would not be as simple.

Because I have the external reservoirs, I'd need to plug the schrader valve hole at the base of the shock, and have a bung welded onto the body of the shock itself and then have hoses made to the right length for the reservoir mounting locations.

It's not an insurmountable amount of work, but it is more involved for the external reservoirs.


Another question: How much data is there right now for 15x11 fitment on NBs? Does it absolutely require tilting the shock tophat inwards and 2.25" springs? Has anyone had any luck on an NB doing just one or the other?
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Old 10-01-2015, 04:11 PM   #4
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So what i want to know is.... if you have threaded aluminum body ASNs, will the Allstar 2.5" perches just thread right on?
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Old 10-01-2015, 04:22 PM   #5
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No idea. I don't know what the threadform or pitch of the threaded ASN body is vs the allstar sleeve.

I would say no, because the ASN threaded body is going to be a smaller diameter than the Allstar perch which has to fit over the steel body bilstein and snap ring. You'd be stuck purchasing the threaded perches from bilstein or whoever makes one for offroad shocks.
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Old 04-21-2016, 04:00 PM   #6
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Delete.

Last edited by Ziggo; 04-21-2016 at 04:06 PM. Reason: Fucking web interface posted to wrong thread
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