ECS Strut Service/Rebuild?

Is anyone aware of any person/company that has made any good progress toward servicing/rebuilding OEM ECS struts?

The best I can find is this forum thread with some good technical info and a tear-down video that includes discussion of some of the hurdles that must be conquered to successfully rebuild an ECS strut: Refill ECS Struts - Thicker oil - Increased Dampening | Mitsubishi 3000GT & Dodge Stealth Forum

With front ECS struts being discontinued and out of stock everywhere, and low-mileage used struts becoming hard to find, I’m very concerned about my original ECS struts with 97k miles eventually failing.


I have brand new original OEM seals in stock right now. I know how to strip down the shocks without the need for drilling or grinding. I just haven’t had the time to put a video together which allows the repair to be done at home. DO NOT throw away your old shocks. They are repairable. If you don’t want them, I will buy them from you. The 3si video link is very informative but i’m afraid that I don’t agree about there being any gas inside.
Please stand by for future updates.


In that thread, someone contacted KYB asking for specifications, including nitrogen gas pressure, and got this reply:

Sorry, we cannot share any drawings or oil specifications as it is Mitsubishi’s proprietary information. I can however tell you that the nitrogen should be charged to approximately 150 psi. Sorry I cannot share much more information than that.

Link: Refill ECS Struts - Thicker oil - Increased Dampening | Page 4 | Mitsubishi 3000GT & Dodge Stealth Forum

He then goes on to describe how one could calculate the amount of liquid nitrogen to pour into the strut before sealing so that it would reach the desired pressure as it warmed and expanded into gas.

Thanks. That’s priceless information. It is still hard to understand why there is no pressure when you open the strut. I have even opened brand new struts and had no gas leak out. Is it a case that the strut is not pressurised by the gas but the gas is just there to remove the air and any impurities?

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My understanding is that the purpose of the pressurized gas in an oil-filled damper is to inhibit formation of bubbles in the oil as it is agitated.

I don’t know what to make of the discrepancy between KYB’s claim of 150 psi nitrogen charge and your experience of no gas pressure release when opening struts. Some possibilities:

  • KYB mistakenly provided incorrect info.
  • There is some internal sealed chamber that is charged with pressurized nitrogen; not the main outer chamber?
  • The amount of air space in the strut that is charged with 150 psi nitrogen is so small that it takes a relatively small amount of nitrogen to create that pressure, and it is not very noticeable when that small amount of gas escapes while opening the strut.
  • Maybe the 150 psi spec is for when the strut is fully compressed rather than extended, so the pressure is much lower when extended? (This seems doubtful)
  • Every strut you have opened (even the new ones) had previously leaked their pressure due to aged/faulty seals?
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@Joe90 I’m curious to know how you un-crimp the crimps that hold the seal in place, then re-crimp it without causing any damage or deformation that could compromise the seal.

As far as I know, it isn’t all that important to have gas inside these shocks. (If there even is or not) I tend to agree with Joe. To my knowledge, there isn’t any gas inside. Gas is indeed used for preventing the oil from airating and losing viscosity, but I doubt it’s all that important in cars such as this.

I’d be super curious to find out if rebuilding a shock without gas (assuming it was manufactured with charged gas inside) would be detrimental to the performance of the shock. I can’t imagine it would.

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I am going to investigate this a little further before I do the how to video. If it turns out the gas is important, it will no longer be a diy video but here’s what I think. There are millions of motorcycles on the road that use this exact same style of shock but with the spring inside and yet they are all user serviceable and none of them use any gas.
If it is presumed that the gas has leaked out of my brand new struts but the strut still works perfectly fine, do we really need the gas?
I think this debate will go on a little longer but either way, don’t throw away your old struts just yet.


My struts are still on my car and seem to be working fine still at 97k miles. I was debating whether to spend ~$500 USD on a used set of all 4 ECS struts with ~30k miles on them as a backup set, but I could really use that money now for more urgent repairs like driveshaft carrier bearings, spark plugs/wires, etc.

Hello joe I’ll be waiting on that video also ,on how to repair the ecs struts. I appreciate any info on the subject

I just want to be 100% sure on this Nitrogen issue before I go ahead but be assured that I am working on solving the question. If anyone can shed any further light on the issue, please let me know. In the mean time, I have started making inquiries about a supply and administration of the gas to the shocks just in case we do need the gas for some reason.

@Joe90 Here’s a recent post on the 3si forum with a detailed suggestion of how to proceed: Refill ECS Struts - Thicker oil - Increased Dampening | Page 5 | Mitsubishi 3000GT & Dodge Stealth Forum

Thanks for the link Jeff but I still can’t find the info on how much gas is supposed to be in there and I just don’t have the time for R and D on something like this. If anyone wants to buy the seals to have a go, I have them in stock now. I can also do the video on how to remove them without damage to the strut. I haven’t done in depth research into the oil but it seems to be about the same viscosity as motorcycle fork oil.


I am part of that thread on 3Si and am very interested to learn your method of rebuilding the struts, Joe :slight_smile:

Mike Randolph

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Thank you for being part of my forum. I have viewed the 3si forum many times over the years and found it to be a forum worth looking up to.
This strut issue has opened up quite a debate which I am hoping we can all work together to solve. It seems that we are all having ideas around the world on what to do to get the original struts back into service. I have invested a considerable amount of money on this item and I thought that I was ready to release a video on how to rebuild them until the liquid nitrogen was thrown into the mix. A quality job means everything to me so I have now put the video on hold until I, or someone else finds the information we need to carry out a high quality rebuild to factory spec. In order to add just a little more to the next step, I will be producing a short video called strut overhaul pt1 in which I will show how to open the strut without damage to the neck. You may also be aware that I have brand new replacement seals ready for when we have solved the remaining problems. In addition to this, I know how to remove and service the electronics without damage. I am not in this for the money so I will be more than happy to share all of the information freely with all forums when the time is right. I also have access to companies that can replicate all of the original parts so at some point in the future, our joint knowledge will see these items restored. Watch out for and feel free to share the strut video if you think it can help others out.


Thank you, Joe!

I completely understand you not wanting to put out a video until you feel it’s 100% ready. I look forward to seeing this project progress (it will be very cool to have some “behind the scenes” knowledge of the video when it is released). Cheers!

Mike Randolph

Generally it’s pretty simple to know if they were low pressure or high pressure gas charged. I’m new to the scene so never have experienced new ECS shocks but am interested in rebuilding mine if possible. If they were gas pressurized from the factory, they would have shaft retention clips on the shock shaft that when removed would either quickly extend the shaft, or slowly. If they didn’t extend at all (or were very slow) chances are they weren’t gas charged. It is possible to low pressurize a shock utilizing nitrogen gas bags made specifically for shock use and that’d be the route i’d take if I was rebuilding regardless if they were pressurized from the factory or no.

If they had 150 psi as some have indicated, you’d know taking it apart as that’s pretty significant pressure. you’d hear it for sure when you released the seals… it’d rocket the shaft across the room if you didn’t restrain the shaft… very dangerous.

One thing I’ve noticed is there is no mention anywhere in the tech manuals, service manuals or marketing materials that the struts are gas pressurized units. Considering the minutiae of what they do describe for the vehicle, it seems that it’s a glaring omission if they were indeed pressurized.

I’m following this with great interest and appreciate the work your doing.


I am no specialist on this subject. I only know what I see and I was of the same opinion as you. When new, the shaft only extends slowly after being compressed. I find it hard to believe that you could pressurise them to 150psi and then compress them by hand. All the same, I must confirm any information is correct before producing the final restoration video. A video for opening the strut without damage is now complete and will be uploaded this week. I have also ordered the production of a custom tool to assist with dismantling. I am only hoping that we can get the gas question answered 100% soon.

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Hello Joe,
Great, I’m waiting impatiently on how rebuilding correctly these ecs-struts.
I have 3 spare ones to experiment on, so let’s hope you can get it figured out how to do it best.

Our shocks are twin tube. If someone wants to change the overall stiffness of the shock it seems you could just reduce the number of shims on the lower non rotating valve. The 150 psi pressure level seems way to large based on the attached video. The nitrogen does seem important to stop foaming and also for proper rebound. The good news is that you can add it as liquid nitrogen so it is not under pressure until it warms up. Pretty slick.