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 Old 09-14-2014, 10:35 AM   #1
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Default Breakdown of MS3 Koni Yellow

Building on this: Breakdown of MS3 front strut

So a number of you all have bought GC's kit and a set of koni yellows.
One of the more interesting things about these struts is how similar they are to the OEMs.
Not only that they are twin tube, emulsion shocks, but also they way in which they are constructed.


The first step is to try to document the nitrogen charge. Once the shock has been opened there won't be any way to know.

I did this in two ways:

1)Several trials of compressing the shock to full compression and recording time until full extension. 3:30 +- 5 secs, 21cm extension

2)Inverting the shock over a bathroom scale to full compression. Not my favorite. I got readings inline with the other times I've done this, but I usually have to collect lots of trials and trim the outliers to get a vaguely accurate reading. 15-30lbs within the last inch of travel

Now that the nitrogen charge is roughly measured, it's time to drill a small hole and release the charge. Good luck disassembling the strut when it's still pressurized. I choose a location on the back of the strut where it would be easy to weld on a 1/4 NPT bung for a schrader valve.

Next you'll need this tool, called a gland nut removal tool. It's an OTC 7463, available all over the place online, or through most autoparts stores. It has a 1/2" attachment and you will need it.

Also, you will definitely need a vise to get that nut off. The sway link arm seems to be the best place, unless you can make a jig to secure the shock body.

Now this is probably the worst part. Having disassembled two of these struts, I know that the torque on the gland nut varies quite a bit. My first strut disassembled with just the gland nut tool and an 18" 1/2" breaker bar and some force. The second one required about an hour, soaking with ATF/Acetone and for the last half repeated use of an impact gun. That nut was torqued way down. No sign of rust/contaminants on the threads once it was removed. If you plan on doing this and there is any chance they have rust on the threads, I would say just start with the soak and impact.

I drained all of the fluid from the shock body and the inner tube by cycling the piston.

I ended up with just shy of 200cc's of oil, which is great because I managed to spill a little in the disassembly. With the previous shock, I sent off a sample of the oil to blackstone and got this back.

ROBERT: We'r glad to hear you mainly want to know about he viscosity. We have never seen this type of system before so we don't know exactly what he used oil should look like. But viscosity is what you want, so viscosity you will get: his was light oil reading in the ISO 22-grade range. The additive package is closet to a hydraulic oil, though there's a lot more phosphorus and zinc than we'd typically see in a hydraulic oil. Phosphorus and zinc are the main additives, so if you can find a 22-grade oil with about this level of Ph +Zn, you've found your replacement oil.

Once I pulled the strut inserts out, I noticed something weird. Two different spacers on inserts along with two different production dates on the struts. Left is 2013, right is 2014.

Neither the spring or the spacer comes close to touching the sides of the exterior tube...

In regards to how it all fits together, the bottom of the insert seats neatly into the flat portion of the strut bottom- keeping the inside tube from moving laterally.

The top of the interior tube is secured with the gland nut, which not only sandwiches the interior tube, but also prevents lateral movement. As far as I can tell, the construction of the exterior seals seem better constructed than the OEM shock.

-Single o-ring for the outer tube, isolated from lateral forces by the gland nut.
-Dust shield for the shaft
-Probably a nice u or v seal inside the shock head under the dust shield, probably replaceable.

In contrast, the OEM strut's seal is a combo seal: outer tube, shock seal, no dust shield. It's not isolated from lateral forces, just compressed between the head and the top of the strut.

Another observation: the inner tube (and therefore the piston) is actually 1mm smaller than OEM (35-36). This is also the same strut that produces damping characteristics strong enough to suit 500-600 ft/lbs springs, as affirmed by the design data provided Koni AND GC. That piston is the same size or smaller than probably the weakest damped shock available, OEM dampers aren't really even enough for stock springs. This should bring into the question one of the touted benefits of monotube shocks for this car- larger pistons suit higher damping forces.

The overall design of the shock body seems very, very similar to the OEM. 2.5mm steel body with a welded cap and welded arm for the sway links. Same OD, and probably ID too (I tossed the original OEM I chopped up). Presumably, if you could get a spare gland nut and inner tube/shaft you might be able to thread and use the OEM body... Not sure why you would want to though.

I'll do some more work on the internals in the future, first I want to reassemble and do a baseline dyno before I go tearing into the inner tube. Also, rears in the future.

Last edited by zenit; 09-14-2014 at 12:18 PM.
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