Ever crack open a koni shock for fun or profit? Then crack open this thread!

I'm in the middle of suspension indecision neverland right now:

ok, I might be at least past the indecision part (for now).

this is all for my ex-scca solo national champ fiat x1/9 - red.

I've got 3 basic suspension options, and where I am right now is planning to use the koni reds (single adjustable) with traditional under the tower camber plates, albeit with much softer springs than was run at nationals. I have 3 fronts, and 2 rears, and all at least pass the "move the shock by hand and feel damping" plus "no significant oil leaks" tests.

one of the rears however, exhibits a slightly odd temporary no damping trait. If I extend the shock about and inch, the damping will resist me. If I push the shock, again, damping. But if I switch quickly from one direction to the other, I get a bit of "undamped" travel before the damping comes back. 

I am clearly no expert but I have assumed this means the shock is a little low on oil.

so I made a tool and took it apart (it is important to note these are not gas charged shocks, so I didn't fear 150psi times the surface area of this upper part):

About here it struck me that I should probably do a bit more research (haha), and I might need to track the volume of fluid that comes out of the shock. So I stopped.

i plan to take these apart, clean anything that needs cleaning, replace any clearly busted o rings, and refill with new fluid.

my questions, as of now:

1. I think I want 30wt shock oil to refill. Does this sound right? Are there better ways to figure this out than guessing?
2. any recommendations on shock oil brands or where to buy?
3. Am I just nuts for even trying?

A few years back I rebuilt some AFCO coilovers for a Miata. The part number was MT59506 but for some reason there isn't a weight listed for the product. I imagine whatever you put in one, you want the same in the opposing side though.

Most shocks that I've rebuilt use 2.5wt or 5wt oil, but I'm not sure what Koni uses. I doubt it is 30wt. Don't use oil weight to try to significantly tune damping, use the shim stacks. 

Maxima makes great shock oil in the powersports world, lots of options there. Note that actual kinematic viscosity varies a lot between brands, even for the same weight. Pick a brand and stick to it if you iterate valving or rebuilds. 

I don't understand why there's no pressure in those struts. How do you bleed them properly? How do they mitigate cavitation? I thought Konis were generally a low pressure gas charged design. The answer to these questions will also feed into the "how much oil" question. Definitely measure what comes out, but if you've got hysteresis or nonlinear damping with the bench test, the shocks have already leaked and are low on oil. 

Definitely not nuts for trying, I love this stuff and rebuild and revalve shocks all the time. Just generally motorcycle stuff, or aftermarket Fox stuff in the car world. 

gearheadE30 said:

How do they mitigate cavitation?

That's the neat part, they don't. In practice it's not a huge deal, the biggest issue is they build heat *way* faster than a gas charged damper. The original (red) koni dampers were not gas charged; "modern" (yellow) dampers that have been rebuilt or converted to double adjustable also aren't gas charged. Personally I wouldn't go out of my way to use these, but if you already have the parts and the rebuild is essentially free, it's probably worth a shot.

I'm not super familiar with oil specifics, maybe do some research and see if one end or the other of the viscosity spectrum is better at cavitation mitigation? You also probably want one with as high of a viscosity index as possible because they will see a wide temperature range. Beyond that I'm not sure it makes a huge difference, but you don't want oils with wildly different properties between a pair of dampers. Either do your best to match the factory oil, or rebuild both of them. Assuming they're mounted fairly vertical and don't have a massive stroke, there should be a pretty wide range of acceptable fill level, especially without gas charge. I think without needing to worry about over-pressuring them, you could basically fill the tube with oil, insert the rod all the way, then dump a bit extra out and be good.

Maybe contact Koni about the oil?

If things are still the same as when I was playing with shocks more, Koni doesn't play well with the public on parts and info.

Typically the custom shop is the right place to start at the suspension guys. In for the learning as I've always wanted to mess around with valving and rebuilds but never took the leap.

Hit up Lee Grimes, maybe. He's not at Koni any more but he's probably just as friendly and helpful as he always has been. I'd definitely talk to Koni about the fluid, it's an important part of shock function. 

Konis are twin tubes, so they rely on gravity to help keep oil and gas separated. 

In reply to Keith Tanner :

Is Lee still involved in car stuff these days since he retired?   He was a huge help to me setting up several Porsche's and other cars for track duty use back in the 2000's. 

Some good ideas here, I'll reach out to koni to see if they still have specs.

part of the problem here is that these shocks are at least 30 years old, and no longer in production by koni (by decades, potentially).

here's a thread I found detailing same shocks and basically the process I'm trying to replicate. This is where I got the 30wt oil suggestion.

https://xwebforums.com/forum/index.php?threads/suspension-koni-strut-servicing.36142/
 

also, 4 of the 5 shocks have true choice stickers on them, indicating they have probably been to true choice for a rebuild, but true choice is no longer in business to my understanding.

dean1484 said:

In reply to Keith Tanner :

Is Lee still involved in car stuff these days since he retired?   He was a huge help to me setting up several Porsche's and other cars for track duty use back in the 2000's. 

Lee is the "partnership relationship manager" at the SCCA. 

Lee will be at my place tomorrow talking K-swapped CRXs.  His son lives out this way now.  I'll ask about shock oil.

Anything else you want to know?

In reply to Andy Hollis :

Oh my gosh that would be incredible! 
 

the story on these shocks is that they came with red the x1/9, which I acquired about 5 years ago. Red was built in the late eighties and early nineties by bill condrashoff in California, and he won 4 consecutive solo nationals titles in DSP in the car. The car was then sold and campaigned at nationals by others as well (which is also a good story but I'll skip for now), until a rule change around 2000 made the x1/9 no longer very competitive. Build thread if you're curious https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/red-national-champ-x19-autocrosser-gets-another-shot/185311/page1/

i believe that these shocks are the shocks that were used for the nationals-winning setups. And since they are still in relatively good condition, I'd like to use them (though I am getting slightly softer springs in an effort to keep my teeth). 

the shocks are koni "reds" I believe, and they are an x1/9 specific application which bolt directly to stock x1/9 knuckles front and rear. They adjust rebound by pushing the shaft all the way in and turning it. I do not believe they are in production anymore. I'm hoping to basically get new oil in the shocks and give them a quick visual inspection for anything significantly out of place. I'm not looking for cutting edge performance from them, but hoping they are still good for a competent sport shock. The car is still being used for autox, but more from a fun perspective. I am not expecting nationals leading performance from these shocks.

I'd like to know if there is an oil manufacturer and/or weight recommendation to get me close, if there is a specific amount of oil I should use to refill (vs simply filling them up as much as possible), and if there is anything else I should be on the lookout for outside of obvious physical damage to shafts and o-rings.

Another person also pm'd me Lee's email address, but I haven't emailed him yet. If he wants me to I certainly can.

thank you!

Robbie (Forum Supporter) said:

(vs simply filling them up as much as possible)

You definitely don't want to do that. At minimum you need to leave some space for the oil to expand as it heats up. Hydrolocking a damper is a bad time all around.

In reply to Andy Hollis :

Make sure to ask him about Konis for the first-gen CRX. He loves that :) And say hi for me. Lee's good people. 

Robbie (Forum Supporter) said:

In reply to Andy Hollis :

 Red was built in the late eighties and early nineties by bill condrashoff in California,

Here's my Bill Condrashoff connection:

He built my earliest data logger.  It was basically a cheap electronic stopwatch with wires running to a box that would actuate the start/stop trips based on an RPM signal.  So you could do acceleration runs to evaluate engine mods.  This is back before chassis dynos became ubiquitous.

Here's a pic:

Andy Hollis said:

Lee will be at my place tomorrow talking K-swapped CRXs.  His son lives out this way now.  I'll ask about shock oil.

Anything else you want to know?

He probably wont remember me (he absolutely won't remember me). but thank him for all the help over the years.  

That xwebforum link has some great info and pictures. I did see the 30wt recommendation, up from original 20wt. There are also some fluid volumes listed there, though 250ish ml of fluid is really not a lot.

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From that thread:

The fluid inside comes in a selection of viscosities, roughly from as little as "1 weight" to as much as "40 weight" (and I'm sure there are more). According to the Koni engineer I know, they use their own proprietary blend of fluid (pretty much every dampener maker does). But it really isn't that critical to use their blend. However the viscosity you choose will make a difference on how the unit performs. He said these can use as light as 10 wt to as heavy as 30 wt. The original fluid for mine (remember it can vary from one to the next) was 20 wt, but I went with 30 wt for the stiffer springs I'm using. Another factor is the quantity (volume) of fluid. This actually makes a bigger difference than the viscosity. There needs to be some air space inside these sealed units, the balance of air and fluid changes the dynamics. He told me my fronts should have 240 mL and the rears 230 mL of fluid each, which is interesting because the rears are longer and can hold more fluid. I chose a synthetic fluid but it is available in different blends. The most affordable fluid source is motorcycle supply stores. They carry a wide selection at a great price. Or again you can get the actual Koni stuff for a lot more money.

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Sounds like we'll get some real info via Andy/Lee, but I'll put my thoughts here anyway in case they're useful.

I didn't realize how the twin tubes on these worked, pretty darn cool and simple vs. some of the monotube stuff. During operation the base valve and shock action will generally keep the cartridge full of oil, and there's an external "reservoir" of fluid in the volume between the cartridge and the strut wall to compensate for shaft displacement. the air chamber, like a motorcycle fork or a gas charged shock, is just an expansion space. The more fluid volume you have, the less air volume you have, which will produce an air spring effect that is stronger the more compressed the damper is. This matters a lot on motorcycles, but I'm not sure how much it really matters on a car as long as there is enough fluid to keep it from sucking air into the inner cartridge. What you really want to be sure of is that you don't overfill - the damper will hydraulically lock if it's overfilled and will blow seals out immediately. If it's underfilled, you may not damage anything, but the cartridge will start sucking air and you'll lose damping. So fluid level matters, but there's a range that's typically acceptable.

If I was rebuilding these in the absence of any other information, I would probably fill the cartridge halfway with oil, slide the piston and rod assembly into the cartridge but leave the seal head at the top pulled up, fill the rest of the way with fluid, and push the seal head into the cartridge. Not totally free of air, but close enough for this type of damper. It will probably slowly leak some oil out of the base valve once this is done. To figure how much oil in the outer section before dropping the filled cartridge into the housing, use some geometry to calculate the free space between the cartridge and the body. Then calculate the volume displaced by the strut rod when fully compressed vs fully extended. Now you know the absolute minimum amount of air space you need to leave. I'd probably multiply this by 2 for safety (this is definitely a SWAG number based on dirt bike forks), subtract it from your total available air space, and then you have roughly how much oil to add between chambers to be "safe". If I'm guessing, which I am, I'd think about half of the outer chamber volume will be air, and half will be oil, as that oil is also one of the main ways that heat is transferred from the damping chamber to the outer shock body for cooling.

You'll also be able to verify you're safe once fully assembled - you should easily be able to fully stroke the damper. If it's remarkably hard to fully compress, you've got too much oil and not enough air. Once you assemble it the first time, it is normal to have to cycle the damper several times to purge remaining air and get consistent damping - air will migrate to the outer chamber as the damper cycles. Try to avoid cycling the damper when inverted, it will pump oil out of the cartridge and pump air back in. It will eventually re-purge itself during operation if this happens, though.

In reply to gearheadE30 :

This makes a lot of sense, thank you!

maybe the simple way to think about it is to fill the inner cylinder all the way, then fill the outer cylinder about halfway? Wouldn't be too hard to check the level with the piston all the way up and all the way down.

I did this in the mid 80s with oem VW rabbit struts measuring the old fluid quantity and replacing it with the same quantity ATF which was noticeably thicker than the old fluid. Having a known viscosity would make tuning much easier. I was a dumb youngun then. Motorcycle suspension fluids are a good idea.

Talked K-CRX's for three hours with Lee and his son (also a Honda nerd).  Remembered at the very end to ask about shock oil.

As mentioned earlier, he said proprietary blend -- dino juice, not synthetic -- 5W.  Suggested just use whatever 5W you can find.  But also suggested that volume is critical and if the shock hasn't been leaking, it doesn't need more oil.

Hand motion on a shock is not sufficient to diagnose functionality -- needs to be on a shock dyno.

Those X1/9 Koni red struts are unobtanium, as are all the internal parts.  Further, adapters to make them work on a shock dyno will need to be machined.

He's willing to chat more, if you send him an email.

That's right, I glossed over that initially. Hand stroking can give you an indication of something being really wrong, but that's about it. The hysteresis that was felt could be a problem or it could just mean the damper was laid on its side recently. My memory is a little fuzzy but iirc non pressurized dampers also generally take longer to cycle oil back into everywhere than gas charged ones do.

Andy Hollis said:

Talked K-CRX's for three hours with Lee and his son (also a Honda nerd).  Remembered at the very end to ask about shock oil.

As mentioned earlier, he said proprietary blend -- dino juice, not synthetic -- 5W.  Suggested just use whatever 5W you can find.  But also suggested that volume is critical and if the shock hasn't been leaking, it doesn't need more oil.

Hand motion on a shock is not sufficient to diagnose functionality -- needs to be on a shock dyno.

Those X1/9 Koni red struts are unobtanium, as are all the internal parts.  Further, adapters to make them work on a shock dyno will need to be machined.

He's willing to chat more, if you send him an email.

Thank you very much for asking!!

Andy Hollis said:

Robbie (Forum Supporter) said:

In reply to Andy Hollis :

 Red was built in the late eighties and early nineties by bill condrashoff in California,

Here's my Bill Condrashoff connection:

He built my earliest data logger.  It was basically a cheap electronic stopwatch with wires running to a box that would actuate the start/stop trips based on an RPM signal.  So you could do acceleration runs to evaluate engine mods.  This is back before chassis dynos became ubiquitous.

Here's a pic:

This is really cool! I have tried to do a little bit by looking at ecu logs and comparing time to rpm increase. It's not perfect but it will give you an idea for sure!