DIY rebuild of early Koni inserts

[davekillen]

I decided to try rebuilding the Special D Koni inserts for my '68 and thought it might help someone down the line if I documented it here. The part number for these is 86R 1394.

First thing is to pry out the three staked points at the top of the shock body. This is all that holds the top together (there are no threads inside the tube), other than the gland nut when the strut is put together, which I would imagine does most of the work. I just used a flathead screwdriver to do this.



Once the stakes are sufficiently... un-staked, I used a puller to extract the top busing-and-seal-holder assembly, exposing the main o-ring. I needed to use a hose clamp to keep the puller arms from popping out; it worked fine once I did this. It doesn't take a ton of force to remove, but was definitely more than I could manage without a puller.




Once that was removed, I drained the oil into a graduated container. This takes some back and forth to make sure you measure it as completely as possible. Both of mine ended up at right around 200ml.





The "foot" at the end of the outer internal tube is a press fit into the end, and fell off on one of my shocks when I was disassembling it. I slightly compressed the end of the tube to deform it and popped the foot back on. There is no need to remove the screw in the center of the foot.




On both of my shocks, there was a washer with rubber or similar residue on it floating on the main shaft, above the upper stop. The same rubber residue was on the bottom of the top bushing/seal assembly. Poking around online, I can't find an explanation of what this once was, but after a lot of thought my guess is that it was an internal bump stop of some kind that softened the impact of the shaft's upper stop hitting the top at full droop?




This is the top of the outer internal tube, and you can see where whatever it was that has now mostly disintegrated was resting. Given the sizes of the ID of this tube, the OD of the now-floating washer, and the remnants of the rubber, I actually don't think this was functioning as a seal between the inner and outer tubes. The two tubes lock together on a machined step in the bushing/seal cap anyway, and I don't think any significant amount of oil would get past that in operation. I really do think this was essentially a cushion that was bonded to the upper cap (you can see a ring in the bottom of the cap that has more rubber residue embedded in it; I would guess this is where it was bonded together, and the washer bonded to the bottom of the rubber cushion)

[davekillen]

Here's what I mean about being able to see where the rubber cushion (or whatever) was bonded to the cap (look at about the 7 o'clock position):



After cleaning up both the washer and the cap, and generally cleaning of all the rest of the components, I reassembled everything with an appropriately sized o-ring taking the place of the (presumed) rubber cushion. This o-ring is not tight to the inner shaft on its OD, nor is it tight to the ID of the outer shaft. It's essentially the exact size of the washer (which floats easily on the shaft, and within the tube). The washer and the o-ring will be able to float along the shaft between the stop and the cap, but since they'll never come into play except at full droop anyway -- if my theory is correct -- this should be fine.

I did not replace the shaft seal, as I've read they are proprietary Koni parts that aren't available to buy separately, and mine seemed to be in good shape. I did replace the main upper o-ring. I believe it's 38mm ID and 3mm thick but I had to experiment a bit to find one that wouldn't get destroyed when putting it all back together.



I filled each outer tube with 210 ml of Motul MTL105929 5W Fork Oil (added 10ml to the amount I took out to account for spillage etc). Then slowly and carefully put the twin tube assembly in, working the shaft up and down a few times to bleed out the air. After that, it was a matter of pressing the cap and o-ring in without destroying the o-ring, which was tricky but doable with a combination of clamps. I found it best to do this with the shock oriented vertically, because the machined lip in the cap needs to "plug" into the outer tube, and it won't easily do this if the assembly is tilted to the side. I also helped it along by tapping the cap with a plastic hammer once the o-ring was mostly past the lip of the outer tube.



Once the o-ring is all the way down, and the cap is fully in, there still needs to be force clamping the entire assembly together before you re-stake the outer tube. The foot at the end of the outer tube needs to be pressed up against the bottom of the tube; this is what keeps it stationery when the shaft is keyed into it and turned to adjust the dampening.

When the assembly is installed in the strut and the gland nut tightened it will accomplish the same thing, but I noticed after I assembled the first strut -- but before I re-staked it -- that I could hear the internals rattle if I shook it, but couldn't on the other shock (which I hadn't disassembled yet). The shaft would also spin freely when inserted into the foot as if to adjust the dampening. Once a little clamping force was applied to compress the components together, both of these issues were eliminated. I re-staked the housings with a clamp in place and at that point the rebuilt shock and the original behaved the same way.

I will report back once these are installed in my car, but I expect they will work fine as in the end it was a pretty simple process. Hope this helps someone down the line!

[snbush67]

Great write up! Looking forward to reading how well they perform.

[davekillen]

I finally got a chance to put some miles on these. They're great so far. Huge improvement over the completely shot Sachs shocks I replaced them with. I guess the real test is longer term, whether they leak etc., but their actual function for 1000 miles or so has been fantastic. I have them at the the softest setting and that's perfect for me, still plenty stiff but soaks up the bumps well and the car handles great.

[Tad240]

Nice work! You should have a good feeling of accomplishment from this DIY rebuild. And appreciate you documenting and sharing. Hopefully they’ll serve you well for many years & miles.

[nickelplated5s]

What # Koni do you have? It shouldn't really matter as they are more or less the same but I have those or similar on a 67. What are you running for the rear? BTW, I'm 30 minutes West of downtown PDX if you want to swap rides, PM. Might be able to get PeteKZ down too.

[davekillen]

Thanks Tad240! Nickelplated, they're 86R 1394. I have some NOS Konis in the rear, they're 80K 1738. I'm down to meet up at some point, though am super busy for the next couple months, I'm running Lemons soon in a Saab 900 and still have some work to do on that haha

[PeteKz]

Count me in for a meetup and car swap.

Good luck at LeMons

[nickelplated5s]

Thanks. Our host has 8040's I think I'll try. It would be interesting to drive the two. Weekends around here are not the best idea until after Halloween anyway. Corn Maizes, etc. Have fun with the Saab.