Koni Shock Service

I recently serviced my front Koni shocks. I thought I would share some of the information I gathered, as it was hard to find information regarding the subject. Please note that this will not be a diy guide, but one might find some useful information here if you are already planning to do the service.

Koni would not provide any information or sell spare parts, but they can do a full rebuild of the shocks. New shocks are also available from Superformance, dinoparts.de and others.

Other threads:
https://ferrarichat.com/forum/308-328/359071-koni-shocks-whats-your-setting.html
https://www.ferrarichat.com/forum/308-328/435216-rebuilding-front-shocks-what-oil-should-i-use.html
https://ferrarichat.com/forum/308-328/340868-stock-308-koni-shocks-adjustable.html
http://www.ferrarichat.com/forum/308-328/323318-my-first-ferrari-3.html (see Peters post #54).

I used a standard hydraulic press to get the springs of. Had a tube and plate on top so that I could press on the plate that holds the spring. After compressing the spring, I removed the two C-clip halves that holds the spring holder. Be careful! Note that the spring has a lot of preload and will extend a lot.
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I built a tool to remove the top cap/ seal holder. For pins i machined down the tip of two M6 bolts to 5mm.

You might be able to use standard pin spanners, but my top cap/ seal holder war stuck and other tools did not work. I applied penetrating spray and also heated the other tube to get it of. I would recommend to tape the shaft so you do not scratch it.

Once the top cap/ seal holder was of, I carefully pulled out the shaft and inner tube.

The oil was very dirty and all the oil ports were gummed up. Even though it was not leaking, it was an "non-working" shock absorber.
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I removed and cleaned all the parts.

Note that some of the parts has to be mounted the right way (washers, springs etc.). Take notes and pictures.

I used a small pin spanner to remove the threaded ring that holds the seals.

To removed the piston, I used a seat post clamp for a bicycle. After tightening the clamp, I mounted the clamp in a vise. Do not use force on the outside of the clamp, as you could damage the piston. The best would be to use right size shaft clamps, if you have that.
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Before I took of the screws that holds the shims on the foot valve, I measured the visible lenght of the threads (so that I could mount it in the same position). These shims control the compression damping, and the shims are preloaded.
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The outer parts were sandblasted and spray painted. I used RAL 2002 Blutorange color.

The oil seals were old, but still working. I could not find any similar seals anywhere. Peter has a post where he mentioned WV packing seals: http://www.ferrarichat.com/forum/308-328/323318-my-first-ferrari-3.html

I ended up machining a seal holder so that I could use U-Cup polyurethane seals. As a static oil seal on the outside of the sealholder I used a #022 25.12x1.78 O-ring. To add radial stability I machined a bearing of Torlon (PAI) that was pressed into the sealholder.

Picture shows old oils seals on left, and the new one on right. I used the same top parts and dust scraper.
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I have a technical drawing of the oil seal holder if anyone should be interested. More pictures below.
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Before.
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After cleaning, with the old oil seals.
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After cleaning, with new type oil seal.
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Regarding oil, the owners manual and workshop manual says that 190ml Agip Oso 35 oil should be used. This is no longer available, but Agip Oso 32 is. That has a dynamic viscosity of 30centi stokes (cst) @40C, and 5,3 cst @100C. I used Putoline Hpx 7,5 suspension fluid with a a dynamic viscosity of 32,1centi stokes (cst) @40C, and 6,31 cst @100C.

All external rubber parts were washed soapy water, dried, lubricated with silicone spray and wiped with a dry cloth.

I bought new mounting bushings from Superformance and pressed them in with an hydraulic press.

I changed the springs to "Uprated" springs from Superformance. Since these are stiffer I changed the adjustment from 1 turn (from 100% counterclocwise) to 1,5 turns. This can be done externally by removing the spring and bottom out bumber, compressing the shock and turning.

The adjustment mainly change the spring preload on the rebound washer, and thus affect the rebound damping. But the adjuster also closes two bypass holes (first one, then the second) on the shaft. As oil is flowing through these in both compression and rebound, the adjustment might also have an effect on the compression damping. Be sure to clean these holes if you service the shock.

 

Finished!
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Thanks guys. You have a good point 911308.
As the Agip Oso 35 would have a slightly higher viscosity than the Agip Oso 32 that I found data on, I guess the oil that I used is pretty close to the original viscosity.

I did clean and reuse the outer seal (o-ring?). As this did not have an o-ring cross section I was not sure if it was a special seal, or just an o-ring that had changed shape. This is looks to be about 100% compressed (no gaps) from tightening the top so I doubt it will leak. Normally it is just air under this seal and the shocks are not pressurized, the only pressure on this seal comes from temperature changes and pressure raising when the shaft enters the shock.

I have attached the sketches I made for myself when I made the sealhead for U-cup seal. The bushing does not have to be made from Torlon, any bearing plastic that is compatible with hydraulic oil will probably work fine.
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