Inside of a 308 Koni

One of the rear shocks on my GT4 was not working properly allowing the tire to contact the fender often when driving on roads that slowly, but completely, cycled the suspension. Over the winter I discovered a split CV joint boot so while I was in there I took the shock apart. Since Konis are "rebuildable" I decided that I had nothing to loose in trying to effect a repair. I suspected that the valves were clogged or that the oil had leaked out over time (although there was no evidence of a leak). What I found was that the main seal had deteriorated to the point that rubber pieces had contaminated the oil (which BTW I measured at much less volume than spec) and clogged every valve and passageway.

The main seal on my shock (model 82P-1831, 1977 vintage) is a stack of rubber washers compressed so as to squeeze the rod and effect an oil seal. This is straight out of the plumbing industry, in fact the washers are 1.125" OD, .625" ID, .125" thick "stem packing washers" from a small industrial size plumbing valve. I decided to retrofit a conventional oil seal like Koni now uses.

For those so inclined, the 308 Workshop manual and the Koni website both show cut away drawings of the shock internals. The 308 manual has the washer stack, the Koni website shows a conventional oil seal. The seal holder is machined a little different so I use a few washers under the oil seal to take up some extra space. I also keep the separate wiper seal, one could have used a double ring oil seal instead as does Koni.

I mentioned working on the shock in another thread and have recieved PMs from a couple people asking for more info and photos. Since I can't figure out how to send photos in PMs (if it is even possible) I decided to post a thread. The main disadvantage of DIY rebuilding is the lack of access to replacement parts if they are needed. Fortunately there isn't much to go bad in these Konis, seals and "O" rings and shock oil are widely available. Also you don't get a shock dyno check of your work although you could have them dynoed by a specialist.

http://www.koni.com/_cars/_general_info/technology/construction/shockabs.html

http://home.att.net/~dirt.tech/susp-oil1.htm

The photos were taken over several months, some resized, different lighting and settings so many aren't as good as I would like.

The first 4 photos show the pin wrench and the basic assemblies of the shock.

 

I drilled a hole and a split line in a small piece of plywood to hold the shock's piston without damaging it. The piston is threaded on the shaft, various pieces from "above" and "below" the piston are shown.

 

I filed a small piece of pipe to fit the seal retaining nut. The washer stack had deteriorated to the point that pieces were coming loose and circulating in the oil supply. The new seal (green) was installed over a couple of plastic spacers. I reused the wiper seal which protrudes though the brass retaining nut. BTW, it's Cicada season in Cincinnati.

 

The crud that I cleaned out of the shock.

 

The foot valve. It snaps into the bottom of the inner tube. The seal holder/bearing, as it is screwed into the shock body, locks the inner tube and the foot valve against the bottom of the shock body.

 

The rebound adjustment nut. When adjusting the shock, the unit is fully compressed with engages the prongs on the nut into the clips on the foot valve. The foot valve, being locked in position by the inner tube and seal holder/bearing can not turn and prevents the adjustment nut from turning when the main shaft is rotated. The turning shaft screws the nut up/down the shaft exposing or covering very tiny holes in the threads on the shaft. During rebound a portion of the oil flow goes through the hollow section of the shaft and exits out any of these holes that are not covered by the nut. Needless to say all of the holes were clogged on my shock.

 

In the photo above, 2 of the tiny holes can be seen in the threads on the shaft. I didn't measure them but I would guess that they are about .005" in diameter.

A couple of shots showing how I removed the spring. I worked the 2 retaining pieces though the hole in the side of the pipe with a small "magnet on a stick". I used a piece of PVC pipe, steel would be safer but PVC was what I had on hand. Note that the hole is small to retain the strength of the pipe.

I still have some work to do before my car is back on the road so I do not know if the "rebuild" is successful. The oil specified in the 308 Workshop manual has been superceded long ago so I don't know it's specs. The link to oil specs (at the top of the thread) shows how many variations of shock oil there are so I ended up just picking one. "Shock" oil (as opposed to "fork" oil) is available at motorcycle shops everywhere.

 

Pete
After taking the first one apart I did the other side as well. It was in a lot better shape.

I use to work with an engineer who went on to a job at Koni here in the Cincinnati area (Hebren, Ky, just across the river) and I have toured the rebuild shop so I have seen them apart before.

Mike

 

The seal and O ring are just off the shelf parts available everywhere. Interestingly the seal holder/bearing and the rod (5/8" dia.) are of American dimensions. The original rubber washers were 1.125" OD, .625" ID, .125" thick "stem packing washers" with a thin fiber disk between each washer. The total stack height was .394", taller than the new seal so I used some washers to take up the "extra" space. The new seal is a typical oil seal of the type used on the cams, crankshaft, shift rod etc. (1.125" OD, .625" ID spring loaded lip seal). The wiper seal is widely used on hydraulic cylinders. I used a # 224 "O" ring (2" od, 1 3/4" id, 1/8" thick) to seal the seal holder/bearing to the main shock body. I am not sure what was originally used as my original part was severely deteriorated. These parts are available everywhere, here are some links to examples of what is typically out there.

http://www.ableindustrial.com/standard_inch_seals.htm
http://www.allorings.com/

Once out of the car, the Konis easily come apart and since most 308 OE shocks are at least 20 years old, a good cleaning and fresh oil can make quite a difference. Imagine not changing engine, trans oil, coolant or brake fluid for 2 decades. If you are like me and love to "tinker" with mechanical things and see how they work then this can be a fun project and a good learning experience. The worst that can happen is that you will be back where you started, ie, needing new shocks. If you want the "latest and greatest", "track" your car or just not interested and want to "write the check and turn the key", then buying new shocks would be a better way to go.

 

The Koni warranty from their web site:

"BUILT FOR A LIFETIME

Last but not least, KONl's are built to last a lifetime. Once you have bought a set of KONl's for your car, they usually will outlive it. KONI street shocks carry a lifetime warranty to the original purchaser for as long as you own the vehicle."

I am not the "original" purchaser, but I am the original purchaser of the set on my daily driver (with well over 100K miles on them) and they will be going back sometime in the not to distant future.