Man, I figured somebody would have responded to this by now. What follows are my opinions, and mine alone. We all know what opinions have been equated to, so take mine as you will. Here goes. It really all depends on how you want to ride your bike. If you want to reliably drag your pegs over all pavement obstacles, the stock suspension is junk right off the showroom floor. If you want to rack up miles on mild curves, changing the fluid front and back every couple of years will keep your stuff working reasonably well for as long as you want to ride the bike. The front forks are a reasonable project someone can learn to do if they have a weekend, a mechanical apptitude and some tools to go with a dirty oil receptacle and clean replacement oil. If you've got a service manual and access to a buddy who knows either there in person or on the phone ( get the right guy on the phone, and he'll have the service manual, too), or even just the book telling you how it comes apart/goes together, you can get through the fork oil change with confidence it was done correctly. Changing the rear shock oil is a little more involved, but aslo doable some weekend if a first-timer has a mechanical apptitude and some tools to go with a dirty oil receptacle and clean replacement oil. Once you have it down you can get it done in a couple-three hours, and that's not busting hump. When viewed from the inside, the big enemy for seals is air. If the fluid is maintained to keep it from breaking down and foaming, the seals will last a long time. This brings us to your question of "How long?" Again, we get "It really all depends on how you want to ride your bike." Some books will tell you the fluid's done after 1,000 miles, and service manuals will tell you the rear shock is permanently sealed and can't be serviced, while the front needs to be changed every 18000 miles (Concours). I usually change mine once a year, and in the back I currently have 15W suspension fluid. When I change I'll go with 10W to try to get a little more damping action. I run 63 psi in my shock because I want both more clearance and spring, so switching to a lighter oil won't affect me the same as someone who runs 7 psi of air. If it's too light, I'll just mix some of the left over 15 with some of the leftover 10 and get somewhere in the middle, the final ratio being dependant on what the 10 weight tells my butt. Up front I changed more than just my oil at one point, and OH BOY WHAT A DIFFERENCE. I was able to scrape up enough walking around money to get a KB fork brace, some Sonic springs and some RaceTec cartridge emulators from Murphs Kits. I added some oil I had already (mixed and matched to get enough, it's about 12W) and my bike no longer wallows around corners. The front end feels a little stiff over bumps just riding down the road, but when you're leaned over a few degrees shy of scraping your peg and you hit a 1-1/2-inch-tall concrete seam, your front wheel rolls over it like it's not even there. With the stock suspension the front wheel will bounce up, the handlebar will go full lock and the bike will begin to travel in a less-than-controlled manner until the front tire touches down again and restores your illusion of control. While all this is happening, don't forget to keep riding the bike. So to try to draw this answer to an end before we all die of boredom, if you do nothing more than change your oil every couple of years, your bike will remain pretty much stock for years. If you want to comfortably keep up with a guy like Dan Paulsen, you might want to beef up the front end a little. Hope this helps.What is the expected lifespan of a Connie's suspension? Chad Wilson 1990 C10: 46k miles
Since I am at home looking for work, I just happen to have the instructions in front of me. Here's what they say. "7) Install the fork fluid. First remove the the fork spring and use the oil viscosity recommended in Table 2. Bleed the fork by pumping them. Install the emulator and then set the oil level with the forks completely bottomed and the springs out." Table 2 shows the proper oil level to be 150mm.Since I am at work and dont that the instructions in front of me. You emulator guys, how was that fork oil measurement, with or without the emulators installed. I gotta start refreshing my memory on them thingies.