It's my opinion some forks out are over complicated. To me these features become more of a liability than advantage. For example I had a fork that had
1) positive air pressure,
2)negative air pressure,
3)dampening for positive,
4)dampening for negative,
5)adjustable lockout blowoff valve.
I look at it as a fork with 5 points of complication. Even with all these features it still doesn't make it perfect for every part of the trail, and this is coming from a hardtail perspective . . . If you have a full suspension MTB now your bring another dynamic into the mix. So nothing is perfect. It's just amatter of how much are you short of perfect. So if your fork with just 1)air pressure and 2)dampening brings you to 8 of 10, is changing to a fork with 3 more adjustments . . . or points of complication . . . that brings you to 8-1/2 of 10 worth it?
If I was a professional, and I didn't have to buy my own equipment; or I was independenly wealthy, I think I'd go with the more complicated fork. For every point of complication, is a point you have to maintain. In my experience it's always easier than done. To put it another way, Henry Rollins says: "The more you own, the more it owns you".
Ok enough said. My fork has been working fine, but I can't remember when the last time I changed the fluid in my fork. It's always good to give it a once over. Check the oil to see what color it is. The first think I look for is if the old oil has a silver tint to it. If it has a silver tint then that means there is aluminum in the oil. This means something maybe mis-aligned, worn out, or broken. More than likely it's a symptom of something that is about to be worn out.
Also over time the seals can dry out a bit. It's a good thing to give them a little cleaning, and a wipe down with fork fluid.
The manufacture suggests the fork fluid to have a viscosity of 7.5. The cycle shop by my house "Mikes", has some Bel-Ray 7wt on hand. . . . btw I like Mike's cycle shop.
Mikes Cycle Center
9615 E 63rd Street
Kansas City, MO 64133
I had a few questions about fork suspension and the questions he couldn't answer he looked up on the internet right there. He had a genuine interest in my needs and wanted to help as well as gain knowlege by finding the answers . . . or as we called them "facts" and not just "here say". Even though he has a "Motorcycle" shop and I was there about a "bicycle", he had the attitude of, Wow that's cool, I'd like to learn more about this. . . . We are more a like, than different.
In stark contrast I was at another cycle shop earlier that day ( . . . just happened to be passing by . . . ), and the fork fluid they had didn't have the viscocity on the bottle, but they were sure it worked . . . . Mmmmm maybe I'll pass.
The viscosity of the oil plays a part in the dampening adjustment. When you adjust the dampening, you adjust how fast the fork returns to it's original position after the fork compresses. Too little dampening, and your front wheel with return like a pongo stick, too much dampening and your fork won't return, and you will bottom out the fork. You can adjust the rate by adjusting the dampening valve.
I don't always run the dampening at the same rate. I adjust it for different trails and trail conditions. Marzzochi suggesst 7.5wt, but you can also use 5wt, 10wt, or I've heard of people mixing their own custom weights. The question you might have is why change the weight of the oil, when you can adjust the dampening rate. If you weight 100lbs, you will not be able to get all the adjustability from your fork as if you weight 165lbs. If you find you have the dampening valve all the way open, and you still want more dampening, you can change the oil in your fork with a heavier weight to achive that for example.
The fluid looked more grey from normal use, than silver. I've taken forks apart where the fluid looked more like liquid metal than oil.
After the oil is out, now I can take the fork legs off, You can get the non dampening side off with a long 15mm and extension, but the dampening side requires a very long 15mm socket to go over the dampening adjustment spindle.
Once the legs are off then you are going to need lockring plyers to take out the internal parts. It's important to lay them out in the order and side they came off. The inspection reveals everything is in perfect condition. The parts all have their anodizing, and the action is precise and smooth. The dampening valve holes are uncloged. Nothing to do here, ready for re-assembly.
Putting the fluid back in. All manufactures have a suggested level range. For example for my body I can fill each fork leg till the fluid comes to within 35mm to 45mm to the top of the fork leg when the fork is compressed. Add the fork fluid til it's about 50mm from the top, then cycle the fork up and down to purge the dampening valves of air. then add fluid till it reaches 35mm to 45mm of the top of the leg when the fork is compressed. This creates the "Air Chamber".
The lower the fluid level, the larger the air chamber; the higher the fluid level, the smaller the air chamber. The larger the air chamber, the softer the ride, but alone with a soft ride comes a fork with a lot of dive.
Dive is the amount of linear movment it takes your fork to stop compressing. For example lets say your fork's initial PSI is 30psi, you ride off a rock and the drop requires fork to stop compressing when the air pressure reaches 90psi. A large air chamber will require the fork to travel further to reach 90psi. than a fork setup with a smaller air chamber.
I'm going to ride this fork on the soft side. This fork has 80mm of travel. Dive will not be as noticable with 80mm vs. a fork with 120mm of travel. I like a soft ride.
The finally adjustment is the air pressure. I'm going to start with 30 psi. Another adjustment is Sag factor. It's the amount the suspension sags when the riders weight is put on it. For example you might want to have a 20% sag factor. 80 x .8 = 64mm. you want the air pressure set to were your static weight compresses the shocks enough to leave 64mm of compression travel.
This leaves 16mm of travel for depressions in the trail so your front wheel remains in contact with the trail. Remember this is suspension. You are suspended . . . suspended on a pillow of air.
Yesterday morning I got to ride it a bit. As far as mechanics go, the fork doesn't leak fluid or air, and it didn't fall apart. But it's not the trail. guess I'll have to wait. It handled pretty good on the way home too, as far as I could tell. After a short ride I decided the snow was going to be too much. I had some problems.
1)The snow was a little to deep for the tires.
2)There was Ice under the snow in mystery places.
3)I had rush hour traffic.
When the snow is high like tonight, you have to ride in the road, in the car tracks. People in cars hate this. So what you do is look back, ride as far as you can before the car behind you gets close. When they get close you get off to the side of the road, let all the cars by, and repeat. Stop, Go, Stop, Go, . . . . . . and it's not fun for me as well.
So I hopped on a bus. The bus can get around good in the snow. The bus is a backup plan I have. A $1.50 get me to where I need to go. However my connection was running 35 minutes behind. That wasn't fun. I think I had 3" built up in my ventholes by the time my bus got there.
Like the Bus says . . . Bike!