Another front suspension question

[Atlas]

Hi all , here's another question on front forks. This one is a little different than the standard "how much oil" . The 1980 ,Gs750 I'm working on has been sitting for 20 some years , there are no leaks in the tubes , and everything seems kosher. But the suspension seems soft compared to my 1979 CB750 Honda . There still is damping , they don't bottom right out , I don't think any oil has leaked out , there are no signs anyway. My question is : How do you know if the suspension is 100% or not ? Could it be that sitting so long has affected the suspension ? All the rubber looks like new. I'd hate to do all of the work on them just to find out that it didn't make a difference by changing the oil.Like I said , it appears a little soft, but could that be the nature of the beast? Everything appears to be stock on this bike. I should also mention that this bike has around 25000 miles on it.

Also was the air valves an option ? I don't have any on my bike , but I notice that some of you have them.

[Big T]

If they don't leak, just drain and refill the oil

The air fork was used on some of the bikes, but not all. Most of us upgraded the springs and don't use the air

[sharpy]

As you have said its been sitting around for 20 years. All things being equal it be better hanging around as the springs wouldnt have sagged. But fresh oil everywhere would be a great thing to do and see how the seals go as its 50/50 whether they like or not i reckon.

Step 1: Extend the fork completely and measure from the wiper (the dust seal atop the slider) to the bottom of the triple clamp (or lower fork casting on inverted forks; Figure 2). This measurement is L1.

Step 2: Take the bike off the sidestand, and put the rider on board in riding position. Get and assistant to balance the bike from the rear, then push down on the front end and let it extend very slowly.



Where it stops, measure the distance between the wiper and the bottom of the triple clamp again. Do not bounce. This measurement is L2.

Step 3: Lift up on the front end and let it drop very slowly. Where it stops, measure again. Don't bounce. This measurement is L3. Once again, L2 and L3 are different due to stiction or drag in the seals and bushings, which is particularly high for telescopic front ends.

Step 4: Just as with the front, halfway between L2 and L3 is where the sag would be with no drag or stiction. Therefore L2 and L3 must be averaged and subtracted from L1 to calculate true spring sag: static spring sag=L1 - [l2 + l3) / 2].

Step 5: To adjust sag use the preload adjusters, if available, or vary the length of the preload spaces inside the fork.

Street bikes run between 25 and 33 percent of their total travel, which equates to 30 to 35mm. Roadrace bikes usually run between 25 and 30mm.

This method of checking sag and taking stiction into account also allows you to check the drag of the linkage and seals. It follows that the greater the difference between the measurements (pushing down and pulling up), the worse the stiction. A good linkage (rear sag) has less than 3mm (0.12") difference, and a bad one has more than 10mm (0.39"). Good forks have less than 15mm difference, and we've seen forks with more than 50mm. (Gee, I wonder why they're harsh?)

It's important to stress that there is no magic number. If you like the feel of the bike with less or more sag than these guidelines, great. Your personal sag and front-to-rear sag bias will depend on chassis geometry, track or road conditions, tire selection and rider weight and riding preference.

Using different sag front and rear will have huge effect on steering characteristics. More sag on the front or less sag on the rear will make the bike turn more slowly. Increasing sag will also decrease bottoming resistance, though spring rate has a bigger effect than sag. Racers often use less sag to keep the bike clearance, and since roadraces work greater than we see on the street, they require a stiffer setup. Of course, setting spring sag is only first step of dialing in your suspension, so stay tuned for future articles on spring rates and damping.

[Atlas]

Sharpy and Big T , thanks for your input , I'll def. do the fork travel test and see how they are and will post the outcome soon, again thanks.

Dave