To air or not to air in the front forks?

[Guest]

My front end on my 80gs1000e is soft. It does not come all the way back and it goes down to easily. I'de say it comes back about 85% of the way. Its soft as hell. I have been reading posts on this topic and I see some people mentioning that having any air at all is a bad thing even though this is the stock setup from Suzuki. Why would that be? Does it potentially compromise the fluids if I read a few posts correctly? I am bidding on a pump with the gauge attached and intend on replacing the fluids and adding the recommended amount of air. I guess at that point I will know if I have any air leaks. I do not see any fluids leaking so that is a good thing I guess. How can I tell if my springs are shot? Bike has 20k on the ODO but I guess even that's not 100% proof. Any suggestions?

[Anonymous]

check the air pressure, there suppose to be some in there.

[Bolder Biker]

When my 1983 GS750ES was delivered new, the mechanic had put about 18 psi in the front forks (I think about 36 psi is the recommended maximum). This gave a nice stiff ride but was probably not conducive to long seal life. Over the years, I settled on about 10 psi as a compromise betwee seal life and good handling. Most recently, I junked the OE springs and went to a set of Progressive springs, which have a higher initial rate, and no air pressure. This gives my bike good handling and hopefully a longer fork seal life (on my 4th set currently).

I doubt that your springs are shot. It probably has more to do with the fact that Suzuki chose a soft spring rate in the first place. The non-return issue on spring extension/rebound may in part be due to the normal static sag (caused by weight of rider and bike), or it could be due to sticking/friction ("stiction") in the fork itself. Do you know if the "anti-friction" teflon-coated bushings have ever been replaced? There are 2 of them in each fork leg (upper/outer and lower/inner), and their function is to prevent friction between the 2 upper and lower parts of the fork as they slide past each other.

BTW, I don't believe that air pressure messes up your fork oil. It's more of an issue of putting increased pressure on the seals.

BB

[Anonymous]

I've been thinking about fork air pressure lately and even thought about starting a thread. From what I have figured out so far, having the ability to change the pressure gives us the ability to tune the suspension to our load and handling needs. It is recommended to set the fork pressure, spring, and damping in relationship with each other. A good way to start is to set each in the middle of their range and adjust all up or down to see how the change affects the ride. Mid-range settings for the spring and damper are three each, and for the forks about 15.

[Dink]

Air preload was a fashion at the time of manufacture, it is a band-aid measure at best, the best way is to set the sag up correctly in the first place, then you only need to use air to temporarily adjust for extra load.
I would also suggest it is worthwhile changing to new fork springs, stock or aftermarket is up to you. then set your forks for approx. 1 and 1/4" of sag and enjoy, knowing you wont blow forkseals etc.
BTW air will aerate your fork oil reducing damping and increasing heat and adding to wear on the bushes inside the forks, and damage the oil eventually by increasing moisture absorption and oxidisation.
Dink

[Don Lobacz]

My 79 GS1000E has 100,000+ miles on it. The forks were designed for air and work extremely well that way. The air supplements the spring preload and lets you set initial sag height (which I like to set at 2/3 total fork travel). The air also puts additional sealing pressure on the seal. I've changed seals once. If you have an air compressor then you can easily set consistent fork pressures. Run the compressor pressure up (or down) to approximately 15 psi. You now have a consistent pressure source that is not going to change any measurable amount just by airing up your forks. Pop the chuck on and off both forks quickly several times and you have perfectly equalized both forks. Sit on the bike and pump the forks up and down several times to see how they feel. If they still feel soft or hard, change the pressure in the compressor and repeat until they feel right. You will have to play with it to find the best setting. Another thing that helps fork action is to pull up the dust boot and spray Armor-All on the fork, pumping the fork so that it works into both the seal and the boot, and wiping off the excess. This really lets the forks operate smoothly.

[80gs1000e]

.......Do you know if the "anti-friction" teflon-coated bushings have ever been replaced? There are 2 of them in each fork leg (upper/outer and lower/inner), and their function is to prevent friction between the 2 upper and lower parts of the fork as they slide past each other. BB

Thanks for all of the info. I do not know about the bushings but I will check them. I need to replace the fluids and check the pressure (if there is any in there). I hope to win my fork pump/gauge and will then be able to check the air. I'm going to look into progressive springs but I heard those can be pretty expensive.

[Anonymous]

[quote="80gs1000e" I do not know about the bushings but I will check them. I need to replace the fluids and check the pressure (if there is any in there). I hope to win my fork pump/gauge and will then be able to check the air. I'm going to look into progressive springs but I heard those can be pretty expensive.[/quote]

I run proggressive springs with the recomended spacers, 10wt.oil. no air
Stainlees brake lines and blck progressive rear shocks. aaahandles and stops very well for the heavy pig it is,
charlie

[Anonymous]

What I've been wondering is whether the pressurized air in the forks reduces foaming of the fork oil, which is the purpose of pressurized gas in shock absorbers in the automobile world.

[Anonymous]

possibly but I believe its more for a supplement for the front suspension.

[Dink]

What I've been wondering is whether the pressurized air in the forks reduces foaming of the fork oil, which is the purpose of pressurized gas in shock absorbers in the automobile world.

No the air and oil are mixed under the pressires inside the forks and are the cause of foaming , this more than anything else is why I recommend against using any air in the forks. Air assist was only a band-aid to allow a certain amount of adaptability to these bikes.
Dink

[Anonymous]

What I've been wondering is whether the pressurized air in the forks reduces foaming of the fork oil, which is the purpose of pressurized gas in shock absorbers in the automobile world.

No the air and oil are mixed under the pressires inside the forks and are the cause of foaming , this more than anything else is why I recommend against using any air in the forks. Air assist was only a band-aid to allow a certain amount of adaptability to these bikes.
Dink

Do you think perhaps the engineers may have considered that when designing the system?

If your seals are blowing it may be an indication of other problems, like a worn or dirty fork tube? 15psi of air pressure should not be blowing fork seals. IMHO

[Joe Nardy]

Domino,

I would first flush and change the fluid. Ryan did that on his 550 as well as adding short (3/4" ??) PVC spacers to add some more spring preload. He used 15 weight fork oil. The Suzuki manual said to use a mix of ATF and motor oil (can't remember what weight). I'd go with the fork oil. Ryan's fork was noitceably stiffer and more controlled after the changes.

Joe

[argonsagas]

Dink has a pretty good point.

Since my GK front end was soft when I bought it, I put in new springs, and built up the pre-load.

Night and day difference in the ride and performance.


That was last year. I notice a slight imbalance now, but I don't want to do tiny adjustments with pre-loads, as it takes too long. It can be corrected with nominal air pressure.

Note, please, that the distance the bike has travelled is not the only deciding factor with spring life. Springs age/weaken because there is a constant pressure on them, even while the bike is sitting, and they will sag over time.

[saaz]

The springs in my forks (78 GS1000) are way soft and really need replacing. Using air alone to compensate is not the best thing to do, but until I get around to replacing the springs that is what I am doing. Once I replace the springs I would be using very little or no air in the forks.

It is interesting that since I have put on some standard shocks on the back while sending away my air shocks for servicing, the back end seems very rough and not at all in balance with the front end.