air shock help needed!

[tranger03]

First of all this site has been a lot of help. I just bought my first motorcycle an 1978 XS1100E. One of the first questions I have (that could not be answered by reading prior posts is: Does anyone one know the proper psi for an S&W Mark II shock. I have purchased a set of the conventional shocks from oldbikebarn and am awaiting there arrival. In the meantime my buddy (harley PHD) told me that the harley air shocks take 30 psi so thats what he set mine at. Does anyone know or remember the proper psi to air these things up to.

Thanks

Camron

[Jerry]

First of all, all the air pressure in the shock does is to set how much initial pressure it will take to compress the shock/spring combination. Remember, it is the spring that does the work; the shock controls the spring action. Changing air pressure does not affect the spring rate, which is force needed to compress the spring a given distance, usually expressed in 1 inch intervals. The XS/XJ rear spring is a dual rate, less force needed to compress the spring the first couple inches, more force needed to compress the last few inches.

On my XJ, which has the stock factory air-adjustable shocks, I run 27 PSI, so the 30 psi recommendation is right in the ballpark.

The "best" pressure is up to you; if you feel the set-up is to stiff, reduce the pressure until you get a comfortable ride without bottoming on larger bumps/potholes. If you feel the set-up is to soft, increase the pressure. Max is probably around 50 PSI; there should be specs with the new shocks that indicate the max limit.

I find that a bicycle pump works well for adjusting shock pressure. The volume is so small that a standard air compressor will over-shoot your target pressure, then you need to bleed out small amounts of air until you get the pressure you want.

Let us know how the your new shocks work out.

[prometheus578]

The volume is so small that a standard air compressor will over-shoot your target pressure,

True. Same as pressurized front forks. If you're using a compressor as an air supply, hold the air chuck over the shock's air valve, and then give it a really quick "blip". Really quick, as it'll instantaineously jump to about 10 pounds. This is not like filling a tire... there is limited space in there to fill, and it'll fill in an instant. Too much pressure can blow the seal, etc.

[tranger03]

I found out first hand how fast the shocks do fill up. My good friend (harley mech) who is helping me get the bike running used a zero loss gauge to get the shocks to exactly 30 psi. (always wondered why schraeder valves had threads) If I am going to keep these shocks I would definately invest in a unit like this to avoid overfilling as both of you have mentioned. All that out of the way I now know the proper way to fill the shocks but I can't find out how much to put in them. In my case I don't think that these are the factory shocks. When my buddy let some air pressure out of the one shock that I tried to air up without the special gauge it seemed as if the amount of air also effected the ride height. Maybe thought that was just because there was way to much air in one. I will try to submit a picture of the shocks as soon as I can get back over to my buddys house where the bike is at. Kind of hectic with the holidays breathing down my neck.

[prometheus578]

What Jerry said...

it seemed as if the amount of air also effected the ride height.

These also act like the "air shocks" that we all put on our Chevelles and Camaro's to raise the rear end clearance for those bigger tires in the '70's. Raised the car, but stiffened the suspension somethin' fierce. (Having no suspension travel snapped off the upper shock mounts on my LeMans after a while.)

[Ken Talbot]

Originally posted by Jerry
The volume is so small that a standard air compressor will over-shoot your target pressure, then you need to bleed out small amounts of air until you get the pressure you want.

Or, here are a few other methods:
- use a good pressure regulator on the output side of your compressor to dial in the pressure you want

- charge the compressor, turn it off, and bleed it down to the pressure you want

- use one of those inexpensive portable air tanks, also charged to just the pressure you want.

[prometheus578]

"Equality for all"

- use one of those inexpensive portable air tanks, also charged to just the pressure you want

Better put a few pounds more in the air tank. Air will flow from the tank till the pressure "equalizes" between the tank and the shock. Yes, the volume of the shock is rather low, but the difference would be measurable. (though slight)
Like when using a tank to fill a flat tire on your car. Don't go out there with the tank filled to 32psi. You'll end up with a tire inflated to 16 psi with 16psi remaining in the tank. Fill the tank to 64psi if you want 32 in the tire.
Ken's tip, as usual, was very good. My reply was more for the example of the car flat tire deal.

[Ken Talbot]

Prom's right, of course but you won't need to put too much more in the portable tank than your desired end pressure. The other thing you'll want to do is apply the chuck to one fork, then the other, then go back and forth a few times. That small difference principle applies here too, wherein the first one you do will have just a bit more than the next one. Cycle back and forth a few times, and all three (tank plus two forks/shocks) will be in equilibrium. OTOH, some folks might say this might be getting just a bit 'retentive' ..

[mro]

will be in equilibrium

The 80LG I recently got won’t be running for awhile so I'm planing to check out the air forks to see if I can tap into right below the valves for a cross connection.

Would be easier to just buy that kit I read about in one of posts here but not as much fun

If it works will do the 80G too!!!
If not will just get the kit



mro

[GNEPIG]

my buddy (harley PHD) told me that the harley air shocks take 30 psi so thats what he set mine at.

.. damn harley mech's, what do they know.. next thing you know they'll be loggin in on this site and trying to tell us how to fix our bikes!.. huh, harley mech's, them no good sun-a-ma ......

.. by the way only put 8 psi in each fork leg
and i think 30psi is the max pressure in the rear suspension of the fl style harleys your buddy is talking about, your bike weighs about 200lbs less then those. i will look in a book tomorrow, but we have been setting up the fl's here at 10 psi for the rear (and 15psi for the fronts of the older ones)
.. i think (uh oh me too!)you should start your air pressure at 10psi and raise it until the bike feels comfortable to you

[GNEPIG]

When my buddy let some air pressure out of the one shock that I tried to air up without the special gauge it seemed as if the amount of air also effected the ride height. Maybe thought that was just because there was way to much air in one.

.. wasn't the air shocks on the xj's a linked system? even the ones on the kawasaki's, which were almost the same, are linked.
.. i wander if he is playing around with a groovy set of after market gas charged shocks.. this will be interesting to see

[tranger03]

gas shocks with schraeder valves? doesn't seem likely...but then again I've never had a set of adjustable gas shocks. I believe that they were linked at one point. I seem to remember saying that he split them and put them each on their own valve because he suspected that one was leaking. As far as my buddy ever signing onto this forum to give advise...I HIGHLY doubt it. He's actually scared of "those damn jap bikes". But he knows that I want to ride and don't have the scrilla for a harley. I've pretty much taken the bike to his house and told him to help me get it running. He said it will be the death of him. I told him it will make him more well rounded. LOL.

Thanks for all of the info. I guess without a spec I will play around with different PSI's or just throw on the progressive spring shocks that I ordered. I think that they look better anyway. Anybody want a couple of AIR shocks.

[DiverRay]

No thanks, I've got the progressives on my daily ride. I REALLY like them.
Ray

[John]

The XJ air shocks are linked together via a hose. The fill port is on the left side shock. I had a set on my XS for many years, and I just recently replaced them with a set of low milage MNS shocks.

[Czekus21]

To avoid over inflating the air shocks ( as well as air in the forks ) A bicycle tire pump Will do the trick just fine. Not alot of work and doesn't cost very much. You can regulate the air alot better. This is the method I've been useing for years and have yet to blow a seal.