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Old 05-28-2004, 07:53 AM
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air ride gauge fluctuation

I have a Firestone AirRide setup. The needle for the gauge showing front end bag pressure remains rock solid while I'm driving but the needle for the rear bags bounces/vibrates when I am under power. Is this normal? I don't seem to have any problem loosing air pressure and the gauge is stable and shows proper pressure when I am sitting still.

Dewey

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Old 05-30-2004, 07:41 AM
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I assume these are direct reading guages. Should be fairly rock solid. First thing I would do is switch the guages/lines to see what happens. Suspect a "nervous"guage , not a real problem. Old single engine pilot solution is put tape over it so it does not distract you .

Trees
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Old 05-30-2004, 10:40 AM
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If you have one air supply switch for the rear air bags and the line T's to each one like a Y, then the bags will always try to equalize to each other thru the T. This action would cause a nervous or confused gauge.

This can actually be a problem of sorts when a tight corner is taken at speed, the force down on the outside bag will try to force air to the inside bag which is the opposite of what you would like to have, or have no shift at all.

The black tape idea is a good one too.
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Old 05-30-2004, 02:17 PM
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Trees,

Luv the black tape idea. For years my wife drove her Toyota with the "Check Engine" light lit. After having it checked by the Toyota garage a few times without any firm diagnosis, she just taped one of my son's Kirby Puckett baseball cards over it.
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Old 06-01-2004, 08:06 AM
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well actually I would be more concerned with the gauge that doesnt move than the one that does. When you are driving your gauges will display dynamic pressure fluctuation. As the airspring compresses under load, the spring rate and the pressure will vary. So it is normal to see them remian in time with the suspension movement. Now if you are having violent fluctuation it could me one of a couple things........ the most obvious is that you are having shock absorber problems and your shocks are not controlling the axle like they should be. The second cause could be a hyper-sensitive gauge...... pretty unlikely but worth checking. Now if the car ride great and everything works as it should, you can actually either reduce the airline size going to the gauge or put a restrictor in of some sort to reduce the amount of airflow seen at the gauge.......

Tony....
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Old 06-01-2004, 05:42 PM
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Tony,

You indicated a concern regarding the gauge that didn't fluctuate (this would be for the front bags) but didn't indicate a cause or a remedy. Clearly this gauge is not showing "dynamic pressure fluctuation" as you suggest it should. What might be the cause of that?

The gauge which DOES fluctuate (the rear bags) probably moves one to two pounds to either side of my base setting - so I wouldn't call it violent. It only moves while under power but does not seem to be moving in unison with bumps or dips in the road - or in unison with the suspension. It's more like a constant flutter or jiggle. I can't really watch it that close because it is mounted on the passenger side of the car - so I can't tell you if the jiggle gets more pronounced as the rear suspension moves.

I'm not that concerned about eliminating the jiggle (installing smaller lines etc) assuming it is fairly natural. I guess I'm more curious now as to what is going on with the front end where I get no jiggle at all.

BTW, I've got Pete and Jakes shorty shocks on the front with only about 2K miles on them. They are mounted on an F150 twin I beam.

Dewey
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Old 06-02-2004, 10:19 AM
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Well if the gauge isnt moving than I would think that we possibly have a sticky gauge or you could be driving with it topped out or over inflated and there simply isnt any movement. If the rear gauge is fluttering, I would bet that it may also be reflecting a friveline vibration or an out of balance / round tire.
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Old 06-02-2004, 06:18 PM
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Took the car out today on a back road so I could get a good look at the gauges on some fairly rough terrain. The needle for the front bags does, in fact, move when the suspension travels. I had not noticed it before because a) the movement is rather minor and b) the movement is more like a gentle sway rather than a rapid move or jerking.

Also, upon close inspection, the movement of the needle for the rear bags does appear to be a direct result of suspension travel - something I couldn't really see before without monitoring the gauges very closely. But here, instead of a gentle swing of the needle in rhythm with the suspension travel, the needle appears to be "bounced" or "jiggled" by the travel.

The rear bags are a different style than the fronts. Both sets are Firestone but the fronts are the double donut type and the rears are straight cylinder type. So I'm thinking the difference I'm seeing in the gauges is just a difference in how these two styles of bags react to suspension travel. The ride itself seems fine. Also, the rear shocks seem fine but I might try some new ones back there in the near future just to see if that might be the cause of the jerky needle response.
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Old 06-02-2004, 06:25 PM
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I would listen to the guy whos name is followed by @AirRideTech
but then again that's just me.
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Old 06-02-2004, 09:22 PM
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Quote:
Originally posted by 48LCCOUPE
I would listen to the guy whos name is followed by @AirRideTech
but then again that's just me.
Yup. That's why I did the test drive and tried to provide more specific detail of what, exactly, was happening.
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Old 06-03-2004, 07:08 AM
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The type of airspring you are ( without knowing the part numbers ) appears to be the correct ones. The tapered sleeve or rolling lobe airspring you are using in the rear have a more gentle spring rate and isnt near as progressive as the front double convoluted airsprings. Thats why you are getting a good ride quality. Now I would bet that after putting some quality shocks in the rear and making sure the tires are balanced you will notice your ride quality improve even more so.......
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Old 06-03-2004, 05:10 PM
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Tony,

Thanks for the follow up on this. The shocks only have 2K miles on them - and the wheel balance as well. But I think I might redo them anyway just to be certain.
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Old 06-04-2004, 08:51 AM
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No problem....... let me know if you need any further help.....
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