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Old 9th August 2010, 01:11 AM
MercedesMike's Avatar
MercedesMike MercedesMike is offline
Join Date: Nov 2008
Location: Chicago Suburb
Posts: 29
Default 6.9 suspension not pressurizing

Hello everyone. Hopefully a simple question. Since I travel for work, there are some weeks when I am not able to take my 6.9 out for a drive and as such, it spends time in the garage unused for five or more days. Sometimes, when left unstarted and undriven for that long, the suspension fails to pressurize after starting up. I fire up the motor, rev it up to 2000rpm and it doesn't pressurize even after the car has reached operating temperature. The suspension sags down mostly in front. The back is ok.

It has five new spheres as of about two years ago. It's a US car (I fitted the Euro bumpers so don't be confused by that).

Sometimes it half-pressurizes and raises to a level that is driveable but clearly not at the standard operating level. In the past, it eventually it works its way out but this weekend, I haven't been able to get it to stand up. Bryan, Michael S.; Gayle, Sean; Romatoski, Zachary J.Should I follow a certain procedure? I've been reading a number of different forums that describe front and back leveling valves. I'd appreciate any thoughts and counsel.

Thank you.
Chicago Suburb
1978 6.9
Black on black
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Old 9th August 2010, 07:13 AM
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Styria Styria is offline
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Join Date: Feb 2008
Location: Sydney
Posts: 8,368
Default Re: 6.9 suspension not pressurizing

Hi MercedesMike, non or infrequent use of 6.9s with the hydraulic suspension set-up will create the sort of problems you have - or at least seem to have. It is obviously a matter of having an air lock in the system and you will need to eliminate that by:

1. Loosening both the Allen headed srew and the large nut located on top of your Pressure Regulator. You will need to have the engine running for that at normal idle, but do not remove either of the two components completely. Just undo them one at a time/both alternatively and you should be able to observe hydraulic air bubbles emanating from either source.

2. Disconnect the adjustment cable from the disc on top of the distribution valve so that you can easily alternate between the low and high position. Also it is important that, when moving the disc (with engine running), that you feel resistance (pressure) when moving the disc. Pressure is easily recognizable when the disc reaches certain operating situations.

Also make sure that your central pressure retaining air cell is in good condition.

If your system is in good working order, there should never be any need to subject t5he engine to high revs in order to build up pressure to make the suspension work. Generally speaking, half a minute at most times, with perhaps slight revs increase, should just about lift any car. Good Luck. Styria
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Old 9th August 2010, 01:21 PM
WGB's Avatar
WGB WGB is offline
Join Date: Feb 2008
Location: Perth Western Australia
Posts: 1,280
Default Re: 6.9 suspension not pressurizing

If the rear lifts but not the front you may have a problem with the front levelling valve.

If neither end lifts it will either be the central valve, pump problem or an airlock as Styria says.

I would think it to be unusual to have an airlock unless the system has been opened - I assume you have checked that the oil in the reservoir is not too low.

My 6.9 will lift in about 15 seconds max after prolonged inactivity on a normal cold start idle.

Usually - they just usually need to be driven more.

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Old 9th August 2010, 03:39 PM
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SEL_69L SEL_69L is offline
Join Date: Feb 2009
Location: Sydney, NSW, Australia
Posts: 1,201
Default Re: 6.9 suspension not pressurizing

MercedesMike: I note that you had all 5 spheres were replaced 2 years ago. Has the problem only developed recently? One of my guesses is that a very slow air leak has developed at the connection with the spheres, and refusal to come to ride height may be connected to this. Make sure that all of the spheres are securely tightened. This will not in itself remove air from the system, but the next step would be to proceed as Styria has above reccomended.

My car normally is at height, or comes to height within 30 seconds after start then idle.

Last edited by SEL_69L; 9th August 2010 at 03:41 PM.
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