Merc Denning Front Air Bags- Kneel Function

[Carpenter]

Hi, another in the series of problem solving for my Merc Denning 0303:

When utilising the Kneel function it works fine on the down- Dump the air but the raise function UP does not lift up beyond the usual ride height level as I am lead to believe it should.

So Q1- Any clues why the Rise function is not operating- an audible alarm sounds but no raising.
Q2- Can the ride height normal be adjusted up for the front bags because it seems quite low and could do with a couple of inch's more.

Thanks in Advance

[Mr Scania]

That is because it is only a kneel feature and not a hi-rise feature.

[Carpenter]

That is because it is only a kneel feature and not a hi-rise feature.

So are you saying that is the case with all Kneel functions- only down and return - No raise.
I was told that it had the 3rd function for raise when going over kerbs, gutters etc??

Also my q#2 can the ride height be adjusted on the front air bags?

[boronia]

It would vary from bus to bus as to what combination of kneel and/or raise it had.

[Mr Scania]

It may have a hi-rise feature if someone has fitted one but I dont think it would have come standard with one.

Yes the front ride height can be raised by lenghthening (making longer) the rod on the front levelling valve. If it has kneel the front rod may be an air cylinder which shortens (becomes shorter) when your kneel switch is activated.

[Carpenter]

Thanks Mr Scania

Any idea why there is an audible alarm sounding when I select the raise (assume) 3rd position on the switch?

Just to add I was told that the alarm was to advise you were in the raised position so you didn't forget to turn off?

[Mr Scania]

Is there also an alarm in the kneeled position ?

[Carpenter]

No Alarm on the kneel down action.
If you centre the rocker switch it comes back to normal ride position
Then if you switch to up (position #3) the audible alarm starts but height position does not change.

[Mr Scania]

You may have a problem either air or electric.
The engine may need to be running.
The park brake may have to be in the off position.
The door may have to be closed.


Another question is should it raise the whole coach or just the front ?

Does it have tag dump ?

[Carpenter]

You may have a problem either air or electric.
The engine may need to be running.-Engine was Running
The park brake may have to be in the off position.Think I tried both but maybe an option
The door may have to be closed.- No longer in use. Moved to Centre of Motorhome


Another question is should it raise the whole coach or just the front ? As far as I have been told its only relevant to the front-

Does it have tag dump ?

No but I am having one installed- Thanks Dirk for the idea

IS there expert help on things like this in the Taree to Coffs Harbour area that anyone can recommend?

[boronia]

Check with one of the larger long established bus/coach operators for recommendations. Eggins might be a start in Taree.

[Carpenter]

OK thanks for that.

[User7526]

The answer to the first question is quite simply this....

If there is a buzzer that sounds (as you stated) when you switch into the raise position then yes it did have that capability originally fitted to the vehicle. A lot of older vehicles start to fail with this function because the height valve rods are actually air rams that extend when the raise position is selected, these rams tend to fail in time and when they do it's normally when they have extended. They don't return to normal length when the ride height is set to normal operation and so a lot of times they have been disconnected by blocking the air hose to the ram or by disconnecting the wires from the solenoid. Most operators would rather save the money of replacement and put up with/work around any inconvenience caused by the raise function being disabled.

Question two.....

As stated earlier, lengthening the rod between the axle and the height valve raises the normal ride height and shortening obviously lowers it. The best setting are basically what the manufacturer recommends, you can go a little either way from that but too much difference means that the suspension bushes and/or bump stops will start to be damaged unnecessarily.

Yes I'm a girl but I've been a heavy vehicle mechanic for nearly 27 years now so I'm giving you the truth.

Peta

[Carpenter]

Thanks Peta great clarity in your description. It gives me something to investigate when I next get a chance to look at the Front End.

Where do you do your mechanicing?

[User7526]

Quote: "Where do you do your mechanicing?"


In Sydney mate, I work for a company in Prestons.

Peta

[Carpenter]

Well good on you. You must enjoy it to hang in this long.
Thanks again Peta