[Glenn]

It sounds as if the tag bags are unloading their air, however the lift chambers are not lifting. how quickly did it lift the tag in the past as most converted coaches are slow to actually lift

[Archived]

As Jeff pointed out the lifting of the tag will initially cause the rear to drop but after a while the drive axle air bags should receive an increase in air pressure to compensate for the loss of lift from the tag axle air bags.

Here is a step by step list of what is happening. This presumes the ignition is on, the air system is fully pressurized and the level low is in the driving position.

The tag axle lift lever is moved. That shifts the three port Norgrens between the tag and drive axles so the air path between the drive and tag axle air bags is closed, and that air from the tag axle air bag is released to atmosphere. Simultaneous with that the tag axle lift chambers are pressurized.

As the tag axle air bag loses air, the weight now has to be carried by the remaining two drive axle air bags per side. Until the drive axle air bags receive more air the bus squats down. When it squats down the ride height valves sense the rear is too low and they open to admit more air to the drive axle air bags. As the pressure in the drive axle air bags increases the rear of the coach begins to rise.

All of this takes both time and a lot of air pressure. You are likely going to need to get near air system maximum pressure into the drive axle air bags to lift the rear because by dumping tag axle air bag air pressure you added about 11,000 pounds of weight to the remaining 4 air bags. The bus should be in high idle and the compressor should be pressurizing the system to the 125 PSI limit.

The coach will reach the ride height eventually and I expect the tag axle wheels will actually clear the ground if the air bags and the lift chambers do not have any leaks.

[Andre]

My tags would not come off the ground so i shortened the attachment points on the chains that connect the tag axle to the lift chambers. Just don’t make them to short. To check with the tags level up see if you have any slack in the chains. Make sure when the tags are down you have slack in the chain.

[Archived]

Actually you need the chain to be slightly loose with the coach raised to its full height on the air bags. That is the correct adjustment.

[Archived]

I would agree with that. Mine were still slack when the tags were suppost to be lifted on level ground.

[Davy]

On our XLV (and I presume many if not most Previosts), the air chamber for the tag life pushes on a bar (lever) that pivots and lifts the chains which raise the tag. On one side, the pivot is frozen (probably corroded) and hence when the air chamber tries to lift the tag the bar doesn’t move and one side of the tag won’t go up. So I have project this spring to try to free up the pivot point which is a bushing on a shaft. You should be able to look between the drive wheels and the tag wheels to see this mechanism and see this working. The air chamber rod that is supposed to actuate the tag lifting bar is bent as a result of trying to push on the frozen tag lifting bar.

There is a zerk fitting on the bar so that the bushing at the pivot point can be lubricated. Apparently this is a lube point often overlooked by “truck shops” when servicing a Prevost. Our Prevost was apparently serviced quite often by a big truck shop in northern Indiana (the service manager told me “we had the nice bus in here regularlly for service).

Check to see that the bar (lever) is moving freely. If it doesn’t, you have a problem.

[Corey]

I’m curious as to how many actually lift the tag. I think I might have lifted the tag on my previous bus a couple of times, and my current bus which I have had for 3 years I haven’t lifted the tag yet.

[Corey]

There is a zerk fitting on the bar so that the bushing at the pivot point can be lubricated. Apparently his is a lube point often overlooked…

I can testify to this. I just had mine replaced at Jeff’s.

Davy

[Archived]

If
I’m maneuvering around on hard surface I unload the tag. Does it help
the scuffing of my new 365’s? Don’t know but it makes me feel good.

[Archived]

Lift the tags all the time. When trying to manuver at my storage location and backing into my driveway on a small street, turning radius is greatly reduced. Saves a bunch of back and forth manuvering.

If not mistaken, there is tank with hydrolic fluid between the wheels I think helps to activate the tags. When I purchased my bus the tank was in desperate need of fluid. Telling me most people do not check!

[Archived]

The tank you mention is part of a “stabilizator” system Prevost offered for a limited time. It automatically supplied hydraulic pressure to a pair of cylinders slightly inboard on the drive axle that were actuated when the tag axle automatically dumped air at the extreme ends of the steering wheel travel.

You mention you lift the tag, but I think if you drop your front bumper and look at the end of the steering arm you will see a stainless steel “cam” that actuates a microswitch that automatically dumps tag axle air for you. When you lift the tag axle manually you over ride that system and as a result the rear will sag because the stabilizator system is not engaged.

If your turning radius is improved by lifting your tag as you describe your automatic system is not functioning as intended and should be repaired. It is a great system when fully functional.

BTW, the correct hydraulic fluid level is when the ball is centered in the site glass when the coach is at the ride height.

[AL]

Will look at the steering column in the front. Question – there is a button on my left array (where the cruise control, jake, etc) is. It has a picture that seemingly locks out the tag lift. Is this a control for the stablizer system you mentioned?

[John]

I believe that switch negates the tag unload, not the tag lift.

[Bob]

the ping tank between the drivers and tag is not a hydraulic resivoil on yours. Check to see if you have air rushing out of the first or 2nd norgren on the drivers side inside frame.——-Between drivers and tag….. As usual block bus up before getting under. a sudden drop is a killer. More info will help diagnose problem. If it doesn’t do it when tag lift is not applied. This will tell. I have a 98 XLE that I just went thru the complete air system. bob

[Archived]

for coach specific go to prevostcar.com to publications enter the last lettter in your serial # Should be W then last 4 numbers Mine is W 6553 for example. If you need to put in type use MTH . Keep us posted. Bob