[Dick]

Trivia……..Our rear axles have 6 air bags, 4 on the drive and 2 on the tag. Except when the tag lift lever is employed they are all joined and have the same internal pressure.

If a typical weight of the drive axle is 20,000 pounds, and the tag axle is 12,000 pounds all 6 air bags are holding the chassis up in the air and carrying 5300 pounds. (Not exactly true because the air bags are different sizes). If we try to lift the tag the four drive axle air bags end up having to carry about 8000 pounds, (also not exactly true because some weight from the steer axle is transferred to the drive axle).

If the bus air pressure could be sufficient to raise the chassis using only the drive axle air bags it is probable the tag wheels will come off the ground. But I suspect the smaller diameter of the drive axle air bags requires a greater pressure than the coach air system can provide within a reasonable period of time.

But why would we want to lift the tag axle anyway? If we need to make an extremely sharp turn or gain some traction just dumping the air in the tag axle shifts a whole lot of weight forward to the drive axle effectively shortening the wheel base for the tight turn, or to get more traction.

[Archived]

Each time we navigate our drive way, we have to make a full lock turn. So I always lift the tag to make it easier on the steer and tag axles. On our vintage, the tag does lift completely off the ground in spite of the drive axle bags allowing the rear to droop. I’ve never waited long enough to see if the drive bags would eventually compensate.

[Towson]

We just picked up a 95 marathon with this hydraulic system at the rear. Our mechanic is reporting it’s leaking and is unsure of need or parts availability. Has anyone removed it? Or sourced parts?

[Andy]

If you are talking about the tag axle lift, it is pneumatic, not hydraulic.

What specifically is leaking, and under what circumstances? The tag axle lift chambers could be leaking, but you would only know that if you tried to lift the tag. Or is there an air leak in the rear, near or at the tag that leaks when you are not lifting the tag? Different situation.

Now to confuse the hell out of this, some 45 foot coaches had a hydraulic system called a stabilizator that stopped the rear of the bus from dropping when the tag was lifted, and that was hydraulic, but it only involved two hydraulic cylinders only visible from beneath the coach which could be leaking.

We need more info to zero in on the problem.

[Archived]

Jon,

Thanks for the response.

”Now to confuse the hell out of this, some 45 foot coaches had a hydraulic system called a stabilizator that stopped the rear of the bus from dropping when the tag was lifted, and that was hydraulic, but it only involved two hydraulic cylinders only visible from beneath the coach which could be leaking.”

This is what I’m referring to. Apparently we have this feature. Does it need it? Has anyone serviced or removed it? I’m trying to minimize any complexity, we will be taking it up the Alcan yearly and I want as little complexity as possible.

It also has another hydraulic system on the front axle (Howard?) that helps with centering the wheels? Apparently it’s leaking as well.

-jeff

[Archived]

Jeff, to answer your question you have to decide how you use your coach, if you lift the tag axle and if lifting the tag axle it is important to keep the rear from dropping.

You are not likely to get much help on this, including from Prevost because the option involved few coaches and I don’t believe it is supported any more.

First, decide if you lift your tag a lot, and then consider why. I ask it that way because I lift my tag only when I need every single inch of turn radius because I got myself in a situation that requires the tightest turn possible. I cannot remember the last time I lifted my tag axle.

But if you do lift your tag then the next question is if your rear end drops until your ride height valves and get sufficient air into the drive axle air bags to raise the rear, or if the ground is level enough does a sagging rear end matter?

My 97 had the stabilizators and while they worked as intended I was never in a situation where from the driver’s seat I could tell if or if it mattered if the rear sagged. I was always careful not to lift the tag when the tail of the bus would hit or drop on anything.

If you don’t need it, ignore it. If you do feel it is important the hydraulic cylinders might be able to be rebuilt if leaking.

[gordon]

Jeff, It is my understanding that the Howard Power Steering Assist system is no longer supported.

[gordon]

Jeff

My 95 marathon had the stabilizator system installed,the rear hydraulic units were both leaking, i have removed the system entirely, it now operates as any other coach, when i activate the tag lift / dump the rear squats but will eventually lift the tag to an extent that they almost clear the wheels, depends how long you wait for it to air fully up. it now operates faster than it did with the non functioning stabiliiizator system installed.

I believe the system is now obsolete and it was just something else underneath that wasn’t operational and not needed.

I also had the Howard steering system installed, my catch tank contained all of the steering system oil, indicating that the ram seals were leaking, i also removed this system along with the ram fitted to the front axle, coach steers as normal and freed up a lot of space in the steer compartment bay into which i mounted an auxillary air compressor, which i can connect either into the auxillary air system if required or use to air up external items.

Gordon

[Jeff]

Forgot to add that when i removed the stabilizator system i spent a lot of time checking the tag lift actuators and the fulcrum pin for free movement, i then aired the coach fully up on the level low and adjusted the lift chains, mine had too much slack in them, this made a big difference to tag lift operation, i also do not use the tag lift function very often but it is now available if i do need it

[Archived]

All, Thanks for the advice and info. My inclination is to remove them both. We lived in our Liberty for 2 years and the tag came up maybe a dozen times.

[Glenn]

Someone? had done a bad job of changing the #36 diaphragm in the tag lifting chamber(see pic-old is left, new is right) so it leaked. I don’t ever raise my tag so it’s no big deal to me.

[Dan]

I always lift tag when making a slow tight turn, however after having two new 365 tires tread cupping on outside edge, I realized making the tag lift chain tighter it actually allows tag to be raised about an inch higher but not completely off the ground. Just another reason not to have 365`s. Lift chain has some slack when in normal ride position.

[Jerry]

If you mess with the lift chain length when you do a whoop-dee-do type of bump where the air bags are compressed and then fully extend in the rebound your tag may be leaving the ground. I don’t know if that can be a problem or not, but I trust the Prevost engineers considered all circumstances when they established the chain length.