-
TEMP SENSITIVE SUSPESION AIR LEAK
-
Alvie,
I stopped raising the tag as it really only lowers the rear of the coach. I asked two Prevost facilities about this and both said motorhomes are so heavy that the bags can’t maintain ride height with the tagged raised.
-
A coach can maintain ride height with the tag raised if certain conditions are met. The coach does need to be well within the axle weight limits in the rear. You have to wait for max pressure to reach the air bags.
Both my 87 and 97 would eventually get the rear to ride height with the tag lifted. The 87 would actually get the tag about 3″ off the ground also. The tag axle on the 97 never actually got daylight beneath it regardless of how high the coach was raised in the rear. I think that was an issue related to the lift chambers.
It seemed to take forever for the coach to raise on both the 87 and 97.
On the 97, going by memory the steer was 14,000 and the drive and tag combined were about 32000. The two front air bags were carrying 7000 each and when the tag was lifted (actually was almost lifted) the four drive axle air bags were carrying 8000 each. It was not uncommon for some conversions of that vintage to have much more weight on the steer axle and proportionately less weight on the rear axles bringing the weight the steer air bags had to carry as much as 8000 pounds while the drives had to lift less than that. It is all about how the weights are distributed
I have not tried to do that with the current coach.
-
My 91 H3 levels up just fine with the tag lifted. I am one that uses the lift every time I come in my drive to keep from scrubbing the tag tires and to make the turn easier. Also when I was at the Hilton Head Motorcoach Resort in December, the guy taking me to my site ask me to raise the tags before backing into the site.
-
I always dump the tag when extreme
maneuvering is needed to get in and out of tight places when on
blacktop or concrete. That’s what the tag was designed to do, make
the turn radius as short at possible while at the same time limiting
the side forces on the tag tires. Have someone drive your bus, turn
the wheel to the stop while the tag is down and go back and watch the
tag tire through the turn. You’ll be lifting the tag from there
forward.Of course there may be times when you can’t lift the tag due to
the low position of the rear.
-
I lift when backing or turning in to tight spot. It helps on those tires.
(Steve) Update on Houston Prevost
Haven’t recieved a ticket on work for air problems will let you know when Shop Manager (Bubba) gets back from Ft Worth Prevost and finalizes ticket.
-
The reason for asking on raising the tag was that as mentioned on our 06 Royale it seems the whole rear drops when tag is raised whereas on the coach I drove from Florida to northern Indiana a week ago http://panterracoach.com/coaches/2001-prevost-thompson-xlii-45/ would actually as Jon mentioned show about 3 inches of clearance under the tires. I guess maybe I just didn’t wait long enough on ours to raise back up to ride height. I’ll check it again sometime when the weather is a bit more conducive to being outdoors. Had our best snow of the season last night!
-
I cannot tell when these features were incorporated into the chassis, but over the years Prevost has changed how the tag axles function.
On my 87 the only way to lift the tag or relieve the pressure the tag put on the ground was to flip the lever. When that happened the tail would sag initialy and then after a while the tag came off the ground and if I waited long enough the rear would return to the normal drive height. When the tag axle lift is initiated the tag axle brakes are disabled. That was a 40 foot coach.
My 97 was a 45 foot coach and it had two features relative to the tag beyond the lever that I could use to lift the tag. As a 45 foot coach Prevost had a system that automatically dumped tag axle air when the steering wheel was turned to the limit in either direction. I suspect most of the folks driving 45 foot coaches have this feature making manual tag operation unnecessary. As you can imagine this feature would cause the rear of the coach to drop. But it did not because my coach and others had a feater called a stabilizator. The stabilizator was a hydraulic system that pressurized two hydraulic devices (that looked like shock absorbers) which kept the coach rear from sinking. If the tag axle was lifted manually via the lever the stabilizator system was not energized. So that model or vintage coach needed no driver input when making extreme turns. I know for sure there are two other PC member’s whose coaches have that stabilizator feature.
My current coach I have no clue about. I know it does not have the stabilizators. I haven’t looked to see if the tag axle air is dumped when I go to extremes with the steering wheel. And I confess I never bother to lift the tag. The turn could be made sharper if I lift the tag or if it lifts automatically but I just never think to do it or see if it has the automatic feature my 97 had.
The automatic lifting of the tag was initially installed on 45 foot coaches because Prevost engineers considered a steerable tag axle but ruled it out due to complexity. I was my understanding that MCI had that feature at the time (around 1994 or 1995) and they were having problems with it. Maybe someone who remembers some of the historical changes on tag axles can jump in and add to this or correct what I may have said in error.
-
-
The raise height of the tag, at least on my 91 H3 is based on the chain length. If the chain is too long the tire wheel not raise completely or not at all. Of course you do not want it too short or the tag will be limited in it’s normal movement.
-
Glen s …
who fixed your foggy window and what did it cost you? Thanks Diane -
WX finally warmed up so the leak chase was on ! Did check as many leaks as possible while temps were cold as you said Hector. Replaced 4-air maniolds & 9-quick connect fittings. Replaced as many as possible with compression fittings, but all three truck parts suppliers locally do not stock compression type. Guess they need repeat business!
After 30 hours had a 3-inch drop to the left side. This is actually the side where three fittings were replaced in the rear over drive & tag axles. All other leaks were in the steering bay with one fitting in Generator bay. Aux air now takes @ 45 mins to bleed off instead of 3 to 5 mins. Will continue the hunt !
-
Steve,
If you are confident the fittings into the air bags are leak free, the drain valves, connections, and small air tanks at each air bag are leak free, and the air bags themselves are leak free you have only the 3 port and 5 port Norgren valves as possible causes for the 3″ drop.
The valves not only can leak from the pressure side through to the exhaust, but because of their design you can also get a leak “sideways” past the O rings out the end caps. But once you have ruled everything else out they are all that is left to leak.
Good job.
-
Jon,Hector,
I did replace two fittings on the left side 5-port & one on the leveling valve. Fittings into 3-port,bags, drain valves, connectons & tanks are leak free as of two days ago. Last year replaced tank drain valves that leaked. Working my way to back side of air bags later since front side showed no leaks, but & I`m assuming they`ve never been replaced & made appointment with Jacksonville to replace. Even got them at the March discount price for when I arrive in May.
Found an Aux air schematic in bus manuals & will pursue using that. Did compare Hector`s suspension diagram to H3-45 setup & it`s somewhat different. Like the plumbing schematic I`ve drawn, the suspension schematic will be next order of business while on the rack and will test the Jacksonville boys on their knowledge.
Really appreciate your help along with Hector`s phone conversation to get started in the right direction to achieve leak free as much as possible.
-
Sounds like you are heading in the right direction Steve.
Keep in mind that Hector’s diagrams are representative of a particular version and that over the years both Prevost and the converters have made changes to the leveling systems on our coaches. The underlying principle has not changed, but the evolution of the system has created many versions.
-
Steve,
Finding and repairing air leaks can be addictive, especially if you have success. I am one that believes that managing pneumatic leaks is part of Prevost ownership maintenance.
The push to fit fittings are not my favorite. They are quick to install and when initially installed, will be leak free. But over time the sealing o’ring seems to leak as the rubber ages.
You appears you are making progress. I enjoyed the telephone chat.
Good luck and work safe.
Hector
Log in to reply.