Tag Axle Modification

[dreamchasers]

I know Prevost has issued a procedure for modification of the pneumatic control for the tag axle to prevent the tag axle from releasing upon loss of aux. air. I have searched the Prevostcar web site to no avail.

Does anybody know where to get a copy of this modification?

Hector

[Jon Wehrenberg]

Hector, we haven't gotten any in a long time but whenever Prevost had a modification they deemed worthwhile they would issue service bulletins that defined a problem, and then the fix or improvement. The details were explicit and showed step by step what had to be done along with a complete parts list.

If you want to follow up on it you may wish to contact their engineering in Canada to see if you can get a copy unless they are posted on-line.

[dreamchasers]

Thanks Jon.

Hector

[Ray Davis]

I checked with that when I owned my CC. As I remember it was a costly upgrade, as it required replumbing a large part of the suspension system.

General opinion it was not worth the cost.

Ray

[Jon Wehrenberg]

Not sure I agree with that Ray.

When the aux pressure drops to some value, like 35 PSI, it dumps air and the bus goes into the leans.

It might be cheaper to do the mod rather than spend megabucks trying to get rid of the aux system leaks on some coaches. Later model coaches will not lean if the aux system goes to zero as long as the 5 port Norgrens are good and there are no air bag or fitting leaks.

[Ray Davis]

I can only comment on my experience. With my CC, when the tag did dump (which in my case wasn't often), it wouldn't lean, by that time is was pretty much just "settling down". I don't ever recall a time that this caused a lean, as wouldn't that generally indicate you had pressure on one set of bags and not on another?

So, in my case, it was simply the coach squatted down to the ground.

As I remember the cost to do this retrofit was several thousands of Lewbucks. Personally I didn't find it worth the expense. I did have problems with leans, but I did track them down through normal methods.

Of course, everyone's coaches are different, and they may want to move forward with this. Just it ain't cheap, as it was more than a simple fix (as it was explained to me by PVML)

Ray

[dreamchasers]

After looking through the Prevostcar website several times to no avail. I call Jim Malcomn, Prevost Texas Region Service Manager, he pointed me in the right direction and 'like magic', we found it.

The link below goes to the pdf file with the modification information.

http://www.dreamchasers.us/pog/Sb96-14B.pdf

Another bit of information I will pass along. The device that in mounted on the inlet air line to the aux air filter/blowdown bowl (mine is gray color) located in the lower cabinet, below the drivers seat is not a regulator. It is a pressure protection valve that will not pass air unless the aux air tank (inlet) is above 75 psi. Its function is to maintain at least 75 psi in the aux air tank for braking. If you had a failure in a aux air component, the pressure protection valve would close once the aux air tank was depressured to 75 psi. Imagine that!



Hector

[Ray Davis]

Wow! Now I know why it cost so much!

[Jon Wehrenberg]

Ray,

By leans I mean the rear squats and now the back end of the bus is downhill.

Hector,

That valve is why if your air systems are down to some low value, you can start the engine and begin airing up the systems, your driver's seat (aux air) won't rise until you get to 75 PSI in the brake systems. At that point the brake and aux air systems fill simultanelously.

[truk4u]

Hector,

I'm confused! Are you saying that the brakes are affected by a reduction in Aux air pressure? How can this be possible when we know the brake tanks, primary and secondary (front & rear) are independent of the Aux tank?