Need Tag Axle Education

[Glennman]

On my '02 MCI D4500, I just returned from our maiden voyage which went quite well (I'll type something up on my Project page), but I did get a flat tire on my passenger tag in the driveway after returning. That has prompted the subject of this post.

My tag axle has a tie rod and apparently steers to a certain degree. At the driver's area, I have a switch that says "Steer Axle", but I have no idea what it actually does or doesn't do. Does anyone know its function?

Another question: If I turn the air off from the tag axles using the valves located in the engine compartment at the passenger side, does that also keep the tag brakes from engaging? My thinking is to shut the air off from the tags while driving around town, then turn it back on before hitting the highway, so that the tags are only riding on the ground but not holding anything up (around town), reducing their wear while making tight turns. Is this a feasible thing?

Any ideas on this at all?

[luvrbus]

The tag switch was to dump air from the tags in winter driving in the snow from the driver seat, no need to dump the air in city driving they turn and they lock in place (straight) at 20 mph if everything is working

[buswarrior]

Tag air should not be left off except for getting unstuck in these coaches. The floppy tag follower steering will get some messed up, without the weight on it. You could actually increase wear, if they flop around.

Depends what was optioned, some had a tag lock switch, some had a tag axle dump switch, depends what original fleet thought was needed.

And then whether any of it is maintained and working correctly? Air valves, steering components, wear and tear...

Happy coaching!
Buswarrior

[Glennman]

So, in looking closely at it this afternoon, there is a solenoid looking device installed next to the horizontal stabilizer shock that is attached to the tag tie rod. This device locks the tie rod so that it stays straight. There are a couple of old wires that are hanging in the air next to this device, but I cannot see where it would attach. It appears that if it was hooked up or otherwise functioning, it would unlock the tie rod so that it can freely move, then you would lock it in place for highway travel (I'm assuming). However, since it's not connected or otherwise functional, it is permanently locked in position. With it locked in position, it never steers and continually skids when turning around town. I'm wondering what this device is called and if it's practical to get it working again or get a new one. I attached a picture of the device. We'll see if it posted correctly.

[luvrbus]

The tag probably needs work,operators would lock the tag instead of replacing worn parts towards the end of their fleet life ,they work great when well maintained but can get expensive to bring back to life

[thomasinnv]

There are 2 pneumatic rams on the the tag axle. The big one on top pushes the angle of the tag axle forward or rearward depending on the direction of travel, so that when the bus turns the tag wheels follow correctly. The smaller ram on the tie rod locks the axle from turning left/right. The wires you speak of are magnetic sensors and are usually attached to the ram and trigger a relay in the electrical compartment next to the driver. Both rams should have 2 sensors each. These sensors, when they trigger the relays up front, then activates the appropriate lights on the dash. I believe they are labelled something like 'tag lock' and 'steering'. When lit, they indicate a problem. There is also a speed sensor which triggers the steering lock Clifford mentioned. The most expensive part of the system is the rams. The upper usually goes for a few grand in good used condition, if you can find one. I got lucky a year ago and found a brand new one in box on eBay for $160. Guy had no idea what he had.

Anyway, when working correctly the steering tag really does make a big difference in maneuverability at slow speeds like when turning into tight spaces or parking lots. Mine took a lot of work to get operational again and a little fabrication to rebuild some extremely worn out bracketry.

[Glennman]

What would happen it was unlocked and was able to steer all the time?

[Coach_and_Crown_Guy]

My experience in driving many MCI's through the years has been that when they start to wear and won't lock up tight on the tag axle the coach tends to wander and won't stay centered in the lane on the freeway. It can be subtle in some buses and not so subtle in others. But the bottom line is that if it doesn't lock up as it should and is free to move around the bus WILL be wandering around at highway speeds and increase the workload on the driver and impact his confidence at controlling the bus. I always made sure to engage the manual lock switch, (if it had one of course, and it worked), and that would improve the handling immediately and drastically for the better.

Mostly this was on the DL I drove lots, the J coach I had on tours was newer and it seemed to work better, but I always had the option to lock the tag, just didn't need it since it still worked as it should. If this were mine I'd simply leave it locked up and don't let the tag steer. It's no different than any other older MCI up to the D's when they first introduced this "improvement". All it really did was provide another damn thing that can and usually did fail in time incurring expensive and proprietary repair parts and labor.

Leave it alone, someone did you a favor. Of course they did it for themselves first while it was still in service but you're the one reaping the reward as a private owner. Lots of Operators knew how to get the most out of their buses and eliminate unnecessary maintenance costs and down time without affecting operations or availability. Simpler is usually much better. Trust me the Operator knew what he was doing. Leave it alone and locked up as it is. You'll thank me later I'm sure.

You won't put enough miles on it to wear out the tag tires, and if so who cares anyway they are the last tire position and usually rather worn anyway. A tag is much easier to change than an inner dual in any universe. I'd invest in seeing that it has the tag axle raising feature so you can make the change easily anywhere. I mean RAISE and not merely un-weight the tag. This was an option few ordered but I've seen some and it's a good feature to have. I've had tag axles blow on my J coach and believe me it's no fun with a load of passengers on the side of the interstate and the tag shredded like a Brillo pad with the body almost touching the ground. That's why God made those handy mobile tire repair truck guys. They are definitely worth the price and can usually do it all in an hour or so. All it takes is a little plastic card and you're back on the road.

[Glennman]

Coach_and_Crown_Guy,

This all sounds like great advice. If I can get it to raise, that would be the way to go. Otherwise, I'll just leave it locked up all the time. The wandering effect makes a lot of sense. Thank you for your advice.

[sledhead]

my coach had a steering tag but before I got it someone changed it so it is locked in when in forward gears and when you put it in reverse the tag unlocks and the top air ram pushes the tag forward a few inches . it has worked this way for the 7 years I have had it 

[luvrbus]

The tag is locked at 20 mph,only time I ever heard of one wandering is when the caster was off,the tag is like a front axle they need to be set toe in and caster ,there is probably over 10,000 MCI buses on the road with the setup.Leave the tag down as BW stated they are only lifted in emergency.Locking one if the linkage,brackets and king pins are worn out is not going to stop the shimmy,shaking and wandering