steerable tag

[davidbrady]

That comes thru very clear Charlie. I imagine when the coach is put into reverse, the tag axle is canted over to create a reverse caster condition (for lack of a better term )? IOW's does the entire axle tilt forward and aft to create positive and negative caster so that the axle follows when the bus is in drive or reverse?

[cvaughn]

I have never noticed the centerline of the axle moving. If it moved enough to change the caster, I think the tire would hit the body.

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These two photos show the "Dog Bone" or torque arm that attach the frame to the rear end housing. As you can see the bushing at the frame is starting to fail. Not hard to fix but hard to get there.

[davidbrady]

(03-18-2013 13:00)cvaughn Wrote:  I hope I have attached a picture showing what to look for as bushing in the suspension start to fail. The red rust indicate the bushing is starting to move around. This particular bushing is on the lockup system of my tag axle.

Excellent high resolution photos Charlie. I'd love to see more pics of the Tag axle and it's articulating components - maybe after the rain passes .

Thanks for giving us an easy way to identify the start of a failed bushing. Bill Mattocks of Ridewell explained to me that the 8 bushings on the torque arms used in our steer and drive axles (8 on each, 16 total) should be good for 350K miles, but of course like our tires they're likely to require replacement due to age rather than miles. I imagine the same wear mileage and time limits apply to the panhard rod (dogbone) bushings.

[davidbrady]

(03-17-2013 15:40)gondolaguy Wrote:  What I remember from past reading on the subject is that the steerable axles, while a good idea on paper, caused the unit to be tail-happy and wander when on inconsistent pavement. This would likely be due to the added potential for play in all the moving parts that allow the steering. It would also explain why they would weld the axles straight versus just relying on the pin to hold it firm. You should check to see if yours is welded as that would make it much harder to restore the feature.

No matter what the current thinking as to being able to restore it or maintain it, I would question the fact that the factory saw fit to weld them straight. That is a pretty radical fix and one that would make me suspect that there is no perfect mechanical fix. I will agree that there could be several series of steerable axle, that could make a difference.

Although this is probably common knowledge, it took me a while to figure out how to easily tell a steerable tag versus non. It turns out it's very easy. Steerable tags have "front wheels" on the tag versus deep dish rear wheels on the non tags.

Corey,

I'm inclined to take the opposite side of this argument.

We're still learning about the Ridewell steerable tag axle used in the LXi, but I think it's safe to assume that it's a caster adjustable suspension system where a linkage allows the axle's caster angle to change for steerability in both the forward and reverse directions.

The axle itself would look like the Dana steer axles on the front of our buses, complete with kingpins, steering ball joints, and a crossbar connecting the ball joints. These parts allow the steering of both tires in unison.

There's also a control mechanism that uses speed and direction signals from the transmission to engage multiple air cylinders at the axle. One set of air cylinders controls the caster angle and another set controls the steering locking mechanism. The caster control needs to lean the axle in the proper direction to allow the tires to self steer. The steering lock control needs to unlock and lock the steering at speeds less than and greater than 15 mph respectively.

I think, although I haven't actually seen the Ridewell system, that the suspension is connected to the the frame carrier via four trailing torque arms (similar to our Ridewell steer and drive axle suspensions); in addition, there may be panhard rod (dogbone) controlling arm to limit lateral movements.

If you've taken a look at the design of our steerless tags you can appreciate the bulk and heft built into the structure in order to handle the tire scrubbing in tight radius turns. You can appreciate the scale of these lateral forces even though they act at zero caster angle. IOW's there's no additional moment created by the offset of the tire contact patch with the kingpin pivot axis.

I wonder if Ridewell was consulted when the Wanderlodge service facility decided to weld the locking pins in place? The intended operation of the axle feeds little if any lateral scrub into the suspension system as the tires steer into the turn. Now imagine what happens when BB came along and welded the locking pin. As the bus is steered into a tight radius, the Ridewell steerable tag is trying to do its job - it wants to steer the tires but it can't because the welded locking pin won't let it. Now all these lateral forces are fed thru the tire contact and into the steering knuckles, into the ball joints and the crosstube, and finally resisted by shear and bending forces at the locking pin, the torque arms, and the panhard rod. I'm inclined to ponder whether Ridewell designed these components to withstand the slow speed, tight radius turning forces induced in a locked pin state?

[Arcticdude]

David,

Wouldn't Ridewell have to account for those forces? They certainly had to consider what if the system fails to correctly operate, right? I wonder if BB consulted Ridewell before welding them up?

[davidbrady]

Could be John. Or, they may have issued a CYA in the form of fine print. LOL Something like "never operate at low speeds with a failed locking pin or severe axle damage can result"! I know that if my LXi had one I'd have ball putting it back into service with modern day parts.

[DOSZORROS]

I have talked with some owners that have had problems with the steerable tag and had it welded in position and some that say they have never had any problem.

It would appear that the success of the steerable tag may have had something to do with quality control and how accurately it was set up during the build process.

Subaru cars were this way during the 1980's. Some would tow great and some would not tow. It depended on the camber that was built in at the time of assembly and it was not adjustable.

The tag axle would be subject to the same conditions; camber and alignment at time of assembly.

[davidbrady]

George,

I've also heard of some very strange, scary, and possibly dangerous handling characteristics mostly related to the drive wheels losing traction either due to slippery surfaces or unloading by driving on unequal surfaces. Under these conditions and at speeds below 15 mph, and possibly at higher speeds if air pressure hasn't built up sufficiently, rear weight can be transferred to the Tag axle and with the self-steering unlocked, the Tag can steer the tail of the bus downhill on off camber or inclined highways. This can put the tail of the bus on the shoulder or in the oncoming lane depending upon road camber. Scary!

I'm beginning to believe that it was these characteristics that put the kibosh on the steerable tag. I'd install an override switch to be able to manually engage the locking pin.

It's interesting that MCI still uses steerable Tags while Prevost has given up on them. Prevost uses a liftable Tag with a very fast lift time and which automatically lifts when the steering wheel is turned to near full lock. To combat the problem of tail sag when the Tag is lifted, Prevost installed hydraulic cylinders that lift and support the rear of the bus when the Tag air is dumped. They call the hydraulic lifts "Stabilizators". (I'm not making this up ).

[davidbrady]

Here's a document with a good drawing of the steerable tag axle used in our LXi's. Note the large air cylinder above the axle (#22 in the lower drawing) that serves to alternate the axle caster as the bus is shifted between Reverse and Drive.


  0019245.pdf (Size: 561.91 KB / Downloads: 648) , starts with CSN: 10052810 (3/6/00), ends with CSN: 10062749

[Richard palmer]

David great info i am getting ready to change my tag shocks and tag stabilizer next week i do have the steerable tag and i cant find part numbers for the shocks or the stabilizer any ideas from all the post i have read looks like everything might be obsolete
any info would be great my tag stabilizer is shot at low speed the tag will start shaking side to side i have to stop the bus before it will stop shaking scary i wonder if this is one of the reasons they welded it i am considering welding mine if that pin were to fail at highway speeds i could only imagine what might happen