4106 Steering rebuild

[DonH4106]

We acquired our 4106 back in November and herded it home to Washington in March. Herded it home might be a very mild term. In fact it may be considered unsafe for most drivers. It has a Shepard steering gear installed that has been professional rebuilt twice. It seems to have an excess amount of slack and why it was not taken out when it was rebuilt I haven't a clue. It wanders from side to side, never holding a straight line. I have noticed the body shift from side to side when the correction are made.
OK plan of attack.
The right angle gear box under the steering shaft is a reduction gear. I plan to remove it to see if it can be replaced or modified. The Shepard box was designed to be used with a 1:1 box and the slack is multiplied with the reduction ratio.
When I gave it a quick look it appears the rubber bushings in all of the axle control rods have never been replaced. It seems when the steering wheel is turned the whole body shifts in the worn out bushings. So all bushings will be replaced if available. Tie rod ends seem to be in OK condition and are not available but a complete aftermarket tie rod assy. is. After the bushing replacement a trip to a alignment shop may last.
What have I overlooked?
Don 

[RJ]

Don -

The right angle gearbox under the driver in the 4106 is a 1.5:1 ratio, even with the factory power assist.  Too much for a Sheppard unit.

The gearbox from a '76 or later 4108/4905 will have a 1:1 ratio, as these came with Sheppard's from the factory.

There can also be a lot of slop in the prop shaft between the right angle box and the steering gear on the axle.  Pull it and have a shop that works on drive lines repair, rebuild or replace it for you.  KEY POINT: DON'T mention that it's for steering.  Say it's a prop shaft that came off the mower you pull behind your John Deere tractor.

King pins may also be worn, check them.

Bad "dog bone" bushings, front AND rear, can make the coach dance when you don't want it to.

Mismatched tire pressure can also do weird things, make sure they're all inflated properly.

Alignment specs are in the shop manual - you do have one, don't you?  Slight positive caster (2-3^o) will help with self-centering the wheels after a turn.

Can't think of anything else at the moment, I'm sure others will chime in with more suggestions.

FWIW & HTH. . .

[OneLapper]

I'll chime in, too.

Everything RJ said, and.......

The rear air bag leveling valves.  Yup.  Wait, what?  How does that affect the steering going down the road, you ask?  I'll tell you.

When I purchased my bus it was down right terrifying to drive home.  The drop links on both rear leveling valves were so worn out, the bus would list to one side while going down the road.  As it would lean to one side, the air bags on the side it was leaning towards would increase in pressure while the other side would release pressure.  When the bus was almost level, it would flop over center onto the deflated air bags.  It was startling to say the least, and it was very difficult to drive a straight line.  It would toss people around inside the bus, and made it impossible to keep it in the lane.

The steering prop shaft was a big issue with my bus.  I had a new one made.  Like RJ said, don't tell them it for steering.  It's an off the shelf truck PTO shaft for a hydraulic pump.  The shop will cut it down to size for you.  I paid $125 for a new assembly.

[HB of CJ]

Is it possible that lots of stuff on and in the chassis has NEVER been properly rebuilt or replaced?  Or never addressed at all?  Good observations already given.  Could your problem be a combination of several different things all adding up?

Deferred maintenance?  Wrong parts in combination?  Parts that normally would not be considered in highway handling characteristics but when combined with other wear situations result in your Bus Conversion being "herded" home?  HB

[DonH4106]

RJ
The right angle gear box is the first thing on the list. I have not looked at how it is made and was wondering if the gears could be made to swap positions to give a 1.5:1 ratio. Also I will be asking around for a 4108/4505 box.
I have closely looked at the prop shaft and it has been replaced and has zero slop. The PO has installed a tilt steering wheel from a Freightliner truck And there is very small amount of slop there. The slop is in the Shepard box input shaft.

PO said one of the king pins was replaced and the other was OK but I will check them.

I am not sure what the "dog bone bushings" are but all of the control arm bushings will be looked at.

I have the both manuals for the 4106 but I have no way of checking 2-3 degrees so I will leave that to a shop.

Onelapper

All of the leveling valves have been replaced. I have read somewhere there is a delay valve in the leveling valves that control what you mentioned. I have noticed that the coach does sway slightly from side to side when the wandering is corrected. I am thinking that it is in the control arm bushings but we will check your suggestion out.

HB
"Deferred Maintenance " is the issue here. It appears nothing has been done under there for decades.

[RJ]

Don -

Sorry, I used some industry jargon w/o defining it for you.  "Dog Bones" is slang for the radius rods that locate both front & rear axles, named thus because the lower ones especially look like a big bone you'd share w/ a puppy.

The lower ones often have the bushings replaced, but the ones in the rear, on top of the differential, are often overlooked - especially on the chassis end.

The Sheppard box works best with a 1:1 right angle gearbox.

Not sure about the Sheppard box slop, I think they have to be sent out for repair/replacement.

Luke at US Coach in NJ would be a good source of info and parts for your project.  When I was there in Nov, I believe he had some 4905 parts buses parked out back.

FWIW & HTH. . .

[DonH4106]

I talked with the PO and he tells me the right angle gear box for the steering came from a Flxible transit bus. It has a reduction ratio of 1.5:1. The slop in the Shepard steering gear is increased by this ratio at the steering wheel. I removed the box turned it up side down and backward and mounted it. This removed the slop by the ratio of 1:1.5 and made it hardly noticeable. It also increased the torque required to turn the steering wheel by the same amount. A road test proved to be acceptable keeping it between the dotted lines but the effort turning the steering wheel would get to you in a few hundred miles. It also still wondered.
I called a friend who is also a school bus mechanic for many years and made an appointment for him to come give his expertise. He believes the pump is not putting out enough pressure to keep the spool valve in the Shepard box centered. This makes since to me so I am looking for a new power steering pump or rebuilding this one.

[Hard Headed Ken]

Don,
Just so you know a Shepard 492 has no provisions for free play adjustment. I sent mine out for a rebuild and it came back with harder steering and the same free play. Lost about $2000 dollars on that deal, but I learned a lot of valuable lessons about steering systems. It's just the design of the 492 gear. I see no way the free play can be repaired. It really can't be rebuilt, it has no piston seals. Once the body is worn that's it, no repair that I know of. At the time I was doing all this I called Shepard and they told me a new gear could have 2" of free play at the steering wheel. There are a few out there that are tight.

The thread below has some good info.
http://www.busconversions.com/bbs/index.php?topic=26737.0
Ken