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Author Topic: 4905 Sheppard Steering  (Read 1060 times)
RJ
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« on: April 16, 2013, 12:23:37 AM »

For the recent Blytheville event that Tom McNally so masterfully put together, I had the delightful opportunity to share behind-the-wheel time with JL Vickers (roadrunnertex) in his extremely nice 1974 Buffalo on the run up and back from the Dallas area.

One thing I noticed about the coach is that the OEM Sheppard steering seemed to be somewhat "heavy" around town, yet just perfect on the highway.  This seemed quite different than the 4905s I used to drive in revenue service, and definitely heavier than the transit fleet I worked at before leaving the industry professionally.

(I'm using the term "heavy" and "heavier" as a way of describing the effort required to turn the stock diameter [22"] steering wheel.)

It got me to wondering if GM might have made some changes to the Sheppard system between JLV's '74 coach and the '76 & '77 4905s that were in the charter fleet I drove for.  Those coaches literally had "finger-tip" effort, as light as most GM cars of the same vintage.

Please do not misunderstand - there doesn't appear to be anything wrong with JLV's bus.  It runs straight down the road with only minor steering corrections needed - even in the headwinds and crosswinds we encountered.  It just seemed to me that the effort required around town was greater than I recalled.

I have no idea what the front end alignment is set at, but based on the rest of the condition of JLV's coach, I'm pretty sure it's set to specs, as there was no abnormal wear pattern on the tires.  Plus JLV's pretty meticulous about PM. . .

Thoughts and/or intelligent snarks, anyone? 
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RJ Long
PD4106-2784 No More
Fresno CA
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« Reply #1 on: April 16, 2013, 03:48:02 AM »

Might be posible the older  4905's had more positive caster, this will make for slightly heavier steering, but more stable, less twitchy.  Could be a newer design steering box
?  Might needed lubed ?
FWIW
Dave M
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MCI7 20+ Yrs
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chessie4905
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« Reply #2 on: April 16, 2013, 05:05:42 AM »

the "heavyiness" is caused by how much positive caster you have set your axle for. The increase in positive caster will lower or eliminate the wander at highway speed at the expense of increased low speed wheel turning effort. Our 4104 was harder to turn at low speed, and I reduced the positive caster about 2 degrees(was set about 4) and effort noticeably dropped without wandering at highway speed. Almost every coach that wanders on the road(requires constant correction) has zero or negative caster setting.Does make the manual steering easier at low speed though.
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Ed Hackenbruch
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« Reply #3 on: April 16, 2013, 05:14:59 AM »

RJ, could it be that it is because back then,...you were younger and stronger?  Grin   Is that a snark?Huh Smiley
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
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« Reply #4 on: April 16, 2013, 06:25:29 AM »

Probably just the tires or air pressure could be his pump setting a friend of mine reduced his pump pressure on his 4905a because he said he wanted more feel at the wheel

 His had nice power steering all it took was 1 finger to turn it setting still in a gravel lot was the easiest to turn I have seen


good luck
« Last Edit: April 16, 2013, 06:36:08 AM by luvrbus » Logged

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« Reply #5 on: April 16, 2013, 01:40:03 PM »

I just had the "ram" rebuilt on the steering on my '73 4905 and it does feel "heavy" at low speed, but I haven't had the alignment done yet that the inspection shop recommended.  I am hoping that the alignment fixes some of that.  Otherwise it is tight w/very, very little slop now!

Steve Toomey
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Steve Toomey
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RJ
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« Reply #6 on: April 21, 2013, 07:49:42 PM »

Thanks, all, for your feedback.

Including Ed's humorous semi-snark. . .   Grin

Don't think tire pressure was a contributor, JLV has it set at 90 psi based on the front axle's weight & tire size.

Engine has the correct Vicker's pump for the higher pressure Sheppard box, he's not sure if the pressure relief valve is set correctly, so he's going to look into that.

Caster might be an issue, and was an excellent suggestion.  JLV's going to call some local charter bus outfits to see who does their front-end alignment work and have it checked.

Again, thanks, all for your feedback, 'tis appreciated.

RJ & JLV
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RJ Long
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Fresno CA
TomC
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« Reply #7 on: April 21, 2013, 09:07:23 PM »

The Sheppard box is very sensitive to pump pressure. When I had my bus switched over, the pump was only putting out 1500psi, and you couldn't turn it when sitting still. Put on a new pump with 2200psi, and all's well. Suggest checking pressure. My steering is always finger tip. Good Luck, TomC
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« Reply #8 on: April 22, 2013, 09:06:10 AM »

take a look at the tilt of the kingpins; the top should be tilted back a little. Too much will cause heavy steering at low speed. The upper link is adjustable to adjust the camber.
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« Reply #9 on: April 22, 2013, 11:09:42 AM »

Why not just use a protractor and read the angle + or -
« Last Edit: April 22, 2013, 11:12:36 AM by luvrbus » Logged

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