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Author Topic: 4104/4106 Question - mountains  (Read 4681 times)
Rick59-4104
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« Reply #30 on: February 14, 2011, 12:26:17 PM »

Paul,
 No hand parking brakes as of now, I need to find the parts..
Rick
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NW Arkansas
1959 GM 4104  No. 4115
1972 Grumman Kurbmaster Stepvan Conversion
1957 Airstream 13 panel Overlander
gus
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« Reply #31 on: February 14, 2011, 02:17:14 PM »

Unlike Rick's, my '54 4104 has no fast idle nor is there any mention of it in any of my manuals.

It did, however, come with a hand throttle which shows as original equipment in my Driver's Manual. I use it both for fast idle and as a cruise control on long straights.

It has been converted to spring parking brakes, thankfully!!
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PD4107-152
PD4104-1274
Ash Flat, AR
JohnEd
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« Reply #32 on: February 14, 2011, 03:04:08 PM »

It seems to me that some don't fully grasp how the fast idle actually works.  The rpm, in fast idle, as I understand it, is CLOSELY controlled by the governor.   The governor applies and subtracts throttle much much faster that a human could if he were standing at the engine with his hand on the throttle.  Add in the delay associated with the throttle linkage, and air throttle is much quicker than cables or rods, and you end up with a somewhat hopeless situation of "lag" in injecting corrections and you end up with a over revved engine that is frying the clutch or you stall out.  The process has you engage the clutch at the absolutely lowest RPM and in the shortest time so as to not fry the clutch.  You use the closely controlled "governed" fast idle to just get things hooked up and then, because fast idle will not apply full throttle, you switch out of fast idle and then depress the throttle to get WOT.  Wallah!  "Huston, we have movement that doesn't involve Exlaxx." Grin

Now, this is just my grasp of things having heard them in various levels of detail over the years.  Please correct me in any way for the sake of those others that don't really understand.  God knows that I shouldn't have the last word around here.

If you don't have fast idle and you have a stick 4 or 5 speed you would benefit from get it installed.  If you have it and it is locked out with the handbrake or any other mech I would suggest you modify your system.  Bus companies often hired less experienced drivers and everyone needed protected from their rookies.  We have a lot of safty systems around us that "Real Men" don't need to be successful with the ladies.

John
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pvcces
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« Reply #33 on: February 14, 2011, 08:08:53 PM »

FWIW, when we try to "feather" the clutch while trying to get rolling against a grade, the coach starts to buck. I attribute this to engine movement causing throttle changes by changing the length of the linkage path when a load is applied. This doesn't have any noticeable effect when the clutch is out.

On the other hand, the governor on fast idle doesn't produce "any" of the bucking, even with a heavy load.

Regarding clutch wear, we have .380" and .408" disc thickness after around 80,000 miles and we're nowhere near the rivets, yet. The worst thing that I remember doing to the clutch was climbing the coach rears up on high blocks at Ted Campbell's place when we were trying to fix a vibration problem. It didn't seem to bother him.

If I can get the coach moving without using the fast idle, I do. It normally works very well.

Tom Caffrey
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Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska
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