I posted awhile back about increased vibration when shifting from Neutral into Drive on the MD3060R, less so in reverse.
Today while driving to dump my tanks, I noticed that my RPMs drop about 50-75 when shifting into Drive which is what is causing the increased vibration. My idle in Neutral had been lowered to about 650 and would drop to right at 600 when put into gear. Increasing the idle Neutral RPM up to the 700-725 RPM that the coach was at when I bought it, takes away the vibration.
So my question is, is this correct behavior on all mechanical 8.3s or is it something not working properly? I never noticed it happening before.
Just bought mine 2 weeks ago and the idle in gear rattles the hell out of everything. A few RPM higher and it smooths out. I am going to raise it. No clue on exact RPM--my tach doesn't work :(
Look up RPM specs as too high idle will overpower the service brakes on steep hills in first gear when the brakes are cold. High idle in gear with parking brake on will also cause the coach to roll if on much of a slope.
Pierce
If you set the idle too high you will not be able to shift out of neutral. Mark
Someone will certainly reply with 100% certainty, yet if I remember correctly, the old c8.3's like my 1997 model should have idle set at 700 +/- 50 and that above 800 RPM is when it will not shift out of neutral.
I apologize if I may have worded my question strangely.
I was trying to find out if everyone else had noticed that their idle RPMs dropped, and stayed down 50-75 RPMs, between Neutral and Drive? I am trying to determine if this is normal behavior for the engine RPMs to lower when put under the load of the transmission.
Mine Drops, think it is normal.
Roland
When you go into drive, the torque converter sees the difference between the spinning crankshaft speed and the now stationary Allison input shaft so uses some energy working against the drag of the ATF so the RPM drops. Normal.
This power/energy robbing slippage continues while in the lower gears until the transmission goes into torque converter lock-up that some of our coaches have.
The heat generated by the slippage is also what is responsible for the necessity of a transmission cooler. So, the end result is a major malfunction and resultant cost that Roland had to endure.
Just another reason why I don't care for automatic transmissions. Modern manual bus transmissions are no harder to drive than a stick shift BMW or Mercedes.
Pierce
Modern truck and bus transmissions that are not the standard "automatic" style are autoshift manuals...some with auto clutches as well. It's a manual style transmission with automatic shifting/rpm matching and sometimes even automatic clutches. It's good for highway driving. In reality, the allison automatic is pretty dang good.
Many car makers are now saying their cars with automatic transmissions are getting better fuel mileage than manuals! I guess due to more gears, computers, etc.?!?
Lots of "Big Trucks" are coming out with automatics now, as well as those big single tires in lieu of dualies, at least the ones I saw in Hagerstown.
Roland
;D i know a guy who can do anything mechanical better than most, BUT given a clutch, gear shift and throttle, completely gets confused, totally lost as in not a clue. Makes for laughter.
So the auto is a must.
Tried to teach him the 10 speed RTO910, not good, found just get him into high gear and you could go to sleep (with the 12V-71) did not need to change gears down to 30 mph. :o