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Author Topic: Driving in 3rd gear?  (Read 8541 times)

Offline 5B Steve

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Driving in 3rd gear?
« on: February 11, 2011, 06:46:02 AM »

   I was just wondering, if and when one was in heavy traffic and you had to downshift to 3rd and had to stay in that gear, how

   long could you go.   It's sounds stupid to ask but I was curious.

Offline smokedetector

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Re: Driving in 3rd gear?
« Reply #1 on: February 11, 2011, 06:48:48 AM »
Until you run out of fuel?
Jon Morgan
Athens, GA

Offline bevans6

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Re: Driving in 3rd gear?
« Reply #2 on: February 11, 2011, 07:03:51 AM »
Aside from the fact that third gear is less efficient than fourth (two additional gear power transfers compared to direct drive in fourth) there's no reason in the world not to run in third gear for as long as you like, presuming it's a manual box.  Automatics I don't know about.

Brian
1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Tatamagouche, Nova Scotia

Offline Oonrahnjay

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Re: Driving in 3rd gear?
« Reply #3 on: February 11, 2011, 07:29:39 AM »
If it's the right gear to match your speed (whether dictated by traffic, terrain or other conditions) and the right engine RPM, it's the right gear.  Stay in it until things change and you need to shift to 2nd or 4th.
Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long
6-cyl, 4-stroke, Leyland O-680 engine

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Offline 5B Steve

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Re: Driving in 3rd gear?
« Reply #4 on: February 11, 2011, 07:58:28 AM »



    Brian, thanks for the response, just like yours it its a 4 speed.

    Steve 5B....

Offline 5B Steve

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Re: Driving in 3rd gear?
« Reply #5 on: February 11, 2011, 08:05:31 AM »
 

  Oonrahnjay, thanks that makes sense for I have been in heavy traffic and keep shifting between 3-4 back to 3rd and so forth.

  I just didn't know how long you could go!


   Steve 5B....

Offline TomC

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Re: Driving in 3rd gear?
« Reply #6 on: February 11, 2011, 08:09:51 AM »
With only 4 speeds, the idea was to rev to the governor and shift.  That's also why the speedo was color coded so not to have you lug the engine down to far.  While you're in the range of 3rd gear, there really isn't anyway you can shift to another gear.  When you get up towards the governor, then shift into 4th.  If the engine accelerates in 4th, then that's the gear you should be in.  Over revving the engine (anything over 1800rpm) is just burning additional fuel and exerting extra wear on the engine.  For the most accurate engine speed analysis, you should have a tachometer.  When I installed my tachometer, with my Allison V730, I was quite startled that you could get 2nd gear lockup as low as around 20mph with the engine dropping down to 1100rpm (on a very light pedal)!  Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline gus

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Re: Driving in 3rd gear?
« Reply #7 on: February 11, 2011, 03:32:23 PM »
I've run my 4104 four speed 7-10 miles on long grades in third and even second part of the time. The engine doesn't care what gear you use as long as you don't lug it. Two strokes don't mind high rpms in fact they like it. They really sound nice too!!

If you lug it in hot weather it will get hot, if you are in a lower gear and not lugging it will stay cool forever if you're moving along.

I've also gone miles in 2-3 in construction zones, no problems at all and no reason for any problems.
PD4107-152
PD4104-1274
Ash Flat, AR

Offline Barn Owl

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Re: Driving in 3rd gear?
« Reply #8 on: February 11, 2011, 03:35:53 PM »
I can run my V730 all day in third gear without any problems!  ;D
L. Christley - W3EYE Amateur Extra
Blue Ridge Mountains, S.W. Virginia
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Have fun, be great, that way you have Great Fun!

Offline Nellie Wilson

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Re: Driving in 3rd gear?
« Reply #9 on: February 11, 2011, 04:52:16 PM »
Steve 5B -

Not contradicting, just offering my 2 cents. Besides, I've got a 5C so figured my experience might be relevant.

When I hit a city limit or construction zone, 3rd is my gear of choice. Has a decent power / speed range - I can keep the revs up or, if need be, just crawl along.  Sometimes I just leave it there, especially at night in hilly terrain (never know what's up ahead). Or just because I'm pure a** lazy...  :D

I might (on second thought) offer one mild (and by no means expert) contradiction:

I know Tom's right about the procedure ("... rev to the governor and shift...") but I seldom do it. I like to shift (up or down) when it's comfortable, usually 'up' around 1600-1700 and 'down' before lugging. I seldom need to double-clutch (unless I screw up  :-[) and the bus seems quite happy this way (but you may be geared differently).

I just love my '5', don't you?  ;)

 Nellie
Had to change a tire... >:(  got to put it on backward... :-\  still trying to fix it on photoshop... ??? ::) ???

Offline Ed Hackenbruch

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Re: Driving in 3rd gear?
« Reply #10 on: February 12, 2011, 06:36:02 AM »
I have run my automatic a loooooooooong way in third before.  A 55 mph speed limit is tough for me, in third i will be running about 21 hundred rpm and i lose about 20% mpg.  My shift point into 4th is about 57 mph but to keep from lugging it i need to be running at least 63 to 65 mph so that my rpms will be 1700-1750.
1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA

Offline gus

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Re: Driving in 3rd gear?
« Reply #11 on: February 12, 2011, 08:03:36 PM »
My V730 will not run in 4th under 50mph so that gives me no choice, however, I love it!!
PD4107-152
PD4104-1274
Ash Flat, AR

Offline buswarrior

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Re: Driving in 3rd gear?
« Reply #12 on: February 12, 2011, 11:07:21 PM »
Ed, what rear gear do you run?

My MC8 with 8V71N, HT740 and 3.7 differential will run at an indicated 50 mph in 4th and accelerate if the land is relatively flat, so no lugging.

If the speed drops much below there with the accelerator pedal depressed, the Allison takes care of business if I don't, by downshifting to 3rd. Somewhere 46/47 mph indicated, so I shift it down myself smoothly with a lift throttle and push forward the shifter ahead of that speed if acceleration is needed.

45 mph speed limits are the devil for my set-up, pretty much right at the minimum shift point.

happy coaching!
buswarrior
Frozen North, Greater Toronto Area

Offline bevans6

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Re: Driving in 3rd gear?
« Reply #13 on: February 13, 2011, 05:33:47 AM »
I think the definition of "lugging" is lacking.  I see no particular harm at running the engine at lower rpm if little power is required, like cruising along at a steady speed on flat ground.  If you need to accelerate, you can always downshift.  But if the engine makes maximum torque between 1200 and 1600 rpm, I just don't see where running it at those speeds can be all that harmful.  The governor based shift points are based on maximum acceleration.

or am I totally out to lunch?  I do cruise along at 45 - 50 in fourth all the time.  Roads around here, with an 80 kmh speed limit, almost demand that.

Brian
1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Tatamagouche, Nova Scotia

Offline Ed Hackenbruch

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Re: Driving in 3rd gear?
« Reply #14 on: February 13, 2011, 06:06:05 AM »
BW, 3.36  and i usually manually downshift my 644 a couple hundred rpm above what it will do on its own, so as to keep my rpm up so i don't start heating up.  Brian, the PO had to rebuild my 8v71 once because he was not paying attention and was "lugging" it for too long.  For optimal cooling on my 5A it needs to run at about 1700 rpm so that the squirrel cages are drawing enough air thru the radiators.  There are a lot of times where i am running at lower rpm but when i do that i keep a very close eye on the temp gauge and if it starts to climb i will downshift to get my rpm back up. I usually run right at 175-180 degrees.
1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA