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Author Topic: MPG  (Read 3875 times)
Lonnie time to go
Lonnie
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« Reply #15 on: June 05, 2008, 07:47:32 PM »

boogiethecat
Wondering what motor you have and if its auto trans .
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1976 4905
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« Reply #16 on: June 06, 2008, 01:20:40 PM »

BS....me thinks it just may be easier (and more fun!) to teach the wife to drive and shift a crash box.  No big deal.  She can do it....I guess the real question is....does she want to? 

An analogy.  My mom was 17 and was going to ferry B17's and B24's by herself from Canada to England.  Canadian Wackes or Waves.  Met my dad in primary flight school instead.  Wow!  Smiley Smiley Smiley
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TomC
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« Reply #17 on: June 06, 2008, 02:54:33 PM »

If you know how to drive the Allison, you won't get your back hit with harsh shifts.  If you have an ATEC, then you hardly know it is shifting.  I don't care how hard it shifts, Allisons are a down right joy to drive-no one with an manual transmission could keep up off the line.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #18 on: June 08, 2008, 07:18:20 PM »

Tom C ,could You tell Me the proper way to drive an allison.  My HT70 will loosen fillings when shifting to high.  Any words of wisdom would be much appreciated.  John
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« Reply #19 on: June 08, 2008, 07:25:49 PM »

Tom C ,could You tell Me the proper way to drive an allison.  My HT70 will loosen fillings when shifting to high.  Any words of wisdom would be much appreciated.  John

I will relate that with my operators manual it states that if you maintain full throttle, the Allison will wait to shift higher.  That definitely adds a jolt.  I've seen many on this forum talk about just keeping their foot on the firewall.  To my thinking that is the wrong way to handle the Allison.  It is also bad for mpg and probably none to good for transmission life.

I drive mine easy for good mpg's.  As long as I'm not pushing it to full throttle, you can hardly notice the shifts.
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bobofthenorth
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« Reply #20 on: June 08, 2008, 07:44:11 PM »

We used to have Allisons in our high flotation spreader trucks.  With them if you kept your foot on the firewall they would rattle your fillings when they shifted but if you held it to the firewall until it was almost ready to shift and then fairly abruptly backed out of the power the Allison would shift almost unnoticed and then you could put the power on again.

Somewhere along the way somebody told me that hard shifts were a design feature for an Allison and I shouldn't worry about them.  And I know on those working trucks the guys would come out of a corner in first and hold it to the firewall through three shifts day after day with no apparent ill effects.  We did engines and diffs almost as a maintenance item but I only recall one transmission in 22 years. 
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R.J.(Bob) Evans
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« Reply #21 on: June 08, 2008, 08:15:46 PM »

It is better for automatic transmissions to shift harshly.  Most automatics don't do so because the owners expect nice smooth shifting.

I had the automatic in my F350 upgraded to handle more power and it shifted very harshly after that.  The rebuilder said that is better for the transmission and I found plenty of others who agreed.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #22 on: June 08, 2008, 08:29:28 PM »

thats just plain BS.

an Alison can shift as smooth as any car transmission is it is proprly maintained has the right fluid and you know how to drive it.  I have found that on allisons that have a harsh shift if you understand your gearing and power curve you can manage the shifts via throttle modulation.

as for modifying a trans to allow more power......harsh shifts are a side effect but has nothing at all to do with making it better for the transmission....bunch of poppycock...likely just a poor engineering design on the modification to allow modified shift points.
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gmbusguy1
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« Reply #23 on: June 08, 2008, 09:24:45 PM »

Doug, That is not B.S at all.

the clutch packs will last much longer if they are not slipping when engaged and a harsher faster if you will shift means less slippage hence longer life for the clutch discs at least

the reason for the softer shifts in your car from the factory is simply drivability

people like smooth shifts so the designers gave them smooth shifts


Chris
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Don4107
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« Reply #24 on: June 08, 2008, 11:23:25 PM »

Its called overlap.  Meaning that in the typical auto tranny the next gear clutch pack starts to engage before the previous gear clutch pack has completely released for a nice smooth shift.  If there was no overlap, the engine could rev between shifts if the timing was not instant and perfect.  This of course causes a certain amount of wear, having two clutches engaged at the same time, at least partially.

The run of the mill shift kit for "improving" performance without improved clutches reduces overlap at full throttle to save the clutches and make quicker, firmer shifts.  Some increase pressure for more positive, quicker shifts. 

From what you are saying, it sounds like at least some applications of the Allison work a bit like a hot rodded auto tranny with shift kit.  Hold her wide open and shift firmly, back off and smoother (more overlap) shifts.

When was the Allison developed?  Being a GM product, are they just a turbohydramatic on steroids? 

I hope to just keep stirring the stick on my Spicer for a while.

What ever tranny you have, Good luck.
Don 4107
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Don 4107 Eastern Washington
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kyle4501
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« Reply #25 on: June 09, 2008, 05:12:28 AM »

A harsh, teeth rattling shift isn't 'good' on anything. Sure the clutches slip less, but the risk of breaking bands or the like increases. Not to mention the jerking of the motor mounts & beating hell out of the rest of the drive train.  Roll Eyes

I have seen the insides of many a th350 & 400s that suffered from too many harsh shifts. Broken bands, stripped out clutch packs, even a sheared output shaft.  Shocked

I think the reason the big allisons survive so much abuse is a testimony to their conservative ratings.   Cool
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I know you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant. (R.M. Nixon)
tekebird
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« Reply #26 on: June 09, 2008, 05:37:04 AM »

Hmmm guess all 4 of our Allisons are broken then, because they all shift very smoothly

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Michael_e
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« Reply #27 on: June 09, 2008, 08:22:31 AM »

Been a long time since i last posted, anyway this thread caught my eye. I was wondering what mgp i should expect with my bus; 1955 GM Scenicrusier pretty much gutted, converted to 8V92TA mechanical with Allison 754, original rear drive-i think it is a 4.11/1, tires are 11R24.5. I haven't got to drive it much since the drive train conversion due to numerous reasons, major one was layoff. And now, selling house to move to Kansas. Will probably have bus trailered, but will be safest thing to do as tires are at least 8 years old. I will be posting more questions soon.
Thanks,

Mike
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1955 GM Scenicrusier, 8V92TA & Allison 754. Totally rewiring all 12v systems and lots of questions.
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« Reply #28 on: June 09, 2008, 08:58:14 AM »

6 I would guess.

Providing the sidewalls are not all cracked and you can bring yourself to drive 5 and stop every so often to let tires cool I'd drive it if it is drivable
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kyle4501
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« Reply #29 on: June 09, 2008, 09:20:06 AM »

Stock rear axle ratio in the scenics is 3.7:1.

Your mileage will depend on the HP your engine is tuned for & how close you are to the peak efficiency (of the motor) while going down the road.

My stock greyhound spec. 8v71 got ~10 on the trip home from Fl.

I'm with Doug, DRIVE IT.  Grin

Put new tires on the steers. There are enough tires on the back that they aren't likely be overloaded. Speed may be something else all together tho . . .
Start out driving, going ~50 ish & have an escort driver to keep an eye on things. . . . If there's a problem, you can stop before it gets big & if you can't fix it, then get it trailered.

If you post the details, you may get a few busnuts to volunteer to help drive.  Grin  Grin  Grin

« Last Edit: June 09, 2008, 09:26:01 AM by kyle4501 » Logged

I know you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant. (R.M. Nixon)
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