ruff shifting 740 allison

[jlaney]

hello from tyler
my transmission is shifting hard. i stay in third gear until i am out on the road or about 50 miles per hour. then go to forth. if i leave it in forth it will down shift and back and forth unless i keep it on the floor. someone said that the computor could need ajusting. what about it someone. thanks j.t

[Jerry32]

What speed are you driving? mine will downshift around 50 if you pushit but after about 60 no problem. runs best about 65 to 70 but below 50 will downshift.  maybe the allison gurus will chime in here Jerry

[niles500]

please post info on drive train - DDEC or not? ATEC or not? mill size?

[jlaney]

hello from tyler tx
engine doesn't have blower or computor,its is a 871 detroit.with 740 allison.
if i leave it in drive and ease down on the pedal it will down shift back and forth until it get up to speed , after it gets up over say 50 mph it  will settle down, and stay on the forth shift. the previous owner , which is charter service says it did the same with him and he just run it in third until out on the road , then manuely shifted to forth.  he installed the transmission after he bought the bus. and nerver had the shifting set up by a tech like stewart and stephenson , just wondering if this something i  could do. the transmission doesn't slip .

[buswarrior]

I suspect your transmission is fine and that you have been given bad advice.

Try this:

Leave it in second gear around town, only shift to third as you reach governed engine speed in 2nd. Only shift to 4th as you reach governed speed in 3rd.

Same thing when slowing down.

In other words, you are selecting the gears, not the tranmsission.

My 8V71/HT740 combo shows me 37 mph in 2nd, 51 mph in 3rd and 70 mph in 4th.

The HT740 isn't smart enough to be left to do its own shifting. It will upshift at the first sign of light throttle, and then downshift again as soon as you demand more pull than it can give.

Bangs back and forth between 2 and 3 pretty good, eh?

The "automatic" in a 740 means that you don't have to row gears and clutch it, it doesn't mean shove it in drive and forget about it.

happy coaching!
buswarrior

[jlaney]

thanks
sounds like someone has the same transmission. i do control the shifting and  don't seem to hurt it. i use it to slow the bus down. what is your input on this.  thanks jt.

[captain ron]

I have the 740A computerized tranny coupled to a 8v92 DDEC and it dose the same thing but at 35 MPH and between 3rd and 4rth if I stay at that speed

[jlaney]

thanks ron
sounds like we are in the same boat. i quess i will keep on shifting along               thanks jt.

[JimC]

My 730 hunts for the correct gear under certain conditions also, when that happens I manually down shift to 2nd and manually up shift when I know I will be going over 50mph consistently
Jim

[jlaney]

thanks jim
i think some of the newer truck shops have a way to set up and make the shifting smoother.  a man i know had a mci and said his shifted to smooth for him to know what gear he was in. some like it to shift some harder to hear the engine load.  may be right thanks jt.

[white-eagle]

i have an 8v92t with my 740, so this may not be helpful, but mine shifts around 30 into 3rd, fourth at about 38 to 40 unless i push the pedal down, then it shifts at 45 to 4th automatically, always.  does not down shift down to 3rd unless i push down hard at maybe 35 or lower.  letting up on the pedal doesn't make a difference until it drops way down.  obviously, i can and do manually shift when it seems appropriate.
seems to me that if it changes too much, it may need an adjustment.  someone told me 45 might be too low for mine to shift up and allison could adjust it up to 50 before it mandatorily upshifts.  Maybe yours could be corrected?

[jlaney]

thank for all the info
so long it doesn't hurt the transmission i quess i will help it alone.  thanks jt.

[Busted Knuckle]

JT,
What you describe is very common, I have seen it numerous times in different coaches! I talked to a friend who is far more knowledgable than I on the subject. He said it's common especially between 3rd-4th, and that he tells his drivers "to manually hold it in 3rd until they get over the {hump spot} then go onto 4th!" My 60 Series / B-500 does the same thing between 5th-6th at around 55 mph! (So I really "can't drive 55!" LOL! to quote Sammy Hagar)
By the way your 318 Detroit does have a "blower" just not a "Turbo"!
FWIW   BK 

[jlaney]

thanks again
i drive it in third even in town. probly not hurting anything. your right about the blower . it just in not blown. i worked for waukesha engines bakin the 60
s and we didn't do much in the detroit line. we called them screaming jimmys
thanks jt.