re allison trans

jlaney · July 05, 2006, 01:24:32 PM

hey
am i the only one who has a allison that shifts a little rough. dallas said it was a computer
regulated one. thats get scary when we see a computer is in control. thank anyway j.t. laney

JackConrad · July 05, 2006, 01:44:06 PM

What make and Model bus? I am not familiar with the ATEC control on the newer Allisons, but my HD740 sometimes shifts harshly, ususally if I am on the throttle a litlle harder than normal. Jack

Dallas · July 05, 2006, 02:29:48 PM

That's right! blame it on Me!

If I knew more about it I'd try to help, but there are lots and lots of Allison guys here that can help you!

Dallas

jlaney · July 05, 2006, 05:29:24 PM

the bus in a 80 model prevost lemirage with a 8v71 with a 740 4 speed auto. which was installed
before i got the rig. i dont slip but if i leave it in fourth gear it will try to down shift a few times before i ger up to road speed. i try to leave it in third untill i get it one the road or about 50 miles
per hour. not a major problem only a disconfort thanks jlaney

jlaney · July 05, 2006, 05:33:13 PM

sorry about the typing errors i realy can spell better than that jlaney

Barn Owl · July 05, 2006, 10:12:57 PM

It might be the nature of the beast. My V730 will give me a good kick in the pants if I am hard on the throttle or doing a hard climb and it downshifts. From what I have been told from some car guys, a smooth shifting transmission is smooth because it slips the clutch packs. When a high performance shift kit is installed into a car or trucks transmission it will shift harsher. It's my understanding that not dragging those clutches will give you longer service life due to longer clutch life. I don't know if it's a connection that can be made, but it would make sense that these transmissions being made for heavy duty use would have a tendency to give harder shifts.

mikeH8H-649 · July 06, 2006, 03:21:16 AM

Jl this is only a guess but going into overdrive at 50 mph might be keeping your eng from lugging which is one of the worse things we can do to these engs,like I said this is only a guess but I am sure someone has the right answer for you Mike

JackConrad · July 06, 2006, 04:51:21 AM

740s do not have an overdrive. Under normal acceleration on a flat road, my 740 shift into 2nd at about 15-20 MPH, 3rd at about 30-35 MPH and into 4th at about 45-50 MPH. Shifts (up & down) are sometimes harsher, sometime softer. Has been this way since we purchased the coach 6 1/2 years and 30,000 miles ago. Jack

DrivingMissLazy · July 06, 2006, 05:27:53 AM

My 740 also had a harsh shift occasionally. Especially under heavy load shifting from 4th to 3rd. I generally tried to anticipate these shifts by manually pulling the shift lever down to third and then easing up on the accelerator while the shift was being made. I also found that the overall performance was better doing this as the shift was completed at a slightly higher RPM and I was able to keep the engine RPM up in a little higher range.
Richard

Quote from: JackConrad on July 06, 2006, 04:51:21 AM
740s do not have an overdrive. Under normal acceleration on a flat road, my 740 shift into 2nd at about 15-20 MPH, 3rd at about 30-35 MPH and into 4th at about 45-50 MPH. Shifts (up & down) are sometimes harsher, sometime softer. Has been this way since we purchased the coach 6 1/2 years and 30,000 miles ago. Jack

jlaney · July 06, 2006, 06:15:21 PM

tyler tx
sounds like mine may be ok, i like to help it shift anyway. i had a 4 speed standard in my old
4501 gmc and had to help it out also. after i got it going in first , i didnt use the clutch until i needed to take off again. thanks for the help jlaney

NJT5047 · July 06, 2006, 06:52:34 PM

As Jack sez, HT740 Allisons (you got an HT748 ATEC, same other than electronic valve body) are 4 speeds...but you feel the converter lock up and that feels like another gear. Lots of folk think they are shifting into 5 gears. You'll see them advertised as "5 spd" autos.
Mine has an occasional harsh 2 to low downshift. Shifts good up...unless you leave in in 3rd, which I'll occasionally do when cruising through a speed zone...then it'll shift funky between second and third...have no idea why. May not want to know why!!?

HT740/HT748s are known to be robust, dependable and relatively inexpensive to replace when compared to other autos such as B500s and later versions.
Just gotta get used to shifting idiosyncrasies....(is that last word speld wright? I dunt have a spel chekker)

Cheers, JR

NJT5047 · July 06, 2006, 07:13:41 PM

Quote from: jlaney on July 05, 2006, 05:29:24 PM
the bus in a 80 model prevost lemirage with a 8v71 with a 740 4 speed auto.

Do you have push button shift tower or a Morse selector lever? Lever goes with HT 740 and push buttons go with HT748 ATEC. If you have an ATEC trans (electronically controlled), someone has installed it as a "stand-alone" ATEC. Not an ideal situation. Dependable...but the trans is missing data without a DDEC engine. It would shift based on a fabricated TPS and road speed (VSS). This could cause some odd shift patterns...shouldn't hurt anything.
An HT740 is an excellent trans and would be a good match for your 8V71. HT740s are not electronically controlled.
What you describe is how they shift...shift into higher gears if you lighten up on the throttle..then if you accelerate they'll downshift. That's why I often leave mine in 3rd gear when driving along at 45 or so MPH. Keeps it from "hunting" gears. My ATEC will shift into high llockup at 40 MPH if just cruising. Supposed to save fuel that way. Just gas it and it'll downshift. That's better than lugging the engine.
JR

jlaney · July 08, 2006, 05:56:04 AM

tyler tx
thanks for the info jlaney

JackConrad · July 08, 2006, 06:49:33 AM

As JR mentioned, when driving in a town at about 40 MPH, I usually pull it into 3rd. If I don't it keeps shifting between 3rd and 4th with any slight deceleration or acceleration. Easier to just leave it in 3rd until we get out of the town. Jack

Hartley · July 08, 2006, 05:37:35 PM

My HT740 also shifts hard at times, But usually if I am in traffic and not quite turning enough RPM
to allow for a solid shift. There are a few shift points that if you don't have your foot to the floor
and the speed is just below or above a shift point the transmission jumps back and forth between gears.
I think this is normal for most Allisons.

I had a V730 in a couple other buses that if you didn't get or stay above or below the shift points
due to running slow they would just about jerk you out of the seat. toggling up and down.

If you must run that close to a shift point then shifting down one gear and letting the engine
speed up is better than banging the transmission between gears or lugging the engine.

Some speed limits are just right to cause the allisons to shift wierd, You try to maintain speed but
if you give it more power and it shifts you have to slow back down to the speed limit. Then the downshift
hits and you drop down slower. It's a balancing act at best....