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Author Topic: re allison trans  (Read 3472 times)
jlaney
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« on: 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
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j.t. laney  tyler texas 1980 prevost lemirage
JackConrad
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« Reply #1 on: 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
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Dallas
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« Reply #2 on: July 05, 2006, 02:29:48 PM »

That's right! blame it on Me!  Grin Grin Grin

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
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jlaney
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« Reply #3 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. 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
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j.t. laney  tyler texas 1980 prevost lemirage
jlaney
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« Reply #4 on: July 05, 2006, 05:33:13 PM »

sorry about the typing errors i realy can spell better than that jlaney
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j.t. laney  tyler texas 1980 prevost lemirage
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« Reply #5 on: 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.
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« Reply #6 on: 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
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JackConrad
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« Reply #7 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
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« Reply #8 on: 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

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
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jlaney
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« Reply #9 on: 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
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j.t. laney  tyler texas 1980 prevost lemirage
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« Reply #10 on: 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!!?  Shocked
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) Wink
Cheers, JR  Cool
« Last Edit: July 06, 2006, 06:54:53 PM by NJT5047 » Logged

JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

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« Reply #11 on: July 06, 2006, 07:13:41 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
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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

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jlaney
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« Reply #12 on: July 08, 2006, 05:56:04 AM »

tyler tx
thanks for the info jlaney
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j.t. laney  tyler texas 1980 prevost lemirage
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« Reply #13 on: 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
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« Reply #14 on: 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....
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« Reply #15 on: July 08, 2006, 06:11:38 PM »

Mine downshifts hard (really easy for everyone on board to feel it) from 2nd to 1st  (i think) when pulling up to a stop sign, etc., for the first few minutes.  Then shift is just fine with no problems.   Tho' I have other problems as our leaks fluid as well - so it goes into the shop next year...   Angry

Best Regards, Phil
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ChuckMC8
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« Reply #16 on: July 10, 2006, 04:55:43 AM »

After I installed a tachometer in my mC8, I really began to see what happens at shift points, etc.  When my trans shifted to 4th at 45 or so, my rpms would drop to 1100 or 1200 and the engine had to climb it way back up to where I wanted it to run (1500+)
Like the other guys, I learned just to leave it in 3rd gear with the shifter unless I needed to go over 50MPH, then drop it into 4th.
I know its not the way its designed, but shifting by the tach and speedo makes the engine a lot happier and also helps the performance and drivilibility. When downshifting at 1500 rpm, I let off the throttle and shift and back on the throttle at the same time. It makes a smooth shift and stays in the power band on the 8V71.
 I know from 4 years of reading the boards that some folks poo at the tach, but I really enjoy mine. For installation in the stock MC8 dash, I moved the bus volt meter out of the panel and mounted it under my b/u monitor. Into that spot, I put a new 2" diameter air gauge that Capt Ron gave me (thanks Ron) That left me with the large opening where the factory air gauge came out. I bought a new tach on ebay and it lives in that spot now. The air gauge is s little more inconvienent that it was, but I made sure that the low air buzzer and warning lights work properly.
 just my .$0.02 worth, but it works for me-complete tach installation with parts was about $75.00
« Last Edit: July 10, 2006, 05:19:50 AM by ChuckMC8 » Logged

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« Reply #17 on: July 10, 2006, 09:10:59 AM »

I second Chuck's tach post. Now that I drive an auto (V730), it's more imperetive to know the revs... what gear I'm in when climbing and what the engine is doing. The trans will shift too soon (based upon throttle position and load, I guess), sometimes trying to pull grades down at 1400rpm in third locked or second locked. By watching the tach, I can pull it into the proper gear range to climb at 1700-1900rpms, partial throttle.

I wish there was a way to install a button to tell the tranny when to lockup. Getting lockup in first would be ideal for those steep, slow grades with twists, and make better use of my Jake in any gear.

Anyways, here's a shot of my dash. Starting at upper left is tranny & engine oil temps (has a selector switch for senders), tranny temp is under that, the ones obscured are the voltmeter and 2" air pressure gauge. On right is speedo, fuel, coolant temp. and tach. It's a nice gauge package, though I'd still like to install a pyro, esp. since my bus had N65's installed during its out-of-frame before I bought it. I've really have to keep an eye on the tailpipe in my left mirror.

Brian Brown
4108-216
Longmont, CO

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Brian Brown
4108-216 w/ V730
Longmont, CO
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