AT545 shifting - what’s normal?

[Douggy]

Hi guys,

Looking to get a reality check on how my bus is changing gear. Not had much of a chance this year to have her on the road, but I am not sure if she is shifting normal for an AT545.

Background:
Eight window dognose Dt466e with an AT545.
Conversion largely complete, and pretty standard - I.e., not much added weight hopefully, after seats removed.
270k miles (dash and auction said 135k miles, BlueFire shocked me with the real mileage!....damn!).
4.11 rear end
Large tires

I am trying to get a feel for what kind of rpm/speed I should be feeling my tranny shifting into the different gears.

I seems like she’s not shifting into 3rd until she moving at 45mph. But it’s also hard to tell what gear she is in because the shift points aren’t hard. It just seems like revs are higher than I’d expect for a shift change.

Any insight from you regular bus drivers would be appreciated.

[turf]

nothing regular about me

as far as i know
the 545 shifts on an rpm range. if you are governed at 2400 rpm then
the 1-2 shift is around 600 rpm
the 2-3 shift is around 900 rpm
the 3-4 shift is around 1500 rpm

[Douggy]

Thanks for the quick reply.

That’s interesting, because I idle at 695/710 rpm. So I should be shifting from 1st to 2nd as soon as I touch the gas?

I need to also determine what my governed engine rpm is (however I do that!).

[cadillackid]

Originally Posted by turf

nothing regular about me

as far as i know
the 545 shifts on an rpm range. if you are governed at 2400 rpm then
the 1-2 shift is around 600 rpm
the 2-3 shift is around 900 rpm
the 3-4 shift is around 1500 rpm

if yours is ahifting like that then you likely have a bad or misadjusted modulator


the speed at which a 545 shifts is highly dependent on the rest of your driveline.. most generallly if you floor one it should go close to 2600 RPM on your engine before it goes to the next gear..



with an 'E' engine there is only 2 shift point adjustements (low and high)... the electric modulator is designed so that if you piut the engine under load or your speed drops low that the computer activates it.. these are known to fail and will prematruely destroy your tramnsmission if they fail in the off position.



if the modulator is failed in ther office position you'll notice it always seems to shift early even if you have your pedal floored ..


to test your modulator there are 2 ways.


1. drive at very light throttle on flat ground and note when it goes into 2 and 3.. you can take it up to 4 but may take you a bit as you accelerate slowly..


pay attention to the MPH that it shifts at light throttle.. not the RPM so much although the RPM should be in the 1500-2000 range..


now take it out on the same road and floor it .. yoiu should note a much higher RPM and faster MPH speeds at each shift... close to 2600 RPM.


another way to test the modulator is to drive at light throttle till it shifts to 4th gear than immediately floor it after the shift.. it should downshift back to 3rd and go up higher in MPH than it did during light throttle..





with there being no lockup converter on an AT545 you wont really feel solid hard shifts although the shifting is definitely going to feel rougher than your average car (unless you have a muscle car with a transmission)..


your shift feel is going to be a 'back and forth' type motion as most of the shifts in the 545 are releasing a clutch pack and then grabbing another.. I believe 1-2 is the harshest due to the clutching sequence.. and its also the noisiest too with the distinct AT545 whine present going from 1-2.



the shift timing should always be in the less than 1 second range for 1-2 and 2-3, 3-4 should be pretty quick.. meaning watch your tech and it when floored you should see it drop fairly quickly as it goes to the next gear.. although the number of RPM it drops wont be particularly high because of the no-lockup but it should not be a 'slow-slide' from one gear to another..



-Christopher

[Shamoke]

Originally Posted by cadillackid

if yours is ahifting like that then you likely have a bad or misadjusted modulator


the speed at which a 545 shifts is highly dependent on the rest of your driveline.. most generallly if you floor one it should go close to 2600 RPM on your engine before it goes to the next gear..



with an 'E' engine there is only 2 shift point adjustements (low and high)... the electric modulator is designed so that if you piut the engine under load or your speed drops low that the computer activates it.. these are known to fail and will prematruely destroy your tramnsmission if they fail in the off position.



if the modulator is failed in ther office position you'll notice it always seems to shift early even if you have your pedal floored ..


to test your modulator there are 2 ways.


1. drive at very light throttle on flat ground and note when it goes into 2 and 3.. you can take it up to 4 but may take you a bit as you accelerate slowly..


pay attention to the MPH that it shifts at light throttle.. not the RPM so much although the RPM should be in the 1500-2000 range..


now take it out on the same road and floor it .. yoiu should note a much higher RPM and faster MPH speeds at each shift... close to 2600 RPM.


another way to test the modulator is to drive at light throttle till it shifts to 4th gear than immediately floor it after the shift.. it should downshift back to 3rd and go up higher in MPH than it did during light throttle..





with there being no lockup converter on an AT545 you wont really feel solid hard shifts although the shifting is definitely going to feel rougher than your average car (unless you have a muscle car with a transmission)..


your shift feel is going to be a 'back and forth' type motion as most of the shifts in the 545 are releasing a clutch pack and then grabbing another.. I believe 1-2 is the harshest due to the clutching sequence.. and its also the noisiest too with the distinct AT545 whine present going from 1-2.



the shift timing should always be in the less than 1 second range for 1-2 and 2-3, 3-4 should be pretty quick.. meaning watch your tech and it when floored you should see it drop fairly quickly as it goes to the next gear.. although the number of RPM it drops wont be particularly high because of the no-lockup but it should not be a 'slow-slide' from one gear to another..



-Christopher

A very informative post, thanks for taking the time to explain all of that. I too have the AT545 in my build sitting behind a cummings 5.9 and I will pay attention to the shift pattern the next time I drive it.

[turf]

I'm not sure how to upload pdf files here, they are on plenty of fb groups. the rpm's that i mentioned were straight off the allison at545 service manual.

its from a chart with a range. starting at a 2400 governed engine.

if your engine is 2600 governed, you can add about 200 rpm to the range.

[cadillackid]

Originally Posted by turf

I'm not sure how to upload pdf files here, they are on plenty of fb groups. the rpm's that i mentioned were straight off the allison at545 service manual.

its from a chart with a range. starting at a 2400 governed engine.

if your engine is 2600 governed, you can add about 200 rpm to the range.

my guess is that those are output shaft RPMs and not engine RPMs


and likely the non-modulated RPMs.. there will be 2 sets and a bunch of in between..


0 modulated default shift output shaft RPM. and a full-throttle (modulated) output shaft shift RPM

[turf]

here is the chart i was referencing from the manual