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Old 12-10-2019, 06:52 AM   #21
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I totally agree that the engine-Allison communications is poor


This one shifts UP from 3rd to 4th at 2500 RPM and it seems to hang at 2500 RPM for a second or so before it decides to do so. The shift from 4th to 5th (overdrive) also waits to happen at 2500 RPM, but takes 2 to 5 seconds at 2500 RPM to kick it up to 5th. This is with full throttle (well, pedal to the floor anyway).


I am running most of the time at full pedal ... it never downshifts until below the 1800 RPM range. It does downshift, eventually.


I am starting to think that the lack of power is a large part of this whole problem. I'll be cleaning out the water separator and since I'll have that off ... replace the filter.

they are likely only using throttle and its very possible that the ECM or TCM was replaced at some point and not properly programmed.. that sounds off.. if an allison is commanded by its computer to shift and delays because of some fluid-pressure or solenoid related cause it will set a code and trip the 'Check Trans' light..



the downshift is controlled by where the RPM will end up in the lower gear.. gear 4 is a 1.00 and gear 5 is a 0.75. thats a steep ratio change.. if you are close to your top RPM AFTER it goes from 5 to 4 then thats all it can do.. but if the drop takes you from 1800 to say 2200. then it should be programmed to go down earlier..



you can also try and drop it using the T handle.. the trans wont ever downshift itself into an over rev condition but a T handle range change will generally let it run to the rev limiter ..



the MT643 suffers from this same issue but in its 3-4 shift.. its a Tall shift on that trans..



I solved alot of my issues when I updated to not only the latest softwsre on my engine ECM but also bought a new ECM from a later year and programmed it with my VIN / ESN. apparently the base firmware (in my case from 00 to 04) was changed enough that it greatly affected how the ECM sent out 'kickdown event requests' in the J1939 stream... so essentially if my engine feels its in trouble.. ie lugging.. it shoots a hard kickdown request to the Trans TCM.. even with my custom programming my TCM will not ignore those.. so it goes down as long as it wont go past the programmed rev limiter (the Trans TCM has a max engine RPM parameter)...


its posible a dealer might have updates for both the ECM and TCM to help.. but its also possible its the unfortunate result of your driving speed being right in that "wrong" spot where it has to choose between downshift or over-rev...



Next time you drive and force it to go down at 1800 from 5 to 4, watch to see where your RPM ends up right after the shift... thats the trick to know whether re-program will help...

-Christopher
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Old 12-10-2019, 10:39 AM   #22
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I might have to take it out and play with it today. We will be headed back to Texas soon and I would like to know more before we do.
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Old 12-10-2019, 10:43 AM   #23
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Thank you for the descriptions ... seems to fit the situation. I want to take it out today because we need to head back soon.
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Old 12-10-2019, 01:23 PM   #24
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Standard rule of thumb for safe oil pressure is at least 10psi/1000rpm.
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Old 12-10-2019, 02:31 PM   #25
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Thank you for the descriptions ... seems to fit the situation. I want to take it out today because we need to head back soon.
Best wishes with the test run! I still recommend after the drive to give a finger check for the temp of all them driveline parts -- won't take you more than a few minutes to confirm those parts are spinning happily!

RE oil pressure -- had you noticed a significant change in the hot idle pressure it could indicate a worn bearing -- that's why I asked.

The oil pressure comes from the resistance to flow through the passage ways of the engine -- a worn bearing will cause a pressure loss.
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Old 12-10-2019, 06:39 PM   #26
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Standard rule of thumb for safe oil pressure is at least 10psi/1000rpm.
I will make an effort to observe the oil pressure more closely on the next drive. My memory fails me. I know I have seen it as low as 25 PSI in the last three years and as high as 45 PSI. I also know it runs at 45 PSI at 2000 RPM to 2500 RPM. Usually, I am not watching the oil pressure when accelerating due to keeping my eyes on traffic.


That is an interesting rule of thumb though. So from idle (750RPM) to MAX (2500 RPM) we have a delta of 1750 RPM, which would be 17.5 PSI by the thumb. Applying the rule in reverse, my idle pressure should be at least 27.5 PSI (45 PSI - 17.5 PSI) ... which seems to fit my recollection.
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Old 12-10-2019, 06:44 PM   #27
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Best wishes with the test run! I still recommend after the drive to give a finger check for the temp of all them driveline parts -- won't take you more than a few minutes to confirm those parts are spinning happily!
Gotcha! Thank you for the best wishes on the test run. Looks like that may happen tomorrow (I hope).


Quote:
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RE oil pressure -- had you noticed a significant change in the hot idle pressure it could indicate a worn bearing -- that's why I asked.

The oil pressure comes from the resistance to flow through the passage ways of the engine -- a worn bearing will cause a pressure loss.
Yeah, I'll be taking an even closer look at the idle pressure. I have not seen any low pressures, but that does not mean they can not happen.
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Old 12-10-2019, 07:26 PM   #28
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Have you checked the clamps on the CAC pipes? Also check for blown hoses. Low boost will cause low power as well as any number of odd noises.

HTH
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Old 12-11-2019, 01:29 PM   #29
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Stay tuned folks ... I just made a couple of videos and am working on uploading.
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Old 12-11-2019, 10:38 PM   #30
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Stay tuned folks ... I just made a couple of videos and am working on uploading.
Argggg... apparently this site does not like 250MB files! It will be a while before I can reduce the file sizes.
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Old 12-11-2019, 10:41 PM   #31
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Argggg... apparently this site does not like 250MB files! It will be a while before I can reduce the file sizes.
Ever heard of YouTube??? Hehehe, it doesn't mind that size at all.
Just make a YT account and upload it there and share the link here.
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Old 12-12-2019, 01:24 AM   #32
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No specific advice to offer, Native, but coming from a professional background working on other (much smaller) vehicles, I'd second Banman's advice in not ruling out the driveshaft assembly because it was overhauled recently. Rather the opposite: Because it was overhauled recently, it would be the first thing I'd consider. The majority of my work involved fixing things other people had already 'fixed'.
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Old 12-12-2019, 02:45 AM   #33
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Given that your driveline was reworked and the problem has cropped up afterward, I begin to wonder if you have U-joints "Out of Phase" with each other, which would cause such a symptom. Basically, each U-joint should be parallel with the next one down the line. Sometimes they get assembled askew - usually the slip-joints. Any reputable driveshaft shop will have ensured the welded yokes are properly in phase and shafts balanced (to this end, see if any welded on weights may have detached).
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Old 12-13-2019, 10:01 AM   #34
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rode in this AMAZING bus last night. Can confirm that up to abuout 50 mph all is normal. Bus is as smooth and quiet as one could hope for.
From 50 up you hear a LOUD resonance that's IN your head its so prevalent. WoooooWoooooWoooooWooooo at a very low frequency range.

Sam's a lot smarter than me, so if he doesn't know what's doing it I'm downright baffled.

The noise is noticeable at lower speeds during partial throttle but nothing at all like 50+ mph. It takes over the whole bus and sounds sorta like a kettle drum.

I sure hope this gets resolved! I've got the same setup so I'm keeping a very close eye on all this.
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Old 12-16-2019, 12:39 AM   #35
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rode in this AMAZING bus last night. Can confirm that up to abuout 50 mph all is normal. Bus is as smooth and quiet as one could hope for.
From 50 up you hear a LOUD resonance that's IN your head its so prevalent. WoooooWoooooWoooooWooooo at a very low frequency range.

Sam's a lot smarter than me, so if he doesn't know what's doing it I'm downright baffled.

The noise is noticeable at lower speeds during partial throttle but nothing at all like 50+ mph. It takes over the whole bus and sounds sorta like a kettle drum.

I sure hope this gets resolved! I've got the same setup so I'm keeping a very close eye on all this.
During our short ride, you mentioned motor mounts. While on the long drive back to Texas, I remembered where I have heard this particular noise before, albeit on a smaller scale. I have a 1960 Ford Falcon that I dropped a 266 then a 302 into. This was many years ago (in the 70's and 80's). When I put my foot into it, the engine would knock on the part of the engine compartment that surrounds the struts. Made a very similar sound. I'll be looking into the motor mounts.


Banman, I felt the U-joints along the driveshaft. The transmission yolk and bearings were warm but no more then the transmission. Same was true of the differentia yolk and bearings. All three of the bearings in the middle (it is a four part drive shaft) were cold. I am not entirely discounting the driveline yet ... but it looks less likely as a cause at this point.


I had a lot of time to play with the speeds and accelerator on the many up and down hill grades along the drive. While listening closely to the GROWL, it does sound like there are two components to it. One is a howl, a very loud howl, that reverberates through your soul. The other component is a rhythmic pattern much like a sewing machine (or a Porsche engine) that occurs simultaneously when the engine is pulling 100% load and 100% torque. It increases its pitch as the engine speed increases. It is very mechanical in nature.


I have been having a hard time getting the video uploaded to this site and also to youtube. Once I get one uploaded, I will post here.
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Old 12-16-2019, 06:12 AM   #36
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" I felt the U-joints along the driveshaft."
Did you check for any play though???
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Old 12-16-2019, 07:10 AM   #37
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driveshaft resonance is a real deal on some busses.. im noit sure which bus ECCB is referring to..is it yours or someone elses?



My Superior had driveshaft resonance even after I rebuilt and re-balanced and rephased the driveshafts.. it occured when the driveshaft speed hit about 3200 RPM or so.. now ive re-geared the bus to a 4.78 gear and its gone.. even at 65 the driveshaft speed is only at 2600-2700 or so.. hard to tell exactly since that bus has an AT540.. im guessing if I ran the bus up to 80 it would come back.. (not that I want to drive a 42 year old bus at 80 MPH so i wont... )....


that bus is a gasser.. there is no "growl" to its engine, its engine is rather quiet..


-Christopher
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Old 12-16-2019, 07:56 AM   #38
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driveshaft resonance is a real deal on some busses.. im noit sure which bus ECCB is referring to..is it yours or someone elses?



My Superior had driveshaft resonance even after I rebuilt and re-balanced and rephased the driveshafts.. it occured when the driveshaft speed hit about 3200 RPM or so.. now ive re-geared the bus to a 4.78 gear and its gone.. even at 65 the driveshaft speed is only at 2600-2700 or so.. hard to tell exactly since that bus has an AT540.. im guessing if I ran the bus up to 80 it would come back.. (not that I want to drive a 42 year old bus at 80 MPH so i wont... )....


that bus is a gasser.. there is no "growl" to its engine, its engine is rather quiet..


-Christopher
I get it about it about 50mph, in high gear for the rear,(two speed rear)not enough to be a worry, but enough to know it is there. And it does it mostly under load, uphill etc. flat ground, steady speed it is not there.
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Old 12-16-2019, 08:15 AM   #39
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Originally Posted by cadillackid View Post
driveshaft resonance is a real deal on some busses.. im noit sure which bus ECCB is referring to..is it yours or someone elses?



My Superior had driveshaft resonance even after I rebuilt and re-balanced and rephased the driveshafts.. it occured when the driveshaft speed hit about 3200 RPM or so.. now ive re-geared the bus to a 4.78 gear and its gone.. even at 65 the driveshaft speed is only at 2600-2700 or so.. hard to tell exactly since that bus has an AT540.. im guessing if I ran the bus up to 80 it would come back.. (not that I want to drive a 42 year old bus at 80 MPH so i wont... )....


that bus is a gasser.. there is no "growl" to its engine, its engine is rather quiet..


-Christopher
Whatever's going on in Native's bus is engine related in some way.

Sam- can you make a one minute video and put it on YouTube?
You guys have to experience this to fully appreciate it. Its WILD.
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Old 12-16-2019, 10:24 AM   #40
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Looking fwd to hearing the sound (cause I like a puzzle!) on youtube...
So hard to go by a verbal description sometimes...

At least you know nothing is seriously wrong with the driveshaft components -- I would not want to experience drive shaft breaking on a bus...

It's also sounding (sorry for the pun...) like there might be two things going on at once...

But if you're back in TX that's a good thing.
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