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Old 12-08-2019, 11:05 PM   #1
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CAT 3126 with a nasty GROWL

We have made our first "skoolie' use of our bus. We moved close to 8000 pounds of garage items from Texas to Florida. Empty curb weight right after taking all but the driver seat out was 16,960 pouds. After filling it up for the trip it was 2,100 pounds with the GVWR at 30,000 pounds. All this is the preamble for the thread.


While driving to Florida, I noticed the engine would make a very loud noise between 1800 RPM and 2150 RPM (55 MPH to 60 MPH). It sounded like we were in a huge kettle drum and the entire orchestra was beating on it with 10 pound mallots. Once the speed rose past 2150 RPM (60 MPH) ... perhaps 2200 RPM (around 61 MPH) it quieted right up. Below 1800 RPM (55 MPH) it was also relatively quiet. It did not do this when empty (or so I thought) or when loaded in 4th. It only happened (or was most pronounced) in 5th (overdrive).


Once the bus was empty again, it was quieter in the "GROWL" range ... but since I now know it does it, I can detect a little growl in the range when not loaded. When empty, it is not noticeable in 1st, 2nd, or 3rd and it was only very slightly noticeable in 4th with a little more easily detectable in 5th (O.D.) When loaded, it was not detectable in 1st, 2nd, or 3rd and was slightly detectable in 4th.



Side note: The Beast does not seem to have as much PEP as she did 3 years ago. It takes a long time to accelerate wheras it was realatively quick off the starting blocks when we got it 3 years ago.


Any ideas what might be causing this GROWL?
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Old 12-08-2019, 11:20 PM   #2
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Can you reproduce the noise in Neutral?

I've heard that the 3126 can have lifter failures that ruin the cam.
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Old 12-08-2019, 11:26 PM   #3
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Can you reproduce the noise in Neutral?

I've heard that the 3126 can have lifter failures that ruin the cam.
I will have to try to rev it up tomorrow. However, I do not remember it ever doing it in neutral.
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Old 12-09-2019, 01:23 AM   #4
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Better yet make a video, post it to youtube and then post the link of the video here....
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Old 12-09-2019, 05:09 AM   #5
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As for the lack of pep, when was the fuel filter last changed? On a diesel with low power issues, that is my *Absolute* first question and the most common cause.


As for the growl, are you *Sure* it's the engine itself? Seems like it would be at that RPM range regardless what gear it's in, or park/neutral. My first thought is check your driveshaft, U-joints and carrier bearings. You want almost *ZERO* slack in the driveshaft (some carrier bearings have rubber mounts which allow a bit of up/down, side/side movement, replace is the rubber is deteriorated). A deflated air suspension has also been known to cause similar issues (as well as a harsh ride).


I had a truck with a *Severe* vibration between 50-55 MPH and turned out the "tabs" that aligned the wheel on the front hub were broken and it was off-center (hub piloted wheel) (this can happen if the nuts aren't tight enough and a hard bump is hit).
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Old 12-09-2019, 07:16 AM   #6
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I too think of u joints or other driveshaft issue in this case. This is the classic early warning signs of a u joint on its way out.
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Old 12-09-2019, 07:19 AM   #7
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a "growl" nbased on throttle? meaning is it an engine growl like you "crowd it" giving it throttle when the transmission is locked up in gear and RPMs are low... thats called Lugging and it is Noisy.. esp in a HEUI engine.. or is this speed related like others mentioned a hum or howl in the driveshafts (which change speed with vehicle speed )..


my 444E will growl pretty good if I lug it... (hard on the engine to lug)..
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Old 12-09-2019, 07:20 AM   #8
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I too think of u joints or other driveshaft issue in this case. This is the classic early warning signs of a u joint on its way out.
Ronnie REALLY knows his stuff when it comes to U-joints! He found my bad one that I couldn't find.
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Old 12-09-2019, 10:49 AM   #9
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s trip.

Quote:
Originally Posted by Ronnie View Post
I too think of u joints or other driveshaft issue in this case. This is the classic early warning signs of a u joint on its way out.
The entire drive shaft (from transmission yolk to differential input) was rebuilt about 300 miles before this trip.
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Old 12-09-2019, 10:53 AM   #10
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a "growl" nbased on throttle? meaning is it an engine growl like you "crowd it" giving it throttle when the transmission is locked up in gear and RPMs are low... thats called Lugging and it is Noisy.. esp in a HEUI engine.. or is this speed related like others mentioned a hum or howl in the driveshafts (which change speed with vehicle speed )..


my 444E will growl pretty good if I lug it... (hard on the engine to lug)..
It does it ONLY in that RPM range. Of course, it is much easier to lug it in overdrive and less so in 4th. In 1st through 3rd, I am not hearing it much at all (if I can hear it at all). The BlueFire shows 100% load and 100% torque when in this noise growl range, which lends to lugging. I have not heard it at other speeds, perhaps due to not getting it heavily loaded.
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Old 12-09-2019, 10:59 AM   #11
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yep thats lugging.. thats the way my 444E sounds if i lug it... and it growls pretty good.. and ill show 100% load
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Old 12-09-2019, 11:02 AM   #12
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Originally Posted by Brad_SwiftFur View Post
As for the lack of pep, when was the fuel filter last changed? On a diesel with low power issues, that is my *Absolute* first question and the most common cause.
The last fuel filter change was about 400 miles prior to this trip. However, I have seen the "water in fuel" light come on for a moment, then go away. Each time this happens, I notice a little debris in th water separator bowl. Thank you for reminding me that I need to clean that out!


Quote:
Originally Posted by Brad_SwiftFur View Post
As for the growl, are you *Sure* it's the engine itself? Seems like it would be at that RPM range regardless what gear it's in, or park/neutral. My first thought is check your driveshaft, U-joints and carrier bearings. You want almost *ZERO* slack in the driveshaft (some carrier bearings have rubber mounts which allow a bit of up/down, side/side movement, replace is the rubber is deteriorated). A deflated air suspension has also been known to cause similar issues (as well as a harsh ride).
I am *pretty* sure it is not the driveshaft as it was rebuilt and balanced (by a driveline shop) also about 300 miles before the trip. Thinking about it, perhaps it was 500 miles.


Quote:
Originally Posted by Brad_SwiftFur View Post
I had a truck with a *Severe* vibration between 50-55 MPH and turned out the "tabs" that aligned the wheel on the front hub were broken and it was off-center (hub piloted wheel) (this can happen if the nuts aren't tight enough and a hard bump is hit).
Funny you mentioned this. On the trip, I noticed a FRESH wear pattern in the passenger steer tire. I did not feel any vibration in the steering though.
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Old 12-09-2019, 11:05 AM   #13
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The entire drive shaft (from transmission yolk to differential input) was rebuilt about 300 miles before this trip.
Who did the work? (eh, that doesn't really matter...)

After years of maintenance I've come to not believe in coincidence...

Did you have this growl before the driveshaft work? Did you test drive before the trip to where you might have noticed a change after the driveshaft work?

Confirm all the drive shaft sections are properly indexed. A U-joint out of index will cause vibration issues. Maybe that's what you're hearing...

Next test drive feel all the U-joints -- they should all be the same temp (the one closest to the tranny will probably be warmer...) but none should be too hot to touch -- same for the carrier bearings -- if one of these parts feels warmer than the others I'd suspect it...
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Old 12-09-2019, 11:31 AM   #14
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Who did the work? (eh, that doesn't really matter...)

After years of maintenance I've come to not believe in coincidence...

Did you have this growl before the driveshaft work? Did you test drive before the trip to where you might have noticed a change after the driveshaft work?

Confirm all the drive shaft sections are properly indexed. A U-joint out of index will cause vibration issues. Maybe that's what you're hearing...

Next test drive feel all the U-joints -- they should all be the same temp (the one closest to the tranny will probably be warmer...) but none should be too hot to touch -- same for the carrier bearings -- if one of these parts feels warmer than the others I'd suspect it...
I really have no reference. This is the first time it was heavily loaded, so I really did not notice it before. Thinking back to just before the trip, there were a few points where it made the thundering growl when it was at 100% load and 100% torque ... like on an incline. Those times were very brief and always abated when I let off of the accelerator. Same with the trip load ... if I backed off of the accelerator, the noise reduced significantly. While on the trip, I would get up to the low end of the growl range and wait for a downhill slope and accelerate through the growl range to the quiet beyond. If in the quiet range and an incline approached, I would lighten up the on accelerator while climbing and let it drift back down below the growl range and hold it just below the growl range until another flat to downhill area. It is a heck of a way to travel!
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Old 12-09-2019, 11:44 AM   #15
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I really have no reference. This is the first time it was heavily loaded, so I really did not notice it before. Thinking back to just before the trip, there were a few points where it made the thundering growl when it was at 100% load and 100% torque ... like on an incline. Those times were very brief and always abated when I let off of the accelerator. Same with the trip load ... if I backed off of the accelerator, the noise reduced significantly. While on the trip, I would get up to the low end of the growl range and wait for a downhill slope and accelerate through the growl range to the quiet beyond. If in the quiet range and an incline approached, I would lighten up the on accelerator while climbing and let it drift back down below the growl range and hold it just below the growl range until another flat to downhill area. It is a heck of a way to travel!
inter-web diagnosis is sketchy at best...

As said if you could post a video/audio that would be very helpful.

a carrier bearing will howl or growl if it's dry, out of alignment, etc. -- and it will run hot compared to the others...

Any change in eng oil pressure? Hot idle pressure now lower than you remember from a year ago?
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Old 12-09-2019, 11:55 AM   #16
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I've got the same engine and chassis but a 545 instead of Sam's 2000. He's coming over later this week and we can compare my smooth quiet bus against his.
Mine does have some driveline shake at 55-70 but its likely due to a ujoint that needs to be replaced.
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Old 12-09-2019, 01:46 PM   #17
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fully loaded and apparently a crappy allison-engine link results in lugging... the allison is likely built to shift off the TPS and not off the true need to shift.. (and people wonder why I custom build my busses)... the result is step on the pedal a little harder and force it to drop down a gear and let uip lightly to get the loading below 90% and it likely wont growl as loud.. if said sound is the engine...
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Old 12-09-2019, 09:15 PM   #18
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Quote:
Originally Posted by banman View Post
inter-web diagnosis is sketchy at best...

As said if you could post a video/audio that would be very helpful.

a carrier bearing will howl or growl if it's dry, out of alignment, etc. -- and it will run hot compared to the others...

Any change in eng oil pressure? Hot idle pressure now lower than you remember from a year ago?
I do appreciate all of the comments we have received from everyone on this topic!


The vehicle is empty now, so a video would be marginally useful. I will see about doing so the next time we take it on the highway.


The engine oil pressure stays at about 42 PSI while cruising. I have seen it as low as 35 PSI at idle and hot.
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Old 12-09-2019, 09:35 PM   #19
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fully loaded and apparently a crappy allison-engine link results in lugging... the allison is likely built to shift off the TPS and not off the true need to shift.. (and people wonder why I custom build my busses)... the result is step on the pedal a little harder and force it to drop down a gear and let uip lightly to get the loading below 90% and it likely wont growl as loud.. if said sound is the engine...
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.
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Old 12-09-2019, 10:27 PM   #20
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I do appreciate all of the comments we have received from everyone on this topic!


The vehicle is empty now, so a video would be marginally useful. I will see about doing so the next time we take it on the highway.


The engine oil pressure stays at about 42 PSI while cruising. I have seen it as low as 35 PSI at idle and hot.
Mine's only around 15 at idle hot. Maybe 20. Hard to remember but I know not anywhere near 35.
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