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Old 10-10-2020, 07:16 AM   #1
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Shuddering under load

Hi folks, I have a 2018 Thor Venetian with the ISL 9 and Allison 3000 trans. I bought the coach new and I have always had a recurring problem with the coach shuddering under hard acceleration. The coach cannot be run with the trans “mode” engaged without shuddering at every acceleration, usually from a stop or going up a hill. Without “mode” engaged, the issue is not as frequent but will happen when I am towing a trailer or my toad.
Freightliner has looked at the coach twice and said that the computer says everything is fine, but they did flash the transmission once. Fuel filters have been changed twice with no improvement.
The shudder is very similar to my old Monaco Diplomat ISL 8.9 when the fuel filters were dirty.
Has anyone run into this issue, or have any other ideas on what I can try? I am still under power train warranty, and the coach has about 13,000 miles now.
Thanks
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Old 10-10-2020, 07:39 AM   #2
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It could be binding somewhere in the drive line, e.g., the drive shaft or differential. A cheap and easy thing to try is greasing the drive shaft to see if it makes any difference.
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Old 10-10-2020, 07:47 AM   #3
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Ride height effects the drive shaft angles and bad angles can cause vibration.

Out of phase universal joints, again on the drive shaft, can also cause vibration.

Axle wrap, the twisting of the axle in its mounts, also change drive shaft angles. That will be more pronounced under load, like accelerating.
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Old 10-10-2020, 08:02 AM   #4
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my bet is rear ride height and drive line alignment or phase. fl should check that first.


followed by lack of lubrication on ujoints and slip joint. they are required to be greased often. mine is every year.
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Old 10-10-2020, 08:13 AM   #5
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Yup, start by verifying RIDE HEIGHT is at spec.


Also, using the Allison shift pad, check for DIAGNOSTIC CODES.
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Old 10-10-2020, 08:18 AM   #6
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Shuddering under load

Does it shudder when it shifts? or between shifts? or does the gear change not effect when shudder occurs?
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Old 10-10-2020, 03:46 PM   #7
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Does it shudder when it shifts? or between shifts? or does the gear change not effect when shudder occurs?


It seems to happen most often in 3rd gear, rpm’s below 1600, but I have noticed it in 2nd through 4th gears. It doesn’t happen during a shift, more like the engine is bogging down while holding the gear. If I push the accelerator to the floor it will downshift and the shudder stops.

The drive shaft has been greased multiple times. I have not yet checked phase or ride height, but outside of heavy acceleration it drives just fine.
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Old 10-10-2020, 04:26 PM   #8
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Shuddering under load

Quote:
Originally Posted by NCVenetian18 View Post
It seems to happen most often in 3rd gear, rpm’s below 1600, but I have noticed it in 2nd through 4th gears. It doesn’t happen during a shift, more like the engine is bogging down while holding the gear. If I push the accelerator to the floor it will downshift and the shudder stops.

The drive shaft has been greased multiple times. I have not yet checked phase or ride height, but outside of heavy acceleration it drives just fine.


That sounds more like a low-rpm engine miss than a transmission shudder. Unless it’s low throttle pressure related and I don’t know enough about Allison transmissions to know if the internal clutch-pack holding pressures are throttle-position regulated.
Was an issue with AOD Fords.

If more throttle pressure makes it go away I would surely apply more throttle. A shudder is not good and neither is lugging your engine. These truck diesel engines were designed to run at or near WOT most of their lives... you won’t hurt it.
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Old 11-30-2020, 11:52 AM   #9
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Quote:
Originally Posted by NCVenetian18 View Post
It seems to happen most often in 3rd gear, rpm’s below 1600, but I have noticed it in 2nd through 4th gears. It doesn’t happen during a shift, more like the engine is bogging down while holding the gear. If I push the accelerator to the floor it will downshift and the shudder stops.

The drive shaft has been greased multiple times. I have not yet checked phase or ride height, but outside of heavy acceleration it drives just fine.
Torque converter clutch shutter, My 2019 does it 5th gear when the converter applies at about 35 mph.

So when the converter clutch is commanded to apply there is not enough pressure to prevent slippage and you will get a shudder feeling that goes away with a down shift.

The torque converter locks after each shift and unlocks before each shift.

If the transmission fluid and filter have not been serviced I would start there and also alert the tech to check for Torque converter shudder they will have a better Idea where to look

Ted.
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Old 11-30-2020, 06:09 PM   #10
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Read my post from a couple of months ago. My shudder was primarily from a dead stop but its easy to check for drive shaft phasing.

https://www.irv2.com/forums/f26/vibr...ed-507196.html

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Old 12-01-2020, 09:46 AM   #11
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One key to the issue, IMO, is your mention of “mode” and the effect it had on the shudder.

The trans is in Performance mode on start up. That causes the trans to downshift sooner under heavy throttle to keep rpms up. In economy mode, the trans will not downshift, even at wide open throttle, until the engine drops to peak torque rpm, or sometimes 200 rpm lower than performance mode, under certain conditions. This downshift delay can cause the engine to lug and a shudder. On acceleration from a stop, Eco mode will upshift sooner under WOT. Again, a rapid upshift can cause lugging and a shudder.
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