2021 Ram 1500 Classic 5.7 / ZF8 — Low-speed moan/resonance around 1,400 RPM after upshifts. Normal?

[BlingRam]

I have a 2021 Ram 1500 Classic Tradesman 5.7 Hemi with the ZF 8-speed, around 141k miles.

The transmission shifts great... no clunks, slipping, harsh shifts, delayed engagement, flare, or shudder. Honestly, it shifts so well that I’d imagine a new ZF8 would feel about the same.

The only thing I’m trying to identify is a brief low-speed “moan / resonance / hum / waaaah” noise that seems to happen mostly right after low-speed upshifts, usually around 15–25 mph. It seems to happen right around or just below 1,400 RPM, especially after shifting into the lower gears — maybe 2nd, 3rd, possibly 4th.

A few observations:

- It is not really a clunk, grind, or harsh mechanical noise.
- It sounds more like a low-RPM resonance/moan/drone.
- It seems RPM/load related more than speed related.
- It usually happens briefly after an upshift under light throttle.
- Tow/Haul mode mostly eliminates it, probably because it keeps the RPMs higher.
- I did hear it very briefly one time in Tow/Haul around 20 mph, but it was rare and hard to reproduce.
- Once fully warmed up, I mostly only noticed it briefly around 15 mph in normal driving mode.
- Shifting still feels excellent.

I’m doing a pan/filter + fluid service soon with the correct Mopar/ZF fluid today. Probably just drain & refill...

My questions:

(1) Is this low-RPM moan/drone around 1,400 RPM a normal/common Hemi/ZF8 resonance?
(2) Could this be MDS, torque-converter lockup, exhaust drone, or low-RPM lugging?
(3) Has anyone else had this mostly disappear in Tow/Haul mode?
(4) Any known heat shield, Y-pipe, exhaust clamp, transmission mount, or crossmember areas that commonly resonate around this RPM?
(5) If your truck does this, did fluid service change it at all, or is it just normal behavior?

I’m ultimately trying to determine whether this is a common/normal annoyance or something that points to a developing transmission/torque-converter issue. Since the truck shifts great and Tow/Haul mostly changes/eliminates the noise, I’m leaning toward low-RPM resonance/lugging/converter/MDS/exhaust drone rather than an actual transmission failure.

In searching forums for this noise, tho, I've only come across issues regarding higher RPMs and speeds, and usually a higher pitched noise (screech?), which doesn't sound like the same issue. So I’d really appreciate any input from others with the same truck/powertrain that might know what my specific issue could be, or where I should be looking.

 

[mdc1990zr1]

I have a 2021 Ram 1500 Classic Tradesman 5.7 Hemi with the ZF 8-speed, around 141k miles.

The transmission shifts great... no clunks, slipping, harsh shifts, delayed engagement, flare, or shudder. Honestly, it shifts so well that I’d imagine a new ZF8 would feel about the same.

The only thing I’m trying to identify is a brief low-speed “moan / resonance / hum / waaaah” noise that seems to happen mostly right after low-speed upshifts, usually around 15–25 mph. It seems to happen right around or just below 1,400 RPM, especially after shifting into the lower gears — maybe 2nd, 3rd, possibly 4th.

A few observations:

- It is not really a clunk, grind, or harsh mechanical noise.
- It sounds more like a low-RPM resonance/moan/drone.
- It seems RPM/load related more than speed related.
- It usually happens briefly after an upshift under light throttle.
- Tow/Haul mode mostly eliminates it, probably because it keeps the RPMs higher.
- I did hear it very briefly one time in Tow/Haul around 20 mph, but it was rare and hard to reproduce.
- Once fully warmed up, I mostly only noticed it briefly around 15 mph in normal driving mode.
- Shifting still feels excellent.

I’m doing a pan/filter + fluid service soon with the correct Mopar/ZF fluid today. Probably just drain & refill...

My questions:

(1) Is this low-RPM moan/drone around 1,400 RPM a normal/common Hemi/ZF8 resonance?
(2) Could this be MDS, torque-converter lockup, exhaust drone, or low-RPM lugging?
(3) Has anyone else had this mostly disappear in Tow/Haul mode?
(4) Any known heat shield, Y-pipe, exhaust clamp, transmission mount, or crossmember areas that commonly resonate around this RPM?
(5) If your truck does this, did fluid service change it at all, or is it just normal behavior?

I’m ultimately trying to determine whether this is a common/normal annoyance or something that points to a developing transmission/torque-converter issue. Since the truck shifts great and Tow/Haul mostly changes/eliminates the noise, I’m leaning toward low-RPM resonance/lugging/converter/MDS/exhaust drone rather than an actual transmission failure.

In searching forums for this noise, tho, I've only come across issues regarding higher RPMs and speeds, and usually a higher pitched noise (screech?), which doesn't sound like the same issue. So I’d really appreciate any input from others with the same truck/powertrain that might know what my specific issue could be, or where I should be looking.

Always start with a fluid change. If the pan has to come off, change the filter too.
My 3500 had a slight delayed disengage at a stop light. Changed the fluid and it was noticeably better. Did another fluid drop with filter and added Lubegard shutter fix and problem seems to have vanished. This was at the tail end of a 50k exchange. My 2500 had a slight flare in the morning that seemed to fade as the transmission temperature rose. Fluid change reduced this considerably. Did another fluid drop but no filter change. No flare detected now. Added some red bottled Lubegard and all is good. The fluid changed out was Maxlife and only had about 15K on it since last full service. I don’t seem to care for the Maxlife or universal fluid as a lot have shown here. I still try to get OEM fluid or Mobil approved dedicated fluid whenever possible. I think the dedicated fluid without all the unnecessary additives seems to be a better/tighter fluid for the application. Just my experience

 

[RamDiver]

I have a 2021 Ram 1500 Classic Tradesman 5.7 Hemi with the ZF 8-speed, around 141k miles.

The transmission shifts great... no clunks, slipping, harsh shifts, delayed engagement, flare, or shudder. Honestly, it shifts so well that I’d imagine a new ZF8 would feel about the same.

The only thing I’m trying to identify is a brief low-speed “moan / resonance / hum / waaaah” noise that seems to happen mostly right after low-speed upshifts, usually around 15–25 mph. It seems to happen right around or just below 1,400 RPM, especially after shifting into the lower gears — maybe 2nd, 3rd, possibly 4th.

A few observations:

- It is not really a clunk, grind, or harsh mechanical noise.
- It sounds more like a low-RPM resonance/moan/drone.
- It seems RPM/load related more than speed related.
- It usually happens briefly after an upshift under light throttle.
- Tow/Haul mode mostly eliminates it, probably because it keeps the RPMs higher.
- I did hear it very briefly one time in Tow/Haul around 20 mph, but it was rare and hard to reproduce.
- Once fully warmed up, I mostly only noticed it briefly around 15 mph in normal driving mode.
- Shifting still feels excellent.

I’m doing a pan/filter + fluid service soon with the correct Mopar/ZF fluid today. Probably just drain & refill...

My questions:

(1) Is this low-RPM moan/drone around 1,400 RPM a normal/common Hemi/ZF8 resonance?
(2) Could this be MDS, torque-converter lockup, exhaust drone, or low-RPM lugging?
(3) Has anyone else had this mostly disappear in Tow/Haul mode?
(4) Any known heat shield, Y-pipe, exhaust clamp, transmission mount, or crossmember areas that commonly resonate around this RPM?
(5) If your truck does this, did fluid service change it at all, or is it just normal behavior?

I’m ultimately trying to determine whether this is a common/normal annoyance or something that points to a developing transmission/torque-converter issue. Since the truck shifts great and Tow/Haul mostly changes/eliminates the noise, I’m leaning toward low-RPM resonance/lugging/converter/MDS/exhaust drone rather than an actual transmission failure.

In searching forums for this noise, tho, I've only come across issues regarding higher RPMs and speeds, and usually a higher pitched noise (screech?), which doesn't sound like the same issue. So I’d really appreciate any input from others with the same truck/powertrain that might know what my specific issue could be, or where I should be looking.

What is the service and maintenance history on the tranny?

When was the last fluid & filter change?
Any regular towing or heavy loads?

ZF calls for a fluid & filter change at 50K-70K miles, depending on the use.
If this is the first fluid & filter change at 141K miles, that might explain the noise.

Can you upload a video with sound to YouTube, and post a link?

Be sure to follow the ZF fluid measurement protocol or print it and provide it to whoever does the work.

Specifically take note that the tranny pan should be levelled, not the truck.
This will require raising the rear end about 8-10" and placement on jackstands to follow the runup routine.

If you search the threads, there are several reports on this task.




.

 

[BlingRam]

I wish I was able to actually do all this myself. I mean, I COULD, and I'd PREFER to do it myself, but I just don't have the time. Took it to the dealer and their master tech AT LEAST currently identified the nois I was experiencing... which was a section of exhaust pipe about half way down the truck. Has an internal baffle that's probably falling apart, I'm guessing. But tapping that certain section of pipe definitely gave a similar note.

Unfortunately, the master tech has "never heard of the transmission pan on these ZF transmissions needing to be level".... in all his years... Of course he knows better than the manufacturer, right?

Why must a customer need to show a master tech the proper way to fill this transmission?

 

[RamInfo]

Hold on…before you jump into tranny maintenance/diagnostics…have you used the +- gear buttons to lock out 8th gear/disable MDS and drove the truck that way for a day or two? Your noise sounds to me like a MDS noise possibly being amplified via exhaust or something else. I mean, you’re due for trans fluid/filter service anyway but before going into that I’d want to verify it’s not something minor like MDS noise.
Just a thought,
RI

 

[Randy Grant]

It could also be the idler/tensor pullies and/or including the serpentine belt. Google it before you break into the tranny(sorry, I'm old school)and break the bank chasing a noise with a cheaper cure.

 

[RamDiver]

While I may not have high expectations of the transmission being the source of this noise, if the tranny meets the ZF criteria for a new filter and fluid, why not just get it done?

The noise may or may not be a critical issue, but to my way of thinking, having to pay out of pocket for a new tranny would be a hit to my finances.

Throughout my working career, whenever approaching a complex electronics related issue that doesn't have a clear solution, I've seen a constant reminder of the benefits of completing the easy required and not necessarily critical repairs first.

This is a SOP to reduce the unknown variables and frequently you get lucky.
At least this has been my experience.

It's not like we should ignore the transmission maintenance because Stellantis chooses to call it sealed or lifetime magic Unicorn oil.

.

 

[pacofortacos]

Hold on…before you jump into tranny maintenance/diagnostics…have you used the +- gear buttons to lock out 8th gear/disable MDS and drove the truck that way for a day or two? Your noise sounds to me like a MDS noise possibly being amplified via exhaust or something else. I mean, you’re due for trans fluid/filter service anyway but before going into that I’d want to verify it’s not something minor like MDS noise.
Just a thought,
RI

this^^

Also with that many miles, it could be a motor/transmission mount wearing out - just another simple thing to check.

Not sure what internal exhaust baffle they are talking about, unless the later models have an internal muffler baffle like the 6.4 muffler does???

 

[BlingRam]

Not the "muffler", per se.... but he took a screwdriver handle and tapped a forward front section of the exhaust pipe.... no noise... kept tapping as he moved backwards... and then there was maybe a 3 ft. section of pipe that had a little "rattle" inside... seems that the 1.4k RPM vibration activates that exhaust "note". Could very well be MDS, also, around that RPM? I'll have to play around with it some more in Tow/Haul mode, etc.... but I'm definitely not as concerned with it as before he showed me that section of pipe.

Transmission filter already replaced and got a drain and refill. It was definitely time.

 

[RamDiver]

Transmission filter already replaced and got a drain and refill. It was definitely time.

Did they follow the ZF fluid measurement protocol as shown on the green sheet posted above?

.