Aisin 2nd Gear RPM Sag

[davi9]

Hi everyone,

So I bought my first Cummins a couple of months ago (2019 3500 Aisin).

I’m loving the truck, but shortly after driving it off the lot, I started to notice a slight sag of about 100 RPM part way through 2nd gear.

With constant throttle, the transmission shifts from 1st to 2nd just fine, then as the RPMs are climbing in 2nd, there’s a sag of about 100 RPM (e.g. drops from about 1600 to 1500 RPM) and then it keeps climbing a few more hundred RPM before shifting to 3rd gear.

There isn’t any flare, i.e. whenever the RPMs are climbing there’s torque being applied to the wheels.

However, there is a noticeable loss of torque (jerky feeling) when the RPMs are sagging that 100 RPM part way through 2nd gear.

The transmission then behaves normally through the rest of the gears.

It seems that the sag/jerkiness is more pronounced when the engine/transmission are cold, but the behaviour is generally always there.

It doesn’t seem to make a difference if I’m in normal or tow/haul mode. I posted a video of it on YouTube (see link below) to hopefully help everyone understand what I’m describing.

I took my truck into the dealership to look at this about a month ago when it had about 3500km (2200 mi) on the odometer.

They flashed my aisin TCM with the latest update, and did a quick re-learn, but there was no change to the ~100RPM sag in 2nd gear afterwards.

They told me that it’s behaving normally, and the RPM sag is the result of Ram’s attempt at softening the shift from 2nd to 3rd.

Something about the jerky nature of it just doesn’t feel right, so I thought I’d seek advice from this forum prior to taking it back to the dealership to ask for further warranty work.

Is this actually ‘normal’ behaviour for these aisin transmissions?

Any input, thoughts, or advice would be very much appreciated!

Thanks in advance!

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[AK Bob]

I don’t recall ever noticing this phenomenon you are describing, but will test drive and look for it tomorrow and report back with results.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon auxiliary fuel tank.

Sent from my iPad using Tapatalk

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[Aboshan]

I have a 2018 with the Aisin and haven't noticed what you are experiencing. I watched your video and kept an eye on mine as I drove low speed through town before getting on the freeway. At first I thought you might be getting into converter lock but after watching it a few more times it looks like the de-fuel the Aisin needs to shift is kicking in at an odd time.

I don't trust dealers when they say something is acting normally. I am dealing with a recurring battery issue on my wife's Cherokee and we put it in for warranty a 3rd time in 6 months. She picked it up from a while I was at work. The tech flat out lied to her about what the issue was with the battery. I would get with a reputable diesel shop and see what they think. I hope you get it figured out.

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[Tugvi]

I don’t recall ever noticing this phenomenon you are describing, but will test drive and look for it tomorrow and report back with results.

2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon auxiliary fuel tank.

Sent from my iPad using Tapatalk

I have never seen it either but starting in 2019 the aisin has new hardware/programmer/controller. They tried to make it a more daily driver trans with softer shifts due to complaints.

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[Aj Grubb]

That looks like torque converter lock up to me... which would be normal. But its hard to tell from the video, cant really hear or feel what's going on.

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[davi9]

Thanks for the input guys. It would be interesting to hear from others with a 2019+ aisin to see if may actually be normal behaviour as a result of Ram trying to soften the shifting in the TCM...

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[davi9]

I have a 2018 with the Aisin and haven't noticed what you are experiencing. I watched your video and kept an eye on mine as I drove low speed through town before getting on the freeway. At first I thought you might be getting into converter lock but after watching it a few more times it looks like the de-fuel the Aisin needs to shift is kicking in at an odd time.

I don't trust dealers when they say something is acting normally. I am dealing with a recurring battery issue on my wife's Cherokee and we put it in for warranty a 3rd time in 6 months. She picked it up from a while I was at work. The tech flat out lied to her about what the issue was with the battery. I would get with a reputable diesel shop and see what they think. I hope you get it figured out.

Sorry to hear about the battery issue!

Yeah, I’m wondering if there’s something causing it to de-fuel twice as it’s preparing to shift from 2nd to 3rd.

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[davi9]

That looks like torque converter lock up to me... which would be normal. But its hard to tell from the video, cant really hear or feel what's going on.

Does the torque converter lock at a set RPM or does it lock at a set vehicle speed?

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[Aj Grubb]

I think the algorithm that controls torque converter lock up is more complicated than just speed or RPM.

I think it is based off of various parameters.

Engine load, throttle position, transmission fluid temperature, road speed, rpm, tow haul mode or not maybe more.

Once warmed up if accelerating through the gears in a similar fashion under similar conditions you should experience the lock up in approximately the same way every time.

In other words it should be repeatable.

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[davi9]

I think the algorithm that controls torque converter lock up is more complicated than just speed or RPM.

I think it is based off of various parameters.

Engine load, throttle position, transmission fluid temperature, road speed, rpm, tow haul mode or not maybe more.

Once warmed up if accelerating through the gears in a similar fashion under similar conditions you should experience the lock up in approximately the same way every time.

In other words it should be repeatable.

This makes sense.

Thanks for the response!

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