6.4 Hemi Powertrain Bucking/Jolting

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xbowhunter86

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2015
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6.4 Hemi
I have a 2015 2500 CC 6'4" bed with a 6.4 Hemi, 66RFE, 3.73 rear and floor shift transfer case. 44k on the odometer.

The truck will buck / jerk during acceleration after slowing down to 15-20 mph. The issue will occur when I accelerate after slowing to 15-20mph to make a turn or slow down to let a vehicle I am following turn off. The truck will buck/jolt after I start accelerating until it downshifts. It totally clears up after it downshifts and never does it taking off from a stop. Only in the slow down reaccelerate scenario. It is much more excessive that just a vibration. It will do it both on a straight away or after a turn and on dry roads as well. The tires are not breaking loose or losing traction.

I have been working with the dealer on the issue for over a year. They replaced the torque converter twice. Replaced the engine mounts because the dealer and Ram star team thought it could be the MDS. Nothing has fixed the issue. Now I am being told it is from the SureTrac rear end and it is "functioning as designed." I am not able to get a clear answer as to what is creating the bucks/jolts or why it only does it until it downshifts.

I am also concerned about the long term effects this is having on the powertrain and the rest of the truck not to mention the discomfort when it occurs. There is days it occurs 6+ times during normal driving.

Has anyone experience something similar?
 

Ratket

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I bet it’s the transmission and the software for the transmission. The transmission probably can’t decide if it wants to down shift or not. See the cumin’s has enough torque it doesn’t need to down shift, but our 6.4 just wants to scream and down shift. Just my thoughts on the issue.
 

Phil21502

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Yeah it's the tranny not wanting to downshift. It's the worst thing about these trucks. A tune and pedal commander made mine a lot less noticeable but it will still do it. Just use more throttle and make it downshift. It's the easiest fix
 

MN-Ram

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I have the same setup but with the turn knob 4x4. My truck has been doing it ever since I bought it. I have 52k on it now, and it still does it.

I believe it is due to the shift points being more in line for a diesel power curve. Just back off the pedal, and press down harder.

I’ve spoken to the dealership about it, and they do not seem to know anything about the issue. I’ve never had them work on the truck for that reason though.

There are other threads on here regarding that issue, but nothing has ever fixed the problem other than custom tunes that also change the shift points. That would void your warranty though.
 

pwjouster

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dealing with the issue for over a year?! you get all these new parts and no resolution?

it must just be the way these trucks are designed....i surely hate it but, if FCA says its normal, we have no choice.

the transmission downshift (downshift to 3rd) is awful and makes me cringe, if i was promised it wont degrade or shorten the life of any parts, id live.

i also have the jerk/clank on application of throttle in certain scenarios like you have described. they call it lash, i call it BS
someone needs to tune this transmission immediately. it always feels like its in tow mode.
 

mohemipar

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So you can certainly tell the way this transmission is geared in favor of the Cummins when you drive it, but I never have experienced any kind of physical bucking or jolting at any point. It shifts very smooth for me at all times. If I let off and start coasting it will usually hold the gear and just slowly start decelerating RPM using the drivetrain to slow the truck. Then when I hit the gas again it will either build RPM in the same gear or downshift. Whatever it does, it never bucks or jolts. Even if I floor it. I was actually impressed with how smooth this trans is after getting the truck. From all I read online you’d think it was a POS, but I don’t find that to be so. I don’t tow heavy in the mountains, so I can’t comment on that. But I certainly don’t baby my truck when I drive it. It ain’t no ZF 8 speed, but I find it certainly acceptable. Maybe software/programming has been tweaked over the years? Idk.
 

A.carlisle

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I have a 16 ram 2500 with the 6.4 and had the same symptoms as you are having after i bought it new. went a couple of months of the dealer trying to figure it out. They thought maybe it was something in the transmission or torque converter. The dealer ended up calling some Chrysler guru who told them what to look at, and it ended up being a bad EGR valve. Not sure if the 15s had this problem,but may be something to mention to the dealer.
 
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xbowhunter86

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Thanks guys, i am taking it back Wednesday to have the district technical advisor take a look at it.
This level of unrefinement is not acceptable in my opinion. My business partner has a 1500 5.7 with an 8 speed that shifts very smooth. Why cant they make a 6.4 with a 6 speed do the same? If this is an electronic / programming issue it seems Ram should step up to the plate and resolve it. This condition has to be hard on the mechanical components. Not something I am willing to live with long term.
 

Softe

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xbowhunter86_have the Brake Tranny Shift Interlock recall notice..they are checking the truck today to see if it needs a new locking pin for the Park position. They also will do a Body Control Module software upgrade that will help on the shifting problem descending a hill. There are other issues this upgrade will address...Egr was one that was mentioned and others...should have asked for a print out, but I didn't..going to the dealer this afternoon..
 

MasonD21

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First off, hello! I made an account just to reply to this post!

Last year I purchased a 2017 RAM Power Wagon. The first 5k miles, the transmission was really tight, but as I got closer to 7k(ish) miles, my truck started doing the "slowdown-clunk-jolt" concern. I'm a service advisor for a dealership auto group, so naturally I went looking for a TSB at our Dodge/RAM shop. TSB# 18-040-17 REV-A outlines this concern. (Legally, I was told I cannot post the actual TSB, but you can google it to find it.)

This TSB not only alleviated this concern, it also updated a lot of great characteristics of the truck overall in terms of powertrain management. Note I said "alleviated" and not "fixed or got rid of".

I will say that I loved my truck before, and I love it even more now. There was an addition in the TSB that made 4x4L a LOT more enjoyable in the way it shifts (no more long 3kRPM pulls before a 1-2 upshift, and fewer downshifts under light throttle to make for a less busy feeling transmission)

Maybe it is related to your concern, maybe it isn't. This update does not work for any 2018 trucks, but it is definitely worth inquiring about the next time you bring your truck in to the dealer for this concern!

I hope this helps!

-Mason
 

mtofell

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What you describe sounds pretty much standard to me. My truck's been operating like this for 4+ years. I can make it better or worse depending on how I drive and how hard I mash the pedal. I agree it sucks but it's just the way it is. Comparing it to a 1500 with an 8spd is irrelevant. I'm sure our trucks also shift worse than a Jaguar.

I'm astonished your dealer has done so much for you. Unless my truck is on fire my dealer says all is just fine.

I've really just learned to operate around the annoying shifting which makes much easier to live with. You can also just drive in tow/haul mode which makes it shift quicker. The pedal commander is another good option.

Maybe I'm just turning into an old guy but it gets me down the road in comfort and does what I need it to do so I'm okay. Is it perfect? Nope... but close enough.
 

ICEMANFiZ

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My 14 does same thing and just had tranny bulletproofed by custom shop. So I’d say it’s the computer causing the issue as well.


Sent from my iPhone using Tapatalk
 

MasonD21

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The bulletin applies to 6.4L trucks with the 66RFE transmission. In a nutshell, it improves shift schedule and torque converter clutch (TCC) lock-up and TCC unlock. When coasting now, the truck will hold a gear until speed drops. Once speed comes down, the transmission will gradually downshift on its own. Those downshifts with the factory flash were what was causing the drivetrain lash. After the update, downshifts feel crisper and refined, and no more slow-down-clunk noise every time (though it still happens once in awhile, more subtly, which at least makes me feel like my transmission isn't jackhammering itself and my U-joints).

MDS transitions are so much better now too. In cold mornings at only around 50-100F engine temp, the MDS would cause a hell of a TCC shudder because it would be in MDS at around 2nd gear at times, then try to shift into 3rd or 4th etc, and would feel like a bucking bronco.

Lastly, which I'm MOST pleased with (which was a secondary affect!) is the 4-Low shift schedule. Holds gears, less busy shifting under load for fewer downshifts because the TCC isn't so aggressive, and no more 1st-2nd 3kRPM slams.

For me, it was a totally different truck. I really hope this helps for those guys struggling to find a solution to the craptastic programming from the factory.
 

ol Steve

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Thanks to MasonD21 & Bobbo7915 for this TSB! I just purchased a 2014 2500 a couple of weeks ago with 85K on it. Really like the truck so far, but I've been trying to figure out the transmission. This thread & TSB makes me think i'm not just crazy. There's random bucking on occasion, but the most noticeable thing is the lugging and shift indecision. Yes, a firm boot on the gas helps it decide, but it really should be figuring out a smooth downshift long before that. Hell, the 2000 Jayco E450 motorhome I just sold figured out timely downshifts better with much less coaxing.

Fortunately, I just dropped it off tonight at the Ram dealer for some items promised at purchase. Gonna call first thing tomorrow morning and see if they'll do this TSB flash for me. Really hope this fixes what I've been feeling - I was getting worried that the transmission was on the verge of failure...not a good feeling when you just bought it!
 
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