Sudden Acceleration in Reverse

[transe]

... Just to clarify, how does any air pocket get to the pump suction side? This cannot happen in any of the previous models due to the fact the return fluid is used in the lube circuit. The 68 is different in this respect and the only way I can see this being possible is all or part of the return fluid is routed directly to the pump intake without going back to the sump. Air returned to the sump is never going to hit the pump intake at the filter so there must be some provision for routing return fluid directly to the pump, given this scenario is possible.



This begs the next question, how is sump fluid cooled if return fluid is not being constantly mixed back into it? Is the fluid path after the filter controlled by a shuttle valve that splits the flow to sump and pump intake? Thanks for the follow up and any more insight into the above question.



My whole point is this seems to be a bit of a engineering glitch. To allow an outsourced non-integral part of the transmission to generate this type of failure is not what I would expect as quality design. I have to think that air in the cooler return would have some bleed path that would not allow it into the pump inlet. That is too easy to ignore implementation of.



I beg to differ, there is frequently an rpm surge. I can't say always because of course I have not seen every possible failure, but, a 150-200 rpm surge is normal. When it jumps 500-600 rpms it is bit more disconcerting. As you pointed out, warm this never happen and if it does there are other issues. However, it is interesting to note that this condition is only possible after the engine has been off for a period of time.

Cooler return oil is routed directly into the pump suction circuit on RFE transmissions. If this fluid were returned to the sump (as you correctly point out that it was on the old RE transmissions), it would go back to zero (actually, atmospheric) pressure and would have to go back through the main sump filter to get back to the pump. On the RFE, we save the energy (residual pressure) that's in this return fluid, and we don't have to draw the entire pump feed through the main sump filter. In addition, any debris from a converter failure (or residual debris in the cooler from a previous trans failure) gets trapped in the cooler return filter, instead of getting fed into the lube circuit.



Although cooler return oil does not go directly into the sump, the pump output feeds not only the converter, but also the valve body, clutches, and lubrication. All of the oil that gets fed to these other circuits eventually ends up returning to the pan. I guess you could view the pump as having two inlets (sump, and cooler return) and two outlets (converter/cooler, and other circuits). Everything gets mixed together as it goes through the pump. So some of the oil from the sump will go to the converter/cooler, and some of the oil from cooler return will go to other circuits (and eventually back to the sump).



Yes, technically some fluctuation in engine RPM (when TCC drag occurs) is not unusual, due to undershoot/overshoot as the PCM tries to maintain the proper idle speed, but the target RPM does not increase.

 

[mwilson]

The fix is to replace the spin-on cooler return filter (P/N 05179267AC) inside the trans. For 2012 trucks, hopefully you can still get this done under warranty. If doing it yourself, use only a Mopar filter, since we have seen inadequate diaphragms on some aftermarket filters. Until you get your filter replaced, allow the truck to idle in Park for a minute or so (after a cold start) before taking off. This will allow any air to be purged before you start driving.



If you have this problem and are getting your filter replaced at a dealer (under warranty), please PM me (or post here if PM doesn't work) BEFORE you take your truck in. I will contact your dealer and arrange to get the bad filter returned to us so we can analyze it. I need to contact the dealer in advance because otherwise they will simply scrap the old filter and by the time I call them it will be too late. Please include the following info in your PM/post:

• VIN (last 8 digits)

• Dealer name

• Dealer location (city and state)

• Your name

• When you plan to take the truck in for filter replacement

Regardless of one's feeling's on the subject this gentleman is trying to help resolve this issue and he needs these filters back.



Things go wrong, vendors make mistakes. **** happens. Humans are involved.

Right now I have a brand new Cascadia truck in the body shop with the roof completely removed. The part number for the replacement roof was superceded incorrectly by a planner at Daimler so the new roof we have does not fit. Daimler has mobilized every resource for us and we should have the correct roof within a week. Point is that they stepped up just like this man is doing.



PLEASE DO AS HE MENTIONS ABOVE IF YOU TAKE YOUR TRUCK TO THE DEALER FOR THIS. HE NEEDS TO BE INVOLVED FROM THE FIRST CONTACT.



Print this thread and lug it in to the Service Desk with you and show the instructions to the dealer.



Take it from me just how valuable this both for you and future owners.



Mike.

 

[PC12Driver]

Pay attention, you might learn something. You haven't been around CR engines long enough to understand their operation if you believe that.

Which was in response to my quote...

There was never an increase in RPMs.

... which was based on this...

I had the presence of mind to look at the tach, and did not see a rise in RPM.

... and this...

The engine speed does not increase. The PCM merely increases fueling to maintain the correct idle speed, which produces more driveline torque and requires the driver to apply more brake pressure to hold the truck.

Pretty sure I didn't misread those. You're the only one that claims an increase in rpm in this particular case. By any chance, do you own a Prius?

 

[cerberusiam]

Cooler return oil is routed directly into the pump suction circuit on RFE transmissions. On the RFE, we save the energy (residual pressure) that's in this return fluid, and we don't have to draw the entire pump feed through the main sump filter.

Thank you, that brings the complete picture into focus.



Are there any revisions to the return circuit in progress that would negate the cascade effect of a drain back failure?



How much pressure is in the return circuit and how is it regulated?

 

[cerberusiam]

Pretty sure I didn't misread those. You're the only one that claims an increase in rpm in this particular case.

Woops! Need a few napkins there to wipe the egg of your face.



ANY load at idle is going to produce an rpm variation. Whether or not the operator sees it, the ECM reports it, is moot. The drop and flare is noticeable to a trained ear and frequently part of the complaint.

Yes, technically some fluctuation in engine RPM (when TCC drag occurs) is not unusual, due to undershoot/overshoot as the PCM tries to maintain the proper idle speed, but the target RPM does not increase.

 

[PC12Driver]

Woops! Need a few napkins there to wipe the egg of your face.

ANY load at idle is going to produce an rpm variation. Whether or not the operator sees it, the ECM reports it, is moot. The drop and flare is noticeable to a trained ear and frequently part of the complaint.

True, the potential for a +/-100 rpm fluctuation would be there as the governor did its business. I think most folks would call that negligible, as this wouldn't even equate to a mph difference in a gear as low as reverse.

Um, yeah, you're right, what was I thinking... ? Boy do I feel silly... ?

 

[TWood]

GBlaksley,

What is the latest? Any updates? Did you take it to the dealer?



cerberusiam

pc12driver,



You both have some good input but

You two guys need to get together and have a beer. Maybe you could talk about your amazing ability to behave like children.

 

[TWood]

Transengineer,



Thank you very much for your contributions to this forum. I was worried some parts of this thread might have run you off.

 

[cerberusiam]

Um, yeah, you're right, what was I thinking... ? Boy do I feel silly... ?

Take a gander and try to follow along. Ample evidence every single thing I said is a reality, despite your lack of experience.



https://www.turbodieselregister.com...when-cold-while-in-gear&p=2350421#post2350421.

Maybe you could talk about your amazing ability to behave like children.

You felt the need to post this because??? By your own stated principals, you are out of line.



Might want to do a little more research about just who is acting out and why. The OP can hope for the best but the evidence is against it, as I tried to explain in the face of repeated insults. Nice to talk about taking the high road, a little harder to actually do when faced by some of the ignorance and idiocy that is the typcal fodder from some.

 

[PC12Driver]

Take a gander and try to follow along. Ample evidence every single thing I said is a reality, despite your lack of experience.

I have a pretty good grasp as to what's going on in this thread. My remark was aimed at your "egg on your face" comment (who's doing the insulting?) in which you were pretty excited that you found evidence that I was "wrong" about the increase in rpms. Even though the evidence you provided only was the description of how any governor-controlled power source behaves when it slightly overshoots its target rpm. Not quite the big deal you're trying to make it out to be.



In regards to my experience, the OP's truck has the symptom a few seconds after startup and then goes away, which is a pretty good indication of transmission fluid drain back. The truck in the link you posted had the problem after being driven for some time, which clearly indicates something other than drain back. So, in my experience, my first thought would be the two causes would be unrelated. A similar result, but the timing of the event points at two different causes.



Actually, the only evidence in this thread that supports your theory are your own unsupported posts. Trans engineer let us in pretty early on a good hypothesis with what appears to be a working knowledge of the 68' to back it up. A knowledge that you have clearly shown that you lack, based on your insulting the knowledge of the trans engineers before one showed up and explained how these things actually work (that would be a proper example of, as you say, "egg on your face").

The OP can hope for the best but the evidence is against it, as I tried to explain in the face of repeated insults

Really, you're a victim? You know you haven't really contributed anything useful, right? Please quote one thing that you have posted in this thread that would have helped the OP.

 

[Oil Stain]

What way to welcome "Transengineer". I know of him from another forum and I always look forward to his replies. This is not to say that there are not others on here or anywhere else that don't have experience or great informative posts, it's just we have a new member and this thread got into a heated debate. We could have at least waited until he had about 12 posts. lol. Forums, are a funny place to be at times.

 

[transe]

"If any man desire to be first, the same shall be last of all... " Mark 9:35

"For whosoever exalteth himself shall be abased; and he that humbleth himself shall be exalted. " Luke 14:11



I believe humility is the best course for all of us.

 

[GBlaksley]

TWood,



I think the truck was sitting so long, that the torqued converter would drain. I wasn't driving it very much, and would sit for up to a week and a half at a time. The problem has disappeared now that I drive it almost daily.

 

[TWood]

GBlaksley



Thanks for the update It is good to hear that you have not had the issue anymore.



pc12driver



Cerberusium



You are right. I was out of line and I appologize. I was so frustrated reading/ sifting through all the bickering that in the moment I could not help myself. It can be very trying to get to the useful information contained in a somewhat heated debate.

 

[cerberusiam]

I have a pretty good grasp as to what's going on in this thread.



Really, you're a victim? You know you haven't really contributed anything useful, right? Please quote one thing that you have posted in this thread that would have helped the OP.

You contributed what? Outdated information on a totally different transmission that was wrong to begin with. Yep, you have "grasp" all right. Your single contribution was taking offense when I suggested there was something missing in the problem description and that possibly indicated an engineering mistake. I guess TranEngineer filling in the missing info that I was pointing out did not exactly sound right and basically confirming this is in fact an engineering screw up NEVER even registered with you. Yeah, you got a "grasp" all right.



I suppose you are going to claim precognizance and utlimate knowledge now that GBlakesly has offered some observations that was NOT in evidence at the start. You just KNEW based on your experience with something you won't believe, can't understand, and have never seen that ANYTHING I had to offer was totally wrong and the outdated info you offered had direct bearing. FYI, the 47RE and 68RFE are totally different animals.



Sorry, it is right there in black and white. Save the bulk of the egg for yourself as that is where it clearly belongs. What I posted is still valid, it is backed up by the post I referenced and a lot more. Whether you choose to believe that is of no concern. If the OP continues to see no other issues then he has a source and a solution. If it ever becomes random and returns with the same or different symptoms, he has a source and a solution. So PC-yutz what I posted and what I asked TransEngineer to clarify does help the OP and any others that read it, does pertain to the subject, and is a valid contribution. Now , what was the babble about a 47RE that was so helpful... ... ... . Yeah, you got a "grasp". :-laf



As for some of the comments deploring the post content, doesn't even register on the problem meter. There is no malice, no animas, no hating in any of them. No threats, no promises of retirbution that could be construed to be such. In fact, there is some good info in the posts even though it sounds like bickering. This is a big boy forum, if you don't like the responses or content, block the senders. It is that simple, but, imagine all the fun and possible nuggets you miss. LIVELY discussion leads to more content, and, this is nothing but lively discussion. If all you want is warm fuzzies then there are places for that, not going to get much content when everybody is concentrating on the mandatory group hug.

I think the truck was sitting so long, that the torqued converter would drain. I wasn't driving it very much, and would sit for up to a week and a half at a time. The problem has disappeared now that I drive it almost daily.

Glad it is working for you and hope that is all it is. I am totally content to be wrong on the source of the problem.

 

[PC12Driver]

You contributed what? Outdated information on a totally different transmission that was wrong to begin with...

Actually, it's basic hydraulics. If the pump isn't turning fast enough, there may not be enough flow to generate enough pressure to keep things locked.



I was aware that hydraulic pressure released the TC on the 68. You don't have to tell me they're different than the old 4-speeds.

So PC-yutz what I posted and what I asked...

I've come to expect the belligerent comments when you can't support your arguements, but the name calling thing is new. Some boards even frown on it. TWood makes a comment and you jump all over him, and then turn around and act like a four-year-old. Get back to me when you can converse like an adult.



Maybe take a look at Graham's Hierarchy of Disagreement sometime and figure out where you fall in the triangle (hint: the bottom is bad).

 

[TulsaOkie]

I've experienced this surge also, and just so happened right after a transmission service. I service it every 60k, and I was beginning to worry. It happens when it's cold, and will stop after a warm up. I don't use the dealer for anything but will mail my filter to anyone to help out on this.
Mr. Barlow glad to see your still hanging out !!!

 

[Bug Out]

Transengineer, thanks for your help on these transmission issues. I learned more on this post( besides the pee contest) about the 68 RFE then I knew before. Keep up the excellent info on a good transmission.

Ed

PS: Thanks for trying to "improve" the future for us RAM owners. Thats what we like to know that someone is actually trying to better the product.

 

[transe]

I've experienced this surge also, and just so happened right after a transmission service. I service it every 60k, and I was beginning to worry. It happens when it's cold, and will stop after a warm up. I don't use the dealer for anything but will mail my filter to anyone to help out on this... .

Your shop probably used an aftermarket spin-on filter (we've seen some issues with those). I don't need any more "suspect" filters returned. First, we only deal with production parts. And second, I've already gotten a number of production filters back from other trucks, so we are OK for now. Thanks anyway for the offer!

 

[NIsaacs]

Any new truck owners of the 2012 68rfe equiped trucks still having this issue? Has it been determined that it is the oil filter causing the flare? My BIL's 2012 3500 SRW is still doing it with 12k miles on it. It will do it in forward or reverse and does not need to sit for a few days. It can do it several times in one day.

Nick