transmission shudder in reverse while towing; factory rep calls it "fluid bending"

[JWGreen]

My 2011 3500 DRW 4WD Laramie with 27K mi. recently developed a shudder when I'm backing my trailer into a campsite. The trailer is a 34 ft. Airstream triple axle and I'm using a Reese load equilizing hitch. I have not noticed any shudder while driving forward at any speed. The trailer weighs about 10K lbs. loaded and I first noticed the shudder when backing into a campsite that was slightly uphill. The shudder was very noticeable and even my wife commented that "we've never had that before. " My previous truck was a 2005 3500 2WD, 5. 9L with a Pac Brake towing the same trailer. Traded it on the 2011 when it had 91K mi. on the clock. Took the 2011 to my dealer to check on the shudder. His mechanic called tech support who told them it was "fluid bending. " Duh! Says its a torque convertor problem, not to worry. Am I getting a silly answer to a legit question? Anybody else ever hear of fluid bending?

 

[JLandry]

JW,



Does it happen ONLY when backing uphill?



If so, I'm wondering if it wasn't just some rear wheel slip and/or the limited-slip differential (if equipped) chattering.



Next time you might try it in 4WD to see if it happens.



John L.

 

[cerberusiam]

I am really trying hard not to bash the "dealer" group, but, it gets harder and harder every day especially posts like this. The question becomes is it the dealers that just won't hire and train adequate people, or, is it corporate policy to outsorce things to a tech support group that just babbles incoherent BS to a legitimate inquiry?



That HAS to be one of the most pathetic, insulting, egregious answers to a legitimate question I have EVER heard from a tech or support. Pure unadulterated BS is all it is. What is scary is the tech actually had the gall or just plain ignorance to repeat it back to a customer. If it was me I would go back and pointedly ask the service manager and owner and whomever else has any pull there why they would allow me to be insulted like that. Unfortunately, it may not be feasible because any other dealer may be worse.



Assuming you have an 68RFE so short answer, they are yanking your chain. Reverse is a clutch applied mechanical reverse in the transmission using planetaries. There is no "fluid bending" invloved and if they keep saying just ask them how they get the TC to spin backwards on the engine. The low\reverse clutch and roller is one of the sub par assemblies in a 68RFE. If it shuddering in reverse under power and it just started doing it, the most likely cause is the reverse clutch pack is slipping and about ready to burn out. Probably going to have to tear it down and fix the problem or it will eventually just have no reverse.



If you have a manual transmission then it is the DMF on its way out. Either way, you have a legitimate problem suggested by some pretty common symptoms and you got a mickey mouse answer to the your concerns. I hope you have better luck with the fix than the diagnosis.

 

[DonFitzwater]

I think Cerb nailed it... ... ...

 

[K5IP]

Cerb,
This may be unrelated but I have an 03 with the NV5600 that does something similar. When backing my 22ft trailer into my drive way I need to turn sharply and back up hill.
The thing chatters and jumps like crazy. Once I can get things straightened out, I can shift into low range and everything goes smoothly. (although it now binds everything up). I have the clutch completely released during this chattering operation and the trailer brakes are disconnected. The clutch has just been replaced, but no joy.
My 95 never did this but I had the ability to disrupt the vacuum to the front axel disconnect and use low range without 4whd. It was a very fine affair.
I can live with this but don't understand it. (remember this is a 5600 with a single disc clutch. )
Rog

 

[RustyJC]

When in reverse, the direction of "axle wrap" is reversed - the nose of the rear axle pinion tries to rotate downward, as opposed to upward rotation during forward acceleration. This can result in some abnormal pinion angles. What is the condition of your u-joints? Could it be that they have deteriorated which is why the problem is just now rearing its head?



Rusty

 

[jgillott]

OK, I'll admid that I'm getting slower as I get older. But, I did major in Chemistry during my undergrad years in college... ..... of course, that was a long time ago. I have never heard of the term "Fluid Bending" used in the context of an alcohol or other fluid under pressure. If you can get the Chrysler rep to answer exactly what that means, I would love to know.



On Edit: I was assuming reading the initial post that the rep was speaking of something happeing to the transmission fluid. I don't know if they mean "fluid bending" in relationship to something else.

 

[rscurtis]

K51P, you have one of the most desirable third- generation trucks available. A free-spin kit will solve your problem.

 

[cerberusiam]

His mechanic called tech support who told them it was "fluid bending. " Duh! Says its a torque convertor problem, not to worry.

Well, if it is a TC problem its a problem and why wouldn't the owner worry? Since the TC or the fluid flow doesn't change direction in reverse the whole response from the tech service just sounds ridiculous.

The TQ rise off low speed backing in reverse is just brutal, the whole drive train is just too small to absorb it. Manual or auto, if its slipping things and shuddering its a bad sign.

 

[Cummins12V98]

Throw it in 4 low and you won't have an issue.

Good practice when backing up a hill with a load.

 

[sag2]

Actually it is fairly common, especially 62TE and 42RLE transmissions. It should be better in 68RFE because the reverse ratio is lower than 1st. In the auto you get fluid pulsations in the converter that sets up kind of a slip/stick situation in torque multiplication. It then sets up a shudder in the vehicle and kind of self induces. The answer is you really need a lower reverse gear, ie 4wd low as has been mentioned. And no it really isn't any more than annoying as nothing is really "slipping" except the normal slip going on in the converter. The other way to reduce or eliminate it is to go WOT, but of course that is not practical or safe when backing a load up the hill. I'm not sure my explanation is any clearer than the technicians, but it really isn't anything to be concerned with.
And the manual transmission trucks are normally much worse than the auto.

 

[transe]

SAG2 is correct. What you are feeling is the result of normal torque pulsations from the converter. I don't know who coined the term "fluid bending," but (as Cerb noted), it is (to put it gently) inaccurate and misleading. Fluid is involved (the converter is, after all, a fluid coupling), but "torque pulsations" would be a better description. Apparently, these pulsations are present, to some degree, in every converter, but some designs / configurations seem to be worse than others. These pulsations are most noticeable at stall (zero output speed) when applying significant input torque (like, backing up a grade with a trailer).



Actually, you should get the same pulsations / shudder in Drive also, although usually you're at heavier throttle openings when launching in 1st gear, so you might not notice it then. Try stopping on a grade with your trailer (in Drive), then gradually tip into the throttle until you just get the truck to creep forward. See if you feel some similar pulsations.



As SAG2 noted, this shudder won't damage anything, but it is annoying, so using 4LO when backing your trailer up a grade is a good suggestion.

 

[JWGreen]

My truck has the 68RFE automatic transmission and the standard, not HO, 6. 7L engine. I just returned from a 2500 mi round trip from Illinois to Massachusetts. I backed into several campsites but none were uphill. Never noticed any shudder during the 3+ week trip. When I get home, I have to back the trailer about 200 ft. from the road to the shed. No shudder. I'm going to try the 4WD low range the next time I back uphill. In the meantime, I plan to visit my dealer again with the replies and see what they have to say. I appreciate the comments and the suggestions.

 

[cerberusiam]

The whole thing is going to center around the OP's interpretation of "shudder" as opposed to a "pulsation". There is a noticeable difference between the 2 when you feel both but it is impossible to describe to someone else.

His description indicates it just started doing it, that along with the inherent weakness in the LR clutch and sprag does raise some flags. Given these transmissions are under clutched and over managed ANY weird vibrations and\or noises in conditions like that are suspicious.

TransEngineer is just to nice with his assessment. That was a STUPID insulting diagnosis from a supposed tech service, even if it may be somewhat accurate.

 

[K5IP]

Rusty,
Thanks for the thought. It seems like the suspension is so heavy that "axel wrap" would be minor. Remember this is happening under light load.
I did check the joints and they seem solid. One other point, the jumping does not occur while backing up in a straight line, it only occurs when I start to turn.
This would imply that the perhaps the front u joints were binding even though unloaded. I jacked the front end up and rotated the tires while turning the wheels from stop to stop and the front u joints seem solid and no binding was apparent.
Also, I do have a Reese round tube slider with my 5th wheel hitch which, with it's additional movement, amplifies the condition.
I really hate backing this thing up under 4whl drive conditions. The wheels brake loose/lay rubber on the concrete and things get so bound up I can hardly get it out of 4 wheel drive. I can just see me breaking a u joint.
I know a free spin kit would do it, but I am just trying to figure this out.
Rog

 

[K5IP]

sag2
Your comment about the manual transmission being worse inspired me do some tests. This may not help everyone, but!
When backing my trailer I let it idle to keep the speed as slow as possible (sharp corner and tight conditions).
I watched my tach as I did this and found that around the sharp up hill corner, the rpm would drop from 800 to about 700. At this point the governor responds and raises rpm but it overshoots to about 900RPM this makes everything lurch and an oscillating condition begins.
I found that if while backing, If preload the system with some brakes applied, even during an idle condition, the control loop (governor) is dampened enough to keep the oscillation from occurring.
Easy fix now that I know what was going on. (I made my living as a control system designer, this might have helped).
Rog

 

[JWGreen]

I wanted to thank everyone for their comments and suggestions. I talked to Dennis, one of the owners of the dealership where I purchased the truck and explained to him that someone at Dodge/RAM was tossing out goofy answers to serious questions. He got back to me a few days later and said the term came from the early 2000's when a FWD mini-van was experiencing a similar condition. He dismissed the term as not applicable to my situation. I agreed to do some more analysis when I back uphill with the trailer. I'm going to have my spouse get out of the truck and watch the rear wheels as I back up, looking for wheel hop. I'll also switch into 4WD low and see if that helps. Because of my Reese load distributing hitch, I'm suspecting the wheel hop when the spring bars are doing their thing by transferring the hitch weight to the front wheels. I'm headed for Kentucky shortly and may find a campsite that involves backing uphill. I'll keep you posted. Also, hello and 73 to K5IP in New Mexico, I'm also a radio ham, call sign W9CJX. Look me up on QRZ.com

 

[transe]

I wanted to thank everyone for their comments and suggestions. I talked to Dennis, one of the owners of the dealership where I purchased the truck and explained to him that someone at Dodge/RAM was tossing out goofy answers to serious questions. He got back to me a few days later and said the term came from the early 2000's when a FWD mini-van was experiencing a similar condition. He dismissed the term as not applicable to my situation. I agreed to do some more analysis when I back uphill with the trailer. I'm going to have my spouse get out of the truck and watch the rear wheels as I back up, looking for wheel hop. I'll also switch into 4WD low and see if that helps. Because of my Reese load distributing hitch, I'm suspecting the wheel hop when the spring bars are doing their thing by transferring the hitch weight to the front wheels. I'm headed for Kentucky shortly and may find a campsite that involves backing uphill. I'll keep you posted. Also, hello and 73 to K5IP in New Mexico, I'm also a radio ham, call sign W9CJX. Look me up on QRZ.com

Actually, the issue with the minivans is exactly the same as what I suspect you are experiencing. In the minivans, torque pulsations from the converter were especially evident when backing up, particularly on a grade. See what you find, but I'm guessing you will NOT see any wheel hop. I think you're probably getting the same phenomenon as we had in the minivans (although obviously, you have a different trans, converter, and engine; but the same principles apply).

 

[JWGreen]

Actually, the issue with the minivans is exactly the same as what I suspect you are experiencing. In the minivans, torque pulsations from the converter were especially evident when backing up, particularly on a grade. See what you find, but I'm guessing you will NOT see any wheel hop. I think you're probably getting the same phenomenon as we had in the minivans (although obviously, you have a different trans, converter, and engine; but the same principles apply).

OK, so the obvious next question is if this is and indication that there is a probable failure of something in the transmission. If so, what would it be? If it is not and indication of a probable failure and/or maintenance issue for the transmission, are there any additional items that I should take special note of? So long as the truck is under the powertrain warranty, any such failure of a transmission component would be a warranty item... yes/or no? I just want to feel better that some transmission catastrophe is eminent and will occur when I'm in the boonies in the desert southwest.

 

[sag2]

It isn't hurting a thing, it's just annoying.