68RFE acting up

[RDThompson]

My 2008 2500 has 78k and has just started a screwy little glitch. After morning start-up it drives and shifts normally up to the point where it does not. At that point it sticks in fourth and I can't change gears up or down until I shut it off and restart it in Park. After that no other problems for the day. I recently drove a 1600 mile loop with a trailer. The first 400 miles the trailer was empty, the next 400 miles I was hauling a 4500lb. vehicle

mostly up hill. On the next 800 mile leg I had a chassis with an engine of approx. 1500lbs. During all this time the truck never stuttered or balked, it went uphill like it was empty. The temp. gauge never really rose out of normal and most of the trip back was downhill or flat. I was in tow/haul with the engine brake on the whole trip.

A week prior to my trip I performed the third transmission service and found nothing in the pan and the oil did not smell burned. I don't get any codes when this happens. Shifting is a bit jerky when tow/haul is engaged now.

I'm wondering if the spin-on filter backed off. I was careful not to over tighten it.

Any speculation, however idle is encouraged.

 

[mpaulson]

Did you remember the seal on the pan filter? I would think you would have had lot more problems if you didn't. The fourth gear means it's going into limp mode. Mine started about last spring with a hang up in fourth about once every two months out of the blue after turning a corner, and this winter it got more frequent till it was doing it once a week while city driving and getting some heat soak happening. Then it got so bad that it was napping three or more times a day. I finally got it to do it while the star scan computer was hooked up and the service technician could see what was happening. Mine turned out to be cross leakage in the valve body which was confusing the TCM because it would see pressure on more that on sensor and think that it was in for eg. 2nd and 4 th gear at the same time and trigger a limp mode which makes it go from 1st or 2nd(can't remember) and jump to fourth. I could shut the truck off and restart it and it would drive normal till it decided to act up again.

Hopefully it is just a filter for your sake.

A buddy of mine just had the same limp mode happen to him once a few weeks ago on his 2008 also. No code, just limp. Then a few days latter the transmission light came on, but still no code stored. He's just waiting to see what it does next.

 

[RDThompson]

Thanks for the reply, I suppose time will tell. If it gets much worse I'll pull the pan and check the filters again. As far as the pan filter seal goes I made an installation tool out of brass stock on the lathe while I had the new seal in hand.

 

[RoosterXP]

My truck doesn't shift out of 4th until the transmission reaches a certain temp then it shifts into 5 and 6. I have noticed this when i first start the truck after its been sitting overnight.

 

[mpaulson]

My truck doesn't shift out of 4th until the transmission reaches a certain temp then it shifts into 5 and 6. I have noticed this when i first start the truck after its been sitting overnight.

That's right, I totally forgot about that and he did mention at first start up. That's most likely all that it was. I have had this happen a few times, it is normal, the transmission is protecting the clutch packs on fifth and sixth because the fluid apparently doesn't flow good enough till the temp hits a certain level. Although I would think that in California it would be rare to be too cold, this only happens to me in the winter and we live in igloos up here.

 

[RDThompson]

I just realized that I've done something that really annoys me when others do it. I left out a principle bit of information. To wit: When I start up in the morning I shift the the transmission down to 4th, set the engine brake to on and engage the Tow/Haul button. If I have a problem it is usually within first fifteen minutes of operation.

I apologize for the omission.

 

[transe]

Bob, you need to have someone (your dealer, likely) read the trans fault code(s) from the TCM. Sounds like you are in full limp-in (4th gear only), which happens either due to a trans fault, or complete loss of 12V power to the trans. The TCM does inhibit 6th gear (and TCC engagement) until the fluid is warmed up, but trans will still shift normally 1-2-3-4-5. Since you are stuck in 4th, that's not just due to cold fluid.



Many of the trans faults (that cause full limp-in) are due to a bad wiring connection, bad sensor, etc. and can be fairly easy (and cheap) to repair (cheaper at least than getting a rebuilt trans!). So let me know what the code(s) are, and I can tell you how to diagnose / troubleshoot each particular fault. If you have your dealer read the codes, ask them to also read the DTC Event Data from the TCM. This is a block of data that gets written into memory whenever a fault is set, and tells us what was happening (current gear, throttle position, line pressure, desired line pressure, sump temperature, engine speed, turbine [input] speed, output speed, pressure switch states, etc. ) when the fault set. See if they can print you a copy of the DTC Event Data, or let you just write it all down off the screen display on the scan tool. It may come in very handy in diagnosing the fault.

 

[RDThompson]

Thanks, I will have the TCM scanned and see if I can get a print out as described.

 

[juicedcummins]

Mine was doing the same thing. Dealer did a tsb on it and has been fine since.

 

[RDThompson]

Well I made to the dealer to have the TCM checked out. The tech said the low reverse clutch pack was nearly out of spec. He indicated that it would occasionally annoy the TCM to the point that it would lock that item out but not set a code. He reflashed the TCM and the values all reset to well within spec. I have had no difficulties since last Friday. If I can find the paper with the values I will post the info.
My thanks to all who offered assistance.

 

[RVTRKN]

You stated the low reverse clutch pack was almost out of spec, does that mean its worn out and there is just enough left to get by for awhile?

 

[transe]

Well I made to the dealer to have the TCM checked out. The tech said the low reverse clutch pack was nearly out of spec. He indicated that it would occasionally annoy the TCM to the point that it would lock that item out but not set a code. He reflashed the TCM and the values all reset to well within spec. I have had no difficulties since last Friday. If I can find the paper with the values I will post the info.

My thanks to all who offered assistance.

Bob, your dealer tech is giving you some misinformation. I presume he's referring to the LR Clutch Volume Index (CVI). Apparently your LR CVI was near the edge of the acceptable range. Did he say whether it was at the high or low end? An out-of-range CVI will not "lock out" that particular clutch. It will affect shift quality, but will not cause you to be stuck in 4th gear. Did he say whether he found any trans faults, or any DTC Event Data?



I hope your problem is now fixed, but I suspect it won't be...