6.7L Cummins Forum

jamespi · #1 (**permalink**) 04-07-2009, 02:53 PM

Over the weekend I had a couple strange problems.
The first is the automatic transmission; when I started up and left I put it in 3rd gear then tried to go into 4th and it would not go up. It would flash the tow/haul light in the dash when I tried to shift up. Then I tried to shift down and it did but still would not shift up. I got down to first gear and had to pull over. I turn the truck off and started it back up and the problem went away. Has anyone else ever had this happen to them and should I be worried?

The second is; when I am in 2nd or 3rd gear and steadily on the gas then let off it revs up and lunges before it slows down. Any thoughts of this problem?

Thanks,

Squid · #2 (**permalink**) 04-07-2009, 07:27 PM

You're talking about using the thumb switch on the shift lever? When you use this and select a gear it won't shift any farther up then the gear you selected unless you use the thumb switch to move the gear selection back up. Select 3 and 3 is as high as she will shift.

As for the second problem maybe you're regenerating and the extra fuel being dumped does add some umpf to the engine.

jamespi · #3 (**permalink**) 04-07-2009, 08:53 PM

Correct, the thumb switch. It would not go to a higher number, it would only go to a lower number.

Squid · #4 (**permalink**) 04-08-2009, 07:43 AM

That's working as advertised

jamespi · #5 (**permalink**) 04-08-2009, 11:06 AM

Maybe I am not saying it right.
I know the thumb switch won’t let you shift in to a lower gear that may harm something, but it will let you shift up threw all the numbers to drive while staying in the gear for the speed.
What it was doing was not letting me shift up threw all the numbers to get out of 3rd (on the dash it read 3) to allow it to go in a higher gear like 4th 5th 6th and drive. I even shifted into neutral then back to drive and the thumb switch still would not change to a higher gear. When I shifted down to 1st it was stuck in 1st, it would not go any higher until I shut the truck off and then restarted. But it sounds like this might have been a fluke.

Vis-a'-vis · #6 (**permalink**) 04-08-2009, 12:02 PM

Sounds like some sort of a software glitch. You should have been able to shift up and down with the thumb switch. Has it repeated itself?
Also, the lunge may be the EB. At 1100 rpms the EB should release. But you can get stuck in a release/brake mode where the truck bucks as the EB creates higher initial rpms, slows the truck and releases and so on.

jamespi · #7 (**permalink**) 04-08-2009, 02:59 PM

No, the shifting problem has not repeated but wanted to see if others had it happen.
Yes, what you described sounds like what is going on with the lunging. Is there a fix for it?

Vis-a'-vis · #8 (**permalink**) 04-09-2009, 09:40 AM

I think that there is a flash for this, do a search on bucking.
I just drive a little differently and it does not happen. Mine mostly happens in 3rd gear with the eb on. If I'm using the eb, I just don't let it get to the 1100 rpm range

jamespi · #9 (**permalink**) 04-09-2009, 10:19 AM

I will check that out. Mine happens in 2nd and 3rd so I will use 4th in the meantime.
I was only using 2nd and 3rd because we where at a campground.
Thanks for the help!

DWRDodge6.7 · #10 (**permalink**) 04-09-2009, 07:40 PM

The latest flash may eliminate both your shifting problems. Although the switch response issue may be the switch itself. We've talked about the lunging problem on here before. Mine does the same lunging thing occasionally. It is usually in 2nd or 3rd when making a turn, right after I lift off the throttle a little or in traffic when I lift off. Seems like the trans is trying to up shift just as i lift off. As I said it does not happen often so I am leaving it be. I am still running the AX flash.

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