6.7L Cummins Forum

Hi,

I have a 6.7 w/6spd auto and I pull a light 5th wheel. When travelling thru the mountains I found that it would slip real bad on a 6-5 and 5-4 downshift when pulling a hill. The motor would over-rev and it could take up to 4 seconds to engage the lower gear. It did NOT ever seem to lock into the new gear, just slowly rev down until it stabilized. I tried it without the trailer and it is still there but not so noticable. I am afraid of what might happen if I upgrade to a heavier trailer. The dealership checked and said they couldn't find a problem... Go figure.

Should I be concerned? The truck has 98000 kms. Warranty runs out at 100K.

Thanks

Unfortunately I live out on the flatlands so I'm not much help but I'll bump this and see if someone else can help.

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2007.5 Dodge Ram 3500 HD,QC, 6.7L Cummins, 6speed Auto, 4X4, Bighorn Edition.
Click for installs: Carr Steps PML Diff Cover Edge Juice with Attitude Volant Intake Hankook ATM RF10

I have a 2008 with the 6 speed auto and it does the same thing. When shifting down from 6-5 or 5-4, engine will over rev, then the transmission will slowly catch and the engine starts pulling. Took it to the local dodge place, said everything was fine. Scares the heck out of me every time it does it. Finally started letting the engine drift until the tranny catches, then fuel it. Always looses about 5 mph in the process.

I took 08 back to Dodge... again they claim nothing is wrong with the tranny and that it is ok for it to slip as it down shifts under load. I also called Chrysler and explained what was happening, they suggested I take the truck to a different dealer due to the fact that all their dealers are independents and that they might use different diagnostics systems and come up with a different answer. Go figure! I've also talked with several other owners that I've met in my travels and so far none their trannys slip during down shift under load. Go figure again.

I will be towing later this week I will see how the Sonnax Line Pressure Booster(see thread on Sonnax) does when towing. I can tell the difference while empty in it is a firmer shift.

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If you bad mouth farmers just make sure your mouth is empty
07.5 2500 quad, sb, auto,4x4, Big Horn. wheel to wheel nerf bars, amp bumper step
08 Jazz 36' 5er, 12,000lbs
28' PJ gooseneck,22,400 gvw

Thanks Dodgefarmer.... looking forward to your reply. I take it your auto would slip during downshifts when loaded? How much weight are you towing?

Hi , I have an 07 with a 6.7 Cummins and the 6 speed trany and I notice the same thing. I pull a 34.5 foot fifth wheel rv. GVWR is 5531 kgs. I always use the tow/haul mode which I believe locks out 6th gear. What I find helps is, when you notice the engine beginning to pull harder and your speed beginning to drop, click it down to 5th gear manually. In other words treat it like a manual tranny when you have some hard pulling ahead. I know this may mean you need to pay a little more attention to the sound and feel of your rig but oh-well.........this may not be a really bad thing. Hope this helps.

I am towing 12,000lbs so I keep it out of 6th gear. Will use 5th on the flats. It did have the slippage, but really not so much of the reving up, more like the TC working before the lock up. The Sonnax is not as noticable as far as firmer ships when towingcompared to empty, I think just a little quicker in locking up. The Sonnax is not a radicle "shift kit" , it just give it a slightly quicker feel to lock up the trans gears clutches. You still have the TC slip during shift but feel the lock -up the gears being more noticable. Not sure if that makes any sense

__________________
If you bad mouth farmers just make sure your mouth is empty
07.5 2500 quad, sb, auto,4x4, Big Horn. wheel to wheel nerf bars, amp bumper step
08 Jazz 36' 5er, 12,000lbs
28' PJ gooseneck,22,400 gvw

When running on level ground I will let mine run in 6th and will treat it like a manual when I get into hills. I pull up to 15000 lbs and typically treat all the loads the same, i.e. shift down manually before I start climbing a hill but the tranny still hesitates and takes 2-3 seconds to make it into the lower gear. The only time I shift out of the tow mode when towing is when descending hills and don't want the tranny to start shifting down on it's own. If 6th with the exhaust brake running will keep my speed in check, then the regular mode will allow the tranny to stay right there, then if I feel the need to shift to 5th then I do so manually. Sounds like the Sonnax might be the hot ticket especially at the price.