Hard 40 mph shift in 65 tow

Highbeam · #1 Tue, May 29th, 2012, 01:18 PM

2000 auto powerstroke.

So I got to tow the big trailer with the family this weekend in the 65 tow setting. The RV trailer weighs about 7500 so it isn't really that big. Truck has 168000 miles and looks to be original trans. I am coming from an NVK4 PCM so I have read that the shifting will be way different.

I really do like everything that the chip does to the shifting except for the shift that happens at about 40 mph. Whether lightly loaded or climbing a hill that shift is very hard like being rear ended and the whole truck lurches forward and then bounces against the drivetrain like I dumped the clutch. I am not sure if this can hurt the truck but it is a hard hit. The next shift is up near 50 mph into fourth, that shift is firm but not a slam.

Is this a hard TC apply? I don't really feel a slippery (unlocked) third gear and after the slam I am locked in third.

Is there something I can do to soften that 40 mph kick? Could this be a sign of a questionable PCM connection. I never did disconnect the batteries for a "relearn" after adding the chip. Fluid level?

cj45lc · #2 Tue, May 29th, 2012, 08:53 PM

Quote:

Originally Posted by Highbeam

2000 auto powerstroke.

So I got to tow the big trailer with the family this weekend in the 65 tow setting. The RV trailer weighs about 7500 so it isn't really that big. Truck has 168000 miles and looks to be original trans. I am coming from an NVK4 PCM so I have read that the shifting will be way different.

I really do like everything that the chip does to the shifting except for the shift that happens at about 40 mph. Whether lightly loaded or climbing a hill that shift is very hard like being rear ended and the whole truck lurches forward and then bounces against the drivetrain like I dumped the clutch. I am not sure if this can hurt the truck but it is a hard hit. The next shift is up near 50 mph into fourth, that shift is firm but not a slam.

Is this a hard TC apply? I don't really feel a slippery (unlocked) third gear and after the slam I am locked in third.

Is there something I can do to soften that 40 mph kick? Could this be a sign of a questionable PCM connection. I never did disconnect the batteries for a "relearn" after adding the chip. Fluid level?

Mine does the same thing in 65tow with about the same weight trailer you are talking about but with 10k lbs or better the shift feels much better. With my horse trailer I usually run mine in the 80dd as I feel the less than 10k lbs doesn't really need the tow tune & the egt has stayed great, less than 1200 deg on a 7% grade. I was told that the firm 2-3 shift was normal in the tow tune & was not going to hurt anything but I still don't use it unless I've got a sure enough load behind me.

If you really want to feel the mule kick try it just driving around empty...lol but really the shift feels much better when you're loaded pretty good & getting on the throttle quite a bit. BTW mine had the NVK5 195k miles original trans...knock on wood

Highbeam · #3 Wed, May 30th, 2012, 09:51 AM

I ran around empty in the 65 tow tune last night trying to figure out just which "shift" is so hard. If I accelerate lightly I can feel the 1-2 and then the 2-3 nice and soft but then bang at 40 mph or so. After reading about this it sounds like the TC can lock in 2nd or the trans can shift to third and then lock up depending on throttle position so what I feel is the 2-3 shift might just be the TC locking in second.

Either 1-2-TC-3-4 or 1-2-3-tc-4 is how cleatus posted.

So, I'm not sure which shift I'm feeling but at about 40 mph it bangs hard when towing 7500. Not so hard when empty and at low/moderate throttle. Almost like the truck can accelerate from the kick vs. absorbing the kick.

I don't feel it as hard in the DD tune or the 100 perf tune. Haven't tried stock. If the hard shifting won't hurt anything then I can try it for awhile but if I had horses in a trailer I would NOT want that kick. It 's a leg breaker.