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jwissler10

Transmission Issues

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I've posted a couple times and still struggling with a shifting problem I'm hoping someone can shed some light.

 

05 built transmission, my problem is that it jumps into od (4th) at about 1800 rpm when towing dropping my rpms to 1300-1400. If I'm on a hill pulling heavy this lugs my motor, if I step on the throttle it downshifts, locks, then immediately upshifts to od within a few seconds. It will never hold 3rd. This is both in drive and tow/haul.

 

I created a RTG that adjusted the regular 3-4 upshift to be later in the rpm range. This works under light throttle <22% but if more throttle it jumps to od like before. I adjusted the 3-4 upshift in tow/haul mode to not shift until 2800rpm and it still jumps at 1800 when I try the same in tow haul. I then tried to tow haul od over-ride and it still shifts at 1800 when going past that 22% throttle. If I'm less than that it never shifts. I'm completely confused because of the shift is completely controlled by the computer it's either not truly getting those maps saved to the truck (but it is taking other adjustments) or it's shifting outside of the trucks computer demand. I also adjusted the TTVA, I could get the shifts to move around but it still does this same shift up when more than 22% throttle. Finally when this upshift happens I can give enough throttle to have it downshift again but it won't hold, it downshifts then immediately upshift regardless of the demand shy of wot, at wot it will shift to 3rd/lock and run up to 2500 rpm then shift to od

 

Really appreciate any help!

Edited by jwissler10

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I've been having problems with transmission tuning as well. I've sent data and videos to the Smarty Guys but have yet to get any answers. The best I can come up with in the blind is that there are some "maximum" values in the trans tuning that we don't have access to. I made a tune that should have locked out 4th and TCC lockup, but it only successfully locked out the TCC, 4th still eventually came on, even though by the tune settings it shouldn't have been able to.

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From my experience the 48's don't always respond to real time changes. With the 68's it not even an option. I would do all the testing as a .ecm file and then once you have it working, see if it will work as an rt.

 

Rob, you are correct that there are limits to what you can do with the transmission tuning. It's not just "maximum" values, but how the "operating system" works. Some of the tuning logic is coded into the ECM's operating system, and is not configurable as a parameter.

 

Another challenge with the 48 is that it is part mechanically controlled and part electronic. For example you can configure it to electronically lockup the torque converter in 2nd gear, but in order for that to work the gear selector has to be in 2, and not drive. Another example is when commanding torque converter lockup the governor pressure has to be able to overcome line pressure (I hope I have that right...). You can command the lockup solenoid to lock the converter but unless the pressures are correct, it won't lock up.

 

The valve body on my 05 is far from stock, and it will override some of the commands that the ecm wants to do. Even though the 3-4 shift is controlled electronically, the modifications done to my valve body allow it the do the 3-4 shift earlier at WOT.

 

The 68 is much more of an electronic transmission, these comments mostly apply to the 48.

 

Paul

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Hey Paul,

 

One of the things I have found that doesn't seem to be configurable is the governor pressure curve. No matter what I set the curve to it seems to have no effect on the actual operation of the trans, the governor pressure at a set throttle and speed is the same as before. And this is via ecm file as well.

 

In theory if you zero out the governor table, the 48re should never leave 1st gear, as I understand it when governor pressure overtakes throttle pressure you get a shift.

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Rob, your first comment is exactly what I'm experiencing. The adjustments I did to the TCC so it locks up later did take and work, but the upshift isn't moving at all no matter what I do. I made the extreme adjustments just to see if it would do anything, but my original file just moved the shift up 300 rpm so I could tow hills at 50 and not bog, but hold 3rd locked. It seems like I have found one of the values, at 23-25% throttle mine always upshifts, and if I'm lower or higher around the 55-60% it will hold 3rd lock until higher rpms. The other really annoying part is if I'm under load and it down shifts it only does it for a few seconds then upshifts right away.

 

Also the TH OD On/Off doesn't work either and will shift at the same point whether on or off.

 

Hopefully those are some of the fixes in the works. Thank you! -John

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Paul,

 

No I haven't put guages on the trans. I did measure by way of the touch and could see that commanded and actual governor pressure did not change after setting the governor curve.

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I haven't tried to modify the governor pressure. I rely on it being at the stock values. Why do you want to change it? Just curious...

 

Paul

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I'd like to bump up the 1-2 shift. I'm as far as I can go with the ttva and not have unintended consequences.

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