Simple question first... At what speed, under light load, will the PCM put the trans into OD? I had heard is only happens at/above 40 MPH.

Why I ask... I've had a Hypertec III with the 93 Oct Pgm loaded for years now. Last Oct the trans went and was rebuilt. After, since I was then watching things about the trans more accurately, I noticed it was only going into OD at 40 or above. It drove nice though, trans is great.

A couple weeks ago I had an electrical issue where I disconnected the battery for a while, then reloaded the same Hypertec pgm as I had before, just freshened it up. Now, the PCM lets the trans go into OD at pretty much any speed. I can be at 30 mph and 1000 rpm.

So, that's why I wonder what 'right' is. I kind of liked it better before the Hypertec reload.

 

From what I know about the Hypertech when I owned one, it does not offer any functionality concerning the shift points for the tranny as I was informed that is mechanical and not controlled by the pcm.

My tranny always shifted to OD early around 30-35 when cruising around with a very light pedal. If I push the pedal a little more, OD usually will not kick in until around 40 or above as you stated.

I would assume after you reflashed the pcm, this is actually normal shifting behavior when you have a very light foot on the pedal.

 

i have always had the problem w/ the trans shifting into OD too early around town so i just started turning OD off if i was under 40-45 to avoid the issue,

 

Mine will go into overdrive as soon as 35mph or so depending on throttle, but I don't have problems with it engaging too soon.

 

35 is too soon for OD it shouldnt kick in until you are over 40 or 45

 

I'm going to live with this low speed OD engagement a while to see how it drives long term.

 

Shrp, Overdrive engages at various speeds depending on the position of the throttle. If you have a very light foot with intention to save gas and wear and tear on the brakes, OD will kick in early as early as 30-35. If you have a heavy foot, then yes, OD will not kick in until around 40-45 mph. The PCM is programmed to use the best optimum gear for mpg and longevity of your truck based on the throttle position and the load it is put under.

 

true it will kick in that early, however having studied this sort of gear design (im a mechanical engineer by trade and degree) transmissions are designed and geared such that OD should not engage below 40 -45 mph, now, the manufactuerers even specify this in SOME Of their documentation (i have seen it in dodge manuals, if i can dig it up i will be more than happy to share it with you), however they do not put a hard limit in the co mputer program on newer transmissions to prevent it from engaging, and COULDNT put a hard limit on the older transmissions to limit it, the reason they dont want it shifting into OD below that speed is that every time the auto trans shifts it wears the clutch plates, and at those speeds (below 40 for sure) if you step on the gas it will downshift into a lower gear to pick up speed, if the grade increases it will downshift, ect ect, basically forcing extra shifts to allow earlier engagement.

Will this be noticed or cared about by the average car buyer, probably not, most people dont know enough to care and dont keep cars long enough to wear out trannys, but it is the way that things work.

 

So ok guys (after all the above), if a 46RE is rebuilt at a reputable shop, would they (or do that have the ability to) reprogram the OD shift point? ... sort of to verify the computer side of the trans is right too?

From my OP, the D had the Hypertec pgm in it, then the trans was done, then I noticed it only shifting to OD at 40+, then I reloaded the Hypertec, and now it can shift to OD below 40.

[EDIT: I just spoke to the trans rebuild guy, bounce all this off him. He said he did no software work in it and mentioned the OD shift point is also a function of throttle position. Being that I also swapped out the exhaust system from a clogged Cat 12 yr old stock one to a full Magnaflow with larger piping, and now use less throttle pressure to be at a speed, the PCM will shift sooner than with the old exhaust.]

 

Interesting. Isn't the Tv cable responsible for shift points?

I put a jeep computer in mine. My shift into OD is now at 55 mph. Before it was 45 mph. Tho my 4.7 is more electronic than your 5.9.