Early Shifting Automatic

[TAchterberg]

I have driven several Cummins pickups in the past, but my recently purchased '93 is the first with an automatic. It seems to be shifting VERY early, even during 1/2 to 3/4 pedal travel it shifts into OD by 40 MPH. Is there a way to adjust this, or does it sound normal?

 

[SFPADGETT]

40 seems a little early as compared to our trucks, but with that being said, most of ours will shift to OD between 45-50 with light throttle. Could the speedometer be off (larger tires?)

 

[JHumphries]

The overdrive engagement is independent of the speed. Even with bigger tires, the overdrive will still engage at the same indicated speed. They both are are dependent on the driveshaft speed. That speed is independent of axle ratio and tire size.
TAchterberg:
Is this the first Dodge auto you have driven? ( 60s-93)
If so, the Dodge auto's have always followed the mantra of shift early and shift often.

 

[TAchterberg]

Yes, this is the first 1st Gen. Auto that I have driven, the others have all been 3rd Gen.



Stock tires.

 

[cerberusiam]

The OD shift is more influenced by TPS position and TV pressure than anything. External and internal adjustments on these will help tune it better.



Actually 40 mph isn't bad, a lot of them are into OD by 35 mph.



How are the 1-2 and 2-3 shifts, early? The first thing to check is the TV cable. Set it to roughly 1/8" play in the slide at WOT and se how it responds to that. Then set your TPS to the high side at idle and see what happens. You should be able to get it up around 50 mph under normal driving with just external adjustments.



If its still early you may have to adjust pressures on the VB to get them high enough to matter.

 

[Flexiheep]

"Actually 40 mph isn't bad, a lot of them are into OD by 35 mph. "



I agree, mine is in by 35 mph... ... ...

 

[Greenleaf]

Welcome to our world. I see OD engage at 35 or before that. The engine won't care but it is tough on the transmission to drive /round at 35 while in OD (light throttle)



Most everyone is selecting "direct" via the sift lever button which is a very nice upgrade to our trucks as they came factory with the little button on the dash board. By keeping the transmission out of OD whith light throttle, you will save wear and tear on the internals. The line pressure is directly effected by the position of the throttle via the throttle cable.



I dohn't know what Alan means by the 1/8th inch in the slide at WOT. I have always read the manual to adjust at idle speed position and on the back side of the pin (inside the slide) No matter, mine is adjusted where I want it and works very well for me. When you tighten up the gap, it shifts late and harsh and I don't need it to down shift to pass anything. This isn't a twin cam six cylinder gasser. I have torque.

 

[cerberusiam]

The line pressure is directly effected by the position of the throttle via the throttle cable.



I dohn't know what Alan means by the 1/8th inch in the slide at WOT. I have always read the manual to adjust at idle speed position and on the back side of the pin (inside the slide) No matter, mine is adjusted where I want it and works very well for me. When you tighten up the gap, it shifts late and harsh and I don't need it to down shift to pass anything.

TV pressure, not line pressure, is effected by position of the cable.



Every one of these trucks I have evidently has enough wear setting the TV to max is the only way to get a decent shift. I set it at WOT then adjust from there as thats the typical sweet spot to get a solid shift and keep OD out until later.



Every trans is different and will react different so its a tuning thing to find what it wants. The stock shift points end up a little low wihtout a lot of TV pressure, especially if one has a lot of fuel dialed in. Too much smoke to be environementally responsible at times. With stock fueling and injectors it is less critical so every truck needs to be adjust differently.

 

[TAchterberg]

Thanks for all the input guys, I'll be experimenting with it shortly. Under light throttle it will go into OD as early as 30-32 MPH currently. Under almost WOT it will wait until about 43 MPH. I'll see what kind of improvement can be made using your suggestions. Thanks again, the info is greatly appreciated.

 

[Greenleaf]

The installation of a potentiometer in place of the O. E. tps will correct many of the OD shifting point problems, providing that the trans is healthy and adjusted properly. It will not correct a bad TV and/or TV cable/adj.



The tps is adjustable, however, they wear out and become wacky to the point adjustment will be null and void. They cost (approx) 300. 00 compared to the 4. 00 (four dollar) potentiometer.

 

[JDancoe]

Greenleaf - or anyone else who might know: Where did you get the gearshift lever with the O/D control button, or did you fab it yourself? Also, does anyone know where I might find one of the older model Turn Signal lever that has the Cruise Control switch in it?
Thanks, Jack

 

[cerberusiam]

Greenleaf - or anyone else who might know: Where did you get the gearshift lever with the O/D control button, or did you fab it yourself?

That item is a MY98+ item and available at any dealer or online.



The cruise is probably NS1 as all the newer ones are on the steering wheel.