YR660R

I recently got a 1999 Cummins auto, it has the trans built and shifts nice and firm, the only issue I am having is most of the time is, it shifts into 4th gear immediatly after shifting into 3rd. (not talking lockup) which lugs the motor down, sometimes it will shift into 4th perfect, about 5 seconds or so after 3rd, but most of the time its instant, and very annoying.

I know the 3-4 shift is computer controlled, I have tried the TV cable, and checked tps voltage with no results. can anyone help me out? Thanks

xmr

I just got through having my auto tranny rebuilt. I would suggest that you find a shop that has a snap-0n scanner and get them to scan the trans. while driving it. If they know what they are doing they can tell if the problem is electrical or mecanical. It really saves a lot of time. The problem is that most shops don't want to take the time to do the scan they just want to sell you a rebuild job. good luck finding a good shop.
A dodge dealer can do this scan also but be sure that they tell you the cost before you let them do it. They don't call them stealerships for nothing.

RowJ

Welcome to DTR!
Who's built tranny is it?
Just a guess, but if your driving with a light right foot, the trannys will sometimes do that.
Does it slip into OD to quickly even when you are accelerating firmly?
I personally lock out OD around town (and under 50). OD is a VERY tall gear (.68) and it gets easy to lug the engine.
Keep RPM's in the sweet spot around 1600 - 2000 rpm and tell us if it still happens.

RJ

YR660R

if I have my foot into it a bit more, it shifts at about the correct time, just really annoying when you are takin it easy, and it shifts into fourth immediatly after 3rd, I guess a stock converter wouldnt do that cause you need more throttle to go the same speed, low stall converter makes it easier to go slow with light pedal. Makes sense right?

RowJ

Makes sense! You don't list truck yr (might want to fill in your signature) but on earlier automatic models, with the 47RH tranny, OD is not locked up all the time. They have similar problem to what you describe.....they cycle in & out of lockup when in OD. IMO, it just the nature of the beast. It's a high torque engine with a tranny trying to search for the best gear, based on your throttle level.
Tell it what you want (by locking out the OD) and it and you will be happier. That's what works for me, anyway.

I remember, when I first got my truck, having to learn how to accelerate through the shifts for smoother operation. Not hard...just different.

RJ

wurkenman

My 02 does the same thing. It just depends on how hard you are on the go pedal. Dont ever worry that you are lugging your truck, especially with the auto.

gooseman495

The pcm contolls overdrive & lockup. A tps not working right could cause fast od shift. If the 1-2 or 2-3 shift was fast at light throttle I would say it is a kickdown cable adjustment problem.

YR660R

I figured it out! you may think im crazy, but I know it fixed it, I had the trans relay pulled and jumped for my lockup switch, for the heck of it I installed the relay back in, and it works perfect now! just to make sure I took it back out and put the jumper back in and the problem returned, put the relay in, and it has the delay it should under light throttle. only problem is now I dont have a working lockup switch.