A friend of mine just bought a 1998 4x4 12v auto Sport package (11/97 mfg date). He had me take it for a ride today as he sensed some issues. I found that it is definately a candidate for the throttle linkage recal as it was like trying to stop an old horse headed for the barn as the throttle was sticking. Also the idle was set aweful high even when I manually returned the pump linkage to the manual position. It was idleing around 1100 rpm which seems a bit high specially for an auto.

What I couldn't figure out was that when going down the freeway and hitting the O/D off button on the shifter the truck seems like it was dropping into 2nd gear instead of 3rd. It would in no was maintain 65mph without redlining. TC clutch was working fine as I was able to get it to lock and unlock by touching the brake on the highway.

Taking off from a stop with o/d on it would hit 1-2-3-od, taking off from a stop with o/d off it would hit 1-2 and that was it.

The only peculular thing is that the previous owner replaced the o/d switch on the shifter right before my friend picked it up.

Could this be an issue with the throttle cable? Mabey the kickdown mechanism is stiff and stuck in kickdown making it drop into 2nd? Is there even a kickdown cable? Or is it all controlled electronically? Could the o/d switch be installed incorrectly???

Hopefully this is not the onset of a failing tranny ad the truck only has 80K miles on it.

I told him to take it in immediately for the throttle recall but we need to get the o/d issue figured out as he is planning a road trip this weekend and would like to be at ease that the tranny is healthy and right now it is his only mode of transportation.

Thanks,

JSF

 

65mph with od off is revving pretty good if you have 3.5 rear gear. If you have 4.10, forget about it.

 

The tach reads 2000 rpm's at 60 mph locked up in O/D and the truck has 245/75-16's on it. I believe to has some pretty deep (4.10) gears. Does this sound about right for 4.10's???

I believe he is going to go to some 285/75-16's when he needs tires again.

JSF

 

Yeah I think you have 4.10s... thats about what my 2500 runs.

 

It sounds like you have one or more issues with the shift linkage, and possibly a stuck or failed throttle position sensor (TPS).

The TPS is located on the bellcrank assembly next to the injection pump and works in conjunction with the vehicle speed sensor (in the tailshaft of the transfer case) and the engine speed sensor (located above the front vibration damper on the engine) to signal the PCM where to set the governor controls on the transmission.

Check the throttle cable for a cracked end at the injection pump and for sticking down at the pedal end. Also check the pedal itself to be sure it is freely moving, it is common for the floor bracket to get rusty and bind the throttle if a truck is used in wet conditions and not allowed to dry. That will result in the TPS failing to read properly, and a high idle.

The throttle valve cable reads the angle of the throttle, and in conjunction with the inputs from the sensors, tells the transmission which gear to select.

There is a transmission throttle valve cable that routes from the transmission to the injection pump linkage. That can stick from old age, or it gets cracked ends, or the bayonet clips on one end or the other break. Make sure it is in good shape and freely moving. Check the cable ends for cracks with a very bright light while someone is standing on the throttle with the engine off. If it is in good shape, make sure it is properly adjusted.

Rule out the linkage issues before turning down the idle.

The sensors are more difficult to diagnose, and I would recommend either the Dodge repair manual or a Haynes Repair Manual #30041 for detailed procedures to check these. However, the front engine speed sensor frequently works loose and bounces around, resulting in a bad signal. That is easy to check, adjust and tighten in place.

It does not sound like the overdrive switch is a problem.

Just guessing, I would predict the TPS is bad, and that the throttle valve cable is bad or not properly adjusted. That combination will do exactly what you describe.