This is my dads dually and first 12V for us so I have to ask. The truck is a 47rh 94 model dually if this helps. The trans has 5k miles on rebuild and shifts great. I was thinking the VSS or sensor on rear diff may cause this. But the speedo works? Aaron

 

Check the TPS, and the transmission temp sensor.

'Something been said about a 1000 ohm resister across the trans temp sensor.

Check the sticky.

Tom

 

Temp only stops the converter from locking so the trans will heat up in cold weather.

If you are sure the converter is locking and OD is not, I would suspect the solenoid coil inside the tranny. An easy test would be to rig a test lamp. There are 3 wires in a plug that points down on top of the tranny at the rear left side of the valve body. If memory serves me correctly the front wire is OD and the rear wire is CL. The center wire is hot. You can run a wire into the cab and hook it to a test lamp. Connect this wire to the front wire on the plug. Connect the other wire on the lamp to a hot source. The lamp will light when the PCM tells OD to lock at speed. If you get a light and OD does not lock the solenoid is bad. If you don't get a light at speed you have a PCM or wire problem. You can test the CL circuit the same way.

One last thing does the OD light come on when you press the switch on the dash?

 

So what you are saying is; the trans temp sensor has nothing to do with the OD?

Tom

 

Yes

The temp sensor is there to keep the transmission from locking the converter in order to heat the transmission up. You can replace the sensor with a 1K ohm resistor to fool the computer into thinking it is warm. This will allow the CL to lock when cold. It will not hurt the tranny unless you are in an area where it gets below -40 F.

 

The trans temp sensor connector on a '94 is in a spot that gets oiled very well from the blowby tube.
Often a good cleaning is all that's necessary.

 

Sorry haven't been on in a few days. Thanks so much for the replies. I was gonna replace the sensor and the VSS at the same time but maybe I can just try the temp sensor? I see someone said it is close to the blowby tube? Thats good I will find it and clean it with CRC electrical sensor. Aaron

 

As I said before: You sensor is fine if your converter is locking. You said it is locking and OD is not working. You would be better off hooking a test lamp up as I said in my last post and not just throw parts at it.

 

Well thanks for the help I guess I will check the overdrive switch on the dash and run the a jumper wire and fool it or whatever. I really know nothing I am swallowing my pride on this one! Aaron

 

This is as simple as I can make it. Splice a wire on the wire on the front side of the plug. The plug is on top of the transmission pointing down. Run this wire into the cab. strip some off the end of it. Take the truck for a test drive and when you get to 45MPH ground that wire to the metal part of the cigarette lighter. If you feel it shift you have a PCM or wire problem. If it does not shift you have a solenoid problem inside the transmission or a bad plug.

Are you sure thet your problem is OD and not the converter lock? An easy test is when the converter is locked and you hit the gas the RPM should not increase fast when driving 50MPH. It should increase with speed. If your RPMs increase fast the converter is not locked.

If OD is the problem you would feel nothing when you hit the OD switch at 50MPH. you never did answer if the yellow light lights on the OD switch.

 

Yea I'm sure the converter is locking. Once I hit 45 the converter locks up dropping about 200-300 rpms then just stays there. With 3.54 rear end at 70 used to be 1700 rpms now at 2000-2100 but not a big deal to me. Thanks Aaron