Strangest issue I've ever come across...

[docluv5150]

Four months ago I bought a 98 EB Expy 2WD with lord knows how many miles on it, seriously. The closest I can guess is about 300K+ from an oil change sticker although the odometer is stuck at 141000. The gentleman that sold it to me said that the transmission wasn't original but I can tell that the engine isn't from the salvage yard markings on the heads and block. I've had to change plugs, fuel filter, some coils, a header gasket, and spend a day cleaning the throttle body to get it to run smoothly, but really, it's in decent shape.

Now to my problem. My transmission has started downshifting at least a gear at 30+ MPH....but only when I turn the steering wheel to the right. If I keep straight or turn left at all, it stays in 3rd or OD all day. But if I turn it to the right, I don't even get to 1 o'clock, and the thing downshifts like I've tromped it. It's not slipping, because if I'm going around a right curve I can keep gas on it and feel power, even winding it out at 3500RPM. Only when I straighten the wheel does it shift back in to OD. If I'm coasting and I turn the wheel to the right, it downshifts and acts like a Jake brake until I stop.

I checked the trans fluid level (looked clean, no smell) and added half a pint even when it wasn't really showing all that low. No change in behavior. I actually thought my OD was going out until I started noticing it only when I turned the wheel to the right, and realizing that I still had power to the wheels even with the engine revving high.

The only other thing that makes me believe that it's something with the rear end is that whenever I have to come to a quick stop, there's a delayed jerk that happens a split second after I put gas to it. Although I'm hesitant to blame the differential because I don't believe that enough time passes for the differential to start "working" after I turn the wheel to the right before the trans changes gears.

At first I was thinking transmission rebuild but now I'm thinking I've got an electronics bug caused by the steering wheel/linkage. Any other ideas?

 

[stamp11127]

Your problems are an odd occurrence. Since the trans has been replaced I'd check the wiring harness that lays over the transmission. Inspect the harness & connector for the vss that is on the tailshaft. Also look at the range selector that is on the left side of the trans. It may be failing/out of adjustment and telling the pcm that you have shifted down manually. If you would like I'll see if I can find the troubleshooting steps for the switch. You'll need at least a dvm.
May want to check the pcm connections. If I remember correctly it is located on the firewall behind the battery.

It isn't your rear end. Their problems make themselves heard in a different "voice" that isn't mistaken. Specifically the howling or whining noise.

 

[toms89]

Does it have to do with a certain degree of g-force pulling to the right or strictly steering wheel position. If its g-force related it could very well be a bad connection, sensor, wire chaffing, etc... that is set off when there are side forces on the vehicle.

I would also like to add that since the pcm shifts based on load, throttle position and rpm it could be an issue with one of engine sensors as well.

If its strictly related to steering wheel position I would be looking for a short in the steering column most likely on the OD switch circuitry.

 

[docluv5150]

Thanks for the ideas. I'm definitely going to check the steering column today.

 

[docluv5150]

Finally had a day off to take it to a transmission shop. Guy took it for a drive and he'd never had a truck do that. Turns out there was a wire rubbing the steering shaft. 10 cent ziptie and now it's back to normal. Tried to pay the guy but he wouldn't take anything. I guess the story that'll start with "You're never gonna believe what this guy's truck was doing...." was enough for him. LOL