Tranny hunting OD
09-08-2018, 07:49 AM
#16
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AJ I replaced the VSS with a new one.....I’m hoping I can get this thing figured out!
Thank folks all the help is much appreciated! I couldn’t do with out it!
Thank folks all the help is much appreciated! I couldn’t do with out it!
09-22-2018, 02:06 PM
#17
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Thread Starter
Update! The truck has been hunting OD all week....so let me describe the matter. In the mornings ...most of the time the truck shifts fine. Once I have been
driving awhile the hunting starts. It will hunt for a while then stay in 3rd for several miles, all at once it shifts into OD and will stay in OD for the rest of the trip.
One thing I figured out is when the tranny is is 3rd the cruise will not engage. Once in OD the cruise will engage again, however the cruise will only last for a little while then shuts off.
So today I put the OD fix found in the sticky into use....the one with governor pressure port...truck shifts into OD about 4 or 5 seconds after going into 3rd.
Hopefully this is fixed permanently!
Thanks for all the help!😁
driving awhile the hunting starts. It will hunt for a while then stay in 3rd for several miles, all at once it shifts into OD and will stay in OD for the rest of the trip.
One thing I figured out is when the tranny is is 3rd the cruise will not engage. Once in OD the cruise will engage again, however the cruise will only last for a little while then shuts off.
So today I put the OD fix found in the sticky into use....the one with governor pressure port...truck shifts into OD about 4 or 5 seconds after going into 3rd.
Hopefully this is fixed permanently!
Thanks for all the help!😁
10-02-2018, 10:01 AM
#18
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Location: Dierks, AR SW
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I have two of these trucks - 91.5 w / intercooler and a 92- with same problem. They have been doing this for years and I have spent several hours troubleshooting. I added a toggle switch to send a ground to the OD solenoid in the tranny to force them into OD. The pressure work around is better because I have to remember to turn my switch before I come to a start.
My point of this post is to say that it is a shame that we have to do a work around to have an OD. It is a shame that someone (especially me) has not figured this out. I still plan to figure this out one day for the satisfaction and to help most owners of these trucks. I think most of us have the same problem but no one can figure it out. I troubleshoot electrical problems every day on Gen Sets and Automatic Transfer Switches and do some pretty amazing things with the controls on both but this has me buffaloed.
Whomever figures this out will have my vote for the best troubleshooter on this site.
Thanks and good luck.
My point of this post is to say that it is a shame that we have to do a work around to have an OD. It is a shame that someone (especially me) has not figured this out. I still plan to figure this out one day for the satisfaction and to help most owners of these trucks. I think most of us have the same problem but no one can figure it out. I troubleshoot electrical problems every day on Gen Sets and Automatic Transfer Switches and do some pretty amazing things with the controls on both but this has me buffaloed.
Whomever figures this out will have my vote for the best troubleshooter on this site.
Thanks and good luck.
10-02-2018, 11:40 AM
#19
Registered User
It's a pretty simple system, the PCM, or the SBEC grounds the solenoid and you get O/D. There are however other circuits that affect what the SBEC does. On a 91.5 the circuit is even simpler in that it doesn't have the crankshaft position sensor so maybe we can rule that out for the time being. What the circuit does go through is an O/D lock out module and a switch.Have either of you ever noticed if the O/D Off switch is illuminating when the hunting is occurring? I remember back in '92 we had some gas trucks that would be cruising down the highway in O/D and all of the sudden it would come out of O/D and the O/D Off switch would be illuminated. Press the switch and it would go right back into O/D and cruise on away. I don't remember ever fixing one though as the condition was so intermittent we could not reliably duplicate it. I always suspected some sort of RF interference either in the harness or from an outside source that was triggering the lock out module as the switch is just a momentary switch. It doesn't sound like what you guys have going on but that module is something to think about. It could also possibly be the driver in the SBEC is old and tired. I purposely used a relay on mine because when I converted it to lock up I was relying on the single driver to provide ground for both solenoids so I didn't want to burn it out.
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