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Discussion Starter #1
Hi there I recently purchased a 93 Chevy c3500 1ton dually with a 350. Truck runs great and has had a transmission rebuild roughly 30,000 miles ago. 1st, 2nd, and 3rd work as they should, but 4th will not engage. When you are in 3rd and let off the gas it idles low as it should as well. Any thoughts would be great! Thanks!
 

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Discussion Starter #2
EDIT: the truck only looses 4th sometimes, it seems more often when it is hot. I have lost 4th and pulled over, turned off truck and let it sit for a minute, then it usually will engage for a little while longer.
 

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Wrench Turner
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4,952 Posts
Ck all wires,plugs,connections.Especially those associated with the TPS.(throttle positin sensor). Also ck oper ation of the TPS.Using a multimeter,probe the wires from the TPS with key on/engine off.Blue wire is 5 volt reference.You should have 5 volts.Black is ground.Gray is the signal wire.It should read approx. .5 volts with throttle fully closed.Slowly open throttle watching meter.Voltage should rise smoothly to 4.5 to 5 volts @ WOT.No spikes or flat spots.
 

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Licenced Automotive Technician
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1,625 Posts
Would hazard a guess that the 3-4 clutch is weak... poor seals, which may explain why it is worse when it is hot....
 
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