View Full Version : C3500 only goes into overdrive sometimes
I recently bought a 93' C3500 dually and when I first brought it home it was running and driving fine not lately the truck doesnt want to go into overdrive. If I pull over and turn it off for about 5 mins and start going again it it fine until the first time it has to go out of overdrive then it will not go back in. I believe its a 4l80E, a mechanic told me it could be input or output speed sensors on the transmission or a transmission control solenoid. Anyone have similar issues?
You need to scan it for codes. If it thinks it should shift but fails it will record a fault code.
I took it to a friends shop and he scaned it, it has no codes...he thinks its the transmission control solenoid. Any ideas I really dont want to throw money at this thing
DmaxMaverick
12-02-2011, 10:22
Your tranny is a 4L80E. It's a fair bet it's related to your other electrical problems. Fix that first, then address the tranny. There may be nothing wrong with the tranny.
If there are no codes set than it didn't try to go into overdrive. Check the brake switch , engine coolant temperature sensor, etc.
Are you sure it's overdrive and not the torque converter clutch? When it's "not in overdirve" pull the shift lever out of the OD position to 3 and see if it shifts down or not.
When I first drive the truck in the more or after its been sitting it goes down the road fine...it shifts smooth and goes into overdrive then all of a sudden it will just kick out of overdrive and will not go back it. It also shifts harder once this happens. I tried replacing the input/out speed sensors and that did not fix the problem. I was having other electrical problems but I replaced the batterys and it seemed to fix the problem.
Also when its not going into OD and I shift it down to D nothing changes
If there are no trans codes then it is not trying to go into overdrive. Solenoids will set fault codes as will speed sensors. Make sure you are reading the trans codes. '93 doesn't have a PCM, just a trans controller. A generic code reader might not work. the fact that you say it shifts hard tells me it is setting fault codes.
I guess we need a GM tech 2 style code reader but the first gen one for older cars...Ive tried to make an appointment at tocal trans shops but the earliest I can get in is Saturday morning...Im debating dropping the pan and replacing all the solenoids If that doesnt fix it I can always return the parts
If that doesnt fix it I can always return the parts
Solenoids will set codes. Can you return them if they're saturated with transmission fluid?
It goes into OD once, so the solenoid works to a point. Also, there are 2 solenoids for 4 speeds, so one solenoid will` affect more than one gear. Thirdly, when the PCM senses a solenoid fault it usually locks out all gears except 2nd (all solenoids off). You are not seeing any of these, so, I still think some external influence is keeping it out of OD. Lastly, even if you get a code for a solenoid, it could be an external electrical fault.
What could it be then? I dropped the pan and was going to replace the tcc solenoid
phantom309
12-06-2011, 16:18
What could it be then? I dropped the pan and was going to replace the tcc solenoid
4L80E,s wear a valve in the VB called an actuator feed limiter, then the tranny loses line pressure and loses overdrive apply pressure,.when your fluid is cold it works,. warms up valve gets loose in its bore you lose pressure, thinner oil etc,.there's a fix where you sleeve the bore and use a new/different valve iiic.
change the filter and and add new fluid first,. there's another fix if i remember about adding a resistor to one of thetranny wires to raise pump pressure with the force motor, the force motor also has a smallscreen that plugs after a while same problem low pressure,.
If i remember correctly,.or maybe this is all 4l60e stuff rolling around in my head,. :eek:
Nick
What could it be then? I dropped the pan and was going to replace the tcc solenoid
Thought the problem was OD (4th).
You need to be sure you have read the codes correctly. If the TCM commands a shift to 4th and the shift doesn't happen then it sets a code (or multiple codes). It measures input and output shaft speeds and calculates the actual ratio. If it isn't right it sets a code.
One way or the other you're going to get a code.
If there are no codes then the command to shift never came and you need to look at external influences that lock out 4th.
If the problem is the TCC that's a whole other can of worms. Still, the calculated ratios will be wrong and codes will set if the TCC is commanded on and doesn't engage.
DmaxMaverick
12-06-2011, 19:34
99% of the time, if the TCC isn't locking when it should, and you don't get a code, the problem is a temp sensor issue. Either a sensor/sender is bad, or the communication is bad (wiring/connector). The remaining 1% of the time, it is really cold enough to delay/prevent expected operation (Nanook's truck), or there are modifications in place to prevent correct data from reaching the PCM.
As John said, if it's supposed to shift, and it doesn't, it will set a code. If the TCC is supposed to lock, and it doesn't, it will set a code. If it isn't shifting like you think it should, and it isn't setting any codes, the tranny is shifting like the PCM thinks it should. Look to external affects for the problem (external to the PCM and tranny). Simple as that.
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