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1992 4L80E question

J

JD.

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Location
Harleton Texas
I bought a 92 3500 single wheel truck a couple months ago that the P.O. had parked 2 years ago because he began having transmission problems with. He told me he used the truck to haul cattle at one job. A new job brought another truck in his drive, semi-retiring this one. He used it to go to town every now and then. One day he made the 5 mile trip but lost OD on the way back. That's when he parked it. Only starting it every couple weeks to keep the engine lubricated. I guess that faded with time as the batteries were dead when I loaded the truck onto the trailer. I put new batteries in it once I got it home and the 6.5 started right up. But when I put it in gear, I got nothing. I dropped the pan only to find a fair amount of clutch dust but no metal slivers. I went ahead and put a new filter in and added fluid back to see if maybe that would help. I got it to bump into reverse for a moment but then nothing else. All of this to ask if there is something I can check or could it be an electrical problem? Or should I just bite the bullet and take it to a shop for a rebuild? The P.O. showed me where he patched wires back together after a rat chewed through the harness at the back of the engine. Other than the rat, everything under the hood is very clean.

Thanks for any replies,

JD
 
I am not very well versed on the tranny's but IIRC it could be a sensor. Also I think the ECT sensor, not sure if it's the one in the head or the cross over will prevent a shift into OD
 
I doubt a sensor will prevent it from going into gear at all as reverse is a hydraulically controlled gear. Are you sure its filled with fluid? Sure sounds like its a loss of prime problem, but the pressure regulator could be stuck open if it sat for too long.
 
The dipstick tube is broke at the tab that bolts it to the back of the engine. In holding the rest of the tube to that spot, the stick reads full. When it went into reverse for that moment, it felt solid but came right back out. I just went out and check the registration sticker and it looks like it may have sat since 06 or earlier.
 
sitting 4 years should not matter. I have seen automatics sit much longer. How are you checking the fluid ? IIRC they have to be running in nuetral, not park. How much fluid did you put in ?
Pump could be shot or TCC.
 
The stick says to check it running and in park. I thought it was to be in neutral too. One of the mechanics at work told me to check the torque converter. Checking this by running my fingers in and trying to spin the turbine, I got it to spin one direction freely but it wouldn't budge the other. He told me that it should be good then.
 
When you changed the fluid did you make shure there was no leftover rubber seals for the filter in the transmission? 2 seals will make them do strange things. A non functioning input speed sensor will make them have no hydraulic pressure. Connect a tech 1 to see what the pcm is seeing. Engine rpm and input speed should be close to each other. The 92-93 also had main connector problems. Many have been updated to the newer style.
 
I would like to say I made sure to only have the new seal when I changed the filter. But I have slept and worked on several other projects since starting this one. lol Where can I find a tech 1? Is there a port I can check the pressure? What problems did the connector have? Sorry for all the questions...

Thanks,
 
The pressure test port is on the drivers side above the shifter. Pressure should jump up when you put it in reverse. I'd have to look up specific pressures. There may be other scan tools that work for the tranny. I wouldn't trust the readings off of a snap-on mt-2500. OTC or MAC may work. A tech 1 is what the dealers had back in the early 90s.
I'm not positive what problems the connector had besides leaking tranny fluid into the connection. The newer style connectors can have that problem also. My 92 still has the old style on it and hasn't had any problems since I bought it 3 years ago. The whole inside harness has to be replaced and a new pigtail put on the external harness. Look all the wires and connector for the input speed sensor over. I had a pin push out of the input speed sensor connector that had me stumped for a bit. The input speed sensor is in front of the shifter. The 4l80e is a very durable tranny. Most problems are minor electrical things. Be shure to check all the fuses. I believe the yellow wire at the main connector should be 12 volts+.
This place sells all the electrical parts. I lost my link to another place when my computer crashed
http://www.bulkpart.com/Merchant2/merchant.mvc?Store_Code=2&Screen=SFNT
 
Thanks! This gives me a place to start checking. I've heard these are tough transmissions and can't see it being a big problem with what the PO told me happened to it.
 
To explain it the way I understand it[might not be perfectly right] is with no input speed reading the pcm thinks it isn't running so it doesn't give the force motor[thing that sets the hydraulic pressure]any power to make pressure. that results in extreme slipping or no movement at all.
Another possibility is that the input speed sensor has metal filings on it and sludge. Sometimes they just need to be wiped off. They are magnetic so they attract filings. The input speed sensors aren't real expensive.
You really need to see what the pcm is seeing to know where to look but a pressure test is a good place to start. With a scan tool connected you can raise and lower the pressure to check the force motor. You can also shift the forward gears to check the shift solenoids function.
 
If there is no power to the force motor teh trans defaults to MAX pressure, this is what happens if you have a solonoid failure or if you unplug it. Minumum pressure is 35 in anything but reverse which is max power going to the force motor. Reverse min is 67. The pressure specs are 35-171 for anything but reverse, and 67-324 while in reverse. The pressure test port is on the drivers side above the shift linkage and pan rail right behind the input speed sensor and is a 1/8" pipe plug.
 
I worked on a 95 sub that someone else put a new engine and transmission in. When i got it running it wouldn't hardly move itself. I connected GMTDScantech . There was no input speed reading and very low pressure especially for a fresh tranny. One of the pins on the input speed sensor connector was pulled loose so it didn't make a connection. I replaced the connector and everything worked as it should, I think with just about any other sensor it does go to max pressure to save itself.
I am no expert by any means. This is just my experience on 1 truck. Perhaps the loose pin shorted the 5 volt reference signal that all the sensors use? When the connector was bad the scan tool had little effect on raising or lowering the hydraulic pressure.
 
A simple test to see if it is hydraulic or electronic is to unplug the round connector on the side of the trans and see what it does. This will resort it to second and reverse at max line pressure. If it still doesn't move your going to have to go inside to see what is up.
 
I'll have to wait for the snow to melt or at least get the temp out of the 20s before I can look at it. Thanks:cheers2:
 
Your trans sat forever and it drained the fluid out of the converter. Mine sat 6 months before I put it in my truck...
Then you changed the fluid - I bet your bucket was full or it went everywhere. Mine was...

You need a good dipstick. You will have to fill the transmission several times to get the converter filled up. As soon as the converter takes all the oil the transmission will not change gears. It takes several min to run out of oil in the pan.

It takes a couple hours to get the level right and the foam/air out.

Rats eating the wires. Who says they only ate one spot?
Also the front and rear speed sensor wires tend to have the insulation fall off them and short out. Closer to the plug the worse it is.
 
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