80-e swap woes...could this be tranny-related
11-07-2005, 10:21 PM
#2
Whats the history of the transmission?
4L80E's are known to wear boost valves and blow stuff apart due to the resulting high line pressure. I Swapped a 60,000 mile 1999 4L80E into my '92 silverado, it originally had a 4L80E. The trans had no reverse. I put a pressure gage on it and found the pressures going 500+ psi.
I researched, I stopped at a shop that showed me blown direct drums, cracked pistons, even a case with a hairline crack causing it to loose reverse.
My problem was the reverse servo pin was too short and the high pressure slammed the servo piston against the case (several times) and broke it.
Theres also a plug in the vb that commonly gets installed wrong that causes no reverse. The plug next to the solenoids.
I've never used the snap on tool, how does it know the pcm is telling it to go in first? Solenoid A is energized and B is not in both reverse and first.
Low line pressure can cause this too. So can misassembly of the trans.
So my guess is the trans has a problem, or it's wired wrong, and or the PSM is telling the ECM or scan tool it's in first when it's not.
How did you wire this trans?
Has the trans been run before?
4L80E's are known to wear boost valves and blow stuff apart due to the resulting high line pressure. I Swapped a 60,000 mile 1999 4L80E into my '92 silverado, it originally had a 4L80E. The trans had no reverse. I put a pressure gage on it and found the pressures going 500+ psi.
I researched, I stopped at a shop that showed me blown direct drums, cracked pistons, even a case with a hairline crack causing it to loose reverse.
My problem was the reverse servo pin was too short and the high pressure slammed the servo piston against the case (several times) and broke it.
Theres also a plug in the vb that commonly gets installed wrong that causes no reverse. The plug next to the solenoids.
I've never used the snap on tool, how does it know the pcm is telling it to go in first? Solenoid A is energized and B is not in both reverse and first.
Low line pressure can cause this too. So can misassembly of the trans.
So my guess is the trans has a problem, or it's wired wrong, and or the PSM is telling the ECM or scan tool it's in first when it's not.
How did you wire this trans?
Has the trans been run before?
11-08-2005, 07:19 AM
#3
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Originally Posted by jxaxsxoxn
Whats the history of the transmission?
4L80E's are known to wear boost valves and blow stuff apart due to the resulting high line pressure. I Swapped a 60,000 mile 1999 4L80E into my '92 silverado, it originally had a 4L80E. The trans had no reverse. I put a pressure gage on it and found the pressures going 500+ psi.
I researched, I stopped at a shop that showed me blown direct drums, cracked pistons, even a case with a hairline crack causing it to loose reverse.
My problem was the reverse servo pin was too short and the high pressure slammed the servo piston against the case (several times) and broke it.
Theres also a plug in the vb that commonly gets installed wrong that causes no reverse. The plug next to the solenoids.
I've never used the snap on tool, how does it know the pcm is telling it to go in first? Solenoid A is energized and B is not in both reverse and first.
Low line pressure can cause this too. So can misassembly of the trans.
So my guess is the trans has a problem, or it's wired wrong, and or the PSM is telling the ECM or scan tool it's in first when it's not.
How did you wire this trans?
Has the trans been run before?
4L80E's are known to wear boost valves and blow stuff apart due to the resulting high line pressure. I Swapped a 60,000 mile 1999 4L80E into my '92 silverado, it originally had a 4L80E. The trans had no reverse. I put a pressure gage on it and found the pressures going 500+ psi.
I researched, I stopped at a shop that showed me blown direct drums, cracked pistons, even a case with a hairline crack causing it to loose reverse.
My problem was the reverse servo pin was too short and the high pressure slammed the servo piston against the case (several times) and broke it.
Theres also a plug in the vb that commonly gets installed wrong that causes no reverse. The plug next to the solenoids.
I've never used the snap on tool, how does it know the pcm is telling it to go in first? Solenoid A is energized and B is not in both reverse and first.
Low line pressure can cause this too. So can misassembly of the trans.
So my guess is the trans has a problem, or it's wired wrong, and or the PSM is telling the ECM or scan tool it's in first when it's not.
How did you wire this trans?
Has the trans been run before?
We never opened up the tranny itself, just the valve body. I had a TransGo shift kit installed. I also installed a Yank 3200-stall converter. I personally have never seen the transmission running. Other than in 1st gear that is. As for the Snap On scan tool....I have no idea. I'm going on what my buddy told me. I didn't see the scan tool 1st hand.
I'll check the wiring again, but we used a Speartech harness. Everything should be okay, and as far as I know none of the sensors have been unplugged. Could one of them be bad maybe?
11-08-2005, 04:21 PM
#4
I think the scanner would pick up on a bad sensor, it should also give some weird reading if something was wired wrong.
That only leaves a mechanical problem with the shift kit installation.
Maybe.
One of the big trans builders here made mention of a box of some kind that plugs right into the transmission bypassing everything else for testing purposes, sounds like this is what you need.
I think the problem is either in the trans or in the vehicle controls and adaptation.
With this box you could narrow it down.
Now if only that guy would post some ideas....
That only leaves a mechanical problem with the shift kit installation.
Maybe.
One of the big trans builders here made mention of a box of some kind that plugs right into the transmission bypassing everything else for testing purposes, sounds like this is what you need.
I think the problem is either in the trans or in the vehicle controls and adaptation.
With this box you could narrow it down.
Now if only that guy would post some ideas....
11-08-2005, 05:27 PM
#5
hey Listen up, same selinoids fireing order for 1st and reverse, so It's not shift selinoids. We really need more information,,,whats the line pressure in reverse? On your snappy scanner you should have reverse when it is shifted their. could be nutral safety switch (PRNDL switch), even if its in reverse it should still move Reverse ....so I doubt that.These transmissions are always losing reverse, and more times than not it is the center support, rings or drum. However I think you've pinched something or misplaced something when you installed the shift kit. It always seems that the smallest of things that mess ya up. I don't think it's in your tune. I'd spend some time in the reverse servo area...just a hunch..Hope this helps Dave
11-08-2005, 05:27 PM
#6
hey Listen up, same selinoids fireing order for 1st and reverse, so It's not shift selinoids. We really need more information,,,whats the line pressure in reverse? On your snappy scanner you should have reverse when it is shifted their. could be nutral safety switch (PRNDL switch), even if its in reverse it should still move Reverse ....so I doubt that.These transmissions are always losing reverse, and more times than not it is the center support, rings or drum. However I think you've pinched something or misplaced something when you installed the shift kit. It always seems that the smallest of things that mess ya up. I don't think it's in your tune. I'd spend some time in the reverse servo area...just a hunch..Hope this helps Dave
