Suddenly lost 4th gear 4L80E
Suddenly lost 4th gear 4L80E Something weird couple of days ago, I lost 4th gear all of a sudden. Not during or after racing, just one morning going to work I realized I have no 4th gear.
All other gears are fine. Fluid looks nice and clear, level is right at the max.
What can I do to at least diagnose the problem?
Tranny is built 4L80E
HELP!
All other gears are fine. Fluid looks nice and clear, level is right at the max.
What can I do to at least diagnose the problem?
Tranny is built 4L80E
HELP!
Noticed interesting thing tonight. Cruising at 40 mph with converter unlocked, if I move shifter from D to 3rd, I can feel the car is holding back very very slightly, like it indeed shifts from 4th to 3rd. If shift back to D at that same speed, I can feel nothing but revs drop very very slightly, 50-100rpm at most. Like there is 4th but it's ratio is almost the same as in 3rd gear.
Do these symptoms provide any clue?
Do these symptoms provide any clue?
Noticed interesting thing tonight. Cruising at 40 mph with converter unlocked, if I move shifter from D to 3rd, I can feel the car is holding back very very slightly, like it indeed shifts from 4th to 3rd. If shift back to D at that same speed, I can feel nothing but revs drop very very slightly, 50-100rpm at most. Like there is 4th but it's ratio is almost the same as in 3rd gear.
Do these symptoms provide any clue?
Do these symptoms provide any clue?
Check shifter cable adjustment closely, if it's not completely in 4th, it may not open D4 oil to the shift valve, if it's partially in neutral it will cause clutch failure.
Today when I came to work, I couldn't put it in Park... Also never happened before
Thank you for your hints, Jake!
While the pan is off, look at the OD clutches, they are in the front and partially visible. If they are cooked, they will be black.
THAT sounds like a shifter linkage issue for sure. If it's not external to the trans, drop the pan and look at the nut on the shifter shaft, if it's loose, it may cause it to do both of your problems. Check the shifter cable first though. If the cable is able to deflect, it will cause the exact issues you're having.
While the pan is off, look at the OD clutches, they are in the front and partially visible. If they are cooked, they will be black.
While the pan is off, look at the OD clutches, they are in the front and partially visible. If they are cooked, they will be black.
I forced it into Park with a bit more strength and now it goes into P just like before, with normal resistance. I was hoping smth. just got out and now it was magically fixed, so I put pan back on, but unfortunately 4th gear didn't come back...
Any further ideas?..
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Verdad Gallardo I'm a bit frustrated since in 4 days I have to go to track 150 miles away, that would be very frustrating to do without 4th gear...
Is there anything else I could check?
Is there anything else I could check?
If you do so, air check the 4th clutches, there is a bolt in the center of the case, towards the front that you blow air into the orifice in the center and it will apply the 4th clutches.
The 4th gear circuit is fairly simple, the A solenoid is turned on, it moves the 3-4 shift valve, opening PRND4 oil to the 4th apply circuit, which goes straight to the bolt mentioned above.
If you have 1st gear electronically controlled, that tells us the A solenoid is functioning, as well as all the wiring from the PCM to it.
Loss of overdrive in a case like yours sounds like a pending code shutting OD off and probably ramping up the pressure. I've seen o2 sensor codes do this, other engine codes. If the PCM sees erroneous data from the pressure switch it can cause it too.
You can check the 3-4 shift valve for freedom of movement but it will require dropping the valve body.
If you do so, air check the 4th clutches, there is a bolt in the center of the case, towards the front that you blow air into the orifice in the center and it will apply the 4th clutches.
The 4th gear circuit is fairly simple, the A solenoid is turned on, it moves the 3-4 shift valve, opening PRND4 oil to the 4th apply circuit, which goes straight to the bolt mentioned above.
If you have 1st gear electronically controlled, that tells us the A solenoid is functioning, as well as all the wiring from the PCM to it.
Loss of overdrive in a case like yours sounds like a pending code shutting OD off and probably ramping up the pressure. I've seen o2 sensor codes do this, other engine codes. If the PCM sees erroneous data from the pressure switch it can cause it too.
If you do so, air check the 4th clutches, there is a bolt in the center of the case, towards the front that you blow air into the orifice in the center and it will apply the 4th clutches.
The 4th gear circuit is fairly simple, the A solenoid is turned on, it moves the 3-4 shift valve, opening PRND4 oil to the 4th apply circuit, which goes straight to the bolt mentioned above.
If you have 1st gear electronically controlled, that tells us the A solenoid is functioning, as well as all the wiring from the PCM to it.
Loss of overdrive in a case like yours sounds like a pending code shutting OD off and probably ramping up the pressure. I've seen o2 sensor codes do this, other engine codes. If the PCM sees erroneous data from the pressure switch it can cause it too.
1) We have 2 possible suspects, PCM not engaging OD, and 3-4 valve died/clogged, right? If 1st gear is OK that means solenoid A along with it's wiring is fine.
2) if that would be PCM, could we rule this out by manually supplying ground to solenoid A?
3) if that is 3-4 valve, to check it, I must take off valve body, which can be done without removing gearbox, right?
1 more fact: the night before the problem occured, I was starting the engine for like 20-30 times while checking voltage drops, could that fry something?
Last edited by Vetal; Jul 8, 2013 at 06:58 PM.
OK bad news for me. Manually grounding solenoid does not engage OD...
So, what can I do now to diagnose?
I can't stop wondering how Park was impossible to engage just couple of days after 4th gear loss...
Help!!!
So, what can I do now to diagnose?
I can't stop wondering how Park was impossible to engage just couple of days after 4th gear loss...
Help!!!
How much time should it take?
If I have to do 300 mile trip, can I do it in Drive, would it harm anything? Or better in 3rd?
edit: I assume I will be able to find and use general 4L80E guidelines to remove valve body and find 3-4 valve?
If I have to do 300 mile trip, can I do it in Drive, would it harm anything? Or better in 3rd?
edit: I assume I will be able to find and use general 4L80E guidelines to remove valve body and find 3-4 valve?
Last edited by Vetal; Jul 9, 2013 at 06:23 PM.
Stupid question, but can I turn tranny upside down to remove valve body? There are some ***** that could fall out? Tranny now sits at the floor, so would be 1000x easier to remove valve body with oil pan facing up
