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Last week I experienced slipping in 3rd and 4th shifter position in my 4L80e.
Usually I have around 120PSI at idle in these shifter positions but now it had dropped to about 65 PSI.
I build the transmission about 3 years ago and it has never had any problem for 400 hours of rough driving in my Chevelle 1970. One month ago I replace the filter and oil in the trans.
This is some info on the original build,
1992 case, complete alto and kolene steels kit, internally dual feed modification, fully rollerized, steel forward hub, case saver, new electronics, bearings, seals, EZ-TCU, 3200 stall converter. Drilled pump against seal blow out, drilled strator against convertor drag, drilled rear strator support and overrun clutch housing for better flow and finally direct drum to prevent centrifugal apply. New style EPC.
Pressure is now around 65 PSI in all shifter positions except reverse where it is about 120PSI.
Same in limp mode, does not change with rpm.
In the past I have also been able to adjust my EZ TCU to performance which has increased pressure, this is not responding.
Yesterday I dropped the pan and cleaned the EPC which had some debris in the filters.
I cleaned the AFL filter but was clean to start with. Also cleaned the shift solenoids. Measured solenoids and EPC, all good resistance.
Inspected the boost valve, looks great. O-ringed version.
After assembly and verifying the oil level as pan gasket level I hit the road.
Everything worked great. 120 PSI at idle in OD, the performance mode increased pressure. All like past 3 years.. Drove 40 minutes and the pressure dropped to 65 PSI. LIMP mode does not increase pressure..
Started car this morning again, thinking it had to do with oil temperature. Nope, starts at 65 PSI. 1st and 2nd was about 100psi for like 10 seconds but then all at same pressure..
No slipping gears but low pressure..
What is my problem? Any ideas?
Since limp does not increase pressure in am thinking an internal problem but pressure came back after I dropped the pan..
Can the EPC be damaged? Sticky valve somewhere? More debris in EPC filter?
I will drop the pan tomorrow again but would be great with some expert feedback and food for thoughts.
Planning to buy a new EPC, vacuum test the VB and replace the filter again since that is where it started..
Last edited by Lindberget; May 2, 2026 at 02:03 PM.
I am neither of them but my move would be to change the EPC , They can be bad even testing electrically good and or stick.
Next would be AFL valve sticking -broken spring and then PR VALVE though doubtful with R line rise though small.
Ill stand with EPC/PCS as first move.
__________________ Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook
Thanks @FranksCustomTrans !
Found some metal today. Not a huge amount in the pan but quite some on the PCS sensor filters…
Enough to block the PCS from doing its job. Most likely the cause of low pressure but not the root cause..
Where would that metal come from? Mix of aluminium and something magnetic. Torque converter?
Worth to clean and continue running or pull the trans immediately?
I will drop the valve body and look in the PCS filter and do some cleaning..
Sharing an overview of my past pan drops to give a better view of the amount of metal I have had in the pan. Have dropped the pan 3 times now.
1, Pan drops march 22, oil and filter change after 400 hours of operation. Some shavings. Size, very few that I could feel between my fingers.
2, pan drop 1st of May. Reason to low pressure and slipping in 3rd & 4th. Less then 5 hours driving.
Still few pieces large enough to feel.
PCS sensor filters full of this.
Did not replace filter or majority of oil.
3, pan drop 3rd of may. Due to pressure loss again. 1 hour of driving.
PCS full again. Dropped the valve body and found the PCS filter broken and almost clean.
This makes me less concerned as it is not strange that the sensor filter got clogged that quickly due to its size.
Very little in pan, some large enough to feel.
But as mentioned, did not clean properly last pan drop and did not change filter. What is in the magnet below is all that is magnetic.
Where does the shavings come from? Little enough to clean and keep going?
I also tried to test the PCS with vaccum but can’t figure out how it is supposed to work. Would like to avoid buying one if not needed, expensive here in Sweden and with the shavings blocking the solenoid filter I have no reason to believe it is damaged..
I measured vaccum on B section, image below, and powered on the solenoid. Unpowered it was 15 and powered 5..
My hypothesis would be that it is free flow between B and A unpowered and limited once it get power. Just hooked up 12 straight from the battery, did not control the amps.
Anyone that knows how it is supposed to work?
I cleaned and measured for vaccum on the valve body, have roughly same vaccum readings as after rebuild. Sorry for unstructured values. After rebuild is values in blue and today’s measurements are in grey below or to the right of the blue ones.
Last edited by Lindberget; May 3, 2026 at 11:52 AM.
Sadly to end up in that little filter the source would have to be the pump itself IMO and would have had to have pushed through the PCS screen in VB or its missing, They I have noted on tear down of cores previously built by others omitted . But even in either case the pump or the converter would have to be the source sadly.
__________________ Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook
Sadly to end up in that little filter the source would have to be the pump itself IMO and would have had to have pushed through the PCS screen in VB or its missing, They I have noted on tear down of cores previously built by others omitted . But even in either case the pump or the converter would have to be the source sadly.
PCS filter was there, but broken. I updated the former post with more pictures. 👆🏽
Do you think it will be ok to put together or will it keep getting worse once this has started?
How does a converter fail, mix of steel and aluminum residue?
I would not bother and if i am right its not converter but pump. Course I am just looking at pictures but certainly one or the other is failing, Common wiith converter is lockup clutch delaminating but generally you will get alot of black with that also . But no I would pull unit and inspect pump first , . Course if either fail they spell the demise of the other.
__________________ Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook
It was the converter, inside split in three and wear in the bearing surface. Is that common?
Pump is ok in my opinion.
Have bought a FTI converter to replace it and some new bearings.
Found that the direct clutch has had some heat. Do I need to replace it? It is 600$ in Sweden… 🫣
They are hot spotted and have alot of the kolene black color transfer.
They need replaced
Do not replace with more kolene.
Its not necessary and just makes a mess
And 99% of people do not properly prep their kolene steels and they just install them as they receive them...which is no bueno...causes a bunch of that black material transfer.
Good you found issue, Make sure you clean and check VB and pr valve train for debris as since the screen let loose in the VB that metall will be all though it .
__________________ Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook
This is the first time seeing a converter fail like that. Did you happen to notice any weird noises while driving? Did your transmission feel like it was slipping? I also have to drop my transmission and inspect it due to it acting up this past weekend. I will be doing a pressure test and transmission drop before I pull it out. I have a feeling my converter also failed.
It was the converter, inside split in three and wear in the bearing surface. Is that common?
Pump is ok in my opinion.
Have bought a FTI converter to replace it and some new bearings.
Found that the direct clutch has had some heat. Do I need to replace it? It is 600$ in Sweden… 🫣
This is the first time seeing a converter fail like that. Did you happen to notice any weird noises while driving? Did your transmission feel like it was slipping? I also have to drop my transmission and inspect it due to it acting up this past weekend. I will be doing a pressure test and transmission drop before I pull it out. I have a feeling my converter also failed.
I have a pressure gauge in the dash to monitor the pressure. Noticed a lower pressure and after some time I started to get some slipping. No noice or vibrations.
Thansk @vorteciroc !
Now fully taken apart and rebuilt. Most debris was in the cooling lines and cooler.
Putting it back in the car tomorrow morning.
Excellent!
Get ALL the Debris OUT!
Many people make the mistake of reusing the Oil Cooler/ Lines/ Torque-Converter...
Then they DESTROY their new Transmission, by circulating all that Debris from the Oil Cooler into the new Trans.
(Often blaming the Transmission Builder).
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4L80e loosing line pressure 
