4l80e reverse and transbrake issue
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4l80e reverse and transbrake issue Need help diagnosing a strange issue I am having. 4l80e has a CK Performance transbrake. D321 AUTO SHIFT TRANSBRAKE VALVE BODY-LATE it was installed in a 4l80e early case with supporting fluid lines retrofit. The issue I have is once the transmission is at normal operating temperature I no longer have reverse gear or transbrake available. On cold start the transmission will engage reverse with no problem and Trans brake works with no problem. All forward gears work fine and OD position auto shifts up and down with no problem even locks converter in 4th when it reaches predetermined settings set on a US Shift TCM. Quick Shift 4 2nd gen.
once the car reaches normal operating temp it stops going into reverse and the transbrake no longer works. However, all forward gears work with no issues, manually and automatically. Its a conundrum we cant seam to figure out. Fluid is on the money checked in neutral while hot and running. Transmission was originally fully built with zero miles. CK Valve body D321 auto shift came out of a fully built transmission with zero mile that went wrong from the get go and ended up reaching undesirable temperatures during test drives. The temperature issues were caused by poorly built transmission internals mixed matched late and early 4l80e case parts and supporting mods were overlooked. We had the transmission rebuilt and used the same Valve body pretty much corrected all the internal issues and supporting mods. Reverse and TB issue continues. All else works like a charm with no issues after rebuild and temperature stays between 175 and 180 degrees. My last resort is to remove the Valve body and send it back to CK for an evaluation and repair. Then re install and hope reverse and TB work as it's supposed to. Any advice on what this issue can be? Most people I spoke to point to the VB. Thanks any help is greatly appreciated.
once the car reaches normal operating temp it stops going into reverse and the transbrake no longer works. However, all forward gears work with no issues, manually and automatically. Its a conundrum we cant seam to figure out. Fluid is on the money checked in neutral while hot and running. Transmission was originally fully built with zero miles. CK Valve body D321 auto shift came out of a fully built transmission with zero mile that went wrong from the get go and ended up reaching undesirable temperatures during test drives. The temperature issues were caused by poorly built transmission internals mixed matched late and early 4l80e case parts and supporting mods were overlooked. We had the transmission rebuilt and used the same Valve body pretty much corrected all the internal issues and supporting mods. Reverse and TB issue continues. All else works like a charm with no issues after rebuild and temperature stays between 175 and 180 degrees. My last resort is to remove the Valve body and send it back to CK for an evaluation and repair. Then re install and hope reverse and TB work as it's supposed to. Any advice on what this issue can be? Most people I spoke to point to the VB. Thanks any help is greatly appreciated.
Last edited by jmederos; Jun 14, 2022 at 10:31 PM.
TECH Junkie
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From: Iowa
sounds like pretty common rear band clearance issue
a pressure test should have been included in your diagnosis and description of the issue.
perform a pressure test and if it is good, you'll need to adjust the rear band clearance
a pressure test should have been included in your diagnosis and description of the issue.
perform a pressure test and if it is good, you'll need to adjust the rear band clearance
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Trans temp 118 degrees 1k rpm (still cold)
P 160 psi
R 120 psi
N 160 psi
D 130 psi
3 130 psi
2 130 psi
2 140 psi
1 100 psi
After 135 degrees we lose reverese and transbrake doesnt work. Reverse tends to go in and out. And at the following temperature the reverse and transbrake completely gone.
Test at operating temperature
Trans temp 160 degrees (operating temp)
P 125 psi
R 60 psi
N 145 psi
D 110 psi
3 90 psi
2 100 psi
1 80 psi
Trans temp 183 degrees (hot )
P 115 psi
R 55 psi
N 120 psi
D 120 psi
3 65 psi
2 90 psi
1 100 psi
This valve body does not have an EPC it is modded to maintain max line pressure. But the line pressure seems to drop psi as temperature increases. The car doesn't seem to have an issue in forward gears. Only issue in reverse. Any ideas? Definitely looksike line pressure issue. But what is causing it?
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From: Iowa
inspect the AFL valve.
Vacuum check would be the best place to start.
You can drill a hole or trim a slot in the separator plate gaskets to force max line in other means...but I wouldn't recommend that other than a last resort
Vacuum check would be the best place to start.
You can drill a hole or trim a slot in the separator plate gaskets to force max line in other means...but I wouldn't recommend that other than a last resort
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The clearance is set to 0.175 or 11/64 seen other forums where people recommenda 0.070 clearance but that seems to be very tight. Reverse band would be rubbing in forward gears right?
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From: Iowa
.175 is too much imo
need to inspect still...if you have fixed line and that is your pressure, you have an issue
I'd also recommend you disassemble the EPC and modify it
There are instances where the pintle inside the epc gets hung open to exhaust and has issue.
modifying it or buying an EPC plug from Jake's Performance would be the proper way to ensure no issue there
need to inspect still...if you have fixed line and that is your pressure, you have an issue
I'd also recommend you disassemble the EPC and modify it
There are instances where the pintle inside the epc gets hung open to exhaust and has issue.
modifying it or buying an EPC plug from Jake's Performance would be the proper way to ensure no issue there
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.175 is too much imo
need to inspect still...if you have fixed line and that is your pressure, you have an issue
I'd also recommend you disassemble the EPC and modify it
There are instances where the pintle inside the epc gets hung open to exhaust and has issue.
modifying it or buying an EPC plug from Jake's Performance would be the proper way to ensure no issue there
need to inspect still...if you have fixed line and that is your pressure, you have an issue
I'd also recommend you disassemble the EPC and modify it
There are instances where the pintle inside the epc gets hung open to exhaust and has issue.
modifying it or buying an EPC plug from Jake's Performance would be the proper way to ensure no issue there
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From: Iowa
if that plug is installed
and pressures are still that low...then you likely have an AFL valve issue or possibly a worn boost valve
Just for peace of mind...I don't see you listing any RPM values for those numbers after the first couple where you say 1000 rpm
Do the tests at 2000 so there is adequate pump volume and if they are still low...THEN start looking for the cause of the pressure loss
If they come up with throttle, we will need to search elsewhere
and pressures are still that low...then you likely have an AFL valve issue or possibly a worn boost valve
Just for peace of mind...I don't see you listing any RPM values for those numbers after the first couple where you say 1000 rpm
Do the tests at 2000 so there is adequate pump volume and if they are still low...THEN start looking for the cause of the pressure loss
If they come up with throttle, we will need to search elsewhere
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if that plug is installed
and pressures are still that low...then you likely have an AFL valve issue or possibly a worn boost valve
Just for peace of mind...I don't see you listing any RPM values for those numbers after the first couple where you say 1000 rpm
Do the tests at 2000 so there is adequate pump volume and if they are still low...THEN start looking for the cause of the pressure loss
If they come up with throttle, we will need to search elsewhere
and pressures are still that low...then you likely have an AFL valve issue or possibly a worn boost valve
Just for peace of mind...I don't see you listing any RPM values for those numbers after the first couple where you say 1000 rpm
Do the tests at 2000 so there is adequate pump volume and if they are still low...THEN start looking for the cause of the pressure loss
If they come up with throttle, we will need to search elsewhere
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The AFL and the Boost Valve were replaced. The boost valve was replaced and modified as per the instructions and the one that came out of the pump. the Reverse band and servo were checked, and the gap was tightened a little more by increasing the length of the stem, this process took like 4 tries' just to get it right... Slapped everything back together and still having the same issue. Our next step is to remove the D321 Valve Body and insert the same style stock VB. the stock VB has been modified to Max line pressure using a modified OEM EPC which will be UNPLUGED. has original Seperator plate, good solenoids and torque converter lock up. I believe it also has all the trans go upgrades for performance. the only thing it will not have is the Trans brake for now. We just want to rule out the VB being the issue. If this works and i do not lose my reverse gear when it reaches 150 degrees or higher operating temps, then we can pinpoint the issue.
The only thing that am wondering about is the following... The current setup with the CK trans brake VB instructions say to use the ***** in position 1, 3, and 10 and delete the rest. However, since I am no longer using the trans brake for this test. instead, I am using modified VB without the trans brake so it should all work as a high-performance transmission operating as normal without the trans brake or epc, should we use all the ***** in the original OEM application, or would it not change the results if I use all the OEM positions for the ***** without deleting the rest as instructed by CK's D321 trans brake inductions?
The only thing that am wondering about is the following... The current setup with the CK trans brake VB instructions say to use the ***** in position 1, 3, and 10 and delete the rest. However, since I am no longer using the trans brake for this test. instead, I am using modified VB without the trans brake so it should all work as a high-performance transmission operating as normal without the trans brake or epc, should we use all the ***** in the original OEM application, or would it not change the results if I use all the OEM positions for the ***** without deleting the rest as instructed by CK's D321 trans brake inductions?
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[QUOTE=truckdoug;20441394]I've had this happen and it turned out to be the case was a leaking near the CS area. quirk of the manufacturing process i suppose.
thanks for sharing this rare problem, i don't have reverse either, gonna work with the servo cup and rod tomorrow, i put the pin extension from the fix kit on the rod, still had no reverse so the pan and valve body is back off, i measured .120" throw distance but this is the higher end of the spec range, gonna try to get it down to .080" if i can. stick a snake cam and a pick up there and see if i can move the band when the cup is applying the rod.
thanks for sharing this rare problem, i don't have reverse either, gonna work with the servo cup and rod tomorrow, i put the pin extension from the fix kit on the rod, still had no reverse so the pan and valve body is back off, i measured .120" throw distance but this is the higher end of the spec range, gonna try to get it down to .080" if i can. stick a snake cam and a pick up there and see if i can move the band when the cup is applying the rod.
