4L60E engine braking/overrun help needed.
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Intermediate
Joined: Dec 2024
Posts: 25
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4L60E engine braking/overrun help needed.
Do any of you guys have a thorough understanding of the operation for the overrun characteristics for a 4L60E in a C5 corvette? I'm trying to understand if what I'm feeling is baked into the DNA of the 4L60E or the C5 vette, or I have a failure or tune issue.
The scenario I have is this: If I'm coasting along at 70mph in 4th and manually pull the gear selector to 3rd, there is no engine braking and it feels just like neutral at zero throttle input. If I apply throttle it accelerates with no issues. Second gear is similar except after I have pulled the selector into 2nd, if I let it coast for about 2 seconds it will engage 2nd gear and have engine braking. If I manually pull it into 2nd and accelerate immediately, leave the selector in 2nd, lift off the throttle it will have engine braking until I select a higher gear. First gear has normal and expected engine braking anytime the selector is in 1st and I'm off the throttle.
The 4L60E in question has been modified/built with parts to handle more than 800hp and a 3200rpm converter, but it does not have the HD shift valve which sounds like a common mod many builders use. I did talk to the builder and they said I'm running too much line psi in the tune file and it's likely not allowing the fluid to bleed off at the appropriate time. I just ran a test with drastically reduced up shift/down shift pressures, and generally drastically reduced commanded pressure throughout. There was zero difference in the engine braking/over run character with lowering the pressure. I copied the original transmission tables from the OE stock file also as a test, also zero change in engine braking/over run character.
Thank you for your time.
The scenario I have is this: If I'm coasting along at 70mph in 4th and manually pull the gear selector to 3rd, there is no engine braking and it feels just like neutral at zero throttle input. If I apply throttle it accelerates with no issues. Second gear is similar except after I have pulled the selector into 2nd, if I let it coast for about 2 seconds it will engage 2nd gear and have engine braking. If I manually pull it into 2nd and accelerate immediately, leave the selector in 2nd, lift off the throttle it will have engine braking until I select a higher gear. First gear has normal and expected engine braking anytime the selector is in 1st and I'm off the throttle.
The 4L60E in question has been modified/built with parts to handle more than 800hp and a 3200rpm converter, but it does not have the HD shift valve which sounds like a common mod many builders use. I did talk to the builder and they said I'm running too much line psi in the tune file and it's likely not allowing the fluid to bleed off at the appropriate time. I just ran a test with drastically reduced up shift/down shift pressures, and generally drastically reduced commanded pressure throughout. There was zero difference in the engine braking/over run character with lowering the pressure. I copied the original transmission tables from the OE stock file also as a test, also zero change in engine braking/over run character.
Thank you for your time.
Safety Car
Joined: Aug 2011
Posts: 4,449
Likes: 409
From: Portland OR
Hmmm. I have a Performabuilt level 2 in mine and it does have engine braking in 3rd. As well as 4th.
It does not have engine braking in manual 2nd.
They use their own shift kit strategy and advised me to leave shift pressures stock.
Next time I drive it I’ll test this stuff and let you know.
FWIW, I installed this trans in 2012. I had bought a 2004 unit for cheap and sent it in. After literally hundreds of low 11 second and now high ten second passes, I finally changed the fluid last year. It was so clean inside, even the pan, it was a waste of time. They done good!
It does not have engine braking in manual 2nd.
They use their own shift kit strategy and advised me to leave shift pressures stock.
Next time I drive it I’ll test this stuff and let you know.
FWIW, I installed this trans in 2012. I had bought a 2004 unit for cheap and sent it in. After literally hundreds of low 11 second and now high ten second passes, I finally changed the fluid last year. It was so clean inside, even the pan, it was a waste of time. They done good!
